Downloaded from http://jmg.bmj.com/ on March 27, 2015 - Published by group.bmj.com
New loci
SHORT REPORT
Mutation in PLK4, encoding a master regulator of centriole formation, defines a novel locus for primordial dwarfism Ranad Shaheen,1 Saeed Al Tala,2 Agaadir Almoisheer,1 Fowzan S Alkuraya1,3 1
Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia 2 Department of Pediatrics, Armed Forces Hospitals Programme-Southern Region, Khamis Mushayt, Saudi Arabia 3 Department of Anatomy and Cell Biology, College of Medicine, Alfaisal University, Riyadh, Saudi Arabia Correspondence to Dr Fowzan S Alkuraya, Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh 11211, Saudi Arabia; [email protected] Accepted 24 September 2014 Published Online First 15 October 2014
To cite: Shaheen R, Al Tala S, Almoisheer A, et al. J Med Genet 2014;51: 814–816. 814
ABSTRACT Background Primordial dwarfism (PD) is a heterogeneous clinical entity characterised by severe prenatal and postnatal growth deficiency. Despite the recent wave of disease gene discovery, the causal mutations in many PD patients remain unknown. Objective To describe a PD family that maps to a novel locus. Methods Clinical, imaging and laboratory phenotyping of a new family with PD followed by autozygosity mapping, linkage analysis and candidate gene sequencing. Results We describe a multiplex consanguineous Saudi family in which two full siblings and one half-sibling presented with classical features of Seckel syndrome in addition to optic nerve hypoplasia. We were able to map the phenotype to a single novel locus on 4q25-q28.2, in which we identified a five base-pair deletion in PLK4, which encodes a master regulator of centriole duplication. Conclusions Our discovery further confirms the role of genes involved in centriole biology in the pathogenesis of PD.
Primordial dwarfism (PD) is a term used to encompass a wide range of clinical conditions that have, in common, severe growth deficiency of prenatal onset, which persists postnatally.1 As such, PD offers a unique opportunity to observe the clinical consequences of perturbing key pathways involved in the growth of multicellular organisms.2 The past decade has witnessed a marked acceleration in the discovery of genes that are mutated in various subtypes of PD. The emerging theme from these discoveries is that DNA damage repair defects and, more commonly, centriole biology abnormalities are key pathogenic mechanisms that underlie virtually all PD forms that have been characterised at the molecular level to date.2 Thus, genes involved in these mechanisms are attractive candidates in the pursuit to capture the full genetic heterogeneity of PD. In the largest published study on the genetics of PD in which we described four novel disease genes, we have shown that many patients with PD remain undiagnosed at the molecular level.1 In an effort to characterise additional PD genes, we recruited a previously undescribed multiplex family. In this family from Southern Saudi Arabia, healthy first cousin once removed parents presented to the medical genetics clinic with two children, a 40-month-old daughter (IV:4) and a 19-month-old son (IV:5), whose clinical phenotypes were
strikingly similar. Both were born following fullterm pregnancies complicated by intrauterine growth retardation. Profound growth deficiency was evident at birth with weight of 1.45 kg (−3.7 SD), length of 40 cm (−4.2 SD) and head circumference of 26 cm (−5.9 SD, birth growth parameters are unavailable for the brother, but he was extremely similar to the sister by parental report). Both siblings have significant global developmental delay, but are not known to have any other medical problems. Physical examination of IV:4 and IV:5 revealed microcephalic PD with weight of 4.5 kg and 3.7 kg (−6.9 SD and −6.5 SD), length of 68 cm and 58 cm (−7.2 SD and −6.4 SD) and head circumference of 33 cm and 31.5 cm (−10.1 SD and −11.8 SD). They both had classical Seckel facies with sloping forehead, prominent nose, prominent eyes and micrognathia (figure 1). Additionally, the sister had prominent metopic sutures. Both had evidence of optic nerve hypoplasia on fundus examination, as well as strabismus. Skeletal survey revealed general symmetrical mild shorting of long bones but no frank dysplastic changes, and karyotyping was normal. Other than microcephaly and an arachnoid cyst, brain MRI on IV:4 was normal. Family history was significant for an affected paternal half-sister (IV:2) whose mother shares the same geographical origin but is not known to be directly related. IV:2 had birth growth parameters of 1.90 kg for weight (−2.9 SD), 43 cm for length (−2.8 SD) and 27 cm for head circumference (−5.2 SD), and current growth parameters (at 18 m of age) of 4 kg for weight (−7 SD), 56 cm for length (−7.5 SD) and 30.5 cm for head circumference (−12.5 SD). Her facial features were identical to those described above, and she also had evidence of optic nerve hypoplasia. The multiplex and consanguineous nature of this family appeared conducive to the application of autozygosity mapping to identify the responsible locus for Seckel syndrome in the probands and their half-sister. After signing a written informed consent form (KFSHRC IRB approval RAC#2080006), venous blood was collected from the two probands, unaffected parents and stepmother and their halfsister. DNA extraction was followed by genomewide genotyping on the Axiom single nucleotide polymorphism (SNP) chip platform and determination of the autozygome per individual using runs of homozygosity as surrogates as described before.3 The autozygomes of the three affected members overlapped on a single autozygous interval
Shaheen R, et al. J Med Genet 2014;51:814–816. doi:10.1136/jmedgenet-2014-102790
Downloaded from http://jmg.bmj.com/ on March 27, 2015 - Published by group.bmj.com
New loci
Figure 1 Identification of a family with Seckel syndrome that maps to a novel locus on chromosome 4. (A) Pedigree of the multiplex family (index is denoted by red arrow). (B) Clinical image of two patients showing the classical Seckel facies with sloping forehead, prominent nose, prominent eyes and micrognathia. (C) AgileMultiIdeogram showing the shared region of homozygosity (ROH) between the three affected in the family on chromosome 4 (dark blue, red arrow). (D) Genome-wide linkage analysis reveals a single peak on chromosome 4. (E) Upper panel: Diagram of PLK4 (triangle indicates the site of the mutation) and sequence chromatogram of the deletion with the control tracing shown for comparison (location of mutation indicated with red line). Lower panel: Schematic of the PLK4 and the location of the frameshift mutation before the cryptic polo-box domain.
(Chr4:112904466-129392060, GRCh37/hg19) that was not shared by any of the unaffected members, which was further confirmed by linkage analysis using EasyLinkage (figure 1). This result confirms that Seckel syndrome in this family maps to a previously undescribed locus on chr4q25-4q28.2. In order to identify the causal mutation within this novel locus, we examined the 144 genes therein for candidacy using the ToppGene tool which ranks genes according to their relevance to a set of training genes that are entered by the user.4 We entered all previously described PD genes in the training set and all the genes within the interval in the test set. Since most of the PD genes play a role in centriolar biology, PLK4 was among the top ranked genes given its established role as a master regulator of centriole duplication (see below). Indeed, full sequencing of PLK4 using custom-made primers (available upon request) revealed a novel five base-pair deletion that fully segregates with the Seckel phenotype in the study family (figure 1). Centrioles are barrel-shaped cellular organelles that play critical roles in dividing cells by nucleating the microtubules in two opposite poles to facilitate the proper segregation of chromosomes (microtubule organising centre).5 In non-dividing cells, centrioles translocate near the cell membrane to function as basal bodies that template the formation of cilia (motile and primary), which are involved in numerous sensing, mechanical and signalling functions.6 Centriole assembly is a complex and highly coordinated process that ensures the formation of only one pair of orthogonally oriented centrioles per cell cycle to Shaheen R, et al. J Med Genet 2014;51:814–816. doi:10.1136/jmedgenet-2014-102790
maintain genomic integrity.7 The earliest known step in centriole assembly is the recruitment of PLK4 to the mother centriole. PLK4 is one of four mammalian polo-like kinases, but is sufficiently divergent from PLK1, 2 and 3, that it was initially described as a distinct member and given the name SAK (for Snk/Plk-akin kinase).8 Depletion of PLK4 has been shown to abolish centriole formation (both de novo and mother centrioletemplated), whereas overexpression results in centriole amplification, hence the designation ‘master regulator’ of centriole assembly.9–11 Recent evidence suggests a complex interaction between PLK4 and CEP192 and CEP152 to form the ninefold symmetry microtubule-based cartwheel scaffold upon which the mature centriole forms and elongates, and in the absence of PLK4, this fundamental early step of procentriole nucleation fails.12 13 Not surprisingly, therefore, complete deficiency of murine Plk4 and its nematode ortholog ZYG-1 is lethal (Plk4 −/− mice die at E7.5).14 15 Deletion mapping and mutagenesis studies have clearly pointed to the CPB (cryptic polo-box) domain (641–880) of the 970aa PLK4 as absolutely essential for its role in centriole assembly since a mutant that retains the kinetic domain but lacks this domain completely fails to induce centriole assembly.16 Mutations in key players in centriole biology have been linked to PD, for example, CENPJ (also known as CPAP), CEP152, PCNT and POC1A (reviewed by Alkuraya, submitted). The prevailing theory is that quantitative or qualitative defects of centrioles greatly impair the dynamics of mitosis, which is 815
Downloaded from http://jmg.bmj.com/ on March 27, 2015 - Published by group.bmj.com
New loci particularly detrimental to early embryonic development when cellular proliferation peaks resulting in a lasting constraint of growth potential.2 Neuroprogenitor cells at the periventricular zones are particularly vulnerable because of their high mitosis index and also because they are extremely sensitive to the plane of cell division that determines the pools of self-renewing progenitors versus differentiated cells that migrate and populate the cerebral cortex, and centrioles play a key role in that process.17 We believe that PLK4, in view of the above, is a compelling candidate gene for PD (Seckel syndrome specifically). It is worth highlighting that a key binding partner of PLK4, CEP152 has already been shown to be mutated in patients with Seckel syndrome as has CENPJ, another core centrosomal protein that is recruited by CEP152 during centriole assembly.18 19 Although lack of patient-derived cells precluded experimental confirmation, we note that the homozygous truncating mutation we identified is predicted to fully abolish the CPB domain, so it is likely to severely impair PLK4 function and result in deficient centriole assembly. However, it appears from the universal lethality of complete deficiency of PLK4 orthologs that at least some function is retained, possibly through retention of the kinase domain to account for the viability of the three patients. Interestingly, Plk4 has been found to be highly expressed in the periventricular zone of the developing mouse brain, which would be consistent with the severe microcephalic component of Seckel syndrome in the study family.8 In summary, we establish a novel locus for Seckel syndrome on 4q25-28.2 and propose PLK4 as a compelling candidate based on a homozygous truncating mutation in a gene known for its necessary role in centriole assembly. Our discovery expands the spectrum of centriole-related genes and establishes centriole biology as a central pathogenic mechanism in PD. Acknowledgements We thank the study family for their enthusiastic participation. We also thank the Genotyping and Sequencing Core Facilities at KFSHRC for their technical help. Contributors RS, ST, FSA: collected and analysed the data and wrote the manuscript. AA: collected and analysed the data. Competing interests None. Patient consent Obtained. Ethics approval KFSHRC IRB. Provenance and peer review Not commissioned; internally peer reviewed.
816
REFERENCES 1
2 3 4
5 6 7 8
9 10
11 12
13
14 15
16 17 18 19
Shaheen R, Faqeih E, Ansari S, Abdel-Salam G, Al-Hassnan ZN, Al-Shidi T, Alomar R, Sogaty S, Alkuraya FS. Genomic analysis of primordial dwarfism reveals novel disease genes. Genome Res 2014;24:291–9. Klingseisen A, Jackson AP. Mechanisms and pathways of growth failure in primordial dwarfism. Genes Dev 2011;25:2011–24. Alkuraya FS. Discovery of rare homozygous mutations from studies of consanguineous pedigrees. Curr Protoc Hum Genet 2012;6.12. 1–6.12. 13. Chen J, Bardes EE, Aronow BJ, Jegga AG. ToppGene Suite for gene list enrichment analysis and candidate gene prioritization. Nucleic Acids Res 2009;37(Suppl 2): W305–11. Basto R. A centriolar lifeline. Nat Rev Mol Cell Biol 2012;13:686. Bettencourt-Dias M, Hildebrandt F, Pellman D, Woods G, Godinho SA. Centrosomes and cilia in human disease. Trends Genet 2011;27:307–15. Avidor-Reiss T, Gopalakrishnan J. Building a centriole. Curr Opin Cell Biol 2013;25:72–7. Fode, C, Motro B, Yousefi S, Heffernan M, Dennis JW. Sak, a murine protein-serine/ threonine kinase that is related to the Drosophila polo kinase and involved in cell proliferation. Proc Natl Acad Sci USA 1994;91:6388–92. Kleylein-Sohn J, Westendorf J, Le Clech M, Habedanck R, Stierhof YD, Nigg EA. Plk4-induced centriole biogenesis in human cells. Dev Cell 2007;13:190–202. Coelho PA, Bury L, Sharif B, Riparbelli MG, Fu J, Callaini G, Glover DM, Zernicka-Goetz M. Spindle formation in the mouse embryo requires plk4 in the absence of centrioles. Dev Cell 2013;27:586–97. Eckerdt F, Yamamoto TM, Lewellyn AL, Maller JL. Identification of a polo-like kinase 4-dependent pathway for de novo centriole formation. Curr Biol 2011;21:428–32. Park SY, Park JE, Kim TS, Kim JH, Kwak MJ, Ku B, Tian L, Murugan RN, Ahn M, Komiya S, Hojo H, Kim NH, Kim BY, Bang JK, Erikson RL, Lee KW, Kim SJ, Oh BH, Yang W, Lee KS. Molecular basis for unidirectional scaffold switching of human Plk4 in centriole biogenesis. Nat Struct Mol Biol 2014;21:696–703. Kim TS, Park JE, Shukla A, Choi S, Murugan RN, Lee JH, Ahn M, Rhee K, Bang JK, Kim BY, Loncarek J, Erikson RL, Lee KS. Hierarchical recruitment of Plk4 and regulation of centriole biogenesis by two centrosomal scaffolds, Cep192 and Cep152. Proc Natl Acad Sci USA 2013;110:E4849–57. Hudson JW, Kozarova A, Cheung P, Macmillan JC, Swallow CJ, Cross CJ, Dennis JW. Late mitotic failure in mice lacking Sak, a polo-like kinase. Curr Biol 2001;11:441–6. Lettman MM, Wong YL, Viscardi V, Niessen S, Chen SH, Shiau AK, Zhou H, Desai A, Oegema K. Direct binding of SAS-6 to ZYG-1 recruits SAS-6 to the mother centriole for cartwheel assembly. Dev Cell 2013;25:284–98. Habedanck R, Stierhof YD, Wilkinson CJ, Nigg EA. The Polo kinase Plk4 functions in centriole duplication. Nat Cell Biol 2005;7:1140–6. Thornton GK, Woods CG. Primary microcephaly: do all roads lead to Rome? Trends Genet 2009;25:501–10. Al-Dosari MS, Shaheen R, Colak D, Alkuraya FS. Novel CENPJ mutation causes Seckel syndrome. J Med Genet 2010;47:411–14. Kalay E, Yigit G, Aslan Y, Brown KE, Pohl E, Bicknell LS, Kayserili H, Li Y, Tüysüz B, Nürnberg G, Kiess W, Koegl M, Baessmann I, Buruk K, Toraman B, Kayipmaz S, Kul S, Ikbal M, Turner DJ, Taylor MS, Aerts J, Scott C, Milstein K, Dollfus H, Wieczorek D, Brunner HG, Hurles M, Jackson AP, Rauch A, Nürnberg P, Karagüzel A, Wollnik B. CEP152 is a genome maintenance protein disrupted in Seckel syndrome. Nat Gene 2011;43:23–6.
Shaheen R, et al. J Med Genet 2014;51:814–816. doi:10.1136/jmedgenet-2014-102790
Downloaded from http://jmg.bmj.com/ on March 27, 2015 - Published by group.bmj.com
Mutation in PLK4, encoding a master regulator of centriole formation, defines a novel locus for primordial dwarfism Ranad Shaheen, Saeed Al Tala, Agaadir Almoisheer and Fowzan S Alkuraya J Med Genet 2014 51: 814-816 originally published online October 15, 2014
doi: 10.1136/jmedgenet-2014-102790 Updated information and services can be found at: http://jmg.bmj.com/content/51/12/814
These include:
References Email alerting service
Topic Collections
This article cites 18 articles, 6 of which you can access for free at: http://jmg.bmj.com/content/51/12/814#BIBL Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article.
Articles on similar topics can be found in the following collections Calcium and bone (291) Molecular genetics (1193)
Notes
To request permissions go to: http://group.bmj.com/group/rights-licensing/permissions To order reprints go to: http://journals.bmj.com/cgi/reprintform To subscribe to BMJ go to: http://group.bmj.com/subscribe/
New loci
SHORT REPORT
Mutation in PLK4, encoding a master regulator of centriole formation, defines a novel locus for primordial dwarfism Ranad Shaheen,1 Saeed Al Tala,2 Agaadir Almoisheer,1 Fowzan S Alkuraya1,3 1
Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia 2 Department of Pediatrics, Armed Forces Hospitals Programme-Southern Region, Khamis Mushayt, Saudi Arabia 3 Department of Anatomy and Cell Biology, College of Medicine, Alfaisal University, Riyadh, Saudi Arabia Correspondence to Dr Fowzan S Alkuraya, Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh 11211, Saudi Arabia; [email protected] Accepted 24 September 2014 Published Online First 15 October 2014
To cite: Shaheen R, Al Tala S, Almoisheer A, et al. J Med Genet 2014;51: 814–816. 814
ABSTRACT Background Primordial dwarfism (PD) is a heterogeneous clinical entity characterised by severe prenatal and postnatal growth deficiency. Despite the recent wave of disease gene discovery, the causal mutations in many PD patients remain unknown. Objective To describe a PD family that maps to a novel locus. Methods Clinical, imaging and laboratory phenotyping of a new family with PD followed by autozygosity mapping, linkage analysis and candidate gene sequencing. Results We describe a multiplex consanguineous Saudi family in which two full siblings and one half-sibling presented with classical features of Seckel syndrome in addition to optic nerve hypoplasia. We were able to map the phenotype to a single novel locus on 4q25-q28.2, in which we identified a five base-pair deletion in PLK4, which encodes a master regulator of centriole duplication. Conclusions Our discovery further confirms the role of genes involved in centriole biology in the pathogenesis of PD.
Primordial dwarfism (PD) is a term used to encompass a wide range of clinical conditions that have, in common, severe growth deficiency of prenatal onset, which persists postnatally.1 As such, PD offers a unique opportunity to observe the clinical consequences of perturbing key pathways involved in the growth of multicellular organisms.2 The past decade has witnessed a marked acceleration in the discovery of genes that are mutated in various subtypes of PD. The emerging theme from these discoveries is that DNA damage repair defects and, more commonly, centriole biology abnormalities are key pathogenic mechanisms that underlie virtually all PD forms that have been characterised at the molecular level to date.2 Thus, genes involved in these mechanisms are attractive candidates in the pursuit to capture the full genetic heterogeneity of PD. In the largest published study on the genetics of PD in which we described four novel disease genes, we have shown that many patients with PD remain undiagnosed at the molecular level.1 In an effort to characterise additional PD genes, we recruited a previously undescribed multiplex family. In this family from Southern Saudi Arabia, healthy first cousin once removed parents presented to the medical genetics clinic with two children, a 40-month-old daughter (IV:4) and a 19-month-old son (IV:5), whose clinical phenotypes were
strikingly similar. Both were born following fullterm pregnancies complicated by intrauterine growth retardation. Profound growth deficiency was evident at birth with weight of 1.45 kg (−3.7 SD), length of 40 cm (−4.2 SD) and head circumference of 26 cm (−5.9 SD, birth growth parameters are unavailable for the brother, but he was extremely similar to the sister by parental report). Both siblings have significant global developmental delay, but are not known to have any other medical problems. Physical examination of IV:4 and IV:5 revealed microcephalic PD with weight of 4.5 kg and 3.7 kg (−6.9 SD and −6.5 SD), length of 68 cm and 58 cm (−7.2 SD and −6.4 SD) and head circumference of 33 cm and 31.5 cm (−10.1 SD and −11.8 SD). They both had classical Seckel facies with sloping forehead, prominent nose, prominent eyes and micrognathia (figure 1). Additionally, the sister had prominent metopic sutures. Both had evidence of optic nerve hypoplasia on fundus examination, as well as strabismus. Skeletal survey revealed general symmetrical mild shorting of long bones but no frank dysplastic changes, and karyotyping was normal. Other than microcephaly and an arachnoid cyst, brain MRI on IV:4 was normal. Family history was significant for an affected paternal half-sister (IV:2) whose mother shares the same geographical origin but is not known to be directly related. IV:2 had birth growth parameters of 1.90 kg for weight (−2.9 SD), 43 cm for length (−2.8 SD) and 27 cm for head circumference (−5.2 SD), and current growth parameters (at 18 m of age) of 4 kg for weight (−7 SD), 56 cm for length (−7.5 SD) and 30.5 cm for head circumference (−12.5 SD). Her facial features were identical to those described above, and she also had evidence of optic nerve hypoplasia. The multiplex and consanguineous nature of this family appeared conducive to the application of autozygosity mapping to identify the responsible locus for Seckel syndrome in the probands and their half-sister. After signing a written informed consent form (KFSHRC IRB approval RAC#2080006), venous blood was collected from the two probands, unaffected parents and stepmother and their halfsister. DNA extraction was followed by genomewide genotyping on the Axiom single nucleotide polymorphism (SNP) chip platform and determination of the autozygome per individual using runs of homozygosity as surrogates as described before.3 The autozygomes of the three affected members overlapped on a single autozygous interval
Shaheen R, et al. J Med Genet 2014;51:814–816. doi:10.1136/jmedgenet-2014-102790
Downloaded from http://jmg.bmj.com/ on March 27, 2015 - Published by group.bmj.com
New loci
Figure 1 Identification of a family with Seckel syndrome that maps to a novel locus on chromosome 4. (A) Pedigree of the multiplex family (index is denoted by red arrow). (B) Clinical image of two patients showing the classical Seckel facies with sloping forehead, prominent nose, prominent eyes and micrognathia. (C) AgileMultiIdeogram showing the shared region of homozygosity (ROH) between the three affected in the family on chromosome 4 (dark blue, red arrow). (D) Genome-wide linkage analysis reveals a single peak on chromosome 4. (E) Upper panel: Diagram of PLK4 (triangle indicates the site of the mutation) and sequence chromatogram of the deletion with the control tracing shown for comparison (location of mutation indicated with red line). Lower panel: Schematic of the PLK4 and the location of the frameshift mutation before the cryptic polo-box domain.
(Chr4:112904466-129392060, GRCh37/hg19) that was not shared by any of the unaffected members, which was further confirmed by linkage analysis using EasyLinkage (figure 1). This result confirms that Seckel syndrome in this family maps to a previously undescribed locus on chr4q25-4q28.2. In order to identify the causal mutation within this novel locus, we examined the 144 genes therein for candidacy using the ToppGene tool which ranks genes according to their relevance to a set of training genes that are entered by the user.4 We entered all previously described PD genes in the training set and all the genes within the interval in the test set. Since most of the PD genes play a role in centriolar biology, PLK4 was among the top ranked genes given its established role as a master regulator of centriole duplication (see below). Indeed, full sequencing of PLK4 using custom-made primers (available upon request) revealed a novel five base-pair deletion that fully segregates with the Seckel phenotype in the study family (figure 1). Centrioles are barrel-shaped cellular organelles that play critical roles in dividing cells by nucleating the microtubules in two opposite poles to facilitate the proper segregation of chromosomes (microtubule organising centre).5 In non-dividing cells, centrioles translocate near the cell membrane to function as basal bodies that template the formation of cilia (motile and primary), which are involved in numerous sensing, mechanical and signalling functions.6 Centriole assembly is a complex and highly coordinated process that ensures the formation of only one pair of orthogonally oriented centrioles per cell cycle to Shaheen R, et al. J Med Genet 2014;51:814–816. doi:10.1136/jmedgenet-2014-102790
maintain genomic integrity.7 The earliest known step in centriole assembly is the recruitment of PLK4 to the mother centriole. PLK4 is one of four mammalian polo-like kinases, but is sufficiently divergent from PLK1, 2 and 3, that it was initially described as a distinct member and given the name SAK (for Snk/Plk-akin kinase).8 Depletion of PLK4 has been shown to abolish centriole formation (both de novo and mother centrioletemplated), whereas overexpression results in centriole amplification, hence the designation ‘master regulator’ of centriole assembly.9–11 Recent evidence suggests a complex interaction between PLK4 and CEP192 and CEP152 to form the ninefold symmetry microtubule-based cartwheel scaffold upon which the mature centriole forms and elongates, and in the absence of PLK4, this fundamental early step of procentriole nucleation fails.12 13 Not surprisingly, therefore, complete deficiency of murine Plk4 and its nematode ortholog ZYG-1 is lethal (Plk4 −/− mice die at E7.5).14 15 Deletion mapping and mutagenesis studies have clearly pointed to the CPB (cryptic polo-box) domain (641–880) of the 970aa PLK4 as absolutely essential for its role in centriole assembly since a mutant that retains the kinetic domain but lacks this domain completely fails to induce centriole assembly.16 Mutations in key players in centriole biology have been linked to PD, for example, CENPJ (also known as CPAP), CEP152, PCNT and POC1A (reviewed by Alkuraya, submitted). The prevailing theory is that quantitative or qualitative defects of centrioles greatly impair the dynamics of mitosis, which is 815
Downloaded from http://jmg.bmj.com/ on March 27, 2015 - Published by group.bmj.com
New loci particularly detrimental to early embryonic development when cellular proliferation peaks resulting in a lasting constraint of growth potential.2 Neuroprogenitor cells at the periventricular zones are particularly vulnerable because of their high mitosis index and also because they are extremely sensitive to the plane of cell division that determines the pools of self-renewing progenitors versus differentiated cells that migrate and populate the cerebral cortex, and centrioles play a key role in that process.17 We believe that PLK4, in view of the above, is a compelling candidate gene for PD (Seckel syndrome specifically). It is worth highlighting that a key binding partner of PLK4, CEP152 has already been shown to be mutated in patients with Seckel syndrome as has CENPJ, another core centrosomal protein that is recruited by CEP152 during centriole assembly.18 19 Although lack of patient-derived cells precluded experimental confirmation, we note that the homozygous truncating mutation we identified is predicted to fully abolish the CPB domain, so it is likely to severely impair PLK4 function and result in deficient centriole assembly. However, it appears from the universal lethality of complete deficiency of PLK4 orthologs that at least some function is retained, possibly through retention of the kinase domain to account for the viability of the three patients. Interestingly, Plk4 has been found to be highly expressed in the periventricular zone of the developing mouse brain, which would be consistent with the severe microcephalic component of Seckel syndrome in the study family.8 In summary, we establish a novel locus for Seckel syndrome on 4q25-28.2 and propose PLK4 as a compelling candidate based on a homozygous truncating mutation in a gene known for its necessary role in centriole assembly. Our discovery expands the spectrum of centriole-related genes and establishes centriole biology as a central pathogenic mechanism in PD. Acknowledgements We thank the study family for their enthusiastic participation. We also thank the Genotyping and Sequencing Core Facilities at KFSHRC for their technical help. Contributors RS, ST, FSA: collected and analysed the data and wrote the manuscript. AA: collected and analysed the data. Competing interests None. Patient consent Obtained. Ethics approval KFSHRC IRB. Provenance and peer review Not commissioned; internally peer reviewed.
816
REFERENCES 1
2 3 4
5 6 7 8
9 10
11 12
13
14 15
16 17 18 19
Shaheen R, Faqeih E, Ansari S, Abdel-Salam G, Al-Hassnan ZN, Al-Shidi T, Alomar R, Sogaty S, Alkuraya FS. Genomic analysis of primordial dwarfism reveals novel disease genes. Genome Res 2014;24:291–9. Klingseisen A, Jackson AP. Mechanisms and pathways of growth failure in primordial dwarfism. Genes Dev 2011;25:2011–24. Alkuraya FS. Discovery of rare homozygous mutations from studies of consanguineous pedigrees. Curr Protoc Hum Genet 2012;6.12. 1–6.12. 13. Chen J, Bardes EE, Aronow BJ, Jegga AG. ToppGene Suite for gene list enrichment analysis and candidate gene prioritization. Nucleic Acids Res 2009;37(Suppl 2): W305–11. Basto R. A centriolar lifeline. Nat Rev Mol Cell Biol 2012;13:686. Bettencourt-Dias M, Hildebrandt F, Pellman D, Woods G, Godinho SA. Centrosomes and cilia in human disease. Trends Genet 2011;27:307–15. Avidor-Reiss T, Gopalakrishnan J. Building a centriole. Curr Opin Cell Biol 2013;25:72–7. Fode, C, Motro B, Yousefi S, Heffernan M, Dennis JW. Sak, a murine protein-serine/ threonine kinase that is related to the Drosophila polo kinase and involved in cell proliferation. Proc Natl Acad Sci USA 1994;91:6388–92. Kleylein-Sohn J, Westendorf J, Le Clech M, Habedanck R, Stierhof YD, Nigg EA. Plk4-induced centriole biogenesis in human cells. Dev Cell 2007;13:190–202. Coelho PA, Bury L, Sharif B, Riparbelli MG, Fu J, Callaini G, Glover DM, Zernicka-Goetz M. Spindle formation in the mouse embryo requires plk4 in the absence of centrioles. Dev Cell 2013;27:586–97. Eckerdt F, Yamamoto TM, Lewellyn AL, Maller JL. Identification of a polo-like kinase 4-dependent pathway for de novo centriole formation. Curr Biol 2011;21:428–32. Park SY, Park JE, Kim TS, Kim JH, Kwak MJ, Ku B, Tian L, Murugan RN, Ahn M, Komiya S, Hojo H, Kim NH, Kim BY, Bang JK, Erikson RL, Lee KW, Kim SJ, Oh BH, Yang W, Lee KS. Molecular basis for unidirectional scaffold switching of human Plk4 in centriole biogenesis. Nat Struct Mol Biol 2014;21:696–703. Kim TS, Park JE, Shukla A, Choi S, Murugan RN, Lee JH, Ahn M, Rhee K, Bang JK, Kim BY, Loncarek J, Erikson RL, Lee KS. Hierarchical recruitment of Plk4 and regulation of centriole biogenesis by two centrosomal scaffolds, Cep192 and Cep152. Proc Natl Acad Sci USA 2013;110:E4849–57. Hudson JW, Kozarova A, Cheung P, Macmillan JC, Swallow CJ, Cross CJ, Dennis JW. Late mitotic failure in mice lacking Sak, a polo-like kinase. Curr Biol 2001;11:441–6. Lettman MM, Wong YL, Viscardi V, Niessen S, Chen SH, Shiau AK, Zhou H, Desai A, Oegema K. Direct binding of SAS-6 to ZYG-1 recruits SAS-6 to the mother centriole for cartwheel assembly. Dev Cell 2013;25:284–98. Habedanck R, Stierhof YD, Wilkinson CJ, Nigg EA. The Polo kinase Plk4 functions in centriole duplication. Nat Cell Biol 2005;7:1140–6. Thornton GK, Woods CG. Primary microcephaly: do all roads lead to Rome? Trends Genet 2009;25:501–10. Al-Dosari MS, Shaheen R, Colak D, Alkuraya FS. Novel CENPJ mutation causes Seckel syndrome. J Med Genet 2010;47:411–14. Kalay E, Yigit G, Aslan Y, Brown KE, Pohl E, Bicknell LS, Kayserili H, Li Y, Tüysüz B, Nürnberg G, Kiess W, Koegl M, Baessmann I, Buruk K, Toraman B, Kayipmaz S, Kul S, Ikbal M, Turner DJ, Taylor MS, Aerts J, Scott C, Milstein K, Dollfus H, Wieczorek D, Brunner HG, Hurles M, Jackson AP, Rauch A, Nürnberg P, Karagüzel A, Wollnik B. CEP152 is a genome maintenance protein disrupted in Seckel syndrome. Nat Gene 2011;43:23–6.
Shaheen R, et al. J Med Genet 2014;51:814–816. doi:10.1136/jmedgenet-2014-102790
Downloaded from http://jmg.bmj.com/ on March 27, 2015 - Published by group.bmj.com
Mutation in PLK4, encoding a master regulator of centriole formation, defines a novel locus for primordial dwarfism Ranad Shaheen, Saeed Al Tala, Agaadir Almoisheer and Fowzan S Alkuraya J Med Genet 2014 51: 814-816 originally published online October 15, 2014
doi: 10.1136/jmedgenet-2014-102790 Updated information and services can be found at: http://jmg.bmj.com/content/51/12/814
These include:
References Email alerting service
Topic Collections
This article cites 18 articles, 6 of which you can access for free at: http://jmg.bmj.com/content/51/12/814#BIBL Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article.
Articles on similar topics can be found in the following collections Calcium and bone (291) Molecular genetics (1193)
Notes
To request permissions go to: http://group.bmj.com/group/rights-licensing/permissions To order reprints go to: http://journals.bmj.com/cgi/reprintform To subscribe to BMJ go to: http://group.bmj.com/subscribe/
