DOI: 10.1111/exd.12498
Commentary
www.wileyonlinelibrary.com/journal/EXD
Will the wound-healing field earn its wings? Aimee E. Anderson1 and Michael J. Galko1,2 1
Department of Biochemistry and Molecular Biology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; 2Genes & Development Graduate Program, The University of Texas Graduate School of Biomedical Sciences, Houston, TX, USA Correspondence: Michael J. Galko, Department of Biochemistry and Molecular Biology, The University of Texas MD Anderson Cancer Center, Unit 1000, 1515 Holcombe Boulevard, Houston, TX 77030, USA, Tel.: 713-792-9182, Fax: 713-834-6291, e-mail: [email protected] Abstract: In a recently published issue of Experimental Dermatology, Dr. Nuria Paricio and colleagues review recent advances using the fruit fly, Drosophila melanogaster, as a woundhealing model. They describe many of the advantages of the fly model for gene discovery and functional analysis, highlighting its particular strengths and limitations for studies of wound healing. This commentary assumes that dermatologist–scientists and fly wound-healing researchers share a common field-wide goal of
discovering all of the clinically relevant wound-healing genes and understanding in molecular detail how those genes work. We ask: how can we cooperate to achieve this shared goal?
At first glance, the dermatologist reading the Paricio review (1) might approach it with some scepticism. If one focuses where dermatologists usually focus, on the skin, there is some basis for this scepticism. As pointed out in the review, fly skin differs from that of mammals, and to a dermatologist, some of those differences will seem quite profound. Epidermal cells in larvae and adult flies form a simple monolayer and do not divide. Perhaps most damning, especially to those interested in the dermal–epidermal crosstalk that ensues following wounding, fly skin does not have an underlying layer of dermal fibroblasts, just a simple basal lamina that separates the epithelial sheet from the haemolymph (blood) of the underlying open circulatory system. Indeed, at first glance, there seems little hope for modelling anything related to epidermal wound healing. And yet, zap fly embryos with a laser, or poke embryos, larvae or adults with a needle, or pinch larvae with forceps, and they will heal their wounds completely and quickly (2–7). This says two things: (i) wound healing is an evolutionarily ancient response that likely possesses a core set of conserved genes; and (ii) Drosophila researchers do not think quite the same way as dermatologists might about this problem of wound healing. This is not to cast stones or suggest that one way of thinking about the woundhealing problem is ‘better’ than another. There is no ‘right’ way to think about it. If one views the shared goal above – discovering all of the clinically relevant wound-healing genes and understanding in molecular detail how those genes work – the field as a whole is going to need all of the quality modes of thinking it can obtain. Is the fact that flies can heal their wounds quickly and efficiently of any utility to clinically-minded wound-healing researchers? Here, there are certainly reasons for optimism. Paricio and colleagues spend most of their review selling the largest strengths of the Drosophila wound-healing system. Flies are best for studying what genes are required, within epidermal cells, for wounds to heal. This is because it is possible, in the Drosophila system, to perform some rather remarkable genetic tricks. Many of these tricks, such as tissue-specific genetic screens and the ability to flu-
orescently label virtually any tissue of interest in vivo, are covered. But what we would like to do briefly here is dramatize the hypothetical plights of an aspiring young dermatologist–researcher and an aspiring junior fly researcher (Fig. 1) and illustrate why we think the time is ripe for them to start working together in earnest towards our field-wide goal. First, let us imagine our dermatologist–researcher. Unable to perform an unbiased genome-wide genetic screen for wound-healing mutants, she does the next best thing: a microarray study of healing wounds. After appropriate analysis, she generates a list of many genes whose expression is changed in the vicinity of the wound. Of course, the perennial difficulty with such studies is how to prioritize the genes on this list, which typically include 50–200 candidates above a certain cut-off (see for example, (8– 15)). But which of these genes are functionally required for healing? As Paricio and colleagues point out, knocking all of these genes out in mice, conditionally or otherwise, is not a feasible option for reasons of both time and money. Should the genes then be prioritized by magnitude of fold-expression change? By a secondary screen such as spatial expression around the wound? By molecular identity of the genes in question and their known or suspected functions? Often, the safest route is the latter. Relatives of proteases, extracellular matrix factors, growth factors and other classes of genes with already established functions in wound healing become highly attractive candidates for analysis when our researcher is thinking shrewdly about the vagaries of publishing and funding. While this strategy is eminently sensible for the junior individual, it cannot help the field advance the field-wide goal of complete elucidation of the functional roles of all wound-healing genes. Probably, there are some great ‘sleeper’ genes further down the microarray candidate list that will remain unstudied because these are much riskier and time intensive to pursue. Now, let us imagine our fly researcher who is employing a new fly wound-healing assay. Using some of the techniques described by Paricio and colleagues, he can screen in an unbiased fashion
ª 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Experimental Dermatology, 2014, 23, 809–810
Key words: collaborative science – Drosophila – functional genomics – model systems – wound healing
Accepted for publication 7 July 2014
809
Anderson and Galko
Figure 1. Conceptual flowchart of a highly productive mouse–fly wound-healing collaboration. A fly researcher (top left, safety glasses) shares data with a dermatologist–researcher (top right, stethoscope). By comparing lists of genes required for wound healing in flies with list of genes upregulated in healing vertebrate wounds, they pinpoint genes at the intersection of the two datasets (green portion of Venn diagram). These are the highest priority candidates for functional testing in mice. Any genes that are also required for healing in the mouse will point to specific pathways, which will likely contain both positively and negatively acting members. These can be examined for function in the fly and expression in the mouse preparatory to developing more sophisticated hypotheses about the role of the pathway in conserved wound-healing processes. From this mouse–fly feedback loop, exciting new avenues of research may emerge.
for genes that are functionally required in the fly epidermis for wound healing. Such an approach can also generate a fairly large list of ‘hits’ (16–18). The fly researcher is now faced with a dilemma that is different but surprisingly similar to that of the dermatologist–researcher. His sincere desire is to find new woundhealing genes that will translate to human skin, but he lacks the expertise and resources to perform these translational studies. So, in isolation, he makes a calculated decision to focus on hits that he knows will establish relevance because they have already been
implicated in mouse wound healing. Again, this is a safe strategy for impressing editors and funding agencies that his new system can find at least some of the ‘right’ genes, but how many exciting, uncharacterized, conserved hits from his screen were left behind? Thus, both young researchers, and indeed the larger field, are really faced with the same problem: partly as a result of understandable pressures and field-wide caution, they do not know if any of their ‘riskier’ hits are functionally required for skin wound healing in mice or humans. As these genes are as yet functionally untested in any system, any of them might hold the key to a new therapy or diagnostic tool that could help patients – but which to test? Their complementary expertise is exactly why these two researchers need each other. Imagine what happens when our two hypothetical researchers meet each other at a conference. The dermatologist–researcher talks excitedly about all those novel genes from her microarray studies but bemoans her inability to test them all functionally. The fly researcher offers to test all of the 100 orthologs’ functional requirements with his Drosophila model and within weeks has identified a number of genes, perhaps 10 or 20, required for wound healing in the fly. These are by far the strongest candidates for further analysis in mice. Later, the Drosophila researcher mentions new exciting hits from his own functional screen, but of course he does not know whether any of these genes are even expressed in mammalian skin. The dermatologist immediately notices several genes on the fly researcher’s list that were also strongly upregulated in her own microarrays. Together, they generate a list of genes that are required for fly wound healing and are upregulated during mouse wound healing. The high bar for investing time and money to analyse conserved but relatively unstudied genes has now been lowered substantially by this collaboration. In their review, Paricio and colleagues give dermatologists the vocabulary they need to understand some of the great tools fly researchers now have ready to offer the field. If we can cooperate to share all of the powerful features of the fly and mammalian model systems, it seems likely that the wound-healing field can truly take flight and advance towards the long-held field-wide goal of identifying all wound-healing genes.
Author contribution M.J.G. and A.E.A. wrote the manuscript. M.J.G. and A.E.A. created the figure, part of which was modified from work by Christine Lesch. The authors wish to thank Seol Hee Im and Heather Turner for useful comments on the manuscript.
Conflict of interest The authors declare no conflicts of interest.
References 1 Munoz-Soriano V, Lopez-Domenech S, Paricio N. Exp Dermatol 2014: 23: 538–542. 2 Galko M J, Krasnow M A. PLoS Biol 2004: 2: E239. 3 Burra S, Wang Y, Brock A R et al. Methods Mol Biol 2013: 1037: 449–461. 4 Wood W, Jacinto A, Grose R et al. Nat Cell Biol 2002: 4: 907–912. 5 Stramer B, Wood W, Galko M J et al. J Cell Biol 2005: 168: 567–573. 6 Ramet M, Lanot R, Zachary D et al. Dev Biol 2002: 241: 145–156.
810
7 Losick V P, Fox D T, Spradling A C. Curr Biol 2013: 23: 2224–2232. 8 Chen L, Arbieva Z H, Guo S et al. BMC Genomics 2010: 11: 471. 9 Colwell A S, Longaker M T, Peter Lorenz H. Wound Repair Regen 2008: 16: 450–459. 10 Cooper L, Johnson C, Burslem F et al. Genome Biol 2005: 6: R5. 11 Li X, Mohan S, Gu W et al. Mamm Genome 2001: 12: 52–59. 12 Roy S, Khanna S, Rink C et al. Physiol Genomics 2008: 34: 162–184.
13 Nuutila K, Siltanen A, Peura M et al. Wound Repair Regen 2012: 20: 830–839. 14 Cole J, Tsou R, Wallace K et al. Wound Repair Regen 2001: 9: 360–370. 15 Chang H Y, Sneddon J B, Alizadeh A A et al. PLoS Biol 2004: 2: E7. 16 Lesch C, Jo J, Wu Y et al. Genetics 2010: 186: 943–957. 17 Campos I, Geiger J A, Santos A C et al. Genetics 2010: 184: 129–140. 18 Juarez M T, Patterson R A, Sandoval-Guillen E et al. PLoS Genet 2011: 7: e1002424.
ª 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Experimental Dermatology, 2014, 23, 809–810
Commentary
www.wileyonlinelibrary.com/journal/EXD
Will the wound-healing field earn its wings? Aimee E. Anderson1 and Michael J. Galko1,2 1
Department of Biochemistry and Molecular Biology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; 2Genes & Development Graduate Program, The University of Texas Graduate School of Biomedical Sciences, Houston, TX, USA Correspondence: Michael J. Galko, Department of Biochemistry and Molecular Biology, The University of Texas MD Anderson Cancer Center, Unit 1000, 1515 Holcombe Boulevard, Houston, TX 77030, USA, Tel.: 713-792-9182, Fax: 713-834-6291, e-mail: [email protected] Abstract: In a recently published issue of Experimental Dermatology, Dr. Nuria Paricio and colleagues review recent advances using the fruit fly, Drosophila melanogaster, as a woundhealing model. They describe many of the advantages of the fly model for gene discovery and functional analysis, highlighting its particular strengths and limitations for studies of wound healing. This commentary assumes that dermatologist–scientists and fly wound-healing researchers share a common field-wide goal of
discovering all of the clinically relevant wound-healing genes and understanding in molecular detail how those genes work. We ask: how can we cooperate to achieve this shared goal?
At first glance, the dermatologist reading the Paricio review (1) might approach it with some scepticism. If one focuses where dermatologists usually focus, on the skin, there is some basis for this scepticism. As pointed out in the review, fly skin differs from that of mammals, and to a dermatologist, some of those differences will seem quite profound. Epidermal cells in larvae and adult flies form a simple monolayer and do not divide. Perhaps most damning, especially to those interested in the dermal–epidermal crosstalk that ensues following wounding, fly skin does not have an underlying layer of dermal fibroblasts, just a simple basal lamina that separates the epithelial sheet from the haemolymph (blood) of the underlying open circulatory system. Indeed, at first glance, there seems little hope for modelling anything related to epidermal wound healing. And yet, zap fly embryos with a laser, or poke embryos, larvae or adults with a needle, or pinch larvae with forceps, and they will heal their wounds completely and quickly (2–7). This says two things: (i) wound healing is an evolutionarily ancient response that likely possesses a core set of conserved genes; and (ii) Drosophila researchers do not think quite the same way as dermatologists might about this problem of wound healing. This is not to cast stones or suggest that one way of thinking about the woundhealing problem is ‘better’ than another. There is no ‘right’ way to think about it. If one views the shared goal above – discovering all of the clinically relevant wound-healing genes and understanding in molecular detail how those genes work – the field as a whole is going to need all of the quality modes of thinking it can obtain. Is the fact that flies can heal their wounds quickly and efficiently of any utility to clinically-minded wound-healing researchers? Here, there are certainly reasons for optimism. Paricio and colleagues spend most of their review selling the largest strengths of the Drosophila wound-healing system. Flies are best for studying what genes are required, within epidermal cells, for wounds to heal. This is because it is possible, in the Drosophila system, to perform some rather remarkable genetic tricks. Many of these tricks, such as tissue-specific genetic screens and the ability to flu-
orescently label virtually any tissue of interest in vivo, are covered. But what we would like to do briefly here is dramatize the hypothetical plights of an aspiring young dermatologist–researcher and an aspiring junior fly researcher (Fig. 1) and illustrate why we think the time is ripe for them to start working together in earnest towards our field-wide goal. First, let us imagine our dermatologist–researcher. Unable to perform an unbiased genome-wide genetic screen for wound-healing mutants, she does the next best thing: a microarray study of healing wounds. After appropriate analysis, she generates a list of many genes whose expression is changed in the vicinity of the wound. Of course, the perennial difficulty with such studies is how to prioritize the genes on this list, which typically include 50–200 candidates above a certain cut-off (see for example, (8– 15)). But which of these genes are functionally required for healing? As Paricio and colleagues point out, knocking all of these genes out in mice, conditionally or otherwise, is not a feasible option for reasons of both time and money. Should the genes then be prioritized by magnitude of fold-expression change? By a secondary screen such as spatial expression around the wound? By molecular identity of the genes in question and their known or suspected functions? Often, the safest route is the latter. Relatives of proteases, extracellular matrix factors, growth factors and other classes of genes with already established functions in wound healing become highly attractive candidates for analysis when our researcher is thinking shrewdly about the vagaries of publishing and funding. While this strategy is eminently sensible for the junior individual, it cannot help the field advance the field-wide goal of complete elucidation of the functional roles of all wound-healing genes. Probably, there are some great ‘sleeper’ genes further down the microarray candidate list that will remain unstudied because these are much riskier and time intensive to pursue. Now, let us imagine our fly researcher who is employing a new fly wound-healing assay. Using some of the techniques described by Paricio and colleagues, he can screen in an unbiased fashion
ª 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Experimental Dermatology, 2014, 23, 809–810
Key words: collaborative science – Drosophila – functional genomics – model systems – wound healing
Accepted for publication 7 July 2014
809
Anderson and Galko
Figure 1. Conceptual flowchart of a highly productive mouse–fly wound-healing collaboration. A fly researcher (top left, safety glasses) shares data with a dermatologist–researcher (top right, stethoscope). By comparing lists of genes required for wound healing in flies with list of genes upregulated in healing vertebrate wounds, they pinpoint genes at the intersection of the two datasets (green portion of Venn diagram). These are the highest priority candidates for functional testing in mice. Any genes that are also required for healing in the mouse will point to specific pathways, which will likely contain both positively and negatively acting members. These can be examined for function in the fly and expression in the mouse preparatory to developing more sophisticated hypotheses about the role of the pathway in conserved wound-healing processes. From this mouse–fly feedback loop, exciting new avenues of research may emerge.
for genes that are functionally required in the fly epidermis for wound healing. Such an approach can also generate a fairly large list of ‘hits’ (16–18). The fly researcher is now faced with a dilemma that is different but surprisingly similar to that of the dermatologist–researcher. His sincere desire is to find new woundhealing genes that will translate to human skin, but he lacks the expertise and resources to perform these translational studies. So, in isolation, he makes a calculated decision to focus on hits that he knows will establish relevance because they have already been
implicated in mouse wound healing. Again, this is a safe strategy for impressing editors and funding agencies that his new system can find at least some of the ‘right’ genes, but how many exciting, uncharacterized, conserved hits from his screen were left behind? Thus, both young researchers, and indeed the larger field, are really faced with the same problem: partly as a result of understandable pressures and field-wide caution, they do not know if any of their ‘riskier’ hits are functionally required for skin wound healing in mice or humans. As these genes are as yet functionally untested in any system, any of them might hold the key to a new therapy or diagnostic tool that could help patients – but which to test? Their complementary expertise is exactly why these two researchers need each other. Imagine what happens when our two hypothetical researchers meet each other at a conference. The dermatologist–researcher talks excitedly about all those novel genes from her microarray studies but bemoans her inability to test them all functionally. The fly researcher offers to test all of the 100 orthologs’ functional requirements with his Drosophila model and within weeks has identified a number of genes, perhaps 10 or 20, required for wound healing in the fly. These are by far the strongest candidates for further analysis in mice. Later, the Drosophila researcher mentions new exciting hits from his own functional screen, but of course he does not know whether any of these genes are even expressed in mammalian skin. The dermatologist immediately notices several genes on the fly researcher’s list that were also strongly upregulated in her own microarrays. Together, they generate a list of genes that are required for fly wound healing and are upregulated during mouse wound healing. The high bar for investing time and money to analyse conserved but relatively unstudied genes has now been lowered substantially by this collaboration. In their review, Paricio and colleagues give dermatologists the vocabulary they need to understand some of the great tools fly researchers now have ready to offer the field. If we can cooperate to share all of the powerful features of the fly and mammalian model systems, it seems likely that the wound-healing field can truly take flight and advance towards the long-held field-wide goal of identifying all wound-healing genes.
Author contribution M.J.G. and A.E.A. wrote the manuscript. M.J.G. and A.E.A. created the figure, part of which was modified from work by Christine Lesch. The authors wish to thank Seol Hee Im and Heather Turner for useful comments on the manuscript.
Conflict of interest The authors declare no conflicts of interest.
References 1 Munoz-Soriano V, Lopez-Domenech S, Paricio N. Exp Dermatol 2014: 23: 538–542. 2 Galko M J, Krasnow M A. PLoS Biol 2004: 2: E239. 3 Burra S, Wang Y, Brock A R et al. Methods Mol Biol 2013: 1037: 449–461. 4 Wood W, Jacinto A, Grose R et al. Nat Cell Biol 2002: 4: 907–912. 5 Stramer B, Wood W, Galko M J et al. J Cell Biol 2005: 168: 567–573. 6 Ramet M, Lanot R, Zachary D et al. Dev Biol 2002: 241: 145–156.
810
7 Losick V P, Fox D T, Spradling A C. Curr Biol 2013: 23: 2224–2232. 8 Chen L, Arbieva Z H, Guo S et al. BMC Genomics 2010: 11: 471. 9 Colwell A S, Longaker M T, Peter Lorenz H. Wound Repair Regen 2008: 16: 450–459. 10 Cooper L, Johnson C, Burslem F et al. Genome Biol 2005: 6: R5. 11 Li X, Mohan S, Gu W et al. Mamm Genome 2001: 12: 52–59. 12 Roy S, Khanna S, Rink C et al. Physiol Genomics 2008: 34: 162–184.
13 Nuutila K, Siltanen A, Peura M et al. Wound Repair Regen 2012: 20: 830–839. 14 Cole J, Tsou R, Wallace K et al. Wound Repair Regen 2001: 9: 360–370. 15 Chang H Y, Sneddon J B, Alizadeh A A et al. PLoS Biol 2004: 2: E7. 16 Lesch C, Jo J, Wu Y et al. Genetics 2010: 186: 943–957. 17 Campos I, Geiger J A, Santos A C et al. Genetics 2010: 184: 129–140. 18 Juarez M T, Patterson R A, Sandoval-Guillen E et al. PLoS Genet 2011: 7: e1002424.
ª 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Experimental Dermatology, 2014, 23, 809–810
