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Martin J Cohn

University of Florida
P.O. Box 103610
Cancer/Genetics Research Complex
Gainesville, FL 32610


Taxa Studied: Invertebrate Animals, Vertebrate Animals
Techniques Employed: Degenerate PCR, Quantitative PCR (qPCR), Microarrays, 454 Pyrosequencing, Solexa (Illumina) Sequencing, Bioinformatics/Sequence Analysis, In Situ Hybridization, Antibody Staining, Sectioning for Histology, Scanning Electron Microscopy, Epifluoresence Microscopy, Confocal Microscopy, Transgenesis
Research Description: The Cohn lab studies how appendages such as limbs and genitalia develop in vertebrate embryos. We combine developmental genetics of the mouse with comparative development of a wide range of organisms to understand the relationships between development and evolution. Early Evolution of Fins and Limbs One focus of my lab is the molecular basis for the origin of fins and for the modification of fins into limbs. Recent discoveries of early vertebrate fossils revealed that median fins (such as dorsal, caudal, and anal fins) evolved before paired fins. These findings led us to hypothesize that the genetic program for fin (and later, limb) development originated in an unexpected position, the dorsal and ventral midline, rather than in the body wall. To test this hypothesis, we are comparing development in two key groups of basal vertebrates, lampreys and sharks. Lampreys are jawless fish that diverged from our lineage after median fins evolved, but before the origin of paired fins. Therefore, lampreys can provide insights into primitive mechanisms of body wall patterning. Sharks are the most primitive living vertebrates with paired fins, and because some shark species retain primitive fin anatomy, they provide a window into how early fins may have formed. Development of External Genitalia The genetic machinery for appendage development was recycled yet again during the evolution of external genitalia. Within vertebrates, true external genital organs are found only in tetrapods (vertebrates with fingers and toes at the ends of their limbs). The origin of external genitalia allowed vertebrates to transition from external fertilization to internal fertilization, an important step toward an obligate terrestrial lifestyle. This new type of appendage underwent another modification near the origin of mammals, when the open groove used for delivery of sperm was remodeled into a closed urethral tube. It is formation of this urethral tube that is affected in a condition called hypospadias, one of the most common birth defects in humans. Hypospadias affects approximately 1 in 250 live births and is characterized by a failure of urethral tube closure. We are interested in the genetic mechanisms involved in development of external genital organs, and identifying how modifications of these mechanisms drove the diversification of genital organs in vertebrates. The incidence of hypospadias has approximately doubled, without explanation, since the late 1960s. It is widely suspected that environmental endocrine-disrupting chemicals (EDCs) contribute to the rising incidence of genitourinary malformations, although how these contaminants interact with the gene networks that regulate development is unknown. Could hypospadias result from exposure of an embryo to EDCs that transiently down-regulate the expression of genes required for urethral tube closure? We are now studying environmental contaminants that induce hypospadias, and using genomic tools to identify transcriptional responses to these chemicals. Our hope is that discovery of the genetic pathways that respond to environmental contaminants will provide a foundation for the development of preventive strategies.
Lab Web Page: http://www.evodevo.net
Willing to Host Undergraduates: YES
Actively Seeking Undergraduates: YES
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