The genetic mechanisms that regulate development of the genitourinary system (reproductive and urologic organs) are among the least understood in developmental biology. Paradoxically, birth defects of the external genitalia are among the most frequently occurring malformations in humans, ranking second only to heart defects. Some of the most common genital malformations in humans -- such as an open urethral tube and a persistant cloaca (a single outlet for urinary and digestive tracts) -- resemble the natural variation seen across vertebrates. Thus, identification of the mechanisms that direct genitourinary development in non-mammalian vertebrates will have implications for our understanding of abnormal genitourinary development in humans. Moreover, comparative developmental studies will identify the genetic mechanisms that drive evolutionary change. This project investigates the developmental basis of external genital evolution in birds, a group that exhibits a broad spectrum of anatomical patterns that range from an almost mammal-like phallus to complete absence of external genitalia. The approach will combine molecular, cellular, and experimental embryological methods to determine the extent to which the genetic circuits that regulate genital development are conserved between birds and mammals. It is expected that the genetic program that directs genital development in mammals also operates in the most primitive birds, which would point to a surprisingly deep origin of a character that had been thought to be exclusive to mammals. In addition, it is predicted that in a specific group of birds (known as the galliformes), failure to form external genitalia results from disruption of an ancient cell survival mechanism, and excessive cell death causes a developmental arrest. Comparative studies using non-traditional model systems, such as birds and reptiles, are needed to develop new models for disease, and this project will contribute this infrastructure to the research community. Identification of new avian (bird) embryo models is especially important given the prohibitive cost of rodent models for many researchers at small colleges and in countries with limited resources. The impacts of the proposed activities extend beyond scientific discovery. By identifying actual mechanisms of evolutionary change, this research will contribute to society's understanding of how evolution works, which will improve our national literacy in evolution. The project dovetails with educational outreach activities involving students from elementary school to undergraduates, and contains specific action items to increase participation of women and other groups underrepresented in science.
This project resulted in eight peer-reviewed publications on evolution of external genital development. Reproductive organs are among the fastest evolving structures and modifications of these structures play a major role in speciation events. In addition, genital organs are affected by birth defects at a frequency second only to heart defects, currently affecting approximately 1 in every 250 live births. Some of the malformations in humans resemble the genital structures of non-human vertebrates; however, little is known about the genetic control of genital development outside of mouse models, and even in the laboratory mouse these processes are not well understood. In this project, we investigated the molecular genetic mechanisms underlying the evolution of reproductive structures in birds (and related reptiles). The study produced results that challenge a longstanding tenet of evolutionary biology known as Dollo’s Law, which states that structures lost to evolution cannot re-appear. We showed that loss of external genitalia in land fowl occurs by an embryonic phase of cell death, which deconstructs the embryonic genital eminence. In birds that lack external genitalia, the entire gene network needed for phallus development is intact and functional prior to this wave of cell death. As such, re-emergence of genital organs can occur simply by blocking cell death. We showed that this is controlled by a growth factor known as bone morphogenetic protein 4 (Bmp4), and antagonism of Bmp signaling can prevent the wave of cell death and restore outgrowth of the phallus. The results suggest that loss of the intromittent phallus in birds resulted from acquisition of a new domain of Bmp4 expression, which promotes cell death and regression of the phallus. A major challenge in evolutionary morphology concerns the relatedness of genital organs in different groups of vertebrates. By studying a range of species with diverse genital morphologies, this project shed light on the ancestral condition and provided new developmental data that help to resolve the evolutionary history of genitourinary organs. Our results indicate that the failure of urethral tube closure in humans can be interpreted as a reversion to the primitive condition. By investigating the genetic events that drove the evolutionary transition from a urethral groove to a urethral tube, this project created an opportunity to identify novel mechanisms of urethral tube closure that could be affected in human birth defects. The project provided training for a total of six female graduate students and postdocs, three of whom are members of groups underrepresented in the sciences. By training these young scientists, the project had a major impact on human resource development in science. This project developed several new model organisms (duck, turtle and anole) for studies of external genital development, which offers new alternatives to rodents. The project also involved outreach to elementary school students and teachers in the local community, as described below: Outreach to elementary, middle and high schools, public lectures, and undergraduate education: 2013. Keynote speaker at Florida Regional Junior Science, Engineering, and Humanities Symposium (JSEHS) for over 250 high school students and teachers. 2013 1 lecture on the genetics of animal development. Talbot Elementary School science class 2013 5 lectures on vertebrate evolution, developmental genetics, natural selection and sexual selection. Kanapaha Middle School 7th grade advanced science class. 2011-2013. 10 lectures each year to 3rd and 5th grade Science Symposia at Wiles Elementary school 2007-2013. Annual visiting lectures and lab demonstrations on embryonic development and evolution, Wiles Elementary School Public lectures at Whitney Marine Lab Evening Lecture Series (2010), and Institute for Learning in Retirement (continuing education for senior citizens). During the tenure of this grant, 18 undergraduate researchers were trained in my laboratory. Mentor for HHMI Science For Life and G.A.T.O.R. (Group Advantaged Training Of Research) programs for high school and undergraduate students interested in
