Sabre and Environmentally Responsive Cell Expansion

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9506308 Emmons The aim of this project is to elucidate the molecular genetic basis for the evolution of a morphological novelty. The organisms to be studied are free living soil nematodes related to the model genetic organism Caenorhabditis elegans. In previous work it has been shown that a novel morphological feature of the male copulatory structure has appeared during evolution of the genus Caenorhabditis. Genetic studies in C. elegans have revealed that development of this feature involves several genes acting in a morphogenetic pathway. One gene of this pathway is the nematode homolog of the transcription factor Pax-6. Pax-6 is found in many multicellular organisms, from insects to vertebrates, and is thought to play an essential role in patterning the central nervous system, as well as in the development of the eye. The role of evolutionary change at the Pax-6 locus in the appearance of the novel morphological feature of nematodes will be investigated. Cell lineages will be determined for several species and compared to those of C. elegans to determine what role change in cell lineage has played in evolution of morphology. The Pax-6 homolog of one non- Caenorhabditis species will be isolated, sequenced, and compared to the gene of C. elegans. The aim is to determine whether genetic changes affecting morphology have occurred upstream of Pax-6, in the promoter of Pax-6, in the protein coding region of Pax-6, or downstream of Pax-6. If the genes of C. elegans and the second species are identical in amino acid sequence and are expressed in the same cells, then evolutionary change must have affected downstream functions. If the two genes are not identical, then a series of hybrid genes constructed from the genes of the two species will be tested in C. elegans and in the second species. By identifying in detail the genetic changes in a developmental gene that have given rise to changes in morphology, Dr. Emmons hopes to help elucidate both the genetic determi nants of morphogenesis, and the nature of the genetic changes that result in evolution of morphology. The results of this study should contribute towards answering several outstanding questions concerning the mechanism of evolution. ***