Dr. Padgett is requesting support for a relatively new area of research for his lab, the identification of TGF-beta signalling pathway components in C. elegans; his previous work on this signalling pathway has been conducted in Drosophila, work which continues. The secreted polypeptides of the TGF-beta family bind to receptors on target cells iniating an assortment of signal dependent events. The receptors are serine-threonine kinases. Dr. Padgett contrasts what is known about the comparatively well-defined tyrosine kinase receptor signalling pathways in Drosophila and C. elegans, in particular, noting the poorly understood state of the signalling events and components of the serine- threonine pathway. He has begun a study of the pathway in C. elegans because of the great potential for genetic dissection in this organism. He began with the information from other groups that two C. elegans genes, known for their participation in the dauer pathway, daf-1 and daf-4 are members of the TGF-beta receptor family. He also noted that mutant alleles have phenotypes suggestive of broader functions, including small body size, sensory ray transformations in the male tail, and egg- laying defects. Reasoning that similar phenotypes in other mutants should suggest candidates for other participants in the TGF-beta pathway, he turned up seven other previously isolated mutants with the small body phenotype. Three of these, sma-2. sma-3 and small-4, have phenotypes identical to those of daf-4. He cloned sma-2, made relatively straightforward as the gene had been mapped fairly precisely and the region to which it had been mapped had been sequenced as part of the worm genome project. The process of conducting these molecular studies, two additional homologs had been identified. These turned out to be sma-3 and -4. Although these proteins are related to one another, they are otherwise novel. Homologies in the N and C terminii separated by divergent proline rich regions led to the hypothesis that these proteins form a complex and act at a similar point in the pathway. It now turns out that these proteins are related to a Drosophila gene that can enhance dpp phenotypes, Mothers against dpp or Mad. The Padgett lab has also cloned three homologs from mice and find they are highly conserved. This group of proteins has been named the DWARFIN family. Genetic mosaic studies were conducted on daf-4 andsma-2 establishing that they have autonomous functions. It was found that sma-2 acts in the same cell as the daf-4 receptor. sma-2 was shown not to be responsible for regulating daf-4 expression, and the current view is that sma-2 is either a signal transducer or a modifier of the receptor. Genetic screens were conducted for new small body size mutants and numerous candidates have been recovered. Dr. Padgett proposes to continue this work in the following ways: First, he proposes several studies of the sma-2, -3, and -4 genes which will be studied together because of their structural similarities. Subcellular localization of the proteins and their temporal and spatial expression patterns will be determined. The null phenotypes will be determined. The nulls will be isolated in non-biased screens so that true nulls might be found. The genetic and molecular analyses will continue with an emphasis on testing the idea that the proteins interact with one another and determining whether the interact with the receptor. Second, Dr. Padgett plans to continue the screens to identify new components by using the small phenotype and by looking for suppressors of the small phenotype of a daf-4 (ts) allele. Finally, he proposes genetic characterization of any new mutants with the aim of cloning and molecular characterization.
| Savage-Dunn, C; Tokarz, R; Wang, H et al. (2000) SMA-3 smad has specific and critical functions in DBL-1/SMA-6 TGFbeta-related signaling. Dev Biol 223:70-6 |
