The C. elegans sex determination hierarchy specifies either one of two sexes: the hermaphrodite or the male. The tra-1 gene is the global terminal regulator of the somatic sex determination pathway. Active TRA-1 promotes female fates in the hermaphrodite by repressing the transcription of genes that direct male development. The objective of the work presented here is to understand how the activity of TRA-1 is regulated. The tra-1 gene encodes two transcripts, tra-1a and tra-1b. Males and hermaphrodites have similar levels of tra-1 transcripts, suggesting that tra-1 is regulated post transcriptionally. Using a new antibody against TRA-1 in whole mount immunostaining I observed that TRA-1 appears to be much more abundant in hermaphrodites than in males. Western blot analysis revealed similar levels of TRA-1A and TRA-1B in lysates from males and hermaphrodites. Additional TRA-1-specific species (90-110 kDa) were present in the hermaphrodite lysates but absent from male lysates. These isoforms are the most abundant form of TRA-1 protein in hermaphrodites. The hermaphrodite-specific TRA-1 isoforms appear to be phosphoisoforms of a single TRA-1 band. Here I also describe the identification of proteins that specifically interact with FEM-2 in affinity chromoatography experiments. Loss-of-function mutants and RNAi silencing of three of these genes appear to partially phenocopy fem-2 mutants. I show evidence that the hermaphrodite-specific isoform is generated by proteolytic processing of TRA-1A. Since the truncated TRA-1A isoforms are present in embryos before sexual differentiation is apparent, they are unlikely to be a result of female differentiation. Therefore I propose that these isoforms are responsible for the feminizing activity of the tra-1 gene. The truncation mapped to the region between amino acids 842 and 921. The observations that both a nonsense mutation that results in the production of a C-terminally truncated TRA-1A protein and truncated TRA-1A transgenes are feminizing, support my hypothesis that the truncated TRA-1 isoforms are responsible for the feminizing activity of the tra-1 gene. Genetic analyses indicate that the fem gene products regulate, directly or indirectly, the activity of TRA-1. Therefore, characterization of these putative FEM-2 binding proteins may identify the mechanism by which the FEMs regulate TRA-1 activity.

The free-living soil nematode 'Caenorhabditis elegans' exists in nature as one of two possible sexes, the male or the self-fertile hermaphrodite. Most genes controlling sex determination in 'C. elegans ' have been cloned and sequenced. These genes have been ordered into a signal transduction cascade based on their epistatic interactions. I have uncovered evidence supporting a direct interaction between the proteins encoded by two of the genes in the pathway, 'her-1' and 'tra-2'. This was achieved through binding assays involving immunofluorescent and immunoblotting techniques. The proposed interaction sheds light on the possible mechanisms by which HER-1 negatively regulates the activity of TRA-2A in male development.

In the germ line of the Caenorhabditis elegans hermaphrodite, nuclei either proliferate through mitosis or initiate meiosis, finally differentiating as spermatids or oocytes. The production of oocytes requires repression of the fem-3 mRNA by cytoplasmic FBF and nuclear MOG proteins. Here we report the identification of the sex determining gene mog-3 and show that in addition to its role in gamete sex determination, it is necessary for meiosis by acting downstream of GLP-1/Notch. Furthermore, we found that MOG-3 binds both to the nuclear proteins MEP-1 and CIR-1. MEP-1 is necessary for oocyte production and somatic differentiation, while the mammalian CIR-1 homolog counters Notch signaling. We propose that MOG-3, MEP-1 and CIR-1 associate in a nuclear complex which regulates different aspects of germ cell development. While FBF triggers the sperm/oocyte switch by directly repressing the fem-3 mRNA in the cytoplasm, the MOG proteins play a more indirect role in the nucleus, perhaps by acting as epigenetic regulators or by controlling precise splicing events.

The annual Evolutionary Biology Meetings in Marseilles serve to gather leading scientists, promote the exchange of ideas and encourage the formation of international collaborations. This book contains the most essential contributions presented at the 14th Evolutionary Biology Meeting, which took place in September 2010. It comprises 19 chapters organized according to the following categories: · Evolutionary Biology Concepts · Biodiversity and Evolution · Macroevolution · Genome Evolution Offering an up-to-date overview of recent results in the field of evolutionary biology, this book is an invaluable source of information for scientists, teachers and advanced students.