A central problem in metazoan development is how cells are regulated to differentiate as one cell type rather than another. In the nematode C. elegans, a cell's sexual fate is regulated by a small number of genes. These "sex-determination" genes include global control genes, required to specify sex in all tissues, and tissue-specific control genes. We propose to study the function and regulation of 3 global (fem-1, fem-2, and tra-2) and 2 tissue- specific (fog-1 and fog-2) sex-determination genes at the molecular level. These genes were selected because they are central to specification of the sexual fate in the germline tissue (sperm or oocyte). One of these genes, tra-2, is cloned (Okkema and Kimble, unpublished); we propose to clone the others by transposon tagging. Then, we will identify and characterize their transcripts during development and we will analyze their DNA sequence and gene structure. Either genetic transformation or a transient assay will be used to confirm the identity of each gene. Our primary goal is to investigate the regulation and function of the sex-determination genes during development. We will test the predictions of a pathway of sex determination control that has been proposed based on the results of genetic experiments and we will elucidate the regulatory relationships among genes that are not accessible to genetic tests. To explore this pathway of control, we will examine the production of sex-determination transcripts in mutants of other sex-determination genes. If transcripts are not regulated, antibodies will be produced to the genes' proteins to seek regulation at that level. In addition, interactions among these genes will be investigated by transient assay after microinjection into the germ line. Dosage effects will be studied by use of transgenes to add extra copies. In particular, we will study whether the amount of fog-1 available specifies the number of sperm produced. Finally, the molecular basis of maternal effects will be examined. In particular, we will study how maternal fem-1 and fem-2 directs the male fate only in the germline of hermaphrodites but in all tissues of males. The health relatedness of this work derives from its contribution to an understanding of mechanisms of control during nematode development. Defects in such controls may lead to congenital defects or cancer in humans. An understanding of nematode controls may lead to a method for the control of human parasitic nematodes.