In hydra, the somatic cells and gametes arise from a population of multipotent stem cells, interstitial cells (I-cells). Although this population was thought to be uniform, recent evidence suggests that there are subpopulations of I-cells with different developmental potentials. One subpopulation has been isolated that is restricted to sperm differentiation. 97% of the cells in this subpopulation label with a monoclonal antibody, AC2, which is specific for cells of the spermatogenic pathway. The 3% that do not bind the antibody are thought to be the precursors to the AC2-binding cells. The importance of this subpopulation in determining sex has been demonstrated during the previous award. The focus of this study will be: 1) to determine if AC2- sperm precursor cells are the only source of the AC2- binding cells. 2) to determine where in the egg lineage pathway suppression of egg production occurs in the presence of male- derived I-cells. This requires isolating markers specific for cells of the egg pathway. 3) to determine if the same I-cell that produces eggs in a female can be induced to make sperm in a male. Finally, 4) to begin looking for a molecular basis for the suppression of egg formation by male I-cells. This will involve producing cDNA libraries containing male or female specific sequences. %%% The main objective of this work is to elucidate the extent to which cell-cell and cell-environment interactions control the determination of sex during development. Dr. Littlefield will use the simple organism Hydra as a model system to address these questions.
