Stephen DiNardo IBN 9418271 Cells within certain lineages must be continually replenished throughout the life of an organism. This is accomplished through the establishment and maintenance of stem cells. The mechanisms that instruct stem cell fate and that regulate the proliferation of their daughter cells are poorly understood. The overall objective of this proposal is to investigate how stem cells are established and maintained, using the model of Drosophila spermatogenesis that provides a unique opportunity to combine experimental and genetic approaches. The experimental manipulations first proposed will attempt to answer two questions: does cell signaling instruct stem cell fate? and are the number of daughter cell divisions internally programmed or controlled by neighboring cells? The first will be addressed by ablating the male hub cells, using a diptheria toxin inducible system, to determine whether the maintenance of the germline stem cell fate is governed by the signals emanating from these somatic cells. Heterospecific transplantation experiments, using two species that differ in the number of stem cell divisions, will determine if counting is intrinsic to daughter germ cells, or imposed by signals from the two somatic cells that surround them. The genetic approaches proposed will identify further mutations that interfere with these decisions. To identify genes that cause under- or over-proliferation of germ cells, or that cause discrete changes in the number of mitotic divisions, a powerful genetic screen, using the FLP/FRT recombinase system, is proposed. Molecular markers will be used to determine whether the primary defect in the mutants selected is in the production, maintenace or division of stem cells, or, alternatively, in the capacity of the daughter cells to divide. ***
