SPECIFICATION, MIGRATION AND ASSEMBLY OF THE SOMATIC-CELLS OF THE DROSOPHILA GONAD

The adult ovaries and testes contain several specialized somatic cell types that support the differentiation of germ cells into mature gamet es, Each of these cell types arise from mesodermal cells that constitu te the embryonic gonad, To explore the mechanisms governing the develo pment and differentiation of these cells, we focus on the formation of the gonad during Drosophila development, Using markers for the precur sors of the somatic cells of the gonad, we identify discrete steps in the development of the gonad, Our results suggest the existence of dif ferent populations of gonadal precursors at early stages in gonadogene sis that represent precursors of cell types found within the adult gon ad, The functions of the homeotic genes abdominal A and Abdominal B ar e required for the development of gonadal precursors, however, here we provide evidence that each plays a distinct role, abd A activity alon e specifies anterior gonadal precursor fates, whereas nbd A and Abd B act together to specify a posterior subpopulation of gonadal precursor s, Once specified, gonadal precursors born within posterior parasegmen ts must move to the site of gonad formation, Here, we show that the pr oper regional identities, as established by homeotic gene function, ar e required for the arrest of migration at the correct position. Finall y, our analysis of late stages of gonadogenesis suggests that abd A is required in a population of cells within parasegments 10 and 11 that partially ensheath the coalescing gonad, Mutations in iab-4 abolish ex pression of abd A within these cells, and as a result block the coales cence of the gonad.