The gonad in all organisms contains both somatic and germline tissues that must be united to produce a functional organ. In C. elegans, the somatic and germline precursor cells coalesce during embryogenesis to form the gonad primordium. Specifically, the somatic gonadal precursors (Z1 and Z4) migrate toward and flank the germline precursors (Z2 and Z3). The 4-celled gonad primordium is arranged with two-fold rotational symmetry in both sexes. This symmetry is maintained throughout hermaphrodite development generating a two-armed gonad, but is broken in males to generate a single-armed gonad. We have set out to dissect the genetic controls of gonad primordium formation. Using genetic screens and RNAi, we have identified at least 4 genes that are required for proper assembly of the gonad primordium. In each of these mutants, the symmetry of the gonad primordium is disrupted resulting in aberrantly-shaped adult gonads. Thus, the proper organization of the gonad primordium is essential for establishing organ shape. In the simplest case, the gonad primordium of
gnd-2 RNAi animals is frequently missing one of the two somatic precursor cells, giving rise to an adult gonad with a single arm.
gnd-1 and
gnd-3 mutants can have asymmetric gonad primordia that lead to a more severely disorganized gonad and sterility. We have also examined previously existing mutants and find that mutations in the sex determination gene
tra-1 result in an asymmetric gonad primordium. We will report our progress in analyzing these mutants phenotypically and molecularly.