Figure 1.

Germline morphogenesis in C. elegans. In each panel, germ cells are outlined in red and somatic cells/tissues are in green. (A) At the L1 stage, there are four cells that will give rise to the entirety of the gonad. Two of these cells, Z1 and Z4, will give rise to the somatic tissues of the gonad, whereas Z2 and Z3 will generate the germline lineage. (B) Proliferation of the germline begins after the transition to the L2 stage. This is also the stage in which the germline syncytium forms. The direction of distal tip cell (green outline) migration is denoted by the dashed arrows. (C) As proliferation continues during the L3 stage, the single gonad tube is bisected by the developing somatic gonad tissues, giving rise to two mirror symmetrical arms. The distal tip cell migrates first ventrally, then back toward the center of the animal (arrows). (D) By the L4 stage, the gonad has mostly assumed its final shape, and spermatogenesis begins. Only one of the two arms is shown, with the proximal arm connected to the developing spermatheca and uterus (green outline). (E) Oogenesis begins after the transition to adulthood and will happen continuously throughout the lifespan of the animal.