Figure 2. Latent niche model of ectopic germline proliferation.

In normally developing L1 to L3 larvae, the gonad is small and all germ cells are in the proximity of the pro-mitotic signals LAG-2 and APX-1 which cause them to remain proliferative. As development proceeds, the germ cells continue to proliferate and are pushed away from the influence of the proliferative signals expressed by the DTC causing the germ cells to differentiate. During the L4 stage, additional somatic gonadal cells express pro-mitotic signals, but do not normally become centers of new proliferation as the neighboring cells are differentiating, non-responsive germ cells. However in certain mutant backgrounds that lead to proximal tumors (Pro), the coordination between somatic and germline development is disrupted such that “proliferation competent” cells are now found in proximity to the proximal sheath cells, thereby establishing a second “latent niche” or proliferative center in addition to that created by the DTC.