The adult C. elegans germ line includes mitotically-dividing cells in the distal gonad and meiotic cells more proximally. A single somatic cell, the distal tip cell (DTC), provides a <
sym08>stem cell niche<
sym09> that promotes germline mitoses by GLP-1/Notch signaling. We will present experiments that address the self-renewal and division pattern of germline stem cells and that further define the DTC niche. To assay self-renewal, we have done BrdU pulse-chase experiments in germline cells in the mitotic region. Multiple regimens all gave the same result. A long pulse of BrdU (~24 hours) effectively labeled all germline cells in the mitotic region, but after a chase of 14 hours, virtually no label was detected in the mitotic region. Instead, the labeled cells were observed in the meiotic region of the gonad. We conclude that the labeled mitotically-dividing cells were able to generate a new population of unlabelled mitotically-dividing cells as well as differentiating gametes the two hallmarks of stem cells. We observed no asymmetric or oriented cell divisions. Our current model is that distal cells within the mitotic region reside in the DTC niche and remain undifferentiated, while more proximal cells begin the transition into differentiation.