Figure 1. The DAF-2/insulin-IGF-like receptor (IIR) promotes age-related loss of germline progenitor cells.

(a) Schematic drawing of the adult C. elegans hermaphrodite germ line. Stem/progenitor cells (grey shading) are located in the distal region of the germ line that is capped by the distal tip cell (DTC), the stem cell niche. As germ cells divide and move proximally, they enter meiosis. Nuclei in early stages of prophase of meiosis I (leptotene and zygotene) are crescent shaped. By convention, the appearance of two or more crescents in a full ring of nuclei marks the proximal border of the progenitor pool37 (dotted line). Germ cells eventually differentiate into sperm that are stored in the spermatheca followed by oocytes that reside in the adult oviduct. In response to signals from the sperm, oocytes mature one by one and are fertilized as they pass through the spermatheca. (b) Representative DAPI-stained wild-type and daf-2(rf) germ lines. Asterisk indicates the distal end of the germ line, and the dotted line indicates the proximal boarder of the proliferative zone. Scale bars, 20 μm. (c) Time course of germline progenitor depletion in wild-type and daf-2(rf) animals. Note that daf-2(rf) mutants start with fewer germline progenitor cells than wild type on adult day 1 (D1) (see text for details). Error bar indicates s.e.m.; ****P<0.0001 by two-tailed Student's t-test; also, pairwise comparisons within genotypes for each time point P<0.0001 by Student's t-test. Allele used: daf-2(e1370). See Supplementary Table 3 for complete data. DAPI, 4,6-diamidino-2-phenylindole.