Mutations in
pam-1, the C. elegans ortholog of the puromycin sensitive aminopeptidase, result in reduced brood sizes and a highly penetrant embryonic lethal phenotype. Phenotypically,
pam-1 embryos display defects in polar body extrusion, sister chromatid segregation, and zygotic cell-fate specification. In addition these functions, we have identified a novel role for PAM-1 in facilitating the transition of the C. elegans germline through meiotic prophase. Germ cells utilize the length of the gonad to systematically transition through the stages of meiotic prophase I. Exit from pachytene and entry into diplotene occurs at the bend between the distal and proximal regions of the gonad, after which the nascent oocytes begin to cellularize, increase in volume, and queue into a single file in preparation for fertilization. However, the gonads of
pam-1 animals display an expanded region of pachytene-stage germ cells that frequently extend past the gonad curvature and into the proximal arm of the gonad. Because the transition from early to late pachytene is triggered by the temporal activation of the conserved MPK-1 signaling pathway, we examined the relationship between PAM-1 and these signaling components. Culture of
let-60,
mek-2, and
mpk-1 reduced-function alleles on
pam-1 RNAi food, or genetically combining
pam-1 with these alleles, produces synergistic increases in the penetrance of the expanded pachytene and fecundity phenotypes. Direct visualization of MPK-1 activity by immunostaining reveals that MPK-1 activation is delayed in the
pam-1 germline. This delay in MPK-1 activation leads to an expansion of the early pachytene region and the extension of the late pachytene region into the proximal gonad. We examined the expression of PAM-1 by creating strains rescued by a
pam-1p:gfp:
pam-1 transgene. GFP:PAM-1 expression was detected in the somatic gonadal tissues, gut cells, and robustly in neurons. GFP:PAM-1 colocalizes with the expression of a gonadal sheath cell-specific transgene (
lim-7p:mCherry), and somatic RNAi deficient
rrf-1(
pk1417) animals cultured on
pam-1(RNAi) food fail to develop the expanded pachytene phenotype. We conclude that in addition to its embryonic responsibilities, PAM-1 functions in the somatic gonad to govern neighboring germline meiotic transitions by regulating the germinal Ras/MAPK pathway, perhaps by facilitating the production and delivery of indeterminate, inductive signaling molecules.