Abstract
Like many animals and humans, reproduction in the nematode C. elegans declines with age. This decline is the cumulative result of age-related changes in several steps of germline function, many of which are highly accessible for experimental investigation in this short-lived model organism. Here we review recent work showing that a very early and major contributing step to reproductive decline is the depletion of the germline stem and progenitor cell pool. Since many cellular and molecular aspects of stem cell biology and aging are conserved across animals, understanding mechanisms of age-related decline of germline stem and progenitor cells in C. elegans has broad implications for aging stem cells, germline stem cells, and reproductive aging.
Highlights
C. elegans is a well-established model for germline development and for aging
Given the complex biology of sperm limitation and oocyte maturation, a major finding that has emerged from recent studies is that the number of germ cells in the progenitor zone (PZ) declines with age
Many open questions remain regarding germline stem and progenitor cell aging, and many of these open questions are experimentally accessible in C. elegans (Corsi et al, 2015)
Summary
C. elegans is a well-established model for germline development and for aging. Several interesting related areas of study include how the C. elegans germ line regulates longevity (see Antebi, 2012, for review) and how reproductive cessation may relate to population success in the wild (see Hughes et al, 2007; Galimov and Gems, 2021). Given the complex biology of sperm limitation and oocyte maturation, a major finding that has emerged from recent studies is that the number of germ cells in the progenitor zone (PZ) declines with age This occurs in both unmated and mated hermaphrodites despite the profound gene expression changes that accompany sperm depletion (Angeles-Albores et al, 2017). Kocsisova et al (2019) examined reproductive aging in mated worms This comprehensive study demonstrated that PZ depletion does occur in sperm-replete conditions, that it includes a depletion of the SYGL-1-positive stem cell pool, that it begins early relative to somatic aging, and that it is a primary contributor to reduced progeny production with age. The DTC phenotype was often restricted to one gonad arm and not the other within individuals, while the presence of endomitotic oocytes in one gonad arm in an individual was correlated with an increased probability of observing an endomitotic oocyte in the other gonad arm of the same individual, suggesting a local mechanism for the former and a possible systemic effect for the latter (Kocsisova et al, 2019)
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