Germ Cell Fate Determination in C. elegans

Abstract

Germ cell development is essential for the sexual reproduction of animals. Germ cells are immortal in that they contribute to successive generations, whereas somatic cells perish with the individual. The nematode Caenorhabditis elegans is a leading system for elucidating the developmental mechanisms controlling the germ cell fate determination because this organism is amenable to molecular genetic and mechanistic analysis. This review discusses the molecular mechanisms specifying the fate of germ cells from their journey in the embryo to fertilization.

Key Concepts

  • Germ cell development is essential for the sexual reproduction of animals.
  • Primordial germ cells are formed early in embryogenesis.
  • Germ cell specification happens in the absence of transcription.
  • Germ cell proliferation in the adult is regulated by the somatic niche.
  • Oocyte meiotic maturation is under hormonal control.
  • Gene expression in germline is regulated by a combination of epigenetic and posttranscriptional mechanisms.

Keywords: germ cell; stem cell; germline; cell fate; germ granules; primordial germ cells; oocyte maturation; totipotency

Figure 1. Embryonic origin of the germline. Embryonic germline lineage from the one‐cell stage to the ∼100‐cell stage and corresponding embryo schematics are shown in the lineage tree. Germ plasm is shown in purple, and P granules as red dots. Orange marks transcriptionally quiescent nuclei.
Figure 2. Adult C. elegans gonad. (a) One of the two hermaphrodite gonads arms. The somatic distal tip cell (DTC) caps the gonad. The colours of the germline nuclei indicate developmental stages: light green, mitotic; green crescent, entry into meiosis; green, pachytene and blue, diplotene and diakinesis. P granules (red) localise at the nuclear periphery until diakinesis. Sperm are brown. (b) Male gonad. The single arm of the gonad is capped with two distal tip cells. The colours of the nuclei indicate mitotic, transition and pachytene stages analogous to that of the hermaphrodite shown in (a); dark purple nuclei: primary spermatocytes; brown: sperm.
Figure 3. Signalling in the stem cell niche. LAG‐2 and APX‐1 ligands expressed in the DTC activate GLP‐1 Notch signalling in the germline. This signalling activates transcription of LST‐1 and SYGL‐1, which maintain germline stem cells. GLD‐1 and GLD‐2 function downstream and regulate the initiation of meiosis. Another critical component of the germ cell niche are gap junction channels composed of the innexin proteins, INX‐8 and ‐9 in the soma and INX‐14 and ‐21 in the germline.
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Voronina, Ekaterina, and Greenstein, David(Apr 2016) Germ Cell Fate Determination in C. elegans. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001501.pub2]