Abstract
Knowing how stem cells and their progeny are positioned within their tissues is essential for understanding their regulation. One paradigm for stem cell regulation is the C. elegans germline, which is maintained by a pool of germline stem cells in the distal gonad, in a region known as the ‘progenitor zone’. The C. elegans germline is widely used as a stem cell model, but the cellular architecture of the progenitor zone has been unclear. Here we characterize this architecture by creating virtual 3D models of the progenitor zone in both sexes. We show that the progenitor zone in adult hermaphrodites is organized like a folded epithelium. The progenitor zone in males is not folded. Analysis of germ cell division shows that daughter cells are born side-by-side along the epithelial-like surface of the germline tissue. Analysis of a key regulator driving differentiation, GLD-1, shows that germ cells in hermaphrodites differentiate along a folded path, with previously described “steps” in GLD-1 expression corresponding to germline folds. Our study provides a three-dimensional view of how C. elegans germ cells progress from stem cell to overt differentiation, with critical implications for regulators driving this transition.
Highlights
Adult stem cells maintain and repair tissues throughout life
Ring channels and the rachis were annotated by staining filamentous actin (F-actin), which localizes to the cortex, but is absent from ring-channel passageways (Figure 1E)
Folds were visible using the plasma membrane marker mCherry∷PLCδPH, confirming the validity of F-actin staining (Figure S3). These results show that the progenitor zone in adult hermaphrodites is folded, and that germ cells in the interior of the progenitor zone reside within epithelial folds (Figure 2I)
Summary
Adult stem cells maintain and repair tissues throughout life Key to their function is that many stem cells reside in specialized positions within tissues. This positioning ensures that stem cells contact local support cells and receive the regulatory signals that maintain stem cells in the 25 self-renewing state (Scheres, 2007). This positioning can orient stem cell divisions (Yamashita and Fuller, 2008) and provide a blueprint for daughter cells as they differentiate (Yang 27 et al, 2017). The behavior of stem cells and their daughters is strongly influenced by cell position and can only be understood in the context of tissue 39 architecture
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