Cell fate specification in the C. elegans embryo

Abstract

Cell specification requires that particular subsets of cells adopt unique expression patterns that ultimately define the fates of their descendants. In C. elegans, cell fate specification involves the combinatorial action of multiple signals that produce activation of a small number of ''blastomere specification'' factors. These initiate expression of gene regulatory networks that drive development forward, leading to activation of ''tissue specification'' factors. In this review, the C. elegans embryo is considered as a model system for studies of cell specification. The techniques used to study cell fate in this species, and the themes that have emerged, are described. Developmental Dynamics 239:1315-1329,

A molecular basis for developmental plasticity in early mammalian embryos

“…To understand this, we need to identify the molecular elements that encode the fate of a cell. In mosaic embryos this is easy as it relies on the biased distribution of lineage-determining transcription factors (Lemaire, 2009;Nishida and Sawada, 2001;Maduro, 2010) to particular cells and their descendants to trigger specific developmental programmes. In regulative embryos, by contrast, independently of how it is initiated, a cell fate is determined in a non-cell-autonomous manner over a large multicellular domain to account for its sensitivity to the size of the embryo.…”

Genomic Strategies for Embryonic Development

“…As in all Mode 1 systems, transcription is active by very early cleavage, and specific blastomeres right away begin to transcribe specific regulatory genes. This has been observed most dramatically using expression constructs driving fluorescent reporters, as well as by in situ hybridization (for a recent general review of early specification processes in this embryo, see Maduro, 2010).…”

“…Here early specification processes typically depend on cell-to-cell signaling that affects only adjacent or almost adjacent cells, in contrast to the broad ranges of the graded signals and signal inhibitors ("morphogen gradients") common in the relatively huge embryonic systems of vertebrate eggs for example. In C. elegans embryos (for review, see Maduro, 2010) and Ciona embryos (Lemaire, 2009) short-range signaling processes are used to specify single individual blastomeres or pairs of blastomeres located in specific positions defined precisely by their adjacency to the signaling cells. In sea urchins the targets of a given short range signal more typically generate an incipient regulatory state territory of identically specified cells, such as the single cell deep ring of gcm positive cells shown in Fig.…”

Reciprocal signaling by Wnt and Notch specifies a muscle precursor in the C. elegans embryo

“…Our results here suggest that the function of the initial inhibition is to prevent precocious activation of lineage-restricted genes in MS and E. During the first few hours of C. elegans embryogenesis, cell cycle times are short, at ∼10-15 min, and a number of cell lineages are specified early during embryogenesis (Sulston et al, 1983). Specification of these precursor blastomeres results from the coordinated action of both maternally supplied factors and the lineage-restricted zygotic expression of transcription factors (see reviews by Schnabel and Priess, 1997;Maduro, 2010). The short cell cycle times demand very precise timing of zygotic expression of lineage-restricted transcription factors in the correct blastomeres.…”