The endoderm gene regulatory network in sea urchin embryos up to mid-blastula stage

Abstract

As the result of early specification processes, sea urchin embryos eventually form various mesodermal cell lineages and a gut consisting of fore-, mid- and hindgut. The progression of specification as well as the overall spatial organization of the organism is encoded in its gene regulatory networks (GRNs). We have analyzed the GRN driving endoderm specification up to the onset of gastrulation and present in this paper the mechanisms which determine this process up to mid-blastula stage. At this stage, the embryo consists of two separate lineages of endoderm precursor cells with distinct regulatory states. One of these lineages, the veg2 cell lineage, gives rise to endoderm and mesoderm cell types. The separation of these cell fates is initiated by the spatially confined activation of the mesoderm GRN superimposed on a generally activated endoderm GRN within veg2 descendants. Here we integrate the architecture of regulatory interactions with the spatial restriction of regulatory gene expression to model the logic control of endoderm development.

Direct development of neurons within foregut endoderm of sea urchin embryos

“…S3 B and C). Although Six3 transcripts are not detectable in the foregut endoderm at gastrula stages (4,14), they are present at mesenchyme blastula stage in the precursors to this part of the gut (Fig. 4 A and B, red), which are adjacent to nonskeletogenic mesenchyme expressing gcm (15) (Fig.…”

“…SoxB1, which is closely related to the vertebrate Sox factors that support a neural precursor state, is also expressed in the foregut throughout gastrulation, suggesting that this region of the fully formed archenteron retains an unexpected pluripotency. Together, these results lead to the unexpected conclusion that, within a cell lineage already specified to be endoderm by a well-established gene regulatory network [Peter IS, Davidson EH (2010) Dev Biol 340: [188][189][190][191][192][193][194][195][196][197][198][199], there also operates a Six3/Nkx3-2-dependent pathway required for the de novo specification of some of the neurons in the pharynx. As a result, neuroendoderm precursors form in the foregut aided by retention of a SoxB1-dependent pluripotent state.…”

Gene expression profiling during the embryo‐to‐larva transition in the giant red sea urchin Mesocentrotus franciscanus

“…During the transition from embryo to larval stage, the interaction of multiple genetic regulatory networks (GRNs) determines the patterns of gene activity and differentiation of developmental modules in marine invertebrates (Raff & Sly, 2000). In echinoderms, for example, the unique combination of regulatory genes (e.g., transcription factors) in embryonic space and time contribute to shaping the regulatory program for larval skeletogenesis (Dylus et al., 2016; Gao & Davidson, 2008), endomesodermal (Peter & Davidson, 2010), and ectodermal specification (Nakata & Minokawa, 2009). Despite the differences in larval development in this group (e.g., pluteus‐, bipinnaria‐, and auricularia‐like larvae), comparisons of their GRN architectures have detected highly conserved orthologous regulatory genes among the extant echinoderm classes (Hinman & Davidson, 2003a,b; Hinman, Nguyen, Cameron, & Davidson, 2003; Hinman, Nguyen, & Davidson, 2003).…”

Divergence of ectodermal and mesodermal gene regulatory network linkages in early development of sea urchins

“…Research on the early development of the euechinoid purple sea urchin Strongylocentrotus purpuratus (Sp) has brought into high resolution the players and molecular logic directing developmental GRNs that specify Sp's early embryonic domains (19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). Abundant comparative evidence exists for other euechinoid taxa as well, including Lytechinus variegatus (Lv) (31)(32)(33)(34)(35)(36)(37) and Paracentrotus lividus (Pl) (38)(39)(40)(41)(42).…”