Repression of mesodermal fate byfoxa, a key endoderm regulator of the sea urchin embryo

Abstract

The foxa gene is an integral component of the endoderm specification subcircuit of the endomesoderm gene regulatory network in the Strongylocentrotus purpuratus embryo. Its transcripts become confined to veg2, then veg1 endodermal territories, and, following gastrulation, throughout the gut. It is also expressed in the stomodeal ectoderm. gatae and otx genes provide input into the pregastrular regulatory system of foxa, and Foxa represses its own transcription, resulting in an oscillatory temporal expression profile. Here, we report three separate essential functions of the foxa gene: it represses mesodermal fate in the veg2 endomesoderm; it is required in postgastrular development for the expression of gut-specific genes; and it is necessary for stomodaeum formation. If its expression is reduced by a morpholino, more endomesoderm cells become pigment and other mesenchymal cell types, less gut is specified, and the larva has no mouth. Experiments in which blastomere transplantation is combined with foxa MASO treatment demonstrate that, in the normal endoderm, a crucial role of Foxa is to repress gcm expression in response to a Notch signal, and hence to repress mesodermal fate. Chimeric recombination experiments in which veg2, veg1 or ectoderm cells contained foxa MASO show which region of foxa expression controls each of the three functions. These experiments show that the foxa gene is a component of three distinct embryonic gene regulatory networks.

Sipuncula: an emerging model of spiralian development and evolution

“…9D). When comparing preliminary results from our work with some previous studies (Arendt et al, 2001;Martindale et al, 2004;Oliveri et al, 2006;Boyle and Seaver, 2008;Hejnol and Martindale, 2008;Boyle and Seaver, 2010;Boyle et al, 2014), several of the candidate genes show a conserved pattern of transcription along the anterior-posterior axis of the gut, typically associated with particular subregions such as ectoderm of the foregut and hindgut, and endoderm of a centralized digestive cavity or midgut (Fig. 10).…”

Development of a feeding trochophore in the polychaete Hydroides elegans

“…a, anus;an, animal pole;at, apical tuft;bp, blastopore;cb, ciliary band;D, dorsal;fg, foregut;hg, hindgut;L, left;m, mouth;mg, midgut;o, oral;R, right;v, ventral. tion in bilaterians and cnidarians, suggesting an ancient role (Fritzenwanker et al, 2004;Scholz and Technau, 2003). In addition to their expression in endoderm and ectoderm precursors that anticipates blastopore formation, FoxA and Brachyury are later expressed in ectoderm and archenteron tip cells that will fuse to form the anal opening of the gut (Arenas-Mena, 2006, similar to the expression of the corresponding orthologs during the formation of the echinoderm and hemichordate mouth (Tagawa et al, 1998;Gross and McClay, 2001;Oliveri et al, 2006). This oral and anal conservation of gene expression suggests that FoxA and Brachyury are involved in the formation of both primary and secondary gut openings in protostomes and deuterostomes.…”

Global regulatory logic for specification of an embryonic cell lineage

“…All methods used in this work have been described: perturbation analysis and mRNA expression (27), microinjection and QPCR (30,47), and in situ hybridization (8,25). Morpholinos (Gene Tools) were injected into fertilized eggs at final concentrations of 200 -400 M. See Table S2 for morpholino sequences.…”