MED GATA factors promote robust development of the C. elegans endoderm

Abstract

The MED-1,2 GATA factors contribute to specification of E, the progenitor of the C. elegans endoderm, through the genes end-1 and end-3, and in parallel with the maternal factors SKN-1, POP-1 and PAL-1. END-1,3 activate elt-2 and elt-7 to initiate a program of intestinal development, which is maintained by positive autoregulation. Here, we advance the understanding of MED-1,2 in E specification. We find that expression of end-1 and end-3 is greatly reduced in med-1,2(−) embryos. We generated strains in which MED sites have been mutated in end-1 and end-3. Without MED input, gut specification relies primarily on POP-1 and PAL-1. 25% of embryos fail to make intestine, while those that do display abnormal numbers of gut cells due to a delayed and stochastic acquisition of intestine fate. Surviving adults exhibit phenotypes consistent with a primary defect in the intestine. Our results establish that MED-1,2 provide robustness to endoderm specification through end-1 and end-3, and reveal that gut differentiation may be more directly linked to specification than previously appreciated. The results argue against an “all-or-none” description of cell specification, and suggest that activation of tissue-specific master regulators, even when expression of these is maintained by positive autoregulation, does not guarantee proper function of differentiated cells.

The Function and Regulation of the GATA Factor ELT-2 in theC. elegansEndoderm

“…In the course of normal C. elegans development, either END-1 or END-3 is necessary to specify the C. elegans endoderm (Maduro et al, 2015;Owraghi et al, 2009), whereas initial ELT-2 function is restricted to differentiation. We examined whether ELT-2 could replace END-1 and END-3 in specifying the endoderm, simply by being expressed earlier.…”

“…Thus, the endoderm network is capable of dynamic reequilibration or self-correction during embryogenesis. A different perturbation of the early endoderm regulatory network has recently been shown to lead to increased numbers of intestinal nuclei in the adult (Maduro et al, 2015). It will be important to determine if such adult phenotypes are due to a persistent perturbation of the transcriptional network and its downstream biochemical pathways or are rather due to some irreversible early cellular defect, such as aberrant cell division in the early embryo.…”

“…We were unable to achieve rescue of the quadruple elt-7 end-1 end-3; elt-4 mutant using a single integrated copy of the end-1prom::elt-2 cDNA transgene. This failure could possibly reflect a position effect, although single-copy insertions of end-1 into this same genomic locus appear to function well (Maduro et al, 2015). Alternatively, perhaps the larger ELT-2 molecule takes longer to be produced than the smaller END-1 and/or END-3 molecules (see below), or perhaps ELT-2 binds less optimally to the early endoderm-specifying genes that are the normal targets of END-1/END-3.…”

“…The core transcription factors have been identified and their functional roles are understood at the level of genetics and cell biology. Current investigations focus on understanding the network at a biochemical level: (1) to define direct interactions between transcription factors and their target genes and (2) to understand how this regulatory network functions quantitatively (Maduro et al, 2015;Nair et al, 2013;Raj et al, 2010).…”

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

“…We investigated whether embryos lacking the inhibitory interaction suffer any developmental consequence in the EMS lineage. The MS and E developmental programs are driven by the lineage-restricted expression of two different sets of transcription factors (for a review, see Maduro, 2015;Maduro et al, 2015). The MS blastomere expresses the T-box transcription factor TBX-35, which, along with the homeodomain transcription factor CEH-51, drives both body wall and pharyngeal muscle programs , 2009.…”