The anterior Hox geneceh-13andelt-1/GATAactivate the posterior Hox genesnob-1andphp-3to specify posterior lineages in theC. elegansembryo

Abstract

Hox transcription factors play a conserved role in specifying positional identity during animal development, with posterior Hox genes typically repressing the expression of more anterior Hox genes. Here, we dissect the regulation of the posterior Hox genes nob-1 and php-3 in the nematode C. elegans. We show that nob-1 and php-3 are co-expressed in gastrulation-stage embryos in cells that previously expressed the anterior Hox gene ceh-13. This expression is controlled by several partially redundant transcriptional enhancers. Surprisingly, these enhancers require ceh-13 for expression, providing an example of an anterior Hox gene positively regulating a posterior Hox gene. Several other regulators including elt-1/GATA, ceh-20/ceh-40/Pbx, unc-62/Meis, pop-1/TCF, ceh-36/Otx and unc-30/Pitx also act positively through nob-1/php-3 enhancers. We identified defects in both cell position and cell division patterns in ceh-13 and nob-1;php-3 mutants, suggesting that these factors regulate lineage identity in addition to positional identity. Taken together, our results highlight the complexity and unexpected flexibility of Hox gene regulation and function.

pop-1/TCF, ref-2/ZIC and T-box factors regulate the development of anterior cells in the C. elegans embryo

“…In contrast with our observation that TBX418 concatemers are sufficient to drive anterior-biased [52,[60][61][62][63][64]. Additionally, we observe modularity within the -3.9 kb enhancer, with three non-overlapping regions of the enhancer each sufficient to drive anteriorbiased expression.…”

“…We found that the predicted enhancers in the promoter region of ref-2 function modularly, such that each enhancer drives different expression patterns, presumably providing multiple inputs to fine-tune the expression pattern of ref-2 . Combined with other recent studies this adds to evidence that enhancer-mediated regulation is widespread during C. elegans embryonic development [54,65–69]. Additionally, we observe modularity within the −3.9 kb enhancer, with three non-overlapping regions of the enhancer each sufficient to drive anterior-biased expression.…”

pop-1/TCF, ref-2/ZIC and T-box factors regulate the development of anterior cells in the C. elegans embryo

“…We found that the predicted enhancers in the promoter region of ref-2 function modularly, such that each enhancer drives different expression patterns, presumably providing multiple inputs to fine-tune the expression pattern of ref-2. Combined with other recent studies this adds to evidence that enhancer-mediated regulation is widespread during C. elegans embryonic development [52,[63][64][65][66][67]. Additionally, we observe modularity within the -3.9 kb enhancer, with three non-overlapping regions of the enhancer each sufficient to drive anteriorbiased expression.…”

“…We fused each putative enhancer to a reporter cassette consisting of a minimal pes-10 promoter and a his-24::mCherry reporter. The pes-10 promoter is widely used, drives no consistent embryonic expression on its own [13,51,52] and is compatible with a wide variety of enhancers [13,51]. We introduced each reporter into worms and used StarryNite to determine in which cells each putative enhancer drives expression.…”

“…The reporter construct for the ref-2 promoter lacking the -3.9 kb enhancer was amplified from N2 genomic DNA by PCR and PCR stitched to the pes-10 minimal promoter::HIS-24::mCherry reporter, and, thus, drives expression through the pes-10 minimal promoter. The pes-10 promoter drives no consistent embryonic expression on its own prior to elongation [13,51,52] and is compatible with a wide variety of enhancers [13,51] (Table S7).…”