Gut Patterning In Development And Evolution: A Comparative Differential Transcriptomics Approach

Abstract

All bilaterians share a common kit of transcription factors and cis-regulatory elements that compose the Gene Regulatory Network (GRN) essential for the development of the body plan. Modifications within the elements of the GRN determine the evolution of animal forms. In this study, the GRN for embryonic gut specification in two echinoderm species, the sea urchin Strongylocentrotus purpuratus and the sea star Patiria miniata, has been studied with the purpose of acquiring further knowledge on the process of gut patterning in the sea urchin larva and to compare it with the sea star embryo, focusing on the role that Xlox and Cdx transcription factors have in this process in both echinoderm species. Taking advantage of genome-wide approaches and modern high-throughput technologies, a partial reconstruction of the sea urchin GRN around Xlox and Cdx transcription factors, known for their key role to start the gut specification process, has been achieved leading to describe the putative interactions of the TFs in the network. An important novel node of the sea urchin GRN featuring the interaction between Sp-Meis, an homeobox gene, and Sp-Lox protein has been revealed and the occupancy of Sp-Lox protein on Sp-Meis regulatory region has been demonstrated by ChIP-PCR. The comparison of the differentially expressed genes after Xlox and Cdx perturbation in both sea urchin and sea star embryos has revealed that, although the absence of these two proteins affects some digestive functions and developmental processes related to its specification, however many of the regulatory genes involved in these mechanisms are not the same in the two species. This result suggests a phenomenon of rewiring of the gut GRN in S. purpuratus and P. miniata that, although belonging to the same phylum Echinodermata, are distant million years in term of evolutionary time, as recorded by fossil records.