Abstract

Understanding how changes in developmental gene expression alter morphogenesis is a fundamental problem in development and evolution. A promising approach to address this problem is to compare the developmental transcriptomes between related species. The echinoderm phylum consists of several model species that have significantly contributed to the understanding of gene regulation and evolution. Particularly, the regulatory networks of the sea star, Patiria miniata (P. miniata), have been extensively studied, however developmental transcriptomes for this species were lacking. Here we generated developmental transcriptomes of P. miniata and compared these with those of two sea urchins species. We demonstrate that the conservation of gene expression depends on gene function, cell type and evolutionary distance. With increasing evolutionary distance the interspecies correlations in gene expression decreases. The reduction is more severe in the correlations between morphologically equivalent stages (diagonal elements) than in the correlation between morphologically distinct stages (off-diagonal elements). This could reflect a decrease in the morphological constraints compared to other constraints that shape gene expression at large evolutionary divergence. Within this trend, the interspecies correlations of developmental control genes maintain their diagonality at large evolutionary distance, and peak at the onset of gastrulation, supporting the hourglass model of phylotypic stage conservation.

Highlights

  • Understanding how changes in developmental gene expression alter morphogenesis is a fundamental problem in development and evolution

  • To study the transcriptional profiles of the sea star species, P. miniata, from fertilized egg to late gastrula stage and compare them to those in the sea urchin species, S. purpuratus and P. lividus we collected embryos at eight developmental stages matching to those studied the sea urchin species[19,26,27] (Fig. 1B)

  • In this paper we generated the developmental transcriptomes of the pacific sea star, P. miniata, and studied them in comparison with the published developmental transcriptomes of two sea urchin species, P. lividus[19] and S. purpuratus[26]

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Summary

Introduction

Understanding how changes in developmental gene expression alter morphogenesis is a fundamental problem in development and evolution. There are both morphological similarities and differences between sea urchin and sea star larval body plans that make these classes very interesting for comparative genetic studies. We previously investigated different aspects of interspecies conservation of gene expression between P. lividus and the pacific sea urchin, Strongylocentrotus purpuratus (S. purpuratus)[18,19] These species diverged from their common ancestor about 40 million years ago and have a highly similar embryonic morphology (Fig. 1A). The interspecies correlations of the expression levels of these two sets of genes show distinct patterns

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