Splicing is dynamically regulated during limb development.

Modifications to highly conserved developmental gene regulatory networks are thought to underlie morphological diversification in evolution and contribute to human congenital malformations. Relationships between gene expression and morphology have been extensively investigated in the limb, where most of the evidence for alterations to gene regulation in development consists of pre-transcriptional mechanisms that affect expression levels, such as epigenetic alterations to regulatory sequences and changes to cis-regulatory elements. Here we report evidence that alternative splicing (AS), a post-transcriptional process that modifies and diversifies mRNA transcripts, is dynamic during limb development in two mammalian species. We evaluated AS patterns in mouse (Mus musculus) and opossum (Monodelphis domestica) across the three key limb developmental stages: the ridge, bud, and paddle. Our data show that splicing patterns are dynamic over developmental time and suggest differences between the two mammalian taxa. Additionally, multiple key limb development genes, including Fgf8, are differentially spliced across the three stages in both species, with expression levels of the conserved splice variants, Fgf8a and Fgf8b, changing across developmental time. Our data demonstrates that AS is a critical mediator of mRNA diversity in limb development and provides an additional mechanism for evolutionary tweaking of gene dosage.