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Mechanism of digit reduction in pig limb development


Digit loss/reductions are evolutionary adaptations in cursorial mammals such as pigs. To gain mechanistic insight into these processes, a recent study published on Cell Reports performed a comparative molecular analysis of limb development in mouse and pig embryos, which revealed a loss of anterior-posterior polarity during distal progression of pig limb bud development. These alterations in pig limb buds were paralleled by changes in the mesenchymal response to Sonic hedgehog (SHH) signaling, which is altered upstream of the reduction and loss of Fgf8 expression in the ectoderm that overlaps the reduced and vestigial digit rudiments of the pig handplate, respectively. Furthermore, genome-wide open chromatin profiling using equivalent developmental stages of mouse and pig limb buds revealed the functional divergence of about one-third of the regulatory genome. This study uncovers widespread alterations in the regulatory landscapes of genes essential for limb development that likely contributed to the morphological diversion of artiodactyl limbs from the pentadactyl archetype of tetrapods.