A novel enhancer near the Pitx1 gene influences development and evolution of pelvic appendages in vertebrates

Abbey C Thompson,David M Kingsley,Douglas B Menke,Carlos R Infante,Catherine A Guenther,Terence D Capellini,Yingguang Frank Chan

doi:10.7554/elife.38555

Abbey C Thompson, David M Kingsley + Show 5 more

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https://doi.org/10.7554/elife.38555

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Abstract

Vertebrate pelvic reduction is a classic example of repeated evolution. Recurrent loss of pelvic appendages in sticklebacks has previously been linked to natural mutations in a pelvic enhancer that maps upstream of Pitx1. The sequence of this upstream PelA enhancer is not conserved to mammals, so we have surveyed a large region surrounding the mouse Pitx1 gene for other possible hind limb control sequences. Here we identify a new pelvic enhancer, PelB, that maps downstream rather than upstream of Pitx1. PelB drives expression in the posterior portion of the developing hind limb, and deleting the sequence from mice alters the size of several hind limb structures. PelB sequences are broadly conserved from fish to mammals. A wild stickleback population lacking the pelvis has an insertion/deletion mutation that disrupts the structure and function of PelB, suggesting that changes in this ancient enhancer contribute to evolutionary modification of pelvic appendages in nature.

Highlights

Vertebrate limbs and fins show remarkable morphological diversity (Flower, 1870; Hinchliffe and Johnson, 1980)
The known Pel enhancer maps upstream of the stickleback Pitx1 gene (Chan et al, 2010), and a mammalian Pel ortholog cannot be identified by sequence alignment, it is possible that a functionally conserved Pel enhancer resides in the same upstream region in mammals
Two large deletions associated with human forelimb abnormalities map upstream of the Pitx1 gene (Figure 1)

Summary

Introduction

Vertebrate limbs and fins show remarkable morphological diversity (Flower, 1870; Hinchliffe and Johnson, 1980). High-resolution genetic mapping and enhancer studies identified a non-coding regulatory sequence located upstream of Pitx, called Pel, that drives expression in the developing pelvic hind fin (Chan et al, 2010). Genetic studies in birds, mice, and humans suggest multiple upstream regions may be involved in Pitx limb expression, but it has been difficult to identify any individual Pitx enhancers that drive hind limb-specific expression (Pennacchio et al, 2006; Spielmann et al, 2012; Domyan et al, 2016; Kragesteen et al, 2018; Sarro et al, 2018). We identify a novel pelvic enhancer located downstream rather than upstream of Pitx, which shows conservation of both sequence and function from mammals to fish Genetic studies suggest this sequence influences development of a subset of normal hind limb features in mice, and has contributed to evolutionary pelvic reduction in natural populations

A BAC scan across the Pitx1 locus

55.9 AK019623

Discussion

Materials and methods

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