Bat accelerated regions identify a bat forelimb specific enhancer in the HoxD locus

Author Summary: The limb is a classic example of vertebrate homology and is represented by a large range of morphological structures such as fins, legs and wings. The evolution of these structures could be driven by alterations in gene regulatory elements that have critical roles during development. To identify elements that may contribute to bat wing development, we characterized sequences that are conserved between vertebrates, but changed significantly in the bat lineage. We then overlapped these sequences with predicted developing limb enhancers as determined by ChIP-seq, finding 166 bat accelerated sequences (BARs). Five BARs that were tested for enhancer activity in mice all drove expression in the limb. Testing the mouse orthologous sequence showed that three had differences in their limb enhancer activity as compared to the bat sequence. Of these, BAR116 was of particular interest as it is located near the HoxD locus, an essential gene complex required for proper spatiotemporal patterning of the developing limb. The bat BAR116 sequence drove robust forelimb expression but the mouse BAR116 sequence did not show enhancer activity. These experiments correspond to analyses of HoxD gene expressions in developing bat limbs, which had strong forelimb versus weak hindlimb expression for Hoxd10 - 11 . Combined, our studies highlight specific genomic regions that could be important in shaping the morphological differences that led to the development of the bat wing.