Hox genes are evolutionarily conserved developmental regulatory genes that function, in part, to pattern the anterior-posterior (AP) axis of organs and organ systems during animal embryonic development. Hoxa5, specifically, is shown to be expressed in the spinal cord, somites, or transient compartments giving rise to the vertebrae and ribs, developing gut, lungs, and limbs of the mouse (Mus musculus). The cis-regulatory elements (CREs), or short DNA sequences, that direct Hoxa5 expression in these embryonic domains have been mapped and functionally tested in the mouse as well. Similar Hoxa5 expression patterns have been observed in chicken (Gallus gallus), American alligator (Alligator mississipiensis), and dogfish shark (Scyliorhinus canicular), but have shown divergence in the anterior limit of expression within the somites. Specifically, while mouse expression begins in somite 3, chicken, alligator, and shark begin in 8, 9, and 9, respectively. Further, no hoxa5 expression has been observed in the somites for teleost fish. Here, we present the embryonic Hoxa5 expression pattern within brown anole lizard (Anolis sagrei). Our data shows that Hoxa5 within the lizard has an anterior limit of expression in somite 6 and exhibits a more similar expression pattern to that of mouse, chicken, alligator, and shark than to teleost fishes. Furthermore, our comparative genomic DNA sequence analyses display that the functional CREs mapped in the mouse are conserved among the tetrapods, but not with the shark or teleost fishes. Our analyses suggest that divergent Hoxa5 expression patterns result from divergence within their respective CREs.


We gratefully acknowledge Dr. Doug Menke from the Department of Genetics of University of Georgia for providing brown anole lizard embryos and the brown anole lizard genome for this research project. This research was made possible by the funding from the University of North Georgia College of Science and Mathematics Faculty-Student Research Grant.