Evolutionary lability inHoxcluster structure and gene expression inAnolislizards

Abstract

Hox genes orchestrate development by patterning the embryonic axis. Vertebrate Hox genes are arranged in four compact clusters, and the spacing between genes is assumed to be crucial for their function. The genomes of squamate reptiles are unusually rich and variable in transposable elements (TEs), and it has been suggested that TE invasion is responsible for the Hox cluster expansion seen in snakes and lizards. Using de novo TE prediction on 17 genomes of lizards and snakes, I show that TE content of Hox clusters are generally 50% lower than genome‐wide TE levels. However, two distantly related lizards of the species‐rich genus Anolis have Hox clusters with a TE content that approaches genomic levels. The age distribution of TEs in Anolis lizards revealed that peaks of TE activity broadly coincide with speciation events. In accordance with theoretical models of Hox cluster regulation, I find that Anolis species with many TEs in their Hox clusters show aberrant Hox gene expression patterns, suggesting a functional link between TE accumulation and embryonic development. These results are consistent with the hypothesis that TEs play a role in developmental processes as well as in evolutionary diversifications.

Chromosome-scale genome assembly of the brown anole (Anolis sagrei), a model species for evolution and ecology

“…Observations from these new assemblies have provided fresh insights into core biological processes. For example, our understanding of recombination 4 , repetitive genetic elements 5,6 , chromosome evolution 7-9 and dosage compensation 4,10,11 have all been fundamentally amended due to results made possible by recent genome assemblies of non-traditional model species.…”

First Genome of Rock Lizard Darevskia valentini Involved in Formation of Several Parthenogenetic Species

“…Yet, as was found in diverse mammalian cell types [ 64 , 65 ], some transposable elements included in genes, such as SINEs and LINEs [ 66 , 67 ], might participate in the splicing of the precursor of mRNA (pre-mRNA) and in the formation of non-coding circular RNAs [ 68 , 69 ], that function as efficient miRNA sponges [ 70 ], thus diminishing the effect of miRNA on transcriptional and post-transcriptional levels of regulation of gene expression [ 71 ]. The functionality of transposons in the Hox cluster became more plausible with the discovery of a correlation between the accumulation of mobile elements and the level of Hox genes’ expression during development in Anolis lizards [ 20 ]. However, so far, it is unclear what part of transposons remains functional, since most of them are considerably degenerated.…”

“…However, comparison between Hox clusters of mouse, chicken, frog and green anole demonstrated atypical enlarged Hox clusters in the anole lizard with a massive accumulation of transposable elements in intergenic space [ 12 ]. A recent study showed that mobile elements accumulation correlates with alterations in Hox genes expression during development in Anolis lizards and can possibly contribute to their speciation [ 20 ].…”

A single locus regulates a female-limited color pattern polymorphism in a reptile

“…Embryos were transferred to methanol through a dilution series in PBS and stored at −20°C. In situ hybridization was performed as previously described ( 51 ). Expression patterns were documented using a Nikon stereo microscope (Nikon SMZ18) with the imaging software NIS-Elements BR 5.02.00.…”