Karyotypic evolution in squamate reptiles: comparative gene mapping revealed highly conserved linkage homology between the butterfly lizard (Leiolepis reevesii rubritaeniata, Agamidae, Lacertilia) and the Japanese four-striped rat snake (Elaphe quadrivirgata, Colubridae, Serpentes)

Abstract

The butterfly lizard (Leiolepis reevesii rubritaeniata) has the diploid chromosome number of 2n = 36, comprising two distinctive components, macrochromosomes and microchromosomes. To clarify the conserved linkage homology between lizard and snake chromosomes and to delineate the process of karyotypic evolution in Squamata, we constructed a cytogenetic map of L. reevesii rubritaeniata with 54 functional genes and compared it with that of the Japanese four-striped rat snake (E. quadrivirgata, 2n = 36). Six pairs of the lizard macrochromosomes were homologous to eight pairs of the snake macrochromosomes. The lizard chromosomes 1, 2, 4, and 6 corresponded to the snake chromosomes 1, 2, 3, and Z, respectively. LRE3p and LRE3q showed the homology with EQU5 and EQU4, respectively, and LRE5p and LRE5q corresponded to EQU7 and EQU6, respectively. These results suggest that the genetic linkages have been highly conserved between the two species and that their karyotypic difference might be caused by the telomere-to-telomere fusion events followed by inactivation of one of two centromeres on the derived dicentric chromosomes in the lineage of L. reevesii rubritaeniata or the centric fission events of the bi-armed macrochromosomes and subsequent centromere repositioning in the lineage of E. quadrivirgata. The homology with L. reevesii rubritaeniata microchromosomes were also identified in the distal regions of EQU1p and 1q, indicating the occurrence of telomere-to-telomere fusions of microchromosomes to the p and q arms of EQU1.

Extensive Homology of Chicken Macrochromosomes in the Karyotypes of <b><i>Trachemys scripta elegans</i></b> and <b><i>Crocodylus niloticus</i></b> Revealed by Chromosome Painting despite Long Divergence Times

“…Further comparisons of GGA chromosome homology with other turtles will uncover the extent of rearrangement of the smaller chromosomes in the known variation of turtle karyotypes [Valenzuela and Adams, 2011]. In most squamates, gene mapping [Srikulnath et al, 2009] and chromosome painting [Pokorná et al, in press] show GGA chromosomes 3, 5 and 7 associated in one of the largest metacentric chromosomes, i.e. a rearrangement distinct from any that we find in turtle and crocodile.…”

The First Cytogenetic Map of the Tuatara, <i>Sphenodon punctatus</i>

“…Synteny and even the order of genes found on macrochromosomes are highly conserved among sauropsids. Genes spanning the length of the snake Z map to a contiguous block of chicken 2p and chromosome 6 of the butterfly lizard [Srikulnath et al, 2009b]. Although no genes that have been located on the snake Z are present on our map, it is likely that tuatara chromosome 4 is equivalent to the snake Z chromosome, which, in all snakes examined to date, is the fourth or fifth largest pair.…”

Are some chromosomes particularly good at sex? Insights from amniotes

“…Similarly, synteny of genes on the snake Z must have arisen by the fusion of ancestral segments (represented by chicken chromosomes 2p and 27) between 166 and 275 MYA because, with the exception of agamid and iguanid lizards (Srikulnath et al 2009b, http://ensembl.org release 64), these regions are always found on separate chromosomes in other tetrapods (Fig. 1b).…”

“…The chicken Z represents a single ancestral chordate chromosome, which is also present as a single chromosome, or chromosome arm, in many reptiles and amphibians (Graves and Shetty 2001;Matsuda et al 2005;Nakatani et al 2007;Nanda et al 2008;Pokorná et al 2011;Srikulnath et al 2009b;Voss et al 2011). In the ancestral karyotypes proposed by Nakatani et al (2007), synteny of the ancestral vertebrate proto-chromosome "A" is conserved in the gnathostome proto-chromosome "A0," the amniote protochromosomes "3" and "26," and is found today in chicken chromosomes Z and 17.…”