Evolutionary Variability of W-Linked Repetitive Content in Lacertid Lizards

Abstract

Lacertid lizards are a widely radiated group of squamate reptiles with long-term stable ZZ/ZW sex chromosomes. Despite their family-wide homology of Z-specific gene content, previous cytogenetic studies revealed significant variability in the size, morphology, and heterochromatin distribution of their W chromosome. However, there is little evidence about the accumulation and distribution of repetitive content on lacertid chromosomes, especially on their W chromosome. In order to expand our knowledge of the evolution of sex chromosome repetitive content, we examined the topology of telomeric and microsatellite motifs that tend to often accumulate on the sex chromosomes of reptiles in the karyotypes of 15 species of lacertids by fluorescence in situ hybridization (FISH). The topology of the above-mentioned motifs was compared to the pattern of heterochromatin distribution, as revealed by C-banding. Our results show that the topologies of the examined motifs on the W chromosome do not seem to follow a strong phylogenetic signal, indicating independent and species-specific accumulations. In addition, the degeneration of the W chromosome can also affect the Z chromosome and potentially also other parts of the genome. Our study provides solid evidence that the repetitive content of the degenerated sex chromosomes is one of the most evolutionary dynamic parts of the genome.

With or Without W? Molecular and Cytogenetic Markers are Not Sufficient for Identification of Environmentally-Induced Sex Reversal in the Bearded Dragon

“…According to previous cytogenetic studies, Z and W are microchromosomes and the W chromosome is highly heterochromatic [Ezaz et al, 2005] and possesses notable accumulations of the AAGG repetitive motif [Matsubara et al, 2016]. Therefore, we applied C-banding visualizing heterochromatin [Sumner, 1972] and FISH with the (AAGG) 8 motif as a probe [for detailed methodology see Altmanová et al, 2016;Suwala et al, 2020] to chromosome spreads from 22 individuals representing all experimental groups: parents and offspring of all genotypic combinations (summarized in online suppl. Table 1).…”

Amplified Fragments of an Autosome-Borne Gene Constitute a Significant Component of the W Sex Chromosome of Eremias velox (Reptilia, Lacertidae)

“…Among the cytogenetically characterized Eremias species, E. multiocellata has a large heterochromatic W chromosome, similar to that of E. velox [74]. Another species, E. arguta, has a small W chromosome [41]. This suggests that the ATF7IP2-derived repeat may be shared by several species of Eremias.…”

Sex chromosome evolution among amniotes: is the origin of sex chromosomes non-random?

“…However, shared repetitive content is a rather poor evidence for homology of genomic regions. Repeat content of degenerated sex chromosomes represents one of the most dynamic genome parts as evidenced by comparative studies, for instance, in oplurid, varanid and lacertid lizards [74][75][76], and frequent homoplasies can be expected in this respect. Indeed, the same repetitions accumulated independently on clearly non-homologous sex chromosomes several times, as well as on autosomes [16,[77][78][79].…”