Satellite DNA and evolution of sex chromosomes

Abstract

The satellite DNA (SATELLITE III) which is mainly represented in the female of Elaphe radiata (Ophidia, Colubridae) has been isolated and its buoyant density has been determined (delta equals 1.700 g cm-3). In situ hybridisation of radioactive complementary RNA of this satellite DNA with the chromosomes of different species has revealed that it is mainly concentrated on the W sex chromosome and its sequences are conserved throughout the sub-order Ophidia. From hybridisation studies these sequences are absent from the primitive family Boidae which represents a primitive state of differentiation of sex chromosomes. Chromosome analysis and C-banding have also revealed the absence of heteromorphism and of an entirely heterochromatic chromosome in the species belonging to the primitive family and their presence in the species of highly evolved families. It is suggested that the origin of satellite DNA (satellite III) in the W chromosome is the first step in differentiation of W from the Z in snakes by generating asynchrony in the DNA replication pattern of Z and W chromosomes and thus conceivably reducing the frequency of crossing-over between them which is the prerequisite of differentiation of sex chromosomes. Presence of similar sex chromosome associated satellite DNA in domestic chicken suggests its existence in a wider range of vertebrates than just the snakes.

Homomorphic sex chromosomes in the lacertid lizard Takydromus sexlineatus

“…(1971) and Singh et aL (1976Singh et aL ( , 1980. Singh et aL, (1976Singh et aL, ( , 1980 demonstrated that the heterochromatinisation of the W-chromosome in several snakes is correlated, at least in part, to the accumulation of a specific sex-linked satellite-DNA.…”

“…(1971) and Singh et aL (1976Singh et aL ( , 1980. Singh et aL, (1976Singh et aL, ( , 1980 demonstrated that the heterochromatinisation of the W-chromosome in several snakes is correlated, at least in part, to the accumulation of a specific sex-linked satellite-DNA. It is possible that there is also a W-linked highly repetitive DNA in Takydromus (and presumably also in other lizards) since the positive C-banding is known to depend on the presence of highly repetitive DNA sequences, often having the characteristics of satellite-DNA (John and Mikios, 1979).…”

“…The presence of homomorphic sex chromosomes, differing from one another only in the degree of heterochromatinisation and in stainability with the C-banding method, is considered to be early stage in the differentiation of sex chromosomes (Ray-Chaudhury et a!., 1971;Singh et aL, 1976Singh et aL, , 1980. Our results are consistent with this hypothesis and indicate that the differentiation of saurian sex chromosomes follows the same steps hypothesised for snakes.…”

Early stages of sex chromosome differentiation in fish as analysed by simple repetitive DNA sequences

“…Comparative studies from different reptiles have been interpreted as indicating that (gata)n/ (gaca)m sequences have been important in sex chromosome evolution. In many animals these sequences hybridize to the sex chromosomes carrying the largest amount ofheterochromatin (Singh et al 1976;Jones 1983). Here experimental evidence is presented that various simple repeats are implicated in the early stages of sex chromosome differentiation.…”

Extension, single-locus conversion and physical mapping of sex chromosome sequences identify the Z microchromosome and pseudo-autosomal region in a dragon lizard, Pogona vitticeps

“…A comparative analysis of sex-related sequences and chromosomes is perhaps the most tractable of these approaches, but it requires the initial identification of sex-related sequences. There are very few sex-specific sequences reported for reptiles (Cooper et al, 1997;Halverson and Spelman, 2002), although repetitive satellite sequences are known to be interspersed throughout the chromosomes of snakes in high copy number (Singh et al, 1976(Singh et al, , 1980 and are concentrated in particularly high density on the W chromosome (Solari, 1994). A number of functional genes have recently been mapped to the Z and W chromosomes of three snakes, a gecko and a turtle (Matsubara et al, 2006;Kawaia et al, 2007;Kawagoshi et al, 2009).…”