An evolutionarily conserved early replicating segment on the sex chromosomes of man and the great apes

Abstract

Replication studies on prometaphase chromosomes of man, the chimpanzee, the pygmy chimpanzee, the gorilla, and the orangutan reveal great interspecific homologies between the autosomes. The early replicating X chromosomes clearly show a high degree of conservation of both the pattern and the time course of replication. An early replicating segment on the short arm of the X chromosomes of man (Xp22.3) which escapes inactivation can be found on the X chromosomes of the great apes as well. Furthermore, the most early replicating segment on the Y chromosomes of all species tested appears to be homologous to this segment on the X chromosomes. Therefore, these early replicating segments in the great apes may correspond to the pseudoautosomal segment proposed to exist in man. From further cytogenetic characterization of the Y chromosomes it is evident that structural alterations have resulted in an extreme divergence in both the euchromatic and heterochromatic parts. It is assumed, therefore, that, in contrast to the X chromosomes, the Y chromosomes have undergone a rapid evolution within the higher primates.

Conservation of human-derived pseudoautosomal sequences on the sex chromosomes of the great apes

“…This segment appears, therefore, to be the most invariant part of the higher primate Y chromosome, whereas other euchromalic parts have undergone important rearrangements, in addition to the spreading or complete disappearance of heterochromatic regions (Weber et al, 1986). Deletion map ping studies in man have shown that the testis-dclcrmining factor (TDF) maps to the distal short arm, proximal to the pscudoautosomal region (Vergnaud ct al.. 1986).…”

DNase I hypersensitive sites along the XY bivalent at meiosis in man include the XpYp pairing region

“…It may well turn out to be, when more species have been examined, that XY pairing regions universally will be found to share these common properties. Data already exist showing that the early replicating band Xp22.3 in the pseudoautosomal region of the human X chromosome is also early replicating in several primate species and shows functional homology with the most early replicating band on the Y (Weber et al, 1986a). In situ hybri disation of human-derived pseudoautosoma!…”

Evolutionary breakpoint analysis on Y chromosomes of higher primates provides insight into human Y evolution

“…Eutherian X and Y chromosomes recombine only at the so-called pseudoautosomal region (PAR), which is located at the tip of one arm of X and Y chromosome, respectively (Gläser et al, , 1999Toder et al, 1997). While the X chromosome seems to be highly conserved throughout the eutherian orders, the Y chromosomes show a broad spectrum of species-specific morphological divergence (Weber et al, 1986;Schempp et al, 1989;Müller, 1993). Indeed, the Y chromosomes of various higher primate species exhibit a wide range of structural rearrangements including enormous differences in the degree of amplification of gene family members within their non-recombining regions (NRYs) (Schempp et al, 1995;Gläser et al, 1998;Wimmer et al, 2002a).…”