Sefton, Louise; (1994) The pseudoautosomal region of the mouse. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The morphologically distinct mammalian X and Y chromosomes pair during male meioses. Within this pairing region chiasmata are formed and regular exchange between the X and Y chromosomes occurs in a region of homology near the telomeres called the pseudoautosomal region (PAR). Recombination between chromosome bivalents is thought to be required for the correct segregation of all chromosomes including the sex chromosomes. Alleles within this region do not exhibit strict sex linked inheritance because of the exchange of genetic material but behave as if they were autosomally inherited hence the term pseudoautosomal. The molecular structure of the pseudoautosomal region has not been defined in mammals other than humans. By comparing the pseudoautosomal region of humans with other species features that are essential to the correct function of this region may be determined. Several approaches to cloning the murine PAR have been undertaken. As the PAR resides in the terminal region of the mouse X chromosome one approach to isolating sequences from the PAR is to generate somatic cell hybrids which retain the distal region of the mouse X chromosome. A panel of irradiation and fusion gene transfer hybrids was generated from a monochromosomal hybrid which retained the mouse X chromosome. The retention of loci across the X chromosome was determined and DNA sequences were isolated from hybrids which were enriched for the terminal region of the mouse X chromosome. None of the probes isolated originated from the PAR. An alternative approach to isolating sequences from the murine PAR involved characterizing yeast artificial chromosomes (YACs) which retained sequences common to the telomeric regions of several chromosomes including the X and Y chromosomes. None of the sequences isolated from these YACs originated from the PAR. The order of loci in the terminal region of the mouse X chromosome was determined in order to initiate a chromosome walk towards the PAR from the closest flanking marker. The order centromere-Pdha1-DXPas18-(Glra2,DXMit12)-Prps2-Amg-telomere of this conserved linkage group agrees with the order found on the human X chromosome (PDHA1/GLRA2-PRPS2/AMG-STS) and enables the order of PRPS2 and AMG to be predicted. As Amg was the closest marker to the PAR, a YAC base chromosomal walk was initiated from this locus. Although sequences from the PAR were not obtained, the distance between the pseudoautosomal boundary and the closest flanking X-linked marker was reduced by 460-640 kb.

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