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The Y* rearrangement in mice: new insights into a perplexing PAR
P S Burgoyne1, S K Mahadevaiah, J Perry
1Laboratory of Developmental Genetics, National Institute for Medical Research, Mill Hill, London, UK. pburgoy@nimr.mrc.ac.uk
Abstract:
In essence, the Y* rearrangement in the mouse is a Y chromosome that has been hijacked by a non-Y centromere attached distal to the pseudoautosomal region (PAR). All the Y-unique material is thought to be unaltered, but the recombinatory behaviour of the Y* with the X during male meioisis led to the conclusion that part of the PAR is inverted. In the course of a cross set up to introduce the X-linked mutation Patchy fur (Paf) into XY* males, the Y* chromosome was found to carry the wild type allele of Paf. Paf maps close to the X PAR boundary, so we hypothesised that the inverted region of the Y* PAR originated from an X chromosome that provided not only an inverted copy of proximal PAR, but also an X PAR boundary together with some adjacent X-unique material that included the Paf locus. This hypothesis was validated by Southern analysis using an X PAR boundary probe to show that Y* has an X PAR boundary. Thus the Y* PAR has resulted from an end to end fusion of an X and a Y PAR. Furthermore, it was shown that in conjunction with this PAR-PAR fusion, there has been deletion of both copies of the distally located pseudoautosomal gene Steroid sulfatase (Sts).
Insights
The mouse Y* chromosome
Area of Science:
- Genetics
- Mammalian Chromosome Structure
- Sex Chromosome Evolution
Background:
- The Y* chromosome in mice exhibits unusual structure, with a non-Y centromere attached distal to the pseudoautosomal region (PAR).
- Recombination patterns between the Y* and X chromosomes suggest an inverted segment within the Y* PAR.
Purpose of the Study:
- To investigate the origin of the inverted PAR segment in the Y* chromosome.
- To determine the genetic composition of the Y* PAR and its relationship to the X chromosome.
Main Methods:
- Southern blot analysis using an X PAR boundary probe.
- Genetic crosses to track X-linked mutations (Patchy fur - Paf) in XY* males.
Main Results:
- The Y* chromosome carries the wild-type allele of the X-linked Patchy fur (Paf) gene.
- Southern analysis confirmed the presence of an X PAR boundary on the Y* chromosome.
- The Y* PAR resulted from an end-to-end fusion of X and Y PARs.
- Deletion of the Steroid sulfatase (Sts) gene occurred concurrently with the PAR fusion.
Conclusions:
- The Y* PAR contains an inverted segment derived from the X chromosome, including the Paf locus.
- The Y* chromosome structure arose from a fusion of X and Y PARs, accompanied by gene deletion.
- This rearrangement provides insights into sex chromosome evolution and structural variation.