The use of specific DNA probes to analyse the Sxr mutation in the mouse

The mouse Y chromosome: enrichment, sizing, and cloning by bivariate flow cytometry

In this report, we demonstrate the utility of interleukin-2 (IL-2) stimulation of spleen cell cultures and bivariate flow cytometry in the analysis and purification of the C57BL/6J mouse Y Chromosome. We determined that the DNA content of the C57BL/6J Y Chromosome is approximately 94.7 Mb, making it similar in size to human Chromosome 16 and significantly larger than previous estimates. In addition, we describe the bulk isolation of mouse Y Chromosomes and demonstrate enrichment of the isolated material using a fluorescence in situ hybridization strategy. We detail the construction of two small insert Y Chromosome-specific libraries, ideal for sampling Y Chromosome sequences. From these libraries 1566 clones were analyzed. We provide a detailed characterization of 103 clones, generating nearly 50 kb of sequence. For 30 of these clones, we identify regions of homology to known Y chromosomal sequences, confirming the enrichment of the sorted DNA. From the remaining characterized clones, we describe the development of 15 male-specific PCR assays and 19 male-female PCR assays potentially originating from the pseudoautosomal region or other areas of X-Y or autosome-Y homology.

Differential male genetic success determines gene flow in an experimentally manipulated mouse population

Sexual selection arises when genetically different males show heritable differences in reproductive success. Mouse mating behaviour involves both male competition and female choice. In this paper we show that introduced Y-linked DNA markers spread more extensively through a natural population than do genes inherited matrilineally. Differences in mating success between the sexes and among individual males may alter the pattern and rate of gene flow in natural populations. Another interesting possibility is that the success of the introduced Y chromosome may be attributable to so-called 'selfish' traits, such as sex-linked meiotic drive or intra-uterine competition. However, this study provides little unequivocal evidence to support this view. Differential success of introduced versus resident males may have implications for the reintroduction of endangered mammals into residual wild populations.

A structural analysis of the Sxr region of the mouse Y chromosome

Three genetic functions have been mapped to the minute Sxr (sex-reversed) region of the mouse Y chromosome. These are Tdy, the primary testis determinant; Hya, the locus (either structural or regulatory) controlling the expression of the male-specific minor histocompatibility antigen H-Y; and Spy, a spermatogenic gene. Hya and Spy map to DNA deleted from the Sxr region in the deletion variant Sxrb (the delta Sxrb DNA). With the object of cloning Hya and Spy, we initiated chromosome walking in the delta Sxrb DNA. From three independent loci--Sx1, Zf2, and T5--we have isolated approximately 270 kb of delta Sxrb DNA lying in three contigs of 145, 60, and 65 kb, respectively. Within 17 kb of the 3' end of the Zfy-2 gene, lowcopy repeat elements were found in a region that extends for approximately 35 kb. Probes isolated from this region detect multiple Sxr loci, some of which map to the delta Sxrb DNA present in the T5 contig DNA. Three of these multicopy probes detect delta Sxrb loci not represented in our three contigs, which means that six distinct delta Sxrb loci have now been identified. Here we present a preliminary model of the molecular structure of the DNA in this unique region.

A mouse Y chromosome pseudogene is related to human ubiquitin activating enzyme E1

A 2041 bp DNA fragment isolated from the Sxr (sex reversed) region of the mouse Y Chromosome (Chr) was sequenced and characterized. The sequence, pY8/b, contains four exons that are highly similar to 525 contiguous bases from the cDNA of human ubiquitin activating enzyme E1. Two of the exons contain stop codons, indicating that pY8/b is not part of a functional gene. Sequences related to pY8/b were amplified from the Y Chr of the inbred mouse strain, C57BL/6J. These sequences may be portions of the recently discovered functional equivalent of pY8/b. Despite a high degree of similarity with the human E1 gene, the functional equivalent of pY8/b is not the mouse E1 gene, because unlike E1, the functional equivalent of pY8/b is expressed in a tissue-specific manner. These data are discussed with respect to theory on the evolution of the mammalian Y Chr, and in particular, to the prediction that functional genes on the Y Chr have a male-specific function.

Homology of a candidate spermatogenic gene from the mouse Y chromosome to the ubiquitin-activating enzyme E1

The Sxr (sex-reversed) region, a fragment of the Y chromosome short arm, can cause chromosomally female XXSxr or XSxrO mice to develop as sterile males. The original Sxr region, termed Sxra, encodes: Tdy, the primary sex-determining gene; Hya, the controlling or structural locus for the minor transplantation antigen H-Y; gene(s) controlling the expression of the serologically detected male antigen (SDMA); Spy, a gene(s) required for the survival and proliferation of A spermatogonia during spermatogenesis; Zfy-1/Zfy-2, zinc-finger-containing genes of unknown function; and Sry, which is probably identical to Tdy. A deletion variant of Sxra, termed Sxrb, which lacks Hya, SDMA expression, Spy and some Zfy-2 sequences, makes positional cloning of these genes possible. We report here the isolation of a new testis-specific gene, Sby, mapping to the DNA deleted from the Sxrb region (the delta Sxrb interval). Sby has extensive homology to the X-linked human ubiquitin-activating enzyme E1. The critical role of this enzyme in nuclear DNA replication together with the testis-specific expression of Sby suggests Sby as a candidate for the spermatogenic gene Spy.

Neuroblastoma consensus deletion maps to 1p36.1-2

At least 70% of human neuroblastomas display cytogenetically visible aberrations in the short arm of chromosome 1. We have used a panel of probes detecting polymorphic DNA loci, most of which were derived from a library of microdissected distal 1p chromosome fragments, to compare the hybridization pattern of DNA on nine different tumors and the corresponding normal tissue. In eight of the neuroblastomas allelic loss was observed with at least two probes. The deletions were of different size. Since a consensus deletion in all eight tumors included the segment 1p36.1-2, we conclude that genetic information related to neuroblastoma tumorigenesis is located within this approximately 10 megabase segment. Previous studies have revealed the amplification of MYCN in neuroblastomas. Our study did not provide evidence for a correlation between MYCN amplification and the 1p deletion, suggesting that the two genetic alterations result from molecular mechanisms that are not directly related to each other.

The Y chromosome of the mouse is decondensed in Sertoli cells

The condensation of the Y chromosome in mouse cells was studied with two repetitive DNA probes, pY353/B and M34. Both DNA probes are specific to the Y chromosome and hybridize in situ along the whole chromosome. Due to the high resolution of the in situ hybridization technique with non-radioactive labeled DNA probes it was possible to observe the degree of condensation of the Y chromosome in the interphase cell nuclei of various somatic tissues and on testes preparations. The Sertoli cells were the only cell type in which the Y chromosome was always observed to be in a highly decondensed state. The decondensation of the Y chromosome in the Sertoli cells supports the view that the genetic activity of the Y chromosome is cell autonomous and opens the way to its molecular analysis.

Chromosome mapping and expression of a putative testis-determining gene in mouse

Isolation and mapping of a mouse complementary DNA sequence (mouse Y-finger) encoding a multiple, potential zinc-binding, finger protein homologous to the candidate human testis-determining factor gene is reported. Four similar sequences were identified in Hind III-digested mouse genomic DNA. Two (7.2 and 2.0 kb) were mapped to the Y chromosome. Only the 2.0-kb fragment, however, was correlated with testis determination. Polymerase chain reaction analysis suggests both Y loci are transcribed in adult testes. A 3.6-kb fragment was mapped to the X chromosome between the T16H and T6R1 translocation breakpoints, and a fourth (6.0 kb) was mapped to chromosome 10. Hence, mYfin sequences have been duplicated several times in the mouse, although they are not duplicated in humans.

Molecular aspects of sex determination in mice: an alternative model for the origin of the Sxr region

Using a combination of in situ mapping and DNA analysis with recombinant DNA probes specific for the Sxr region of the mouse Y chromosome, we show that both the gene(s) controlling primary sex determination and the expression of the male-specific antigen H-Y (Tdy and Hya respectively) are located on the minute short arm of the mouse Y chromosome. We demonstrate that the H-Y- variant of Sxr (Sxr') arose by a partial deletion within the Sxr region and propose an alternative model for the generation of the original Sxr region.