This strain contains an abnormal LT/Sv-derived Y Chromosome comprising a spontaneous rearrangement (Eicher et al. 1991), formally designated Y(IsXPAR;Y)Ei and informally called Y*. Burgoyne et. al, (1998), updated the original description of the cytogenetic changes in this abnormal Y Chromosome, as an end-to-end fusion of two pseudoautosomal regions (PAR). Males with this abnormal Y Chromosome (XY*) are fully fertile and can be used to transmit this chromosomal aberration. Duplication of the PAR in Y* males permits generation of X and Y reciprocal translocation products during meiosis (see figure 1 in Eicher et.al 1991). Sperm produced by XY* males contain either a normal X Chromosome, the intact, complete Y*, a large marker sex chromosome comprising an X Chromosome and most of the Y (Y*), or a tiny cytogenetic marker sex chromosome (YX). Among offspring are the following genotypes and corresponding phenotypes:
XY*, which are fully fertile males
XX, normal females
XXY*, which are sterile males in which gonad development is normal but spermatogenesis fails resulting in smaller testes after puberty. These males can be classified by manually palpating for testes size after 6 weeks of age. The testes are significantly smaller compared with any normal control male of the same age. Also these mice have a very large marker Chromosome (Fig 1, Eicher et al. 1991) easily seen after simple Giemsa staining (G-banding is not necessary. Alternatively these mice have nearly 2 complete X Chromosomes so these mice can be differentiated from normal XY<*> males by an Xist expression assay (Werler et al. 2011).
XY*X females, which are fertile but litter size and number of litters produced will be less than expected for C57BL/6. These mice have a tiny cytogenetic marker (Fig 1, Eicher et al. 1991) easily seen after Giemsa staining of mitotic metaphase preparations.
Y(IsXPAR;Y)Ei, also called Y*, arose during the backcrossing of Pgk1a from wild-derived mice of Danish origin onto the LT/Sv inbred background (Eicher et al., 1991). Sterile males with small testes and a very large X chromosome by cytology were identified in the ninth backcross generation. Later this mutation was backcrossed along with Tyrp1B-lt from the strain LT/SvEi-Y* onto C57BL/6JEi by consecutive crosses of a male carrying an abnormal LT Y chromosome, XY*, to a C57BL/6JEi female. In 1994 embryos were cryopreserved from C57BL/6JEi females bred to carrier males at backcross generation N21, still segregating for Tyrp1B-lt. That frozen bankstock is Stock No. 017764. The strain remained on the shelf maintained by backcrossing to C57BL/6JEi; Tyrp1B-lt was bred out subsequent to the 1994 freeze. In 1998 this line was rescued by in vitro fertilization using a male at generation N28 and C57BL/6J females and the rescued line continued to be maintained by backcrossing to C57BL/6JEi. In 2007 sperm were cryopreserved for this C57BL/6JEi consomic from a carrier male at generation N28N1N13.
|Allele Name||Chr Y, insertion of X pseudoautosomal region to Y pseudoautosomal region, Eicher|
|Allele Synonym(s)||T(XA1?;InY)8Ei; T8Ei; Y star; Y*|
|Gene Symbol and Name||Y(IsXPAR;Y)Ei, Chr Y, insertion of X PAR region to Y PAR region, Eva Eicher|
|Strain of Origin||LT/Sv|
|Molecular Note||The Y* PAR chromosome has resulted from an end to end fusion of an X and a Y PAR. Furthermore, it was shown that in conjuction with this PAR-PAR fusion, there has been a deletion of both copies of the distally located pseudoautosomal gene Steroid sulfatase (Sts). The arrangement of the two PAR regions permits reciprocal translocation of X and Y chromatin at every meiotic event in the male resulting in half of the sperm produced bearing one of two abnormal sex chromosome.|
When maintaining a live colony, C57BL/6EiJ females (Stock No. 000924) are bred to B6Ei.LT-Y* males. Genotypes produced from this breeding scheme are non-recombinant (wildtype) XX females, XY* males, XY*X females, and XXY* sterile males.
When using the B6Ei.LT-Y(IsXPAR;Y)Ei/EiJ mouse strain in a publication, please cite the originating article(s) and include JAX stock #002021 in your Materials and Methods section.