FREQUENCY OF X-Y CHROMOSOME DISSOCIATION IN MOUSE SPERMATOCYTES FROM INTERSTRAIN CROSSES, RECOMBINANT INBRED STRAINS, AND CHIMERAS - POSSIBLE INVOLVEMENT OF PATERNAL GENOME IMPRINTING

The frequency of dissociation of the X-Y chromosome bivalent in diakin esis-metaphase I spermatocytes differs significantly between two inbre d mouse strains, CBA (29%) and KE (7%), that were used to obtain recip rocal F1 hybrids, and to develop recombinant inbred (RI) strains. The level of X-Y dissociation was significantly higher in (KExCBA)F1 hybri ds sired by the CBA males (24%) than in reciprocal F1 hybrids (12%), r evealing the inheritance after the father. Among 14 RI strains, nine w ere concordant with KE, one with CBA, and four had intermediate phenot ype, significantly different from both progenitor strains. This shows that at least two genes are involved, and their possible linkage with agouti and Trf loci is suggested. The linkage with agouti was confirme d by testing additional 10 CBXE incipient RI strains. There was no sig nificant difference in the level of X-Y dissociation between EXCB RI s trains derived from the original cross sired by the CBA males and CBXE RI strains derived from the reciprocal cross. The involvement of the Y chromosome-linked factors was unlikely because it was found earlier (Krzanowska, 1989: Gamete Res 23:357-365) that two congenic strains, K E and KE.CBA, differing with respect to the source of the Y chromosome , had the same level of X-Y dissociation. Thus, the difference obtaine d between reciprocal F1 hybrids is interpreted in terms of paternal ge nome imprinting imposed by CBA males and propagated only in the presen ce of some alleles derived from this strain. Analysis of six KE <-> CB A-TG chimeras, among them three germ line chimeras, points to the conc lusion that the tendency to low or high level of X-Y chromosome dissoc iation is expressed rather autonomously by KE or CBA-T6 spermatocytes (as recognized by a marker chromosome pair), respectively, and was not modified by the presence of somatic cells of the opposite strain. (C) 1994 Wiley-Liss, Inc.