Two new X-autosome translocations in the mouse

Abstract

The reciprocal translocations T(X;4)37H and T(X;11)38H were induced by acute X-irradiation of spermatozoa. Male heterozygotes are completely aspermic with a spermatogenic block at pachytene and testis masses about one third of normal, though metaphase I is very occasionally reached in T37H. For both translocations the X chromosome breakpoints are in band XA2, and the autosomal breakpoints are in 4D3 for T37H and 11E1 for T38H, leading to long and short marker chromosomes. Chain quadrivalents predominated in oocytes at MI, with no rings; there were 32% trivalent + univalent configurations in T37H and 40% in T38H. These generated (1) XO mice, (2) tertiary trisomies carrying 20 bivalents and the small X⁴ (T37H) or X¹¹(T38H) markers. These trisomies were apparently lethal in T37H but sub-viable in T38H and sometimes fertile as XX¹¹ and trisomic XXX¹¹ females, though sterile as XX¹¹ Y males. However, many developed exencephaly in utero, probably because of the distal duplication on chromosome 11. No tertiary monosomies were found in 12 to 14 day embryos. Seven percent of all female progeny were XO, with a higher than expected frequency in T37H and a lower than expected one in T38H. T37H is about two units and T38H about five units from the spf locus on the X chromosome with evidence for some crossover suppression between the T38H breakpoint and Ta. Autosomal linkages found were T37H-ra-6 (R.F. of 16 + 4% between T37H and m) and T38H-/Re^wc (R.F. of 5 + 3%). T37H/+ females weighed about 10% less than normal females at birth and about 30% less at weaning; there was little if any effect in T38H/+ females or in males carrying either translocation. Neither translocation had any marked effect on viability. T37H/ + females showed variegation when heterozygous for b with the wild type allele in the long 4^X marker. On average, about 20% of the coat was brown rather than black. However, no clear evidence for m variegation was found.

Synaptonemal complexes in Gerbillidae: probable role of intercalated heterochromatin in gonosome-autosome translocations

“…In the case of X-autosome translocations, sterility appears to be the rule, as has been observed in the mouse (Ashley et al, 1982(Ashley et al, , 1983Searle et al, 1983), but few human cases have been studied as yet. The only human meiotic study carried out, on a t(X;l), showed the formation of a chain quadrivalent at diakinesis and the frequent absence of "sex vesicles" at the pachytene stage (Dutrillaux et al, 1972).…”

Attenuated spread of X-inactivation in an X;autosome translocation

“…Illustrations of the T37H translocation (25), together with probes and markers used in this study, are shown in Fig. 1 A-C.…”

X-Chromosome inactivation: a repeat hypothesis

“…Several involve Chr 7, bearing the coat colour genes albino, c, and pink-eyed dilution, p, and others involve Chr 4, with the gene brown, b, all of which undergo variegation. Data on some of these translocations are incomplete, but Table 1 shows results from five in which both cytogenetic breakpoints and levels of variegation have been described (Russell and Montgomery, 1970;Russell, 1983;Searle et al, 1983). The per cent of the coat of translocation carriers which shows mutant colour may be taken as a measure of inactivation of the wild-type allele on the translocation chromosome, with a mean of 50 % indicating full inactivation.…”