| First Author | Cattanach BM | Year | 1988 |
| Journal | Mouse News Lett | Volume | 80 |
| Pages | 156-57 | Mgi Jnum | J:18279 |
| Mgi Id | MGI:66282 | Citation | Cattanach BM, et al. (1988) A new steel allele with pre-implantation homozygous lethality. Mouse News Lett 80:156-57 |
| abstractText | Full text of MNL contribution: Research News. 1. A new steel allele with pre-implantation homozygous lethality. A presumptive Sl mutation detected in a combined HU-X-ray mutation experiment (Cattanach and Rasberry MNL 75:25-26, 1986) has proven to be a Sl allele in crosses with Sl-con and has been designated Sl-12H. However, it differs from other known Sl alleles in a number of ways. Sl-12H heterozygotes appear rather small as adults and tend to be smaller than their + sibs at weaning age. In addition, a proportion of their young from crosses with + (C3H/HeH x 101/F-1) mice are noticeably small at birth. Thus, among 335 young observed within a few hours of birth 119 were small, and 23 of these failed to survive more than a few days. At weaning age most of the surviving small mice (88/96) proved to be Sl-12H heterozygotes, so indicating small size and reduced viability to be associated with this genotype, but some (20) normal sized young at birth subsequently also proved to be Sl-12H+. In total, 108 Sl-12H+ young were observed at weaning and 227 were + and, even if all post-natal losses (23 small + 4 normal sized) are taken to be heterozygotes there is still a significant shortage of this genotype (135 Sl-12H+ : + 227; X = 23.38; P = 1.3 x 10-(-6). Some pre-natal loss was therefore also indicated and this was further suggested by a reduced litter size (6.35 cf. ~9.0 for the + hybrid). Intercrosses between heterozygotes yielded 30 Sl-12H+ and 20+ young at weaning, the departure from the expected 2:l ratio again demonstrating the reduced viability of the heterozygote. Further, the absence of any anaemic, black-eyed-white young indicated that the homozygotes die prenatally. Consistent with these findings was that of a greatly reduced litter size, 3.9. To investigate the indicated pre-natal losses pregnant females from the following crosses were opened at 17 days' gestation. Four males were used for each type of cross. Cross: + females X + males; No. 13; Live embryos: 113; Late deaths: 1; Moles: 11; Corpora lutea: 136; Moles/Implants: 8.8%; Late deaths/Implants: 0.8%; Pre-impl. Loss: 8%. Cross: + females x Sl-12H+ males; No. 25; Live embryos: 189; Late deaths: 9; Moles: 11; Corpora lutea: 249; Moles/Implants: 5.2%; Late deaths/Implants: 4.3%; Pre-impl. Loss: 12%. Cross: + females x + males (from Sl-12H matings); No. 14; Live embryos: 117; Late deaths: 1; Moles: 7; Corpora lutea: 144; Moles/Implants: 5.6%; Late deaths/Implants: 0.8%; Pre-impl. Loss: 13%. Cross: Sl-12H+ females X Sl-12H+ males; No. 14; Live embryos: 58; Late deaths: 3; Moles 9; Corpora lutea: 102; Moles/implants: 12.9%; Late deaths/Implants: 4.3%; Pre-impl. Loss: 31%. The frequency of late deaths in the Sl-12H+ x + crosses was higher than in either of the + x + controls but this was not high enough to account for the estimated shortage of S1-12H heterozygotes at birth. Some of the live foetuses were clearly very small, however, and it is likely that these might not have survived up to or beyond birth. In addition, 9 living and 3 dead foetuses were exencephalic and since these were not produced in the crosses involving + sibs the abnormality may be associated with the Sl-12H mutation. An increased level of late deaths and exencephalics was also found in the intercrosses and may be attributed to the heterozygotes but among the implanted embryos no indication of homozygotes other than a slightly raised early post-implantation death (moles) was found. Their absence could be accounted for by the high level of pre-implantation loss in the cross. Examination of 3.5 d embryos from Sl-12H+ intercrosses revealed that 72(50%) were morulae, 60(41%) were blastulae and 13(9%) were degenerating. Outcrosses, by contrast, yielded 28(27%) morulae, 68(67%) blastulae and 6(6%) abnormal. These results suggested that S1-12H homozygotes may be lagging in development and may subsequently fail to implant, as suggested by the openings data. It is possible that the viability problems associated with S1-l2H homozygotes and heterozygotes may reflect a deletion event associated with the mutation. (Cattanach, Rasberry and Beechey). |
