P. H. Glenister

A new allele sash (wsh) at the w-locus and a spontaneous recessive lethal in mice.

A mutation to an apparently new allele at the WMocus of the mouse arose spontaneously in a cross between two inbred strains. Heterozygotes have a broad white sash, leading to the name and symbol sash, W. Homozygotes are black-eyed whites which are viable, fertile and not anaemic, although the gene does cause mild haematopoietic defects. The original mutant animal also carried a spontaneous recessive lethal mutation on chromosome 5, mapping at 2 cM distal to the JF-locus.

Reduced reproductive performance in androgen-resistant Tfm/Tfm female mice

Androgen-resistant female mice (Tfm/Tfm) homozygous for the mutant gene Tfm were bred by making use of males chimaeric for the Tfm gene. All seven Tfm/Tfm females found were fertile, confirming that a normal level of androgen receptor protein is not essential for reproduction in female mice. However, when five of the seven were studied throughout their reproductive life they proved to have impaired reproductive performance and premature cessation of reproduction. No impairment of reproduction was seen in heterozygous Tfm/ + females. The ovarian histology suggested that in Tfm/Tfm the normal ageing processes were accelerated. This work is consistent with the work of others in that androgen is involved in the control of follicular maturation and atresia, and that the effect is mediated by the androgen receptor coded by the Tfm locus.

Long-term storage of mouse embryos at —196 °C: the effect of background radiation

In order to test the feasibility of preservation, of genetic stocks of mice by storage in liquid nitrogen, mouse embryos at the 8-cell stage, were frozen and stored in liquid nitrogen at – 196 °C under increased radiation exposures of 1·8×, 9× and 84× background levels for periods of 6–8 months, 10–12 and 27–29 months, the 1·8 × level being regarded as a control. Their survival rates to the blastocyst stage, and after transfer to recipient females, to foetal or liveborn stages were then compared with those of unfrozen or short term frozen control embryos. The freezing process per se caused a marked loss of viability, in comparison with the unfrozen controls, but at the 1·8× radiation level there was then no further loss in viability even at the longest storage time (27–29 months). Similarly, at the 9× radiation level there was no loss of viability during storage up to 29 months, but at the 84× level the proportions of implanted embryos and live foetuses were slightly reduced. It was not clear if this was a true effect of radiation, since it was not related to time of storage. Considering all groups, about 20–30% of the embryos originally frozen were recovered as foetuses or liveborn young. It is concluded that the preservation of genetic stocks by storage in liquid nitrogen is a feasible proposition.

Re-establishment of breeding stocks of mutant and inbred strains of mice from embryos stored at –196 °C for prolonged periods

Breeding stocks were re-established from embryos of various mutant and inbred strains of mice after prolonged storage in liquid nitrogen at the 8-cell stage even with strains where only a proportion of the progeny were of the desired type, i.e. in the Mo dP and XO strains. Gonadotrophin treatment failed to produce superovulation consistently in any of the strains tested. Although the initial survival of embryos after thawing and culture to the morula and blastocyst stage was highest for embryos from XO mothers (61%), these embryos suffered the heaviest early postimplantation loss after transfer (61%). The proportion of embryos, originally frozen, developing into foetuses and offspring was variable (13% HT, 14% PT, 20% Mo dP , 14% XO, 21% CBA and CBA-T6) and lower than previously reported for hybrid 3H1 embryos (20–30%). The sex ratio of the liveborn young was within the normal expected limits except for the Mo dp strain, where it differed significantly from the exected 2♂:1♀ ratio. The proportion of young of the desired type from the frozen embryos of Mo dp and XO females was less than expected (17 and 3% respectively). In all cases a normal breeding stock was reestablished whose performance was within normal limits for each strain. Even without further improvements in embryo collection and the freezing technique per se , the storage of embryos in liquid nitrogen is an extremely economic way of preserving mouse genetic stocks.

Long-term storage of eight-cell mouse embryos at - 196 degrees C.

Stocks of mutant mice have been reestablished from eight-cell embryos stored in liquid nitrogen for varying periods up to 11 years, and no evidence has been found of deterioration of survival with time of storage. Also, studies on the simulated cumulative effect of background radiation during storage failed to find any detrimental effect when embryos were exposed to the equivalent of about 2000 years of background radiation. However, in some cases embryos that carry mutant genes or chromosome anomalies tend to survive the freezing and thawing procedure less well than F1 hybrid embryos. Although this effect is probably independent of storage time, recent improvements in technique upon embryonic survival are to be welcomed.

A presumed deletion covering the W and Ph loci of the mouse

A new allele at the W -locus ( W 19 H ), found in a mutagenesis experiment in which females were irradiated, involves a presumed deletion. The deletion covers the Ph locus (which forms part of a gene complex with the W , Ph and Rw loci), and the locus of a recessive lethal 2 cM distal to W . It does not extend distally to the bl locus; nor does it involve the Rw locus, W 19 H / Rw compounds being viable and fertile. Thus, the length of the deletion is 2–7 cM. The non-involvement of Rw shows that, in the gene triplet Rw , W , Ph , Rw must lie proximal to W and Ph , whose relative position remains unknown. Heteozygotes for W 19 H are not anaemic, show only minimal white spotting and no pigment dilution; they thus resemble heterozygotes for the original W mutant allele and differ from W / Ph trans heterozygotes, which have extensive white spotting. In addition W 19 H heterozygotes may be small and runted, many are believed to die prenatally, and some in the nest. Their radiosensitivity is increased. Homozygotes die at the pre-implantation stage.

Dose-response curve for the yield of translocations in mouse spermatogonia after repeated small radiation doses.

Abstract When male mice were given small doses of about 10.4 rad γ-rays at high dose rate (17–18 rad/min) on 5 days/week for 12 weeks the yield of translocations in spermatocytes irradiated as spermatogonia was less than after the same total dose (620 rad) given in a single exposure. A dose-response curve for the yields of translocations after 3, 6, 9 or 12 weeks of such daily repeated irradiation was linear but with intercept on the ordinate significantly different from the control. The interpretation was that the reduced effect of repeated small doses was due to change in susceptibility of the spermatogonial cell population after repeated irradiation.

A recessive allele of the mouse agouti locus showing lethality with yellow, Ay.

The radiation-induced agouti allele a 1 is recessive to the alleles a and a 4H (which resembles a e ). It is lethal when homozygous and also in combination with the dominant yellow allele A y . The ethylnitrosourea induced allele a 16H is also lethal when homozygous, and when heterozygous with a shows a phenotype like that of a x , with black back and lighter belly. Like a x it is not lethal with A y , and it is also not lethal with a 1 , a 1 is believed to be the first recessive allele which is lethal with A y , and may be useful in elucidating the complexity of the agouti locus.

The mutagenic effect of repeated small radiation doses to mouse spermatogonia. Iii. Does repeated irradiation reduce translocation yield from a large radiation dose.

Abstract Previous results had suggested that daily repeated doses of 10 rad X- or γ-rays to mouse spermatogonia decreased their sensitivity to translocation yield. This was tested by comparing the effects of a dose of 300 rad γ-rays given before, 24 h after, or 8 days after, 30 daily doses of 10 rad γ-rays to male mice. The yield of translocations per cell from those receiving the 300 rad dose 24 h after the repeated ones (7.3%) was significantly lower than that from the other two regimes (9.4 and 9.7% respectively). This was consistent with the explanation that the repeated irradiation had temporarily increased the resistance of the spermatogonial cell population to translocation yield. However, there must remain some doubt about this interpretation since the absolute values of translocations found were too high, and the yield from those which had received the 300-rad dose 24 h after the repeated ones was not significantly below the sum of those from a single dose and from repeated doses given separately.

A SEARCH FOR STRAIN DIFFERENCES IN RESPONSE OF MICE TO MUTAGENESIS BY THIO-TEPA

After treatment of mice with thio-TEPA Malashenko and colleagues found differences among inbred strains in yield of dominant lethals and of chromosome aberrations in bone marrow, which they attributed to genes affecting repair. An attempt was made to confirm this work by comparing yields of dominant lethals in different strains of females mated to the same strain of males. However, no differences were found, all strain combinations giving 42-49% dominant lethals after a dose of 2 mg/kg thio-TEPA to late spermatids. Thus, the existence of genetic differences in repair of thio-TEPA induced lesions between strains CBA and C57BL/6J and between C3H/He and 101/H is not confirmed. Possible reasons for the discrepant results are discussed.