Comparison of some properties of oocytes segregating in F2 hybrids between KE and CBA/Kw inbred strains of mice

The time taken to dissolve the zona pellucida was compared with fertilizability as well as the meiotic maturation rate of the oocytes from the same (KE × CBA) F₂ females. The presence of granular material in oocyte cytoplasm was also examined. It was found that for F₂ females in which the zona pellucida digestion was fast, the number of fertilized oocytes was high; for F₂ females with zonae pellucidae more resistant to enzyme, the number of fertilized oocytes was low. The correlation between the two characters was significant, indicating their common genetic and/or physiological control. The low or high solubility of zona pellucida did not correlate with the rate of meiotic maturation of the oocyte. This suggests separate factors controlling these two characters. A separate factor seems to control the appearance of granules in cytoplasm since their presence interfered neither with zona pellucida solubility nor with maturation rate of the oocyte.     

Preferential segregation of marker chromosomes 14 and 18 in mouse recombinant inbred strains derived from the KE and CBA/Kw strains

The segregation pattern of chromosomes 14 and 18 were analyzed in recombinant inbred strains of mice developed from KE and CBA/Kw strains. The analysis was possible owing to the fact that the C-band on chromosomes 14 of the CBA/Kw strain and that of chromosome 18 of the KE strain show size polymorphism: while the CBA/Kw mice have a small sized C-band on chromosome 14, the KE mice show small C-bands on chromosome 18. Chromosomes were identified by G-banding and FISH. The results show that the chromosomes with small centromeric chromatin segregate preferentially.     

Analysis of oocyte quality in recombinant inbred mouse strains developed from KE and CBA strains that differ in fertilization efficiency

Recombinant inbred (RI) mouse strains were developed from reciprocal crosses between two inbred strains differing in the proportion of fertilized ova (CBA, 100%; KE, 77%), to analyse the underlying factors. A correlation (r = 0.83, P < 0.01) between fertilization efficiency within 22 RI strains and after mating RI females with KE males proved that oocyte quality was involved. The following oocyte parameters were analysed in RI and progenitor strains: time of meiotic maturation, rapidity of enzymatic removal of egg investments, and proportion of fertilized ova with supplementary spermatozoa in the perivitelline space. Among the RI strains, high incidence of supplementary spermatozoa was correlated with lower efficiency of fertilization (r = -0.58, P < 0.05) and with slow meiotic maturation (r = -64, P < 0.01), suggesting that delayed maturation may affect oocyte ability of being fertilized by the first penetrating spermatozoon. However, significant correlations were also found between characters which coexist within the progenitor strains, but are not likely to be physiologically related; this suggests that RI strains have inherited large blocks of progenitor genomes, not disrupted by recombination. The strain distribution pattern (SDP) of the analysed traits revealed CBA-like, KE-like, and intermediate phenotypes, indicating that they are polygenically determined. No linkages were found between the studied traits and 12 enzymatic markers. However, the SDP for fertilization efficiency showed a preponderance of non-matching strains (15/19) in relation to agouti locus; the known instability of this chromosome region makes it possible that a putative linkage was disrupted by recombination when RI strains were created.     

Sperm penetration in vitro into ovarian and tubal oocytes from mice of the inbred KE and C57 strains

The method of in vitro fertilization was applied to test a previous suggestion that the lowered fertilizability of the tubal oocytes of female KE strain mice and the high resistance of their zona pellucida to proteolytic enzymes, are due to the premature cortical reaction taking place near the time of ovulation. Therefore higher fertilizability of ovarian oocytes is expected. The effectiveness of F₁ hybrid sperm penetration into ovarian and tubal KE oocytes confirmed these assumptions. The ovarian KE oocytes recovered 9–10 hours after administration of human chorionic gonadotropin (HCG) showed significantly higher penetrability (70–83%) than did the tubal oocytes recovered 12 hours after HCG (about 50%) and 14–16 hours after HCG (20%). Similar results were obtained with C57 oocytes. Sperm penetration into ovarian oocytes (10 hours after HCG) was much more effective (67%) than into tubal oocytes (18%); this finding correlated with more rapid zona dissolution by chymotrypsin. On the basis of these results one might speculate that premature cortical reaction takes place also in the C57 strain.     

Effects of housing density and cage floor space on three strains of young adult inbred mice

Some recommendations in the Guide for the Care and Use of Laboratory Animals (the Guide) are based on best professional judgment. Our current efforts are directed toward replacement with data-driven standards. We demonstrated earlier that young adult C57BL/6J mice could be housed with half the floor space recommended in the Guide without discernable negative effects. This report extends that work by examining optimal housing densities for young adult male and female BALB/cJ, NOD/LtJ, and FVB/NJ mice. These 8-week studies were initiated with 3-week-old BALB/cJ and NOD/LtJ mice and 3- to 5-week-old FVB/NJ mice housed in three cage types. We adjusted the number of mice per cage to house them with the floor space recommended in the Guide (approximately 12 in2 [ca. 77 cm2] per mouse) down to 5.6 in2 [ca. 36 cm2] per mouse. Early-onset aggression occurred among FVB/NJ male mice housed at all densities in cages having 51.7 in2 (ca. 333 cm2) or 112.9 in2 (ca. 728 cm2) of space. FVB/NJ male mice housed in shoebox (67.6 in2 [ca. 436 cm2]) cages did not exhibit aggression until the fifth week. Urinary testosterone output was density-dependent only for BALB/cJ male mice in shoebox cages (output decreased with increasing density) and FVB/NJ male mice. We conclude that all but FVB/NJ male mice can be housed with half the floor space specified in the Guide. The aggression noted for male FVB/NJ mice may have been due to their age span, although this did not impact negatively on the female FVB/NJ mice.     

Changes in germ cells population and in vitro oocyte maturation in female mice with imperforated vagina

This study characterized female mice with a congenital defect in their reproductive tract. In females derived from an outbred colony maintained in the Department of Genetics and Evolution, the frequency of the imperforated vaginae was approximately 2%. A consequence of this defect is infertility. Affected animals developed hydrometrocolpos (the uterus and vagina were greatly distended by fluid). Morphology of the ovary and oviduct was normal and similar to that of control mice. In the females with an imperforated vagina numerous corpora lutea were observed. Accordingly, we have found that both spontaneous as well as exogenous gonadotrophin-induced ovulation occurs in such females. Nevertheless, oocytes derived from ovaries of occluded females exhibited a partial block during in vitro maturation. Histological analysis of ovarian tissue revealed an increase in the number of primary follicles (type I follicles) and a decrease in the number of secondary and antral follicles (type IV and type VI follicles) when compared with control mice. The concentration of androgens in the ovarian tissue was higher in the affected females. Our data show that females with an imperforated vagina can be a useful model for studying the mechanism of genetic control of the development of the urogenital tract in mammals.     

CBXC: a set of recombinant inbred strains between CBA/Ca and BALB/c

A new set of nine recombinant inbred strains designated CBXC-1 to CBXC-9 has been developed from a cross between CBA/Ca female and BALB/c male mice. All of the strains have been brother x sister mated for more than 20 generations, and have been characterized at eight electrophoretic, one immunological and two coat colour loci at which the progenitor strains differ. This set of strains should be useful in investigating the genetics of any characters which differ between the two progenitor strains.     

Different response of maturing oocytes from two inbred strains of mice to sperm penetration

Oocytes from two inbred strains of mice, CBA and KE, were inseminated at prometaphase of the first meiotic division. Pronuclei were formed in 21-36% of inseminated oocytes from the CBA strain. In the KE strain the formation of pronuclei occurred in 2-5% of oocytes and was at the same level as in the non-inseminated control. These results show that in oocytes of the CBA strain maturity of the cytoplasm is acquired earlier than in those of the KE or other so far studied strains of mice. This fact is discussed in the context of different maturation rates of oocytes from different strains. In oocytes which remained non-activated after penetration, transformation of sperm heads into separate chromosomes was observed. An interstrain difference in efficiency of this process was also found.     

Effects of gossypol on sperm counts in two inbred strains of mice

Gossypol acetic acid was administered orally to mice of two inbred strains, BALB/c/O1a and CBA/Gr, at daily doses of 10 or 20 mg/kg for about 4 weeks. Treated mice of both strains showed a reduction in sperm counts. This was more marked in CBA mice, which also had smaller testes size than did BALB/c mice. The treatment had no significant effect on testicular weight but the caput epididymidis and seminal vesicles of treated mice weighed less than those of control mice.     

Effect of cadmium chloride on the ovulation and structure of ovary in the inbred KP and CBA mice strains

A single dose of cadmium chloride (2.2 mumol/100 g of body weight) brought about in the sensitive KP strain alterations of the ovarian structure and disturbances in the ovarian cycle manifested by a prolongation of diestrus. Following cadmium administration and increase in the amount of atretic follicles, especially those showing stages 1I and 2II of degeneration, was observed in the ovaries of KP mice. The corpora lutea contained numerous degenerated cells and were infiltrated by abundant connective tissue cells. The used dose of cadmium chloride showed no influences upon progesterone level. The absence of changes in the ovarian morphology and in the duration of the oestrus cycle in CBA females suggest that this strain is resistant to cadmium chloride.     

Muscarinic receptors in brain from four strains of inbred mice

The density of brain muscarinic receptors from four strains of inbred mice was determined. C57BL/6J mice had a significantly higher density of muscarinic receptors in the forebrain than Balb/cJ or C57BL/10J mice. In the midbrain, C57BL/6J mice also had the highest density of receptors and in the hindbrain, C57BL/6J and AKR/J mice had a two fold higher receptor density compared to the other two strains. These findings demonstrate that inbred strains of mice which exhibit a range of genetically-determined behaviors, have varying densities of muscarinic receptors.     

Fibroblast cell lines from young adult mice of long-lived mutant strains are resistant to multiple forms of stress

Previous studies have shown that dermal fibroblast cell lines derived from young adult mice of the long-lived Snell dwarf mutant stock are resistant, in vitro, to the cytotoxic effects of H(2)O(2), cadmium, UV light, paraquat, and heat. We show here that similar resistance profiles are seen in fibroblast cells derived from a related mutant, the Ames dwarf mouse, and that cells from growth hormone receptor-null mice are resistant to H(2)O(2), paraquat, and UV but not to cadmium. Resistance to UV light, cadmium, and H(2)O(2) are similar in cells derived from 1-wk-old Snell dwarf or normal mice, and thus the resistance of cell lines derived from young adult donors reflects developmental processes, presumably hormone dependent, that take place in the first few months of life. The resistance of cells from Snell dwarf mice to these stresses does not reflect merely antioxidant defenses: dwarf-derived cells are also resistant to the DNA-alkylating agent methyl methanesulfonate. Furthermore, inhibitor studies show that fibroblast resistance to UV light is unaffected by the antioxidants ascorbic acid and N-acetyl-L-cysteine. These data suggest that postnatal exposure to altered levels of pituitary hormones leads to development of cellular resistance to oxidative and nonoxidative stressors, which are stable through many rounds of in vitro cell division and could contribute to the remarkable disease resistance of long-lived mutant mice.