Inheritance of a meiosis I error expressed in mouse oocytes and modulated by a maternal factor

Transgenic mice and their impact on kidney research

The kidney is a key organ in the maintenance of ion and fluid homeostasis and specific transport systems localized along the nephron guarantee this function. Due to its large functional heterogeneity, experiments on the whole organ level cannot be easily performed, and thus more refined tools are needed, like for example the development of specific recombination systems to gain knowledge on the physiological role of single proteins implicated in ion transport. This review introduces the transgenic technology developed over the past decades, and then focuses on recent strategies for generating kidney-specific gene targeting, over-expression, and gene ablation in mice, that will help to understand the physiological role of proteins implicated in salt and water balance in the kidney.

Inheritance of a meiotic abnormality that causes the ovulation of primary oocytes and the production of digynic triploid mice

Previous studies have demonstrated that the LT/SvKau strain of mice ovulates a high proportion of oocytes as diploid primary oocytes rather than secondary oocytes. These ovulated primary oocytes are arrested at meiotic metaphase I but may be fertilized to produce digynic triploid embryos. In the present study, 40.4% of eggs analysed from LT/SvKau females were ovulated as primary oocytes, compared to 1.2% from control C57BL/Ws strain mothers. These two inbred strains were intercrossed to produce eight sets of F1, F2 and backcross females and the frequency of triploidy was investigated. The results are compatible with segregation of a co-dominant, autosomal gene that has a major influence on the incidence of triploidy. We suggest that the provisional gene symbol Poo (primary oocyte ovulation) be assigned to this gene, with alleles Poo(l) (the 'mutant' allele present in the LT/SvKau strain) and Poo(b) (the normal allele present in C57BL/Ws mice). Poo is incompletely penetrant and has variable expressivity because the proportion of oocytes ovulated as primary oocytes by LT/SvKau mice was variable and, in some cases, nil. In putative Poo(l)/Poo(b) heterozygotes the frequency of ovulated primary oocytes was increased only marginally (from 1.2% to 6.6%) by the presence of one copy of the Poo(l) allele, but this increase was found consistently (in two reciprocal F1 crosses) and was statistically significant. No evidence was found for tight genetic linkage between Poo and two Mendelian loci (brown on chromosome 4 and glucose phosphate isomerase on chromosome 7), that were segregating in the crosses. The Poo(l) mutant in the LT/SvKau strain of mice provides a valuable resource to study the cell and molecular biology of mammalian oocyte maturation and the control of meiosis.

Paternal inheritance of egg traits in mice: a case of genomic imprinting

Eggs from reciprocal hybrids between the C57BL/6By and BALB/cBy strains were tested for their susceptibility to attack by hyaluronidase and pronase. There were significant reciprocal differences between the F1 females in the responses of their unfertilized eggs to both enzymes. The F1 hybrids from BALB mothers showed the increased susceptibility characteristic of C57BL whilst the F1 hybrids with C57BL mothers were more resistant to both enzymes, like BALB mice. Eggs from the four kinds of reciprocal F2 hybrid females also showed patroclinous patterns of susceptibility. A patroclinous difference was found between reciprocal crosses of the CXBD and CXBE recombinant inbred strains but not in crosses between recombinant inbred strains with similar phenotypes. Cross fostering did not alter the phenotypes of the C57BL and BALB females or those of their reciprocal F1 hybrids. The findings are interpreted in terms of differential genomic imprinting of paternally inherited information. The possible general usefulness of patroclinous differences between reciprocal F1 females in revealing differences in imprinting is noted.