Targeted mutagenesis in mice, a powerful tool for the analysis of gene function and human disease, makes extensive use of 129 mouse substrains. Although all are named 129, we document that outcrossing of these substrains, both deliberate and accidental, has lead to extensive genetic variability among substrains and embryonic stem cells derived from them. This clearer understanding of 129 substrain variability allows consideration of its negative impact on targeting technology, including: homologous recombination frequencies, preparation of inbred animals, and availability of appropriate controls. Based on these considerations we suggest a number of recommendations for future experimental design.

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Severely reduced fertility is a common finding in cystic fibrosis (CF). We used in situ hybridization to examine the cell-specific expression of CFTR in the reproductive organs of rodents. In males CFTR mRNA is found in the round spermatids (spermatogenic stages V-X) and in the principal cells that line the initial segment of the epididymis. In both the testis and the epididymis, CFTR expression is developmentally regulated suggesting that the defect in the genital tract of male CF patients is of developmental origin. CFTR expression in the luminal and glandular epithelium of the uterus is regulated during the oestrous cycle and is maximal at pro-oestrus. Our results provide a biological rationale for the reduced fertility of CF patients, and suggest a possible cause for the comparatively poorer prognosis for women with CF.

Characterization of genetically engineered mice requires consideration of the gene of interest and the genetic background on which the mutation is maintained. A fundamental prerequisite to deciphering the genetic factors that influence the phenotype of a mutant mouse is an understanding of genetic nomenclature. Mutations and transgenes are often maintained on segregating or mixed backgrounds of often-unspecified origin. Minimizing the importance of strain and substrain differences, especially among 129 strains, can lead to poor experimental design or faulty interpretations of data. Genetic factors that influence phenotype can be categorized as traits that are unique to the background strain, unique to the gene of interest, or an interaction of both the background strain and the gene of interest. The commonly used inbred strains are generally well characterized and understood; however, specific genetic alterations combined with genes unique to the background inbred strain may lead to unexpected results. Genetic background effects can be analyzed and controlled for by using specific targeting and breeding strategies. Selection of appropriate experimental controls is critical. Ideally, mutations or transgenes should be characterized on more than one genetic background and in hybrids of the two progenitor strains. This approach may lead to the identification of novel genetic modifiers of the "gene of interest." Conditional mutagenesis technologies increase the options for controlling genetic background effects in addition to permitting the study of developmental and temporal changes in gene and protein expression and thus phenotype.

Recently, a mouse Sertoli cell line (MSC-1) was established from transgenic mice carrying a fusion gene composed of human Müllerian inhibitory substance transcriptional regulatory sequences linked to the SV40 T-antigen gene. This cell line contained a morphologically heterogeneous population of cells that expressed characteristic Sertoli cell mRNAs such as transferrin, the beta-subunit for inhibin, and sulfated glycoprotein-2 (SGP-2). In this study, we compared various characteristics of MSC-1 cells to primary cultures of Sertoli cells from immature rats or adult mice. Our observations indicated that: 1) These cells were ultrastructurally similar to mouse Sertoli cells in culture; 2) MSC-1 cells expressed mRNA for androgen-binding protein (ABP) and SGP-1, but not the receptor for FSH; 3) The expression of SGP-2 mRNA and secretion of SGP-2 increased approximately 2-fold when cells were cultured at 41 degrees C, the nonpermissive temperature for the SV40 virus, while SGP-1 and transferrin mRNA levels and secretion were unaffected; 4) Proliferation of these cells was serum-dose dependent and temperature dependent and could be inhibited by incubating MSC-1 cells at 41 degrees C; 5) Proliferation was also significantly reduced after cells were incubated in the presence of dibutyryl cAMP (dbcAMP) for 6 days; 6) Fifteen subcultures produced from single MSC-1 cells displayed similar levels of mRNA expression for transferrin or SGP-1. Together these data indicate that the MSC-1 cell line is composed of a single cell type displaying numerous characteristics of Sertoli cells. This cell line may provide a unique source of tissue for studying various aspects of Sertoli cell behavior.

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Human cataracts may be congenital or appear later in life; nuclear, cortical and lens epithelial proliferation forms have all been described. Due to the high degree of genetic homology, it is not surprising that multiple spontaneous or induced single gene mutations result in morphologically similar forms in the mouse. There are many different mutations in inbred strains of mice in which cataracts are a part of the phenotype. These mutations are of potential value in deciphering the molecular mechanisms involved in cataract formation. This report reviews the currently published cataract mutations in mice