Homozygous deletion of floxed Fgfr2 alleles using Sf1Cre, which is expressed primarily in somatic cells within the gonad, resulted in partial XY sex reversal, with ovotestis formation commonly observed at 15.5 dpc. Deletion of Fgfr2 with Ck19:Cre, a line that deletes in epiblast-derived cells in a mosaic fashion, also resulted in variable and partial XY gonadal sex reversal. Complete sex reversal was observed after Fgfr2 deletion at 10.5 dpc with a heat-shock inducible Cre line, Hs-Cre, but there were variable numbers of SOX9-positive cells observed in mutant gonads. Incomplete deletion of floxed alleles may contribute to phenotypic variability, as might residual genetic background variation. The constitutive Fgfr2hob allele affords a detailed study of the role of FGFR2 in mouse sex determination on a stable genetic and phenotypic background. The value of forward genetics in the identification of developmental loci, including the provision of new and useful alleles of genes of known function, is underlined by this study. The appearance of OMCs varies according to mouse strain. In neonatal MRL/MpJ mice, OMCs are more abundant than in other strains, including C57BL/6N, and they are distributed beneath the ovarian SE. In the present study, OMC density differed between MRLB6F1 and B6MRLF1, but was similar between F2 crosses, implying that maternally inherited mitochondrial haplotypes have no influence on this trait. These results led 
us to hypothesize that maternal factors during pregnancy could affect the number of OMCs in perinatal mice. In contrast, no difference was found in SEMC ratio between direct and reciprocal F1 hybrids. In addition, SEMC ratio was not affected by the progesterone-induced delayed parturition in both MRL/MpJ and C57BL/6N mice, indicating that MC distribution beneath the ovarian SE was not regulated by parental strains. In MRL/MpJ fetuses with artificially delayed parturition, OMC density at E21.5 was significantly higher than in age-matched mice at P2. Fetuses were exposed to high doses of steroid hormones during late pregnancy, and both of estradiol and progesterone levels have been shown to affect MC migration. Although plasma levels of these hormones were measured as putative maternal factors BI-9564 affecting OMC number, no differences were detected between MRL/MpJ and C57BL/6N mice at E18.5 of normal pregnancy. Taken together, these findings indicate that maternal factors during pregnancy influences OMC number by altering the fetal environment through factors other than plasma steroid hormone levels. Because of these processes, each protein can exist as multiple variants in vivo, thus making the human proteome far more complex than the human genome and its,25,000 human genes. Therefore, tailored strategies are needed to study the protein diversity and understand its role in health and disease. Protein variants were initially studied via gel electrophoresis. One-dimensional gel isoelectric focusing was the Ginsenoside-F4 method of choice, contributing to the discovery of variants for proteins such as hemoglobin, alpha-antitrypsin, amylase, and prealbumin. Subsequently, two-dimensional gel electrophoresis provided increased resolving power for simultaneous analysis of hundreds of proteins and their variants, especially when coupled to mass spectrometricidentification of the protein spots from the gel. Two-dimensional difference gel electrophoresishas been used in delineating protein variations across populations.