No description available.

The expectation for a gene dose effect in an X-linked phenotype is that the corresponding metrical trait in heterozygous females will lie between values for affected hemizygous males and unaffected males and females. I made sequential measurements (at 30, 60, 90, 120 and 150 days) of serum phosphate concentration and tail length in mice with X-linked hypophosphatemia (mutant genotypes: Hyp/+, Hyp/Y and Hyp/Hyp) and in their normal littermates (genotypes: +/+ +/Y). I also measured renal mitochondrial 24-OHase activity in mice fed control and low phosphate diets and representing all five genotypes. I further studied serum AP activity and vertebral bone histomorphometry in the five genotypes. The mutant animals all had uniformly and significantly different values than unaffected littermates. There was no evidence of a gene dose effect because values were not significantly different among the three mutant genotypes. / I also studied the influence of gamete of origin on serum phosphate, tail length, renal mitochondrial 24-OHase activity, serum AP activity and vertebral bone histomorphometry in the Hyp/+ offspring of affected males (Hyp/Y) or affected females (Hyp/+ or Hyp/Hyp). I found no effect on the distribution of trait values. / I conclude that parental origin of the mutant allele does not explain the absence of a gene dose effect in Hyp mice.

Early identification of mutant embryos prior to the manifestation of a defect facilitates the study of dysmorphogenesis. The In(l)lRk inversion was used as a cytogenetic marker to distinguish embryonic day 9 (D9) splotch (Sp) and splotch-delayed $(Sp sp{d})$ mouse mutants from heterozygous and wild-type littermates, and cellular aspects of abnormal neurulation and NCC migration were examined before inherent neural tube defects (NTDs) and deficiencies in neural crest cell (NCC) derivatives developed. In vitro analysis of NCC emigration from D9 neural tube explants revealed a delay in the release of NCCs from mutant neural tubes compared to controls, suggesting that the primary effect of the mutation was intrinsic to the neuroepithelium. Immunofluorescent localization of the neural cell adhesion molecule (N-CAM) antibody in situ demonstrated an increased intensity of antibody fluorescence in mutant tissue compared to controls, and further characterization by immunoblot analysis showed an altered embryonic N-CAM profile in both Sp and $Sp sp{d}$ mutants at D9 of gestation. The importance of N-CAMs in mediating cellular organization and communication has been well documented, supporting the idea that an alteration in this adhesion mechanism could result in the types of defects seen in splotch locus mouse mutants.

The X-linked Hyp mutation is characterized by a specific defect in phosphate (Pi) transport at the renal brush-border membrane (BBM). To understand the mechanism for the 50% decrease in Vmax of the high affinity Pi transport system in BBM of Hyp mice, we compared the effects of external Na$ sp+$ concentration, membrane potential, external pH, and Pi transport inhibitors on Pi uptake in BBM vesicles (BBMV) prepared from normal mice and Hyp littermates. / The apparent affinity for Na$ sp+$, the Na$ sp+{:}$Pi stoichiometry, the response to membrane potential and the response to external pH are similar in BBMV from both normals and mutants. / The Ki for phosphonoformic acid (PFA) inhibition of Na$ sp+$-Pi cotransport is lower in BBMV prepared from Hyp mice when compared to normal mice but not different in BBMV from Pi-deprived mice which are characterized by an increase in Vmax of the high affinity Na$ sp+$-Pi cotransport system. / We conclude that the decrease in Vmax of the high affinity Na$ sp+$-Pi cotransport system in the Hyp mouse is not the result of an inappropriate response of the transport system to Na$ sp+$, membrane potential or pH.

The genetics and epigenetics of cortisone-induced cleft palate in the mouse have been examined. The SW/Fr strain, in which 6% of newborns have a cleft palate in the absence of treatment, has the greatest reactivity to cortisone of any strain tested so far and closes it palate comparatively late in development. After cortisone treatment, the mean of the distribution on palate closure stage is shifted towards later gestational ages without changing the variance. / The genetic basis for the DBA/2-C57BL/6 difference in susceptibility to cortisone-induced cleft palate is relatively simple. One dominant gene on chromosome 5 contributes predominantly to the strain difference in susceptibility, but the embryonic response appears also to be influenced by genes on the X chromosome. The H-2 haplotype does not affect the cortisone-induced cleft palate response in the two congenic strains C57BL/10 (B10) and B10.A by altering the stage of palate closure.

Na$ sp+$-Pi cotransport across the brush border membrane is the rate limiting step in renal Pi reabsorption. To determine its precise role in the maintenance of Pi homeostasis, we cloned and characterized the renal-specific Na$ sp+$-Pi cotransporter/Npt2 gene and generated a gene targeting vector for the creation of a knockout mouse. The gene was cloned by screening a genomic DNA library with a rat Npt2 cDNA probe. The Npt2 gene is approximately 17kb and contains 13 exons and 12 introns. A targeting construct was generated by inserting 5$ sp prime$ and 3$ sp prime$ homologous arms of 2.1 and 2kb, respectively, into the pPNT vector and replacing 7.7kb of Npt2 with a neomycin resistance gene. The vector also contained the herpes simplex virus thymidine kinase gene for negative selection. After electroporation into embryonic stem cells, clones were picked following selection in G418 and FIAU. Of 100 doubly-resistant clones that were screened by Southern analysis, 6 positive clones were detected giving a targeting frequency of 6%.

Cell adhesion molecules are known to play crucial roles in a variety of developmental processes. The neural cell adhesion molecule N-CAM is strongly implicated in neurulation and neural crest cell (NCC) migration and was thus studied in splotch (Sp) neural tube defect mutant embryos. At the 20 somite-stage of gestation day 9, Sp N-CAM was found to contain polysialic acid (PSA) side chains which are normally only present beginning at gestational day 11. Younger embryos at 12 and 14 somites also showed the presence of PSA on N-CAM, which was absent in controls. Enzymatic removal of PSA from N-CAM resulted in isoforms which migrated identically to PSA-free N-CAM isoforms in SDS-polyacrylamide gels. The post-translational modification of N-CAM appears to be the primary target of the Sp gene. In view of N-CAM's importance during development, an alteration at a critical stage is likely to result in the cascade of abnormalities seen in Sp mutants. / A new genotyping assay was also implemented for examination of N-CAM in Sp and other related wildtype strains.

No description available.

The goal of the work presented here was to investigate the hypothesis that cytoplasmic SLBP is required for translation of somatic H1 mRNA, and their translational repression is due to a lack of SLBP in the cytoplasm of oocytes, and early cleavage-stage embryos. To this end, the expression of SLBP in murine oocytes and pre-implantation embryos was characterized by RT-PCR, Western blotting, and immunocytochemical. techniques. / mRNA encoding SLBP was detected throughout oogenesis and pre-implantation development, from small growing oocytes to the late blastocyst stage. SLBP protein was found in the nucleus and cytoplasm of growing and fully-gown prophase I-arrested oocytes. SLBP accumulated to extremely high levels during meiotic maturation in a process requiring translation. The protein remained abundant both in the nucleus and cytoplasm throughout the 1- and 2-cell stages. SLBP was depleted in 4-cell embryos in a process independent of DNA replication, and was not detected again until the late 8-cell stage. From the late 8-cell stage to the early blastocyst stage, SLBP was detected exclusively in the cytoplasm. Interestingly, in late blastocysts, SLBP was translocated to the nucleus. (Abstract shortened by UMI.)

This study shows that mice homozygous for the disrupted renal sodium-phosphate (Na+-Pi) cotransporter, Npt2, (Npt2 KO) failed to show an age-dependent decrease in renal Na+-Pi cotransport or an adaptive increase in renal Na+-Pi cotransport in response to dietary Pi restriction. None of the other known renal Na+ -Pi cotransporters could compensate for the loss of Npt2. Additionally, Npt2 gene ablation resulted in a marked decrease in osteoclast number that persisted with age. Although mineral apposition rate was normal at 25- and 115-days of age in Npt2 KO mice, bone formation rate was increased at 115-days of age. These data demonstrate that Npt2 gene expression is necessary for an age-dependent decrease in renal Na+-Pi cotransport and for the renal adaptive response to dietary Pi deprivation, and that Npt2 expression is essential for normal osteoclast function and influences bone formation.