Mouse Gestation Length Is Genetically Determined

Background: Preterm birth is an enormous public health problem, affecting over 12 % of live births and costing over $26 billion in the United States alone. The causes are complex, but twin studies support the role of genetics in determining gestation length. Despite widespread use of the mouse in studies of the genetics of preterm birth, there have been few studies that actually address the precise natural gestation length of the mouse, and to what degree the timing of labor and birth is genetically determined. Methodology/Principal Findings: To further develop the mouse as a genetic model of preterm birth, we developed a highthroughput monitoring system and measured the gestation length in 15 inbred strains. Our results show an unexpectedly wide variation in overall gestation length between strains that approaches two full days, while intra-strain variation is quite low. Although litter size shows a strong inverse correlation with gestation length, genetic difference alone accounts for a significant portion of the variation. In addition, ovarian transplant experiments support a primary role of maternal genetics in the determination of gestation length. Preliminary analysis of gestation length in the C57BL/6J-Chr # A/J /NaJ chromosome substitution strain (B.A CSS) panel suggests complex genetic control of gestation length. Conclusions/Significance: Together, these data support the role of genetics in regulating gestation length and present th

Data summary from individual strain measurements.

<p>Total litter size includes all (live and dead) pups identified. Weight per live pup is the average of all surviving pups for each individual strain. Dead pups were often found desiccated and partially cannibalized and are thus excluded. Survival rate is the percentage of total pups identified that survived until at least postnatal day 3. Maternal weight was measured and recorded following the identification of a copulation plug and at E14.5 to calculate weight gain. At this time point, females were housed in front of the cameras and not disturbed until a birth was recorded. Pregnancy load is the maternal weight gained as a percentage of initial weight following a successful mating.</p

Highly significant differences in gestation length among inbred mouse strains.

<p>(A) Gestational length presented in total hours, measured from the midpoint of the dark cycle prior to the appearance of a copulation plug to the recorded appearance of the first pup. The total number of pregnancies monitored is indicated for each strain and data are presented as the mean +/− S.E.M. A detailed description of the animal husbandry and measurement procedures is provided in the supplementary methods (6). (B) Live litter size (number of pups), maternal weight gain (at E14.5) and maternal load (% weight gain) for each of the 15 inbred strains measured in (A). Complete data are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0012418#pone-0012418-t001" target="_blank">Table 1</a>. (C) Effects test (analysis of covariance) demonstrating significant differences in GL among inbred strains independent of the effect of total litter size and maternal load. Litter size is also significantly different among strains and is strongly correlated with GL. (D) Graphical representation of strains with significantly different GLs independent of all other factors. Strains that are not associated by a letter are significantly different from each other (p<0.05).</p

Gestation length is primarily dependent upon maternal genotype.

<p>(A) Gestation length presented in hours of C57BL/6J, A/J, B6.CB17-<i>Prkdc^scid</i>/SzJ (B6-<i>scid</i>), and B6-scid with transplanted A/J ovaries (AJ-ov-B6-<i>scid</i>). In order to directly compare the effect of pure B6 and A/J pups in a B6 maternal background, B6-<i>scid</i> mice were sham manipulated and mated to B6-scid males, while AJ-ov-B6-<i>scid</i> females were mated to A/J males following recovery from ovary transplant (see materials and methods for details). (B) Graphical representation of strains with significantly different GLs independent of all other factors. Strains that are not associated by a letter are significantly different from each other (p<0.05), demonstrating that B6 females show no statistical difference in gestation time, regardless of the genotype of the pups.</p

Complex, polygenic regulation of gestation length is revealed by the B.A CSS panel.

<p>(A) Mean gestation time in total hours for each of 20 CSS. The total number of pregnancies monitored is indicated for each strain and data are presented as the mean +/− S.E.M. (B) Graphical representation of individual CSS with significantly different GLs independent of all other factors. Strains that are not associated by a letter are significantly different from each other (p<0.05).</p

Genetic analysis of Pycr1 and Pycr2 in mice.

The final step in proline biosynthesis is catalyzed by three pyrroline-5-carboxylate reductases, PYCR1, PYCR2, and PYCR3, which convert pyrroline-5-carboxylate (P5C) to proline. Mutations in human PYCR1 and ALDH18A1 (P5C Synthetase) cause Cutis Laxa (CL), whereas mutations in PYCR2 cause hypomyelinating leukodystrophy 10 (HLD10). Here, we investigated the genetics of Pycr1 and Pycr2 in mice. A null allele of Pycr1 did not show integument or CL-related phenotypes. We also studied a novel chemically-induced mutation in Pycr2. Mice with recessive loss-of-function mutations in Pycr2 showed phenotypes consistent with neurological and neuromuscular disorders, including weight loss, kyphosis, and hind-limb clasping. The peripheral nervous system was largely unaffected, with only mild axonal atrophy in peripheral nerves. A severe loss of subcutaneous fat in Pycr2 mutant mice is reminiscent of a CL-like phenotype, but primary features such as elastin abnormalities were not observed. Aged Pycr2 mutant mice had reduced white blood cell counts and altered lipid metabolism, suggesting a generalized metabolic disorder. PYCR1 and -2 have similar enzymatic and cellular activities, and consistent with previous studies, both were localized in the mitochondria in fibroblasts. Both PYCR1 and -2 were able to complement the loss of Pro3, the yeast enzyme that converts P5C to proline, confirming their activity as P5C reductases. In mice, Pycr1; Pycr2 double mutants were sub-viable and unhealthy compared to either single mutant, indicating the genes are largely functionally redundant. Proline levels were not reduced, and precursors were not increased in serum from Pycr2 mutant mice or in lysates from skin fibroblast cultures, but placing Pycr2 mutant mice on a proline-free diet worsened the phenotype. Thus, Pycr1 and -2 have redundant functions in proline biosynthesis, and their loss makes proline a semi-essential amino acid. These findings have implications for understanding the genetics of CL and HLD10, and for modeling these disorders in mice

Exome sequencing reveals pathogenic mutations in 91 strains of mice with Mendelian disorders.

Spontaneously arising mouse mutations have served as the foundation for understanding gene function for more than 100 years. We have used exome sequencing in an effort to identify the causative mutations for 172 distinct, spontaneously arising mouse models of Mendelian disorders, including a broad range of clinically relevant phenotypes. To analyze the resulting data, we developed an analytics pipeline that is optimized for mouse exome data and a variation database that allows for reproducible, user-defined data mining as well as nomination of mutation candidates through knowledge-based integration of sample and variant data. Using these new tools, putative pathogenic mutations were identified for 91 (53%) of the strains in our study. Despite the increased power offered by potentially unlimited pedigrees and controlled breeding, about half of our exome cases remained unsolved. Using a combination of manual analyses of exome alignments and whole-genome sequencing, we provide evidence that a large fraction of unsolved exome cases have underlying structural mutations. This result directly informs efforts to investigate the similar proportion of apparently Mendelian human phenotypes that are recalcitrant to exome sequencing. Genome Res 2015 Jul; 25(7):948-57

Extensive identification of genes involved in congenital and structural heart disorders and cardiomyopathy

Clinical presentation of congenital heart disease is heterogeneous, making identification of the disease-causing genes and their genetic pathways and mechanisms of action challenging. By using in vivo electrocardiography, transthoracic echocardiography and microcomputed tomography imaging to screen 3,894 single-gene-null mouse lines for structural and functional cardiac abnormalities, here we identify 705 lines with cardiac arrhythmia, myocardial hypertrophy and/or ventricular dilation. Among these 705 genes, 486 have not been previously associated with cardiac dysfunction in humans, and some of them represent variants of unknown relevance (VUR). Mice with mutations in Casz1, Dnajc18, Pde4dip, Rnf38 or Tmem161b genes show developmental cardiac structural abnormalities, with their human orthologs being categorized as VUR. Using UK Biobank data, we validate the importance of the DNAJC18 gene for cardiac homeostasis by showing that its loss of function is associated with altered left ventricular systolic function. Our results identify hundreds of previously unappreciated genes with potential function in congenital heart disease and suggest causal function of five VUR in congenital heart disease