Genetic interaction between a maternal factor and the zygotic genome controls the intestine length in PRM/Alf mice

Association of germ-free mice with a simplified human intestinal microbiota results in a shortened intestine

Genetic, nutritional, and gut microbiota-derived factors have been proposed to play a role in the development of the whole intestine that is around 40% longer in PRM/Alf mice compared with other mouse strains. The PRM/Alf genotype explains 60% of this length difference. The remaining 40% are due to a maternal effect that could depend on the gut microbiota transmitted by the mother to their pups. Germ-free PRM/Alf mice and C3H/He mice were associated with a simplified human microbiota (SIHUMI) to study its impact on gut length. The small intestines of the SIHUMI-associated mice were 16.4% (PRM/Alf) and 9.7% (C3H/He) shorter than those of the corresponding germ-free counterparts. Temporal temperature gradient gel electrophoresis and quantitative real-time PCR revealed differences in microbiota composition between both SIHUMI-associated mouse strains. Anaerostipes caccae was one log lower in PRM/Alf mice than in C3H/He mice. Since polyamines and short-chain fatty acids (SCFAs) are important intestinal growth factors, their concentrations were explored. Cecal concentrations of putrescine, spermine, spermidine, and N-acetylspermine were 1.5-fold, 3.7-fold, 2.2-fold, and 1.4-fold higher, respectively, in the SIHUMI-C3H/He mice compared with the SIHUMI-PRM/Alf mice. In addition, cecal acetate, propionate, and butyrate concentrations in SIHUMI-C3H/He mice were 1.4-fold, 1.1-fold, and 2.1-fold higher, respectively, than in SIHUMI-PRM/Alf mice. These results indicate that polyamines and SCFAs did not promote gut lengthening in any of the two mouse strains. This suggests that as yet unknown factors provided by the SIHUMI prevented gut lengthening in the SIHUMI-associated mice compared with the germfree mice.

Maternal environment interacts with modifier genes to influence progression of nephrotic syndrome

Mutations in the NPHS2 gene, which encodes podocin, are responsible for some cases of sporadic and familial autosomal recessive steroid-resistant nephrotic syndrome. Inter- and intrafamilial variability in the progression of renal disease among patients bearing NPHS2 mutations suggests a potential role for modifier genes. Using a mouse model in which the podocin gene is constitutively inactivated, we sought to identify genetic determinants of the development and progression of renal disease as a result of the nephrotic syndrome. We report that the evolution of renal disease as a result of nephrotic syndrome in Nphs2-null mice depends on genetic background. Furthermore, the maternal environment significantly interacts with genetic determinants to modify survival and progression of renal disease. Quantitative trait locus mapping suggested that these genetic determinants may be encoded for by genes on the distal end of chromosome 3, which are linked to proteinuria, and on the distal end of chromosome 7, which are linked to a composite trait of urea, creatinine, and potassium. These loci demonstrate epistatic interactions with other chromosomal regions, highlighting the complex genetics of renal disease progression. In summary, constitutive inactivation of podocin models the complex interactions between maternal and genetically determined factors on the progression of renal disease as a result of nephrotic syndrome in mice.

Effects on kidney disease, fertility and development in mice inheriting a protein-truncating Denys-Drash syndrome allele (Wt1tmT396)

Denys-Drash syndrome (DDS) is caused by heterozygous mutations of the Wilms' tumour suppressor gene, WT1, characterised by early-onset diffuse mesangial sclerosis often associated with male pseudohermaphroditism and/or Wilms' tumourigenesis. Previously, we reported that the Wt1tmT396 allele induces DDS kidney disease in mice. In the present study heterozygotes (Wt1tmT396/+) were generated on inbred (129/Ola), crossbred (B6/129) and MF1 second backcross (MF1-N2) backgrounds. Whereas male heterozygotes on each background were fertile, inbred heterozygous females were infertile. Kidney disease (proteinuria and sclerosis) was not congenital and developed significantly earlier in inbred mice, although with variable onset. Disease onset in MF1-N2 stocks occurred later in Wt1tmT396/+ mice than reported previously for Wt1R394W/+ mice, and while no kidney disease has been reported in B6/129 Wt1+/- mice, B6/129 Wt1tmT396/+ mice were affected. Offspring of both male and female B6/129 and MF1-N2 Wt1tmT396/+ mice developed kidney disease, but its incidence was significantly higher in offspring of female heterozygotes. Wt1tmT396/tmT396 embryos exhibited identical developmental abnormalities to those reported for Wt1-/- embryos. The results indicate that the Wt1 (tmT396) allele does not predispose to Wilms' tumourigenesis or male pseudohermaphroditism, its effect on kidney disease and female fertility depends on genetic background, stochastic factors may affect disease onset, and disease transmission is subject to a partial parent-of-origin effect. Since the Wt1tmT396 allele has no detectable intrinsic functional activity in vivo, and kidney disease progression is affected by the type of Wt1 mutation, the data support the view that DDS nephropathy results from a dominant-negative action rather than WT1 haploinsufficiency or gain-of-function.

Accelerated intestinal transit in inbred mice with an increased number of interstitial cells of Cajal

The interstitial cells of Cajal (ICC) play an important role in coordinating intestinal motility, and structural alterations in ICC are found in several human digestive diseases. Mouse models with defects in ICC allow a better understanding of their functions. We investigated the pattern of intestinal motility and the distribution of ICC in the PRM/Alf inbred mouse strain, characterized by a selective intestinal lengthening. In PRM/Alf mice, the digestive transit time, evaluated by using thermophilic Bacillus subtilis spores, was normal, indicating accelerated transit. The contractility and slow-wave frequency, recorded on isolated segments from the proximal small intestine, were significantly increased. The number of ICC was also significantly higher along the small intestine and the colon. The concomitant increase of the contractility, the slow-wave frequency, and the number of ICC is consistent with the proposal of a role of ICC number increase in the higher intestinal transit speed. The PRM/Alf model should be useful to further investigate the roles of ICC in the control of digestive motility.