Ganglioside abnormalities associated with failed neural differentiation in a T-locus mutant mouse embryo

The T-locus on mouse chromosome 17 contains a number of mutations that disrupt cellular differentiation and embryonic development. Because of their purported role in neuronal differentiation and brain development, gangliosides were studied in mouse embryos homozygous for two T-locus mutations: T and twl. Mice homozygous for the dominant T mutation die from failed mesodermal differentiation in the notochord, whereas mice homozygous for the recessive twl mutation die from failed neural differentiation in the ventral portion of the neural tube. No major ganglioside abnormalities were found in T/T mutant embryos at Embryonic Day 10 (E-10). In contrast, E-11 twl/twl mutants expressed a marked deficiency of the tetrasialoganglioside GQ1. Since this ganglioside migrates with GQ1b in three different thin-layer solvent systems, it may have the same structure as GQ1b. To gain insight into regional distribution, gangliosides were examined in head regions and body regions of normal (+/+) E-11 embryos. The ganglioside composition of these regions was the same as that of the whole embryo, with GM3 and GD3 comprising about 75% of the total ganglioside distribution. Moreover, N-acetylneuraminic acid was the only sialic acid species detectable in the E-10 and the E-11 embryos. These findings indicate that N-acetylneuraminic acid-containing gangliosides are synthesized actively in E-10 and E-11 mouse embryos and also suggest that the GQ1 deficiency in the twl/twl mutants is closely associated with failed neural differentiation.     

The karyotype of the mouse

A denaturating and renaturating technique, applied to mouse chromosomes, makes visible characteristic banding patterns by which all elements of the karyotype can be individually distinguished. The Y chromosome as a whole appears darkly stained. The X chromosome comprises 6.33% of the homogametic haploid set. The banding pattern of the chromosomes is compared with that obtained by aid of the quinacrine dihydrochloride fluorescence technique. After its use a banding pattern results which is similar to, but less distinct than, that found after the renaturation procedure.     

The corticosteroid metabolic profile of the mouse

Data are presented on the urinary corticosteroid metabolic profile of the mouse strain 129/svJ. Through the use of GC/MS we have characterized, or tentatively identified corticosterone (Kendall's compound B) metabolites of both the 11beta-hydroxy and 11-carbonyl (compound A) series in urine. Full mass spectra of the methyloxime-trimethylether derivatives of 15 metabolites are included in the paper as an aid to other researchers in the field. Metabolites ranged in polarity from tetrahydrocorticosterone (THB) to dihydroxy-corticosterone with dominance of highly polar steroids. We found that prior to excretion corticosterone can undergo oxidation at position 11beta, reduction at position 20 and A-ring reduction. Metabolites retaining the 3-oxo-4-ene structure can be hydroxylated at position 6beta- as well as at an unidentified position, probably 16alpha-. Saturated steroids can be hydroxylated at positions 1beta-, 6alpha-, 15alpha- and 16alpha. A pair of hydroxy-20-dihydro-corticosterone metabolites (OH-DHB) were the most important excretory products accounting for about 40% of the total. One metabolite of this type was identified as 6beta-hydroxy-DHB; the other, of similar quantitative importance was probably 16alpha-hydroxy-DHB. The ratio of metabolites of corticosterone (B) to those of 11-dehydro-corticosterone (A) was greater than 9:1, considerably higher than that for the equivalent "human" ratio of 1:1 for cortisol to cortisone metabolites. Results from this study allowed the evaluation of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) activity in mice with deleted glucose-6-phosphate transporter (G6PT). These mice had attenuated back-conversion of A to B resulting in an increased ratio of A-metabolites to B-metabolites [Walker EA, Ahmed A, Lavery GG, Tomlinson JW, Kim SY, Cooper MS, Stewart PM, 11beta-Hydroxysteroid dehydrogenase type 1 regulation by intracellular glucose-6-phosphate, provides evidence for a novel link between glucose metabolism and HPA axis function. J Biol Chem 2007;282:27030-6]. We believe this study is currently the most comprehensive on the urinary steroid metabolic profile of the mouse. Quantitatively less steroid is excreted in urine than in feces by this species but urine analysis is more straightforward and the hepatic metabolites are less subject to microbial degradation than if feces was analyzed.     

The wobbler mouse

Various mutations in humans and animals lead to the selective and progressive degeneration of motoneurons, resulting in muscular weakness, subsequent paralysis, and death (1-3). Amyotrophic lateral sclerosis (ALS) is the most common adult human motoneuron disease, but the vast majority of sporadic and familial cases of ALS are still of unknown origin (4). Murine models of motoneuron diseases, derived from spontaneous mutations in the colonies, have been known for half a century. Prior to the first identifications of the mutated proteins in human ALS, they have largely been used to explore the disease etiology. The chromosomal localization of these mutations does not favor a genetic similarity between these murine models and the few human forms of the disease for which the mutation or the chromosomal localization is known. Yet the fact that most human ALS cases are of unknown etiology and the recent discovery of molecules with no known role in motoneuron survival (5-7), indicate that these murine mutants may still contribute to the understanding of motoneuronal degenerative processes. This can be exemplified by the work performed on the wobbler mouse, one of the oldest and most extensively studied models, which is reviewed here.     

The relationship of mouse spermatozoal to mouse testicular cathepsins

Mouse testicular and sperm-associated cathepsin activities were compared for optimal conditions of assay, molecular sieving properties, inhibition data, and electrophoretic mobility. An extract of testes had several isoenzymes of cathepsin among which cathepsin B1 may be a major form while a sperm-associated component may be a minor form. The sperm-associated component was highly sensitive to pepstatin and may be cathepsin D.