Mouse lipidomics reveals inherent flexibility of a mammalian lipidome.

Lipidomics has become an indispensable method for the quantitative assessment of lipid metabolism in basic, clinical, and pharmaceutical research. It allows for the generation of information-dense datasets in a large variety of experimental setups and model organisms. Previous studies, mostly conducted in mice (Mus musculus), have shown a remarkable specificity of the lipid compositions of different cell types, tissues, and organs. However, a systematic analysis of the overall variation of the mouse lipidome is lacking. To fill this gap, in the present study, the effect of diet, sex, and genotype on the lipidomes of mouse tissues, organs, and bodily fluids has been investigated. Baseline quantitative lipidomes consisting of 796 individual lipid molecules belonging to 24 lipid classes are provided for 10 different sample types. Furthermore, the susceptibility of lipidomes to the tested parameters is assessed, providing insights into the organ-specific lipidomic plasticity and flexibility. This dataset provides a valuable resource for basic and pharmaceutical researchers working with murine models and complements existing proteomic and transcriptomic datasets. It will inform experimental design and facilitate interpretation of lipidomic datasets.

Lengthening Neurogenic Period during Neocortical Development Causes a Hallmark of Neocortex Expansion.

A hallmark of the evolutionary expansion of the neocortex is a specific increase in the number of neurons generated for the upper neocortical layers during development. The cause underlying this increase is unknown. Here, we show that lengthening the neurogenic period during neocortical development is sufficient to specifically increase upper-layer neuron generation. Thus, embryos of mouse strains with longer gestation exhibited a longer neurogenic period and generated more upper-layer, but not more deep-layer, neurons than embryos with shorter gestation. Accordingly, long-gestation embryos showed a greater abundance of neurogenic progenitors in the subventricular zone than short-gestation embryos at late stages of cortical neurogenesis. Analysis of a mouse-rat chimeric embryo, developing inside a rat mother, pointed to factors in the rat environment that influenced the upper-layer neuron generation by the mouse progenitors. Exploring a potential maternal source of such factors, short-gestation strain mouse embryos transferred to long-gestation strain mothers exhibited an increase in the length of the neurogenic period and upper-layer neuron generation. The opposite was the case for long-gestation strain mouse embryos transferred to short-gestation strain mothers, indicating a dominant maternal influence on the length of the neurogenic period and hence upper-layer neuron generation. In summary, our study uncovers a hitherto unknown link between embryonic cortical neurogenesis and the maternal gestational environment and provides experimental evidence that lengthening the neurogenic period during neocortical development underlies a key aspect of neocortical expansion.

In Vivo Targeting of Neural Progenitor Cells in Ferret Neocortex by In Utero Electroporation.

Manipulation of gene expression in vivo during embryonic development is the method of choice when analyzing the role of individual genes during mammalian development. In utero electroporation is a key technique for the manipulation of gene expression in the embryonic mammalian brain in vivo. A protocol for in utero electroporation of the embryonic neocortex of ferrets, a small carnivore, is presented here. The ferret is increasingly being used as a model for neocortex development, because its neocortex exhibits a series of anatomical, histological, cellular, and molecular features that are also present in human and nonhuman primates, but absent in rodent models, such as mouse or rat. In utero electroporation was performed at embryonic day (E) 33, a midneurogenesis stage in ferret. In utero electroporation targets neural progenitor cells lining the lateral ventricles of the brain. During neurogenesis, these progenitor cells give rise to all other neural cell types. This work shows representative results and analyses at E37, postnatal day (P) 1, and P16, corresponding to 4, 9, and 24 days after in utero electroporation, respectively. At earlier stages, the progeny of targeted cells consists mainly of various neural progenitor subtypes, whereas at later stages most labeled cells are postmitotic neurons. Thus, in utero electroporation enables the study of the effect of genetic manipulation on the cellular and molecular features of various types of neural cells. Through its effect on various cell populations, in utero electroporation can also be used for the manipulation of histological and anatomical features of the ferret neocortex. Importantly, all these effects are acute and are performed with a spatiotemporal specificity determined by the user.

Phytoestrogen-containing diets offer benefits for mouse embryology but lead to fewer offspring being produced.

One of the most commonly used protein sources in rodent diets is soy, which is naturally rich in phytoestrogens. Although phytoestrogens have shown potential health benefits in humans, they may also have the ability to disrupt reproduction. Consequently, there has been a tendency to try to exclude them from rodent diets. In the current study, we investigated whether phytoestrogen content in the mouse diet could affect reproduction in mice used as embryo donors. Donor mice (C57BL/6JOlaHsd) were maintained with three different diets: high phytoestrogen (ca. 400 mg/kg genistein), low phytoestrogen (ca. 10 mg/kg genistein) and standard breeding diet (ca. 120 mg/kg genistein). Mice fed a high phytoestrogen diet had a high yield of plugs, embryos, and injectable embryos, as well as producing good quality embryos. Results from donor mice fed a low phytoestrogen diet were consistently but only slightly inferior, whereas mice fed a standard diet performed the poorest. Interestingly, the largest number of born and weaned offspring were observed when recipient females received embryos from the standard diet group. Sperm yield and quality of stud males did not differ between the groups. We surmize that for experimental endpoints requiring fertilized embryos it may be more beneficial to feed mice a diet containing phytoestrogen, but if the goal is to produce transgenic mice, a diet high in phytoestrogen may be inadvisable. In conclusion, care should be taken when selecting a diet for experimental mouse colonies as phytoestrogen could influence the study outcome.

Phase II metabolism of the soy isoflavones genistein and daidzein in humans, rats and mice: a cross-species and sex comparison.

Soy isoflavones (IF) are in the focus of biomedical research since more than two decades. To assess their bioactivity, IF are investigated in rats and mice as a model. As the biological activity of IF is affected by their biotransformation, our aim was to comprehensively compare the conjugative and microbial metabolism of daidzein and genistein in adult humans, rats and mice of both sexes. One identical soy extract and a validated LC-MS method were used for all studies. We detected considerable differences between the three species. In rats and mice, sex-specific differences were observed in addition. The major plasma phase II metabolites in humans were the 7-sulfo-4'-glucuronides (39-49 %) and, in case of genistein, also the diglucuronide (34 %), whereas in mice monosulfates (33-41 %) and monoglucuronides (30-40 %) predominated. In male rats the disulfates (23-62 %) and 7-sulfo-4'-glucuronides (19-54 %) were predominant, while in female rats the 7-glucuronides (81-93 %) exhibited highest concentrations. The portion of aglycones was low in humans (0.5-1.3 %) and rats (0.5-3.1 %) but comparatively high in mice (3.1-26.0 %), especially in the case of daidzein. Furthermore, substantial differences were observed between daidzein and genistein metabolism. In contrast to humans, all rats and mice were equol producer, independent of their sex. In conclusion, there are marked differences between humans, rats and mice in the profile of major metabolites following IF phase II metabolism. These differences may contribute to resolve inconsistencies in results concerning the bioactivity of IF and should be considered when applying findings of animal studies to humans, e.g., for risk assessment.

Mutations in mouse Aspm (abnormal spindle-like microcephaly associated) cause not only microcephaly but also major defects in the germline.

Mutations in ASPM (abnormal spindle-like microcephaly associated) cause primary microcephaly in humans, a disorder characterized by a major reduction in brain size in the apparent absence of nonneurological anomalies. The function of the Aspm protein in neural progenitor cell expansion, as well as its localization to the mitotic spindle and midbody, suggest that it regulates brain development by a cell division-related mechanism. Furthermore, evidence that positive selection affected ASPM during primate evolution has led to suggestions that such a function changed during primate evolution. Here, we report that in Aspm mutant mice, truncated Aspm proteins similar to those causing microcephaly in humans fail to localize to the midbody during M-phase and cause mild microcephaly. A human ASPM transgene rescues this phenotype but, interestingly, does not cause a gain of function. Strikingly, truncated Aspm proteins also cause a massive loss of germ cells, resulting in a severe reduction in testis and ovary size accompanied by reduced fertility. These germline effects, too, are fully rescued by the human ASPM transgene, indicating that ASPM is functionally similar in mice and humans. Our findings broaden the spectrum of phenotypic effects of ASPM mutations and raise the possibility that positive selection of ASPM during primate evolution reflects its function in the germline.