Methionine overcomes neural tube defects in rat embryos cultured on sera from laminin-immunized monkeys

Mouse whole embryo culture: Evaluating the requirement for rat serum as culture medium

Background

Whole embryo culture is a valuable research method in mammalian developmental biology and birth defects research, enabling longitudinal studies of explanted organogenesis‐stage rodent embryos. Rat serum is the primary culture medium, and can sustain growth and development over limited periods as in utero. However, the cost, labor, and time to produce culture serum are factors limiting the uptake of the methodology. The goal of replacing or at least reducing rat serum usage in culture would be in accordance with the principles of “replacement, reduction, and refinement” of animals in research (the 3Rs).

Methods

We performed cultures of mouse embryos for 24 hr from embryonic day 8.5 in serum‐free media or in rat serum diluted with defined media, compared with 100% rat serum. Developmental parameters scored after culture included yolk sac circulation, dorsal axial length, somite number, protein content, and completion of cranial neural tube closure.

Results

A literature review revealed use of both serum‐free and diluted rat serum‐based media in whole embryo culture studies, but with almost no formal comparisons of culture success against 100% rat serum. Two serum‐free media were tested, but neither could sustain development as in 100% rat serum. Dilution of rat serum 1:1 with Glasgow Minimum Essential Medium plus defined supplements supported growth and development as well as whole rat serum, whereas other diluent media yielded substandard outcomes.

Conclusion

Rat serum usage cannot be avoided, to achieve high quality mouse embryo cultures, but rat usage can be reduced using medium containing diluted serum.

Mono-2-ethylhexyl phthalate (MEHP) alters histiotrophic nutrition pathways and epigenetic processes in the developing conceptus

Histiotrophic nutrition pathways (HNPs) are processes by which the organogenesis-stage conceptus obtains nutrients, amino acids, vitamins and cofactors required for protein biosynthesis and metabolic activities. Nutrients are captured from the maternal milieu as whole proteins and cargoes via receptor-mediated endocytosis in the visceral yolk sac (VYS), degraded by lysosomal proteolysis and delivered to the developing embryo (EMB). Several nutrients obtained by HNPs are required substrates for one-carbon (C1) metabolism and supply methyl groups required for epigenetic processes, including DNA and histone methylation. Increased availability of methyl donors has been associated with reduced risk for neural tube defects (NTDs). Here, we show that mono-2-ethylhexyl phthalate (MEHP) treatment (100 or 250μM) alters HNPs, C1 metabolism and epigenetic programming in the organogenesis-stage conceptus. Specifically, 3-h MEHP treatment of mouse EMBs in whole culture resulted in dose-dependent reduction of HNP activity in the conceptus. To observe nutrient consequences of decreased HNP function, C1 components and substrates and epigenetic outcomes were quantified at 24h. Treatment with 100-μM MEHP resulted in decreased dietary methyl donor concentrations, while treatment with 100- or 250-μM MEHP resulted in dose-dependent elevated C1 products and substrates. In MEHP-treated EMBs with NTDs, H3K4 methylation was significantly increased, while no effects were seen in treated VYS. DNA methylation was reduced in MEHP-treated EMB with and without NTDs. This research suggests that environmental toxicants such as MEHP decrease embryonic nutrition in a time-dependent manner and that epigenetic consequences of HNP disruption may be exacerbated in EMB with NTDs.

Hyperhomocysteinaemia and associated disease

An elevated plasma homocysteine level may result from various environmental and genetic factors. Herediatary causes of severe hyperhomo-cysteinaemia are very rare and usually lead to disease in childhood or adolescence. Common pathology consists of early atherosclerotic vascular changes, arterioocclusive complications and venous thrombosis. Mildly elevated genetically determined plasma homocysteine levels are observed in 5% of the general population. In the last two decades research has shown mild hyperhomocysteinaemia to be linked to an increased risk of premature atherosclerosis, pregnancies complicated by neural tube defects and early pregnancy loss, and venous thrombosis. Homozygosity for thermolabile MTHFR deficiency has been identified as one important genetic factor, which expression is modified by dietary folate intake. Although mild hyperhomocysteinaemia can easily be treated by vitamin supplementation the beneficial effects of such treatment remains to be shown.