Arthur E. Wild

Adaptive Responses by Mouse Early Embryos to Maternal Diet Protect Fetal Growth but Predispose to Adult Onset Disease

Abstract Poor maternal nutrition during pregnancy can alter postnatal phenotype and increase susceptibility to adult cardiovascular and metabolic diseases. However, underlying mechanisms are largely unknown. Here, we show that maternal low protein diet (LPD), fed exclusively during mouse preimplantation development, leads to offspring with increased weight from birth, sustained hypertension, and abnormal anxiety-related behavior, especially in females. These adverse outcomes were interrelated with increased perinatal weight being predictive of later adult overweight and hypertension. Embryo transfer experiments revealed that the increase in perinatal weight was induced within blastocysts responding to preimplantation LPD, independent of subsequent maternal environment during later pregnancy. We further identified the embryo-derived visceral yolk sac endoderm (VYSE) as one mediator of this response. VYSE contributes to fetal growth through endocytosis of maternal proteins, mainly via the multiligand megalin (LRP2) receptor and supply of liberated amino acids. Thus, LPD maintained throughout gestation stimulated VYSE nutrient transport capacity and megalin expression in late pregnancy, with enhanced megalin expression evident even when LPD was limited to the preimplantation period. Our results demonstrate that in a nutrient-restricted environment, the preimplantation embryo activates physiological mechanisms of developmental plasticity to stablize conceptus growth and enhance postnatal fitness. However, activation of such responses may also lead to adult excess growth and cardiovascular and behavioral diseases.

Direct evidence for pH-dependent Fc receptors on proximal enterocytes of suckling rat gut.

By means of an erythrocyte-antibody rosette technique, Fc receptors, functional at pH 6.0 but not at 7.2, were shown to be present on enterocytes isolated from duodenum and jejunum (but absent from ileum) of 12–20-day-old suckling rats.

The route of maternal IgM transport to the rabbit fetus

The route of IgM transport to the rabbit fetus was investigated by comparing its localization with that of IgG in the yolk sac splanchnopleure and uterine tissues using direct immunofluorescence and immunodiffusion analysis. IgM was first detected in fetal serum at 20 days of gestation but was present in uterine fluid at 18 days, the earliest stage tissues and fluids were examined. IgM was co-localized with IgG in the yolk sac endoderm basement membrane and in the vascular mesenchyme of the yolk sac splanchnopleure providing evidence of its transport to fetal blood; it was also present in vesicles in the yolk sac endoderm. IgM could not be detected in uterine fluid of nonpregnant uterine horns of rabbits unilaterally pregnant. Human IgM injected into the maternal circulation was readily transported to the uterine fluid and across the yolk sac splanchnopleure to fetal blood indicating that IgM secreting plasma cells, found to be present in the uterine stroma, contributed little towards IgM in the uterine fluid. Degenerating paraplacental decidual tissue, a feature of rabbit pregnancy, is suggested to be a major route for maternal immunoglobulin transport to the uterine fluid.

Receptors for IgG2b on cells of the mouse metrial gland

Single cells prepared from metrial glands of mice killed at days 10, 13 and 17 of pregnancy were assayed for the expression of Fc gamma receptors in a standard rosetting assay using sheep red blood cells sensitised with a mouse monoclonal IgG2b antibody. Rosettes, indicating Fc gamma receptors, were found on both granulated metrial gland (GMG) cells and non-GMG cells, comprising mainly stromal cells, from each stage of pregnancy. Some animals were given an intravenous injection of horseradish peroxidase 2 h before they were killed in order to identify endocytic cells. No GMG cells were found to have endocytosed the horseradish peroxidase. Non-GMG cells which showed endocytic activity all expressed Fc gamma receptors but these receptors were also found on some of the non-GMG cells which had not exhibited endocytosis. The finding of Fc gamma receptors on GMG cells provides further evidence that these cells may be related to NK cells.

Distribution of FCγ receptors on isolated gut enterocytes of the suckling rat

Abstract An erythrocyte-antibody rosette assay has been used to study the presence and distribution of Fcγ receptors on enterocytes isolated from 12-day-old suckling rat gut by means of a buffer medium containing EGTA. Such receptors were found to be restricted to enterocytes in the proximal region (duodenum and jejunum) of the small intestine and to be acid-pH dependent. For the majority of enterocytes indicator red cells bound in high density to the abluminal plasmalemma but not to the apical microvillous brush border. Since immunofluorescence studies revealed strong binding of added IgG to the microvillous region, a likely explanation is that there is a paucity of Fcγ receptors from the tips of microvilli (at least under the conditions of the rosette assay) and that receptors more deeply situated as inaccessible to indicator red cells was readily inhibited by rabbit, human, guinea pig and rat IgG but less so by bovine IgG, and of the two sub-classes, bovine IgG2 inhibited much more readily than bovine IgG1. Cortisone acetate injection virtually abolished Fcγ receptor expression on isolated enterocytes within three days. These findings correlate both with selective transport of IgG of different species in vivo and the known effect of cortisone acetate to terminate such transport.

Evidence that Fcγ receptors in rabbit yolk sac endoderm do not depend upon an acid pH to effect IgG binding and transcytosis in vitro

An in vitro culture system has been devised creating apical and basal compartments separated by rabbit visceral yolk sac (VYS) with an intact epithelium. Selective transcytosis and binding of heterologous IgG applied to the apical yolk sac endoderm (YSE) was demonstrated in vitro using double label immunofluorescence. Thus, whilst both human and bovine IgG could be detected in endosomes in YSE, only human IgG could be detected in the basement membrane and vascular mesenchyme. This mirrors what is found in vivo. The Fc fragment of human Ig was transcytosed but not the Fab fragment, indicating that Fc receptors were expressed in the cultured YSE. When VYS was previously chilled to 4 degrees C to prevent endocytosis and treated with rabbit serum albumin to prevent non-specific binding, human IgG, but not bovine IgG, became specifically bound to YSE apical plasma membrane; comparison of binding at pH 6.0, 7.3 (the average pH of rabbit uterine fluid) and 8.0 revealed no obvious difference. Pre-exposure of VYS for up to 5 min in monensin, followed by culture in monensin and immunoglobulin-containing medium, did not prevent the selective transcystosis of human IgG, suggesting that an acidic compartment may not be needed for transcytosis. An acid pH dependent Fc gamma receptor equivalent to that on suckling rat gut jejunal enterocyte plasma membranes could not be isolated from rabbit YSE following exposure of solubilized membrane to affinity matrix bound IgG at pH 6.0 and elution at pH 8.0. These results contradict a recent suggestion that Fc receptors on all IgG transcytosing epithelia require an acid pH to effect IgG binding and selective transcytosis.

IgG transport across the gut of the suckling opposum (Monodelphis domestica)

We investigated IgG transport across the gut of suckling opossums to see whether it is likely to be Fc gamma R-mediated. Enterocytes isolated from the proximal and distal regions of the small intestine of suckling aged 12-52 days, and reacted with indicator SRBC at pH 6.0 or 7.2, bound opossum IgG in rosette assays. Considerable overall variation was observed in the numbers of enterocytes forming rosettes. No binding was seen with rabbit IgG at these ages, or with opossum and rabbit IgG when enterocytes were obtained from opossums aged 55-73 days. Opossum anti-SRBC antibody (IgG) fed to sucklings at 52 days and earlier (but not later) could subsequently be detected in the serum. However, rabbit anti-SRBC antibody (IgG) could not be detected in the blood serum when fed to sucklings of any age. Fluorescent tracing of FITC-labelled opossum and rabbit IgG fed to suckling opossums, and of endogenous opossum IgG, pointed to transport of the homologous IgG occurring across gut enterocytes of the proximal region. These results suggest that IgG is recognised and transcytosed by specific Fc gamma Rs present on opossum enterocytes prior to weaning.

Effect of dexamethasone on Fc γ receptor expression in foetal and neonatal rat gut

When injected into 12-day-old suckling rats, dexamethasone caused a precocious disappearance of Fc γ receptors from enterocytes of the proximal small intestine. However, dexamethasone appeared to be necessary for the maintenance or production of such receptors in foetal rat gut cultured in vitro.

Ontogeny of the Fcγ receptor in rat small intestine

Abstract The time course of Fcγ receptor expression on isolated enterocytes of the small intestine of rat fetuses and sucklings has been studied. This was achieved principally using indicator sheep red blood cells (SRBC) sensitized with rabbit IgG in an erythrocyte-antibody rosette assay which detects receptors located mainly on the lateral and basal plasma membrane, and in a more limited way using binding of rabbit IgG to metabolically inhibited gut as detected by immunofluorescence and which detects receptors located on the apical brush border. From the time they were first detectable in the rosette assay (20-day-old fetuses) to the time they disappeared (22-day-old sucklings) such receptors were found always to be acid pH dependent and restricted to enterocytes from the proximal region. Acid pH, Fc-dependent binding of rabbit IgG to metabolically inhibited gut was first detectable at 21 days gestation and there were indications that receptors differentiate on enterocytes in a proximal to distal direction. This was also indicated by electron microscope studies using rabbit PAP injected into the duodenum of 21-day-old fetuses. Such studies also provided evidence for the receptor-mediated translocation of IgG across the duodenum of the fetal rat in a manner similar to that described for older sucklings.

Cell Polarity and Mouse Early Development

Publisher Summary This chapter reviews the cell-biological characteristics of cell polarity during mouse cleavage and the consequences for blastocyst differentiation and tissue diversification. The influence of polarity at a molecular level with respect to the differentiation of multimolecular adhesive junctions in trophectoderm and the origin of differential gene expression in the embryo is discussed in the chapter. Cell polarity occurs for the first time during mouse embryogenesis at the 8-cell stage, about 2.5 days after fertilization. Blastomere polarization is likely to be of widespread importance in the early development of eutherian mammals since it occurs in several species other than the mouse. In the mouse, it is a stable state in that polarized cells have not been shown to lose their polarity even in isolation. In the intact embryo, this stability is conducive with the polar lineage maintaining cell position and orientation, and in acquiring further structural and molecular features of polarity with time, such as occurs in intercellular junction formation.