Comparative placental structure

Significant differences between mouse and human trophinins are revealed by their expression patterns and targeted disruption of mouse trophinin gene

Trophinin has been identified as a membrane protein mediating apical cell adhesion between two human cell lines: trophoblastic HT-H cells, and endometrial epithelial SNG-M cells. Expression patterns of trophinin in humans suggested its involvement in embryo implantation and early placental development. The mouse trophinin gene maps to the distal part of the X chromosome and corresponds to human chromosome Xp11.21-22, the locus where the human trophinin gene maps. Western blot analysis indicates that the molecular weight of mouse trophinin is 110 kDa, which is consistent with the calculated value of 107 kDa. Positive signals for trophinin proteins were detected in preimplantation mouse embryos at the morula and blastocyst stages. Implanting blastocysts do not show detectable levels of trophinin protein, demonstrating that trophinin is not involved in blastocyst adhesion to the uterus in the mouse. Mouse embryo strongly expressed trophinin in the epiblast 1 day after implantation. Trophinin protein was not found in the mouse uteri and placenta after 5.5 days postcoitus (dpc). Targeted disruption of the trophinin gene in the mouse showed a partial embryonic lethality in a 129/SvJ background, but the cause of this lethality remains undetermined. The present study indicates significant differences between mouse and human trophinins in their expression patterns, and it suggests that trophinin is not involved in embryo implantation and placental development in the mouse.

Reproductive Immunosuppression and Diet

Pregnancy sickness, a suite of "symptoms" that frequently co-occur during pregnancy, may be an adaptation providing behavioral prophylaxis against infection. Maternal immunosupression, necessary for tolerance of the fetus, results in gestational vulnerability to pathogens. Throughout the period of maximal vulnerability, dietary behavior is significantly altered via changes in nausea susceptibility and olfaction and the development of marked aversions and cravings. Of food types, meat is both the most likely to carry pathogens and the principal target of gestational aversions and pregnancy taboos. Because meat was prominent in ancestral human diets but hygienic procedures that effectively eliminate the risk of meat-borne infection are recent, such pathogens likely constituted a source of selective pressure on pregnant females throughout human history. Both the relatively low protein and energy demands of the first trimester and the existense of nonmeat alternatives would have allowed for the evolution of time-limited gestational meat-avoidance mechanisms.Complementing these mechanisms, gestational cravings target substances that may influence immune functioning and affect the availability of iron in the gastro-intestinal tract, thereby limiting the proliferation of iron-dependent pathogens. Clinical and ethnographic findings are examined in light of these proposals, and directions for future research are outlined.

Use of transgenic mice model for understanding the placentation: towards clinical applications in human obstetrical pathologies?

The mammalian embryo and fetus are unable to develop without a well-established, functional placenta. This transitory yet indispensable structure attaches the conceptus to the uterus and establishes the vascular connections necessary for nutrient and gaseous exchange between maternal and fetal compartments. Genetic targeting strategy allows the generation of mice lacking a specific gene. Such approaches reveal: (i) the high incidence of mutant embryonic or fetal death in utero, and (ii) the extraembryonic (placental) causes of these deaths. Due to the similarities presented between mouse and human placenta, we propose to use the potential of mouse targeting experiments as a model in order to understand human obstetrical pathologies. In this paper, we first review genes that have been demonstrated to be required in mice for implantation, choriovitelline and chorioallantoic placentation. Using examples (integrins, homeoboxs, hepatocyte growth factor or epidermal growth factor receptor...) we demonstrate the reality and efficiency of such an approach. Other candidate genes (receptor of leukemia inhibitory factor, Wnt2 or retinoic acid receptor alpha...) in order to understand, prevent and treat human obstetrical pathologies.

The origins and roles of cholesterol and fatty acids in the fetus

The fetus grows at a rate that is unparalleled by that at any other stage of life. Significant amounts of cholesterol and fatty acids are required to maintain membrane growth. Recent studies have shown that these lipids are also necessary mediators of processes that are essential for proper development.

The cell biological basis of human implantation

Understanding the cellular basis of implantation and placental development depends on a combination of the limited morphological evidence in the human with data from other primates, separate studies of pre-implantation embryos and endometrium and in vitro models. There is increasing evidence of a dialogue between embryo and endometrium that begins prior to implantation and evolves rapidly through the successive epithelial and stromal/vascular phases. This includes paracrine signals passing to endometrial tissue from the embryo, and vice versa. The production and timing of these signals by endometrium, and its ability to respond to signals from the blastocyst, are dependent on steroidal sensitization. A complex cascade of cell adhesion mechanisms and local tissue remodelling are required for the establishment of a stable haemochorial interface.

Controlling drug delivery across the placenta

A challenge in modern drug therapy is to develop strategies for safer and more selective targeting of drug delivery in pregnancy. Specifically, approaches are needed that would restrict unnecessary drug exposure to either mother or fetus. There is evidence emerging that indicates the placenta does express natural transport and metabolism processes that function to control drug and nutrient distribution between the mother and fetus. Further, in vitro techniques developed in the past 10 years now provide some of the tools necessary to elucidate transport and metabolism processes typical of the human placenta. As a consequence, pharmaceutical scientists are in a position to contribute significantly to the design and development of drugs for pregnancy.