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Retinoid binding proteins in mouse yolk sac and chorio-allantoic placentas
S Johansson1, A L Gustafson, M Donovan
1Department of Pharmaceutical Biosciences, Uppsala Biomedical Center, Uppsala University, Sweden.
Insights
Maternal vitamin A (retinol) transport to the fetus primarily occurs via the yolk sac placenta, not the chorio-allantoic placenta. This highlights the yolk sac
Area of Science:
- Developmental Biology
- Maternal-Fetal Medicine
- Nutritional Biochemistry
Background:
- Retinol (vitamin A) transport and metabolism involve specific binding proteins like plasma retinol binding protein (RBP) and cellular retinol binding protein type I (CRBP I).
- The mechanisms regulating maternal-fetal vitamin A transport are not fully understood.
Purpose of the Study:
- To investigate the localization of key retinol-binding proteins and receptors during mouse placental development.
- To determine the roles of the chorio-allantoic and yolk sac placentas in materno-fetal retinol transfer.
Main Methods:
- Examined the expression of RBP (mRNA and protein) and RBP-receptor-like antigens in developing mouse placentas.
- Assessed the localization of cellular retinol binding protein type I (CRBP I) within placental tissues.
- Investigated the accumulation of radiolabeled retinoids in placental structures.
Main Results:
- The chorio-allantoic placenta's labyrinthine region lacked RBP and RBP-receptor-like antigens.
- The visceral endoderm of the yolk sac placenta showed the presence of RBP and accumulated radiolabeled retinoids.
- CRBP I was found in the placental labyrinth's trophoblast layer and the yolk sac's visceral endoderm.
Conclusions:
- The yolk sac placenta is the primary site for retinol transfer to the embryo/fetus throughout gestation.
- The chorio-allantoic placenta does not appear to mediate significant retinol transfer.
- CRBP I presence suggests a role in retinol metabolism within both placental types.
Abstract:
In the adult, as well as in the embryo, a number of specific extra- and intracellular binding proteins such as the plasma retinol binding protein (RBP), the cellular retinol binding protein type I (CRBP I), and also the cellular receptors for RBP are thought to regulate transport and metabolism of retinol (vitamin A). Since the regulation of materno-fetal transport of vitamin A is not well understood, we examined the localization of these proteins during the development of the mouse chorio-allantoic and yolk sac placentas. The labyrinthine region of the chorio-allantoic placenta, where exchange of substances can occur between the maternal and fetal circulations, did not contain RBP (mRNA or protein) or antigen(s) similar to the bovine RBP-receptor p63, whereas the visceral endoderm of the yolk sac placenta, the second site for materno-fetal transport, did. Furthermore, only the endodermal cells of the visceral yolk sac appeared to strongly accumulate radiolabelled retinoids. The cellular retinol binding protein (CRBP I) was detected both in the trophoblast layer of the placental labyrinth closest to the fetal endothelium (layer III), and in the visceral endoderm of the yolk sac. Together, these findings suggest that the yolk sac placenta mediates retinol transfer to the embryo/fetus throughout the entire gestation. The chorio-allantoic placenta, on the other hand, does not appear to have this capacity, while the presence of CRBP I does suggest a retinol-metabolizing capability.