Murine placenta.
Keywords: mouse, placenta, intimate, histology, human
Image size:1920 x 902 px
This histologic image of a murine placenta shows the intimate relationship between the fetal and maternal compartments in this species, more intimate than in any of the domestic species. It is fascinating because the fetal and maternal compartments are so easy to differentiate. That is because of the presence of nucleated red blood cells (RBCs) in the fetal compartment (green arrow). In general, most fetal RBCs have nuclei and most maternal RBCs (yellow arrow) do not. Also, fetal RBCs are significantly larger than the maternal RBCs .
The reader is reminded that not all fetal red blood cells are nucleated, and that the proportion of nucleated RBCs varies through gestation and from one species to another. In young murine fetuses for example, the site of hematopoesis in is the liver, not the spleen or bone marrow and RBCs from the liver do not have nuclei. By contrast, in equine young fetuses virtually all RBCs are nucleated, declining to the time of foaling, when nucleated RBCs are rare. Also, some adult domestic animals such as new world camelids and some breeds of dogs (Schauzers and Dachshunds) normally have low nucleated RBC counts.
Anatomy: In the case of the mouse, the vessels of the maternal and fetal placentas intertwine with one another in an labyrinth of entanglement; a 'spongiotrophoblast' In the human, fetal villi are bath in maternal blood. that lies in spaces between the villi. The comparative histological structures of these placentas has been well illustrated E. Maltepe et al.
Human and murine placentas are similar; intimate and single discoid in gross anatomy. This explains why the mouse is often used as a model to study human placental function. Although the placentas are similar, in human placentation, blood in intervillous spaces baths the chorion of the fetus directly. In the mouse, maternal endothelial cells, not blood itself, come to lie against the chorion. Contrary to older data, in neither case are fetal endothelial cells exposed to maternal blood. Those data suggested that human placenta were hemo-endothelial, a situation that does not exist. Currently, human and murine placentas are respectively classified as hemo-chorial and endotheliochorial. As found in many placentas, multinucleate syncytiotrophoblasts (literally fused cells with many nuclei that feed and grow) are present at the interface of the fetus and endometrium. In the murine placenta two of these multinuceate layers separate the endothelia of the fetal and maternal capilliaries from one another. Only a few multinucleated cells (white arrow) can be seen in this image.
The large ringed cell is a "giant cell" of fetal origin These are common in the placentas of rabbits, squirrels, marmots, rats and mice. They are highly invasive and interestingly,.usually polyploid, having up to four time the diploid number of chromosomes in the rest of the fetus! These are also important secretory cells, producing placental lactogen, growth hormone and cytokines that control placental re-modeling as the fetus grows.
The yellow arrow points to cells that are probably part of the so called junctional zone that lies between the labrinthe (closest to the fetus) and the dicidual zone, (Georgiades et al.) which is embedded in the endometrium.
References:
- Maltepe1, E. et al. 2010. The placenta: transcriptional, epigenetic, and physiological integration during development. J Clin Invest.120:1016–1025.
- Blood and Blood Formation Russell, E.S. and Bernstein S.E. http://www.informatics.jax.org/greenbook/frames/frame17.shtml
- Simmons G et al. 2007. Diverse subtypes and developmental origins of trophoblast giant cells in the mouse placenta. Developmental Biol.304:567–578
- Mossman, Harland, W. Vertebrate Fetal Membranes. ISBN: 0-8135-1132-1.
- Nuceated red blood cells: https://ahdc.vet.cornell.edu/sects/clinpath/modules/hemogram/nrbc.htm
- Allen A.L. et al. 1998 Hematology of Equine Fetuses with Comparisons to Their Dams Vet. Clin. Path. 27: 93-98.
Georgiades, P. aet al. 2001, Roles for genomic imprinting and the zygotic genome in placental development. Proc. Nat. Acad. Sci. 98: 4522–4527
