Invasive Cells in the Placentome of Andean Populations of Mabuya: An Endotheliochorial Contribution to the Placenta?

Abstract

New world lizards of the genus Mabuya have the most specialized level of placentotrophy among reptiles known to date, and related to that, they have the most complex allantoplacenta characterized by a series of morphological specializations that converge with those known for eutherian mammals. One of these specializations is the placentome that is found in the embryonic pole of the incubation chamber. In the mature allantoplacenta, this structure is morphologically the most complex, which could support an important amount of nutrient exchange between mother and fetus. According to the relationship between the chorioallantois and the syncytial uterine epithelia, the placenta of Mabuya populations shows some interesting similarities to the synepitheliochorial type. Recently, cells of chorionic origin have been found invading the syncytial uterine epithelium, and in very close proximity with uterine blood vessels. In this study, we describe the relationship between these invasive chorionic cells, the uterine syncytium, and the subjacent blood vessels of several populations of this genus, by means of high resolution optical microscopy and transmission electron microscopy. Cell groups originating from the chorion, of variable size and shape, penetrate the uterine syncytial epithelium extending complex cytoplasmic projections that come in contact with uterine capillaries and form an extensive and complex double-membrane system that surrounds the capillary. The close relationship between the chorion and the maternal circulation suggests that the Mabuya placentome shows some characteristics of an endotheliochorial placenta. This finding constitutes so far the only documented example of an endotheliochorial placentation in Reptilia. Anat Rec, 290:1508Rec, 290: -1518Rec, 290: , 2007 2007 Wiley-Liss, Inc.

The evolution of viviparity: molecular and genomic data from squamate reptiles advance understanding of live birth in amniotes

“…Exceptions may occur in skinks of the genera Mabuya and Trachylepis, both of which exhibit invasive placental specializations that may facilitate attachment to uterine tissues. In Mabuya, embryonic cells from the chorioallantois send cytoplasmic projections through the syncytial cells of the uterine epithelium to interact with uterine capillaries (Vieira et al 2007). In Trachylepis, embryonic epithelial cells from the chorioallantois invade, and ultimately replace, uterine epithelial tissue, and lie in direct contact with the uterine capillaries (Blackburn & Flemming 2012).…”

“…most species; Blackburn & Vitt 2002, Adams et al 2005, respiratory gases must cross the uterine and embryonic epithelial tissues to reach apposing capillaries. Respiratory gas transport may differ in Mabuya and Trachylepis, both of which exhibit specializations of embryonic tissues that interact with uterine capillaries (Vieira et al 2007, Blackburn & Flemming 2012. As in mammals, fetal hemoglobins of viviparous squamates exhibit higher oxygen affinity than do maternal hemoglobins, which should maximize oxygen diffusion from maternal to fetal circulation (Blackburn 1993a).…”

Evolution of mammalian pregnancy and the origin of the decidual stromal cell

“…4A) or through the fusion of fetal (trophoblast) and maternal (LE) epithelia (bandicoots). Penetration of the LE by cytoplasmatic extension of trophoblast cells has also been described in a non-mammalian species, the South American skink Mabuya (Vieira et al, 2007). The apparent purpose of this form of invasiveness seems to be to bring the maternal and placental blood capillaries into closer proximity, a situation that can also be achieved to some degree without breaching the LE, as is the case in wallaby (Fig.…”

Biología reproductiva y placentotrofía en lagartijas del género Mabuya

“…38(Supl. ):106-17, 2014 de este tipo de placentación entre Reptilia y que tampoco se ha descrito en otro clado con placentación compleja o con placentotrofía (Vieira et al, 2007).…”