Placentation in Sigmodontinae: a rodent taxon native to South America

Phelipe O Favaron,Carlos E Ambrósio,Maria A Miglino,Moacir F De Oliveira,Adriana C Morini,Anthony M Carter,Andrea M Mess

doi:10.1186/1477-7827-9-55

Abstract

BackgroundSigmodontinae, known as "New World rats and mice," is a large subfamily of Cricetidae for which we herein provide the first comprehensive investigation of the placenta.MethodsPlacentas of various gestational ages ranging from early pregnancy to near term were obtained for five genera, i.e. Necromys, Euryoryzomys, Cerradomys, Hylaeamys, and Oligoryzomys. They were investigated by means of histology, immunohistochemistry, a proliferation marker, DBA-lectin staining and transmission electron microscopy.ResultsThe chorioallantoic placenta was organized in a labyrinthine zone, spongy zone and decidua and an inverted yolk sac persisted until term. The chorioallantoic placenta was hemotrichorial. The interhemal barrier comprised fetal capillary endothelium and three layers of trophoblast, an outermost, cellular layer and two syncytial ones, with interspersed trophoblast giant cells (TGC). In addition, accumulations of TGC occurred below Reichert's membrane. The junctional zone contained syncytial trophoblast, proliferative cellular trophoblast, glycogen cells and TGC that were situated near to the maternal blood channels. In three of the genera, TGC were also accumulated in distinct areas at the placental periphery. PAS-positive glycogen cells derived from the junctional zone invaded the decidua. Abundant maternal uNK cells with positive response to PAS, vimentin and DBA-lectin were found in the decidua. The visceral yolk sac was completely inverted and villous.ConclusionThe general aspect of the fetal membranes in Sigmodontinae resembled that found in other cricetid rodents. Compared to murid rodents there were larger numbers of giant cells and in some genera these were seen to congregate at the periphery of the placental disk. Glycogen cells were found to invade the decidua but we did not identify trophoblast in the walls of the deeper decidual arteries. In contrast these vessels were surrounded by large numbers of uNK cells. This survey of wild-trapped specimens from five genera is a useful starting point for the study of placentation in an important subfamily of South American rodents. We note, however, that some of these rodents can be captive bred and recommend that future studies focus on the study of time dated pregnancies.

Highlights

Sigmodontinae, known as “New World rats and mice,” is a large subfamily of Cricetidae for which we provide the first comprehensive investigation of the placenta
Macroscopic structure In all taxa investigated the chorioallantoic placenta was situated at the antimesometrial side of the bicornuate
In summary the general aspect of the fetal membranes in Sigmodontinae resembled that found in other cricetid rodents

Summary

Introduction

Sigmodontinae, known as “New World rats and mice,” is a large subfamily of Cricetidae for which we provide the first comprehensive investigation of the placenta. Sigmodontine rodents form a monophyletic clade [23,24,25] These rodents are largely confined to the Neotropics [26], and are often referred to as “New World rats and mice”. They are known to transmit diseases to humans and domestic animals. Antibody prevalence indicates that sigmodontine species are reservoirs of Hantavirus in the several regions of Brazil and other parts of Latin America [27] They are the most important reservoirs of zoonotic cutaneous leishmaniasis throughout their range [24]. A better understanding of reproductive biology in these species is desirable and needs to include a comprehensive analysis of placental development and structure

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