Chorioallantoic and yolk sac placentation in Thrichomys laurentinus (Echimyidae) and the evolution of hystricognath rodents

Abstract

The evolutionary history of Hystricognathi is associated with major transformations in their placental system. Data so far indicate that key characters are independent from size dimensions in medium to very large species. To better understand the situation in smaller species, we analyzed placental development in a spiny rat, Thrichomys laurentinus. Fourteen individuals ranging from early implantation to near term were investigated by histology, immunohistochemistry, proliferation activity and electron microscopy. Placentation in Thrichomys revealed major parallels to the guinea pig and other hystricognath rodents with respect to the early and invasive implantation, the process of trophoblast invasion, the internal organization of the labyrinth and the trophospongium as well as the establishment of the complete inverted yolk sac placenta. In contrast to systematically related small-sized species, the placental regionalization in Thrichomys was characterized by a remarkable lobulated structure and associated growing processes. Reverse to former perspectives, these conditions represented ancient character states of hystricognaths. The subplacenta was temporarily supplied by both the maternal and fetal blood systems, a rare condition among hystricognaths. The extraplacental trophoblast originating from the subplacenta was partly proliferative in mid gestation. In conclusion, the presented results indicated that only minor variations occurred in small-sized hystricognath species, independent of their systematic interrelationships. Previous views were supported that placentation in hystricognaths followed an extraordinary stable pattern, although the group had distinct habitats in South America and Africa that were separated 30-40 million years ago.

Placental Evolution within the Supraordinal Clades of Eutheria with the Perspective of Alternative Animal Models for Human Placentation

“…Thus, several taxa including rare or wildlife species have been studied by means of histology and modern methods like immunohistochemistry or proper fine structural investigations by electron microscopy. Among 2 Advances in Biology them are nonmurine rodents native to South America and Africa [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], as was shown by Figure 2, bats [41][42][43], anteaters and armadillos [44,45], and some other taxa [46][47][48][49][50][51]. Also, there were several promising attempts to reinvestigate historical histological material from museum collections such as neotropical primates [52] or great apes [53][54][55][56] in order to answer open questions.…”

“…Other derived character conditions of hystricognaths are the ring-shaped placenta with radial flow of maternal blood in order to increase the capacity for passive diffusion [26]. The visceral yolk sac is completely inverted, facilitates substance exchange with the placenta, and has a fibrovascular capillary ring system [13,26,30,33,40,171,172]. Finally, hystricognaths have relatively long gestational periods, associated with precocial newborn [71,171,221].…”

Development and maturation of the lung in fetuses of Galea spixii and expression of markers

“…Fetuses were already fixed in formalin 10% or buffered glutaraldehyde 2.5% and were used in other previous studies related to placentation (OLIVEIRA et al, 2012). The research was registered with the IBAMA (Protocol 1478912) and was approved by the Ethics Committee of the UFERSA (Protocol 23091.001975/10-24).…”

“…For that, it was followed a formal protocol (OLIVEIRA et al, 2012). Negative controls was performed using IgG (Goat anti-Mouse IgG -AP 308F, Chemical International).…”

“…The cavy (Galea spixii) shows interesting characteristics related to reproduction and embryonic development, such as a long gestation period of around 48 days (OLIVEIRA et al, 2012) and reduced time of growth (ROBERTS & PERRY, 1974) when compared to other rodents. In this way, it was studied the development and maturation of the lung in the cavy in order to describe the macroscopic and histological characteristics, including cell proliferation and the presence of pluripotent cells during fetal life.…”