Chorioallantoic placentation in Galea spixii (Rodentia, Caviomorpha, Caviidae)
© Oliveira et al; licensee BioMed Central Ltd. 2008
Received: 14 June 2008
Accepted: 04 September 2008
Published: 04 September 2008
Placentas of guinea pig-related rodents are appropriate animal models for human placentation because of their striking similarities to those of humans. To optimize the pool of potential models in this context, it is essential to identify the occurrence of characters in close relatives.
In this study we first analyzed chorioallantoic placentation in the prea, Galea spixii, as one of the guinea pig's closest relatives. Material was collected from a breeding group at the University of Mossoró, Brazil, including 18 individuals covering an ontogenetic sequence from initial pregnancy to term. Placentas were investigated by means of histology, electron microscopy, immunohistochemistry (vimentin, α-smooth muscle actin, cytokeration) and proliferation activity (PCNA).
Placentation in Galea is primarily characterized by an apparent regionalization into labyrinth, trophospongium and subplacenta. It also has associated growing processes with clusters of proliferating trophoblast cells at the placental margin, internally directed projections and a second centre of proliferation in the labyrinth. Finally, the subplacenta, which is temporarily supplied in parallel by the maternal and fetal blood systems, served as the center of origin for trophoblast invasion.
Placentation in Galea reveals major parallels to the guinea pig and other caviomorphs with respect to the regionalization of the placenta, the associated growing processes, as well as trophoblast invasion. A principal difference compared to the guinea pig occurred in the blood supply of the subplacenta. Characteristics of the invasion and expanding processes indicate that Galea may serve as an additional animal model that is much smaller than the guinea pig and where the subplacenta partly has access to both maternal and fetal blood systems.
Investigated material of Galea spixii
Phase of pregnancy
Number of animals
Crown-rump length (CRL)
Diameter of the placenta
< 10 mm
4 – 8 mm
9 – 12
11 – 28 mm
9 – 12 mm
16 – 32
36 – 73 mm
13 – 18 mm
Near term to term
36 – 48
76 – 110 mm
20 – 35 mm
Immunohistochemistry. Complete description data related to the performed immunohistochemistry reactions
Dako Protein Block
Carpinteria, CA, U.S.A
Vimentin (Type: V9, sc-6260), Dilution: 1:200
Santa Cruz Biotechnology
Santa Cruz, California, U.S.A.
Cytokeratin (PU071-UP), Dilution 1:500
San Ramon, California, U.S.A.
A-smooth muscle actin (Clone 1A4), Dilution 1:300
Carpinteria, CA, U.S.A
PCNA (PC10, sc-56), Dilution 1:800
Santa Cruz Biotechnology
Santa Cruz, California, U.S.A.
Streptavidin-HRP; LSAB®+ System-HRP
Carpinteria, CA, U.S.A.
Aminoethyl carbazole, AEC Substrate Kit
South San Francisco, CA, U.S.A.
Carpinteria, CA, U.S.A.
Goat anti-Mouse IgG (AP308F) Dilution 1:500
Temecula, CA, USA
Placental development in Galea spixii is, in principle, equivalent to that of the guinea pig. Similarities include a highly lobulated, labyrinthine placenta that includes labyrinth, trophospongium and subplacenta as distinct areas with a characteristic structure [5, 10, 11], an invasive haemochorial placental type with a thin interhaemal barrier [1–3, 5, 7, 10], trophoblast invasion related to the subplacenta that is functionally analogous to the cell columns in the human placenta [2, 5, 7], trophoblast cell clusters as growing zones at the periphery and in the labyrinth  and the presence of the parietal yolk sac and Reichert's membrane . These features are typical for placentation in caviomorph rodents and represent the ancestral condition or stem species pattern of the group [6, 10, 12, 26, 33]. However, two differences were observed. Primarily, Cavia possesses no coexistence between the fetal and maternal blood supply of the subplacenta [5, 27–29]: supply by the maternal arterial system is stopped by coagulation, resulting in detritus-filled spaces and collapse of the lacunes, once the fetal capillaries achieve access to the subplacenta. This condition was regarded as typical for caviomorphs, although mostly only a few stages were studied [8–18]. In two individuals of Galea in early pregnancy and at mid gestation, both fetal and maternal blood systems are present inside the subplacenta with only some, but not all, of the maternal blood spaces occluded by detritus. The data indicate coexistence between both blood systems. Such a condition was recently documented for another caviomorph species, the degu Octodon degus, in which fetal vessels first arise while maternal blood lacunae are still present . Moreover, very recent data indicate an overlap for the capybara too [Kanashiro et al., pers. comm.]. In all three species the maternal and fetal blood systems are separated by several layers of fetal mesenchyme, cytotrophoblast and syncytiotrophoblast, suggesting that the labyrinth is more appropriate for fetomaternal exchange . Thus far, no functional or physiological significance for the overlap in the blood supply of the subplacenta is available. However, according to PAS-staining the subplacental syncytiotrophoblast accumulates glycogen or related substances such as mucopolysacharides, glycoproteins or proteoglycans. This may indicate a secretory function, e.g. for growth factors, hormones or cytokines which might be given to the fetal unit to shut down physiological functions that are not needed during fetal life. Otherwise it could have been accumulated after degeneration of the subplacenta and may be involved in the forthcoming birth, as was previously discussed by several authors [5, 11, 15, 29–32]. Finally, even in late pregnancy the parietal yolk sac is partly multilayered in Galea and related species [12–18], whereas this condition has been lost in Cavia . In this case, Galea exhibits the caviomorph stem species pattern, whereas Cavia possesses a derived character condition .
Development of the placenta in Galea exhibits major parallels to the guinea pig and other caviomorphs. Due to similarities in invasion and the expanding processes, it may serve as an additional animal model for human placentation. Galea is smaller than the guinea pig and may thus be beneficial for some projects. Moreover, it could serve as an alternative where the center of origin for trophoblast invasion temporarily has access to both maternal and fetal blood systems during pregnancy.
List of all abbreviations
maternal blood channel
parietal yolk sac
visceral yolk sac
We are grateful for technical support to several members of the University Sao Paulo, Brazil, the Universidade Federal Rural do Semi-Árido, Mossoró, Brazil and the Humboldt-University of Berlin, Germany. Finally, we want to thank Jason Dunlop for help with the English revision.
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