Arrangement and fine structure of collagen fibrils in the decidualized mouse endometrium

Abstract

The adaptations of the mouse uterus to pregnancy include extensive modifications of the cells and extracellular matrix of the endometrial connective tissue that surround the embryos. Around each implanted embryo this tissue redifferentiates into a transient structure called decidua, which is formed by polygonal cells joined by intercellular junctions. In the mouse, thick collagen fibrils with irregular profile appear in decidualized areas of the endometrium but not in the nondecidualized stroma and interimplantation sites. The fine organization of these thick fibrils has not yet been established. This work was addressed to understand the arrangement and fine structure of collagen fibrils of the decidua of pregnant mice during the periimplantation stage. Major modifications occurred in collagen fibrils that surrounded decidual cells: (1) the fibrils, which were arranged in parallel bundles in nonpregnant animals, became organized as baskets around decidual cells; (2) very thick collagen fibrils with very irregular profiles appeared around decidual cells. Analysis of replicas and serial sections suggests that the thick collagen fibrils form by the lateral aggregation of thinner fibrils to a central fibril resulting in very irregular profile observed in cross sections of thick fibrils. The sum of modifications of the collagen fibrils seem to represent an adaptation of the endometrium to better support the decidual cells while they hold the embryos during the beginning of their development. The deposition of thick collagen fibrils in the decidua may contribute to form a barrier that impedes leukocyte migration within the decidua, preventing immunological rejection of genetically dissimilar embryonic tissues.

Changes in cell cycle and extracellular matrix gene expression during placental development in deer mouse (Peromyscus) hybrids

“…Both collagens and Timp proteins are required at the maternal-fetal interface of the placenta (Apte et al 1994;Carbone et al 2006). Together, these data suggest improper ECM formation both within the fetal placenta and the decidua of the PO × BW cross.…”

Collagen types I, III, and V constitute the thick collagen fibrils of the mouse decidua

“…In fact, we have previously shown that at least part of the thick collagen fibrils formed during decidualization in the mouse originates by lateral fusion of thin collagen fibrils present in the endometrium before the onset of decidualization (Carbone et al, 2006). Moreover, serial sections of thick fibrils showed that although its central part was homogeneous, close to the surface the fibrils became subdivided into segments (subfibrils), which were often arranged helicoidally along the main fibril (Carbone et al, 2006). It is therefore possible that only type V collagen epitopes situated at the outermost portion of the helical fibrils were accessed by the antibody.…”

“…Observation of thin serial sections of decidualized regions of mice uterine horns showed that at least a fraction of the thick collagen fibrils are formed by lateral aggregation of pre-existing thin fibrils (Carbone et al, 2006). However, it is not known whether thin and thick collagen fibrils or both contain more than one distinct collagen molecules.…”

Differences in collagen ultrastructure of human first trimester decidua basalis and parietalis: Implications for trophoblastic invasion of the placental bed

“…The region of mature decidual cells showed the thickest fibrils reaching 370 nm in diameter . Neither the genesis nor the role of these large decidual collagen fibrils is known, but some have speculated that they arise by lateral association of smaller diameter fibrils . That they appear to occur only after 9 weeks of gestation and not before suggest a possible stimulus or signal for their formation from the developing embryo, the stimulus or signal being highly localized.…”