SPARC expression in the mouse decidua, placenta, and fetus: correlations with SPP1 expression

Secreted protein acidic and rich in cysteine (SPARC) and secreted phosphoprotein 1 (SPP1) are matricellular proteins implicated in many physiological processes including cell migration, tissue remodeling, and angiogenesis. The role of SPP1 in the pregnancies of many species has been studied extensively, however the contributions of SPARC to pregnancy are not well understood.

Here, we examine the localization of Sparc mRNA and protein in mouse fetuses, endometrial decidua, and placentae during various days of pregnancy in the delayed implantation model to identify potential interactions between SPARC and SPP1 in mouse pregnancy.

In situ hybridization and immunofluorescence microscopy localized Sparc mRNA and protein to the endometrial stroma at implantation sites on gestational day (GD)5-6, and to the parietal yolk sac, Reichert's membrane, and select trophoblast lineages on GD9-16. Spp1 mRNA is strongly expressed in the endometrial luminal epithelium at inter-implantation sites and SPP1 is detected in uterine natural killer cells (uNKs) and glycogen trophoblast cells of the placenta. SPARC and SPP1 both localized to many regions of the GD16 fetus, including separate chondroblastic lineages within the developing cartilage.

The placental expression pattern of these two matricellular proteins suggests possible spatio-temporal and mechanistic relationships between SPARC and SPP1 during pregnancy. While future studies are needed to elucidate the functional roles of SPARC, results from this study demonstrate that SPARC is a prominent component of the matricellular milieu throughout gestation.