Localization of transforming growth factor beta2 (TGFbeta2) and its receptors, TbetaRI and TbetaRII, in uteri and blastocysts of the stripe-faced dunnart (Sminthopsis macroura) during gastrulation

This study describes for the first time the spatial and temporal distribution of a growth factor and its receptors in uteri and conceptuses of a marsupial species during the peri-gastrulation period. Uteri (gravid and non-gravid) and blastocysts from 40 female stripe-faced dunnarts (Sminthopsis macroura) were collected over the peri-gastrula period (days 6.0-8.5) and stained immunohistochemically for transforming growth factor beta2 (TGFbeta2) and its receptors, TbetaRI and TbetaRII, to determine possible roles for TGFbeta2 in marsupial embryonic development. The events that occurred during the period examined included the appearance and proliferation of hypoblast and mesoderm, primitive streak and node formation, and early neurulation. Differences in TGFbeta2 quantities between gravid and non-gravid uteri reflect differences in uterine morphology, indicating a role for TGFbeta2 in endometrial remodelling. In blastocysts, large quantities of all three proteins in the trophectoderm during the node stage coincide with both blastocyst expansion before implantation and the appearance of multinucleated cells, indicating that TGFbeta2 plays a role in conceptus elongation and trophectoderm differentiation. In contrast, lack of TbetaRII in blastocysts during hypoblast formation and proliferation negates any role for TGFbeta2 in these processes, as both receptors are required for a response to TGFbeta2. High concentrations of TGFbeta2 but low concentrations of TbetaRII in blastocysts during early primitive streak formation indicate that paracrinal embryo-maternal signalling may be occurring, as blastocysts cannot respond to TGFbeta2 at this stage, but uteri could. A similar situation, but reversed, also occurs during primitive node formation.