EXPRESSION OF HEPARAN-SULFATE PROTEOGLYCAN (PERLECAN) IN THE MOUSE BLASTOCYST IS REGULATED DURING NORMAL AND DELAYED IMPLANTATION

Previous studies have shown that expression of the heparan sulfate pro teoglycan, perlecan, on the external trophectodermal cell surfaces of mouse blastocysts increases during acquisition of attachment competenc e. However it is not clear if this change in perlecan protein expressi on also is reflected at the level of perlecan mRNA expression. In the present investigation, the spatial and temporal patterns of perlecan m RNA expression in the mouse embryo during the periimplantation period were examined by in situ hybridization and reverse transcriptase-polym erase chain reaction. In addition, a delayed implantation model was us ed to determine the expression of perlecan mRNA and protein in dormant and estrogen-activated hatched blastocysts. The results demonstrate t hat perlecan mRNA expression is low in morulae, but increases in Day 4 blastocysts, attaining maximal expression in Day 4.5 attachment-compe tent blastocysts. In contrast, perlecan mRNA is detected in both the d ormant and estrogen-activated delayed blastocysts; however, within 12 hr of blastocyst activation by estrogen, both perlecan protein and hep aran sulfate chain expression markedly increase. Taken together, these results suggest that during normal development perlecan mRNA expressi on increases with the acquisition of attachment competence. Moreover, perlecan protein expression also is attenuated during delayed implanta tion and appears to increase in response to nidatory estrogen, perhaps via the increased translation of preexisting perlecan mRNA. (C) 1997 Academic Press.