IMMUNOHISTOCHEMICAL LOCALIZATION OF TISSUE TRANSGLUTAMINASE AND BCL-2IN RAT UTERINE TISSUES DURING EMBRYO IMPLANTATION AND POSTPARTUM INVOLUTION

Rat pregnancy is characterized by a progressive continuous induction o f apoptosis in the maternal tissues lining the conceptus. Different ce ll types (decidual cells, giant cells, epithelial cells, etc.) undergo apoptosis at the different stages of development. We demonstrated her e that, independently from their origin and stage of pregnancy, the dy ing cells were invariably characterized by the presence of 'tissue' tr ansglutaminase (tTG) and negligible amounts of Bcl-2 proteins. This fi nding confirms the antithetic roles played by these two gene products within the apoptotic pathway. It is noteworthy that Bcl-2 was detected in decidual cells just after the implant; however, starting from day 9, its positive detection was reduced in the maternal tissues and appe ared in the embryonal ones. The apoptotic nature of death was also sug gested by the presence of a high phagocytic activity in the maternal i nvoluting regions and by morphological observations showing that the t TG positive cell remnants displayed typical phenotypic features of apo ptosis. The possibility that the cells lining the conceptus that die b y apoptosis could be envisaged as an inert barrier between the materna l and fetal tissues is discussed.