EXPRESSION OF EPIDERMAL GROWTH-FACTOR RECEPTOR IN THE PREIMPLANTATIONUTERUS AND BLASTOCYST OF THE WESTERN SPOTTED SKUNK

The western spotted skunk is unique in that its blastocysts undergo a 180-220-day period of arrested development before implantation. We inv estigated the potential role of epidermal growth factor (EGF)-related growth factors in regulating uterine and embryonic development in this species by studying the status of EGF receptor (EGF-R) in these tissu es during delayed implantation and resumption of embryonic development . The cell-specific distribution of EGF binding sites and the expressi on of EGF-R mRNA were assayed by autoradiography and Northern blot ana lysis, respectively. The size of EGF-R was determined by affinity cros s-linking studies, and its bioactivity was examined by determining EGF -dependent subcellular protein tyrosine kinase (PTK) activity. EGF bin ding sites were localized in the uterine luminal and glandular epithel ium, endometrial stroma, myometrium, and blood vessels during both sta ges of pregnancy. As examined by Northern blot hybridization, a cRNA p robe specific to mouse EGF-R hybridized to poly(A)(+) RNA of skunk ute ri. Transcripts similar to those of mouse uterine EGF-R were identifie d. [I-125]-EGF was cross-linked to a 170-kDa protein both in the uteru s and in blastocysts collected during the delayed implantation and per iimplantation periods. However, EGF-induced PTK activity was significa ntly elevated above background levels during the period of renewed emb ryonic development, but not during arrested embryonic development. The results suggest that EGF-related growth factors may play an important role in regulating embryonic development in this species and that a c hange in the number and/or functional status of the EGF-R may be a pre requisite for blastocyst activation and implantation in the spotted sk unk.