DIFFERENTIAL EXPRESSION OF THE FULL-LENGTH AND TRUNCATED FORMS OF THEEPIDERMAL GROWTH-FACTOR RECEPTOR IN THE PREIMPLANTATION MOUSE UTERUS AND BLASTOCYST

The present investigation examined the differential expression of the full-length (fl) and the truncated (tr) forms of the epidermal growth factor receptor (EGFr) in the preimplantation mouse uterus and blastoc yst. Northern blot hybridization using a complementary RNA probe speci fic to the full-length form (EGFr-fl) detected a 6.5-kb transcript, wh ereas that of the truncated form (EGFr-tr) detected a 2.7-kb transcrip t in the preimplantation mouse uterus on days 1 and 4 of pregnancy (da y 1 = vaginal plug). In situ hybridization using these probes detected the EGFr-fl transcripts only in the stroma and myometrium, but not in the epithelium, whereas EGFr-tr transcripts were detected in all majo r uterine cell-types. To confirm the results of in situ hybridization, RT-PCR was performed on RNA isolated from separated uterine cell-type s on day 4 of pregnancy using sequence specific primers for the two fo rms of the receptor. The results concur that the EGFr-tr transcript is expressed in the epithelium, stroma and myometrium, whereas that of t he EGFr-fl transcript is not expressed in the epithelium. In the preim plantation blastocyst, RT-PCR detected the EGFr-fl messenger RNA, but not the EGFr-tr messenger RNA. These results suggest that the blastocy st, not the uterine epithelium, is the target for EGF family of growth factors in embryo-uterine interaction during implantation.