Quantification of transforming growth factor beta 1 (TGF beta(1)) mRNA expression in mouse preimplantation embryos and determination of TGF beta receptor (type I and type II) expression in mouse embryos and reproductive tract

We hypothesized that transforming growth factor beta1 (TGF beta (1)) and it s receptors play a role in the interaction between the preimplantation embr yo and the reproductive tract. To investigate this hypothesis, TGF beta (1) mRNA in mouse embryos was quantified by competitive reverse transcription- polymerase chain reaction using an RNA mimic. TGF beta (1) was first detect ed in the unfertilized oocyte, disappeared after fertilization and was expr essed again at the 2-cell stage (4410 +/- 1330 transcripts/embryo). Its exp ression increased gradually, peaked at the 8-cell stage (58 600 +/- 17 300 transcripts/embryo) and declined rapidly after the morula stage reaching a concentration of 1520 +/- 546 transcripts/embryo at the blastocyst stage. T he mRNA levels of TGF beta (1) at the 8-cell and morula stages were signifi cantly higher than that at other cell stages (P < 0.05). The expression of TGF receptors in embryos and in the reproductive tract was also investigate d. Both TGF<beta>(1) type I (ALK-5) and type II TGF beta receptors were det ected in embryos from I-cell to blastocyst stage by immunohistochemistry. N orthern hybridization and immunohistochemistry showed a constant expression of both TGF beta receptors in the oviduct from day 1 to day 4 of pregnancy , whilst in the uterus there was a marked increase in the expression of TGF beta type I receptor on day 3. Expression of TGF beta type II receptor in the uterus remained unaltered throughout the study period. This study has s hown that preimplantation mouse embryos produce TGF beta (1) and that both the embryos and the reproductive tract are responsive to TGF beta (1) in th e preimplantation period.