Quantification of transforming growth factor β1 (TGFβ1) mRNA expression in mouse preimplantation embryos and determination of TGFβ receptor (type I and type II) expression in mouse embryos and reproductive tract

Abstract

We hypothesized that transforming growth factor β1 (TGFβ 1) and its receptors play a role in the interaction between the preimplantation embryo and the reproductive tract. To investigate this hypothesis, TGFβ 1 mRNA in mouse embryos was quantified by competitive reverse transcription-polymerase chain reaction using an RNA mimic. TGFβ 1 was first detected in the unfertilized oocyte, disappeared after fertilization and was expressed again at the 2-cell stage (4410 ± 1330 transcripts/embryo). Its expression 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. The mRNA levels of TGFβ 1 at the 8-cell and morula stages were significantly higher than that at other cell stages (P < 0.05). The expression of TGF receptors in embryos and in the reproductive tract was also investigated. Both TGFβ 1 type I (ALK-5) and type II TGFβ receptors were detected in embryos from 1-cell to blastocyst stage by immunohistochemistry. Northern hybridization and immunohistochemistry showed a constant expression of both TGFβ 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 TGFβ type I receptor on day 3. Expression of TGFβ type II receptor in the uterus remained unaltered throughout the study period. This study has shown that preimplantation mouse embryos produce TGFβ 1 and that both the embryos and the reproductive tract are responsive to TGFβ 1 in the preimplantation period.