Relaxin gene expression in human reproductive tissues by in situ hybridization.

The expression of the two human relaxin genes termed H1 and H2 in human reproductive tissues ranges from high to very low copy number depending upon the tissue and reproductive state. The aim of this study was to use two approaches to identify total relaxin transcripts (HI and H2) at the cellular level by using a human relaxin H2 riboprobe and a series of six 48-mer synthetic oligoprobes. The results obtained with both methods were similar in all tissues studied; however, a lower background was achieved with the riboprobe. This was especially noticeable after long exposure times, and a better resolution was generally achieved without clustering of the signals. Treatment of the tissues with proteinase-K failed to increase the sensitivity in any tissue with either probe. The relative levels of expression of the total relaxin gene transcripts was estimated from the different exposure times needed to obtain a good hybridization signal. Thus, the order of expression was: corpus luteum of pregnancy > corpus luteum of the cycle > placenta and prostate > decidua parietalis. The results agree well with immunolocalization of the peptide hormone previously performed with both heterologous and homologous relaxin antibodies; the exception was the lack of hybridization signal over the cells of the chorionic cytotrophoblast of the chorion laeve. This suggests that the levels of relaxin gene expression was below the level of detectability with the in situ hybridization technique or that these cells sequester, but do not synthesize, relaxin. Expression in the term placenta varied greatly from tissue to tissue and within any one tissue. A similar variability has been noted for relaxin in this tissue by immunocytochemistry. Methodology for the detection of total relaxin transcripts at the cellular level when expressed in a wide range of copy number will allow the developmental regulation of relaxin gene expression in reproductive and nonreproductive tissues to be visualized.