Use of internal controls to increase quantitative capabilities of the ribonuclease protection assay.

Through the use of two internal controls, we have developed an improved method of quantitating ribonuclease protection assay (RPA) results. A truncated sense RNA fragment and an antisense RNA fragment for the gene of interest were transcribed from PCR fragments containing T7 bacterial promoters. An 18S ribosomal RNA fragment was also used. When radiolabeled antisense and 18S probes, along with sense fragment and sample RNA, were hybridized, digested with RNase A/T1 and gel-electrophoresed, three distinct bands resulted. The antisense RNA fragment bound to the sense RNA fragment confirmed the integrity of the reaction. The antisense RNA fragment bound to endogenous mRNA measured the amount of specific gene expression in the sample. The 18S RNA fragment bound to endogenous mRNA determined the actual amount of sample added to the gel. Using the specific activities of the antisense and 18S transcripts, and scintillation counts of the protected fragments, we calculated the amounts of message and total RNA on the gel, determining picogram of message per microgram of total RNA. Final results were not based on assumed original amounts of RNA placed in the assay nor were they biased by lane-to-lane variations. Through the described adaptations, we have developed a well-controlled RPA that accurately and reproducibly quantifies gene expression.

Quantitative analysis of androgen receptor messenger ribonucleic acid in developing Leydig cells and Sertoli cells by in situ hybridization.

Testosterone produced by Leydig cells is critical for the maintenance of spermatogenesis by Sertoli cells throughout adulthood in the rat. However, the presence of androgen receptors (AR) in Leydig cells in prepubertal rats suggests additional roles for androgen in early Leydig cell function and differentiation. In the present study, AR messenger RNA (mRNA) was directly measured by in situ hybridization in sections of rat testes at three developmental stages: on day 21 postpartum, when Leydig cells exist as mesenchymal-like progenitors; on day 35, when they are still immature, producing low amounts of testosterone; and on day 90, when they are fully functional in the sexually mature animal. Testicular AR mRNA was detected in Leydig cells, pericytes, peritubular myoid cells, and Sertoli cells. On day 90, AR mRNA levels in Sertoli cells varied with the cycle of the seminiferous epithelium, achieving peak intensity at stages VII-VIII. Measurements were made by image analysis and expressed as integrated signal intensities per unit labeled area (mean +/- SEM; n = 3 rats at each age). The results showed that levels of Leydig cell and Sertoli cell AR mRNA change significantly during development (P < 0.05). Leydig cell AR mRNA was intermediate on day 21 (at 17.3 +/- 0.7), highest on day 35 (at 26.9 +/- 1.6), and lowest on day 90 (at 11.8 +/- 1.1). The trend for isolated Leydig cells from these three ages was identical. In contrast, Sertoli cell AR mRNA was lowest on day 21 (at 19.3 +/- 1.0), intermediate on day 35 (at 24.5 +/- 1.4), and highest on day 90 (at 36.9 +/- 0.5). In Leydig cells, the highest level of AR mRNA was present during puberty, whereas the greatest amount of AR mRNA in Sertoli cells was present on day 90. This indicates that Leydig cells and Sertoli cells use different mechanisms to maintain AR levels. We infer from these data that Leydig cells are maximally sensitive to androgen during puberty, which is consistent with our hypothesis that androgens facilitate their differentiation.