Expression of Receptors during the Cycle of the Seminiferous Epitheliuma

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Abstract
The data presented in this manuscript are all based on some inferences drawn from past experimental observations. The first is that the synchronized testis model is representative of the normal testis. Support for this premise comes from the studies on SGP-2, SGP-1 and transferrin where results using in situ hybridization and Northern blots are similar for normal and for synchronized testes. The second inference is that normalizing all of the data to the relative levels of SGP-1 mRNA adjusts for the possible differential loading of mRNA samples. The logic of this practice is based on the observation obtained using in situ hybridization that SGP-1 mRNA levels did not change across the cycle. The third assumption was that total mRNA levels do not change greatly across the cycle. Wholesale changes in testicular mRNA such as the doubling of all of the mRNA transcripts per testis would not be accounted for by these studies. We feel that this is an unlikely complication because of the strong correlation between much of the data and the known biology. In addition, there is a strong correlation between our data on the FSHR mRNA and the binding data for FSH obtained by another laboratory and different techniques. The available data in the literature reveals that most of the Sertoli cell products which change in relative concentrations during the cycle of the seminiferous epithelium appear to have a maximum in either stages VII or IX or in stages XIII to III. Thus, the Sertoli cells in the cycle could be described has having two different functional modes. In mode A maximal levels of mRNA for a specific Sertoli cell product are roughly found in stages VII-IX and in mode B the maximal levels are found in stages XIII to III (Fig. 5). The distribution of the receptor mRNA and ABP mRNA can also be described in terms of these two modes of Sertoli cell function. Transferrin receptors, retinoic acid receptors, and androgen-binding protein appear to fall into mode A while FSH and androgen receptors fall into mode B (Table 1). Products which have antithetical functions such as FSH and inhibin or cystatin and cathepsin L are found in different modes. We propose that most of the actions of the Sertoli cell during the cycle can be specified by the dual modes described above rather than by an infinite number of operational modes.(ABSTRACT TRUNCATED AT 400 WORDS)