Ubiquitous Thioredoxin Systems In Testis
Before discussing on the individual spermatid-specific thioredoxins, it is very important to detail what is known about the ubiquitous thioredoxin systems in t3st1s. The expression of the cytosolic thioredoxin system has been examined in rat t3st1s by immunocytochemistry, and it was found that Trx-1 is highly expressed in all Leydig cells, but only in a small fraction of spermatogonia (10-15%) and very little in Sertoli cells. The more differentiated germ cells such as spermatocytes or spermatids do not express it (33, 80). Surprisingly, TrxR1 expression was found mainly in those cell types negative for Trx-1, namely Sertoli cells, spermatocytes and spermatids (80). This result is somehow intriguing, as it was expected that both proteins should colocalize to constitute an active thioredoxin system, and prompted us to attempt a more thorough developmental analysis of the expression of these two proteins during spermatogenesis. Our preliminary data indicate that both Trx-1 and TrxR1 are mostly found in the cytoplasm and tail of elongating spermatids, a more consistent localization as expected for a coordinated system (Oko et al., unpublished results).
The mitochondrial thioredoxin system in t3st1s has been studied by northern analysis showing a relatively high level of both Trx-2 and TrxR2 as expected for a high-metabolic rate tissue (21, 53, 54, 90). Immunolocalization data are only available for Trx-2 where it is predominantly found in the germ line (21). Finally, both Txl-1/Trp32 and ERdj5/JPDI mRNA levels have been found to be moderate to high in t3st1s but no immunolocalization in this tissue has been reported (19, 36, 45, 55).
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