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 testis. The expression of the
cytosolic thioredoxin system has been examined in rat testis 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unpublished results).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
testis 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 testis but no immunolocalization in this tissue
has been reported (19,
36, 45, 55).
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