Organization and regulation of sex-specific thioredoxin encoding genes in the genus Drosophila

Abstract

Thioredoxins are small thiol proteins that have a conserved active site sequence, WCGPC, and reduce disulfide bonds in various proteins using the two active site cysteines, a reaction that oxidizes thioredoxin and renders it inactive. Thioredoxin reductase returns thioredoxin to its reduced, active form in a reaction that converts NADPH to NADP(+). The biological functions of thioredoxins vary widely; they have roles in oxidative stress protection, act as electron donors for ribonucleotide reductase, and form structural components of enzymes. To date, three thioredoxin genes have been characterized in Drosophila melanogaster: the generally expressed Thioredoxin-2 (Trx-2) and the two sex-specific genes ThioredoxinT (TrxT) and deadhead (dhd). The male-specific TrxT and the female-specific dhd are located as a gene pair, transcribed in opposite directions, with only 470 bp between their transcription start points. We show in this study that all three D. melanogaster thioredoxins are conserved in 11 other Drosophilid species, which are believed to have diverged up to 40 Ma ago and that Trx-2 is conserved all the way to Tribolium castaneum. We have found that the intriguing gene organization and regulation of TrxT and dhd is remarkably well conserved and identified potential conserved regulatory sequences. In addition, we show that the 50-70 C terminal amino acids of TrxT constitute a hyper-variable domain, which could play a role in sexual conflict and male-female co-evolution.

Unlocking sperm chromatin at fertilization requires a dedicated egg thioredoxin in Drosophila

“…As Trx-T is strictly expressed in the male germline18, the dhd J5 allele can be used to specifically address the maternal function of dhd 19. In addition, the dhd maternal effect embryonic lethal phenotype is fully rescued by a genomic transgene containing dhd but not Trx-T 19 (Fig.…”

“…dhd is apparently the most recent thioredoxin gene in Drosophila and likely originated after the duplication of the ancestral Trx-2 gene18. It is thus tempting to propose that the emergence of this highly specialized protein could reflect the adaptation of the oocyte to the rapid evolution of sperm chromatin architecture.…”

“…Three classical thioredoxins are found in Drosophila melanogaster . Trx-2 is a non-essential ubiquitous protein that participates in the protection against oxidative stress1516, whereas TrxT and DHD are sex-specific thioredoxins encoded by a pair of adjacent genes1718. While the role of the testis-specific TrxT is unknown, DHD is specifically expressed in the female germline and is essential for embryo development1920.…”

Functional characterization of thioredoxin 3 (TRX-3), a Caenorhabditis elegans intestine-specific thioredoxin

“…In mammals, tissue-specific thioredoxins have only been identified in spermatozoa and lung ciliated epithelial cells [44]. Germ-cell-specific expression of thioredoxins has also been reported in Drosophila [45]. Interestingly, we have identified novel tissue-specific expression patterns in the C. elegans thioredoxin family.…”

Cloning and characterization of thioredoxin h in the three-pistil line of common wheat

“…It contained 5 β-folds surrounded by 4 α-helices. The active site (WCGPC), the conserved structure of the Trx family (Svensson et al, 2007), was located at the end of the second b-fold and initial side of the second α-helix ( Figure 6B). Overexpression in E. coli, purification, and enzyme activity of the TPTrxh protein SDS-PAGE was used for expression analysis of protein extracts from recombinants in E. coli BL21 (DE3) strains after induction with isopropyl β-D-1-thiogalactopyranoside (Figure 7).…”