A naturally occurring variant of the human androgen receptor (AR) named AR45 has been identified. It lacks the entire region encoded by exon 1 of the AR gene and is composed of the AR DNA‐binding domain, hinge region and ligand‐binding domain, preceded by a novel seven amino‐acid long N‐terminal extension. A survey of human tissues revealed that AR45 was expressed mainly in heart and skeletal muscle. In cotransfection experiments, AR45 inhibited AR function, an effect necessitating intact DNA‐ and ligand‐binding properties. Overexpression of AR45 reduced the proliferation rate of the androgen‐dependent LNCaP cells, in line with the repressive effects of AR45 on AR growth‐promoting function. AR45 interacted with the AR N‐terminal domain in two‐hybrid assays, suggesting that AR inhibition was due to the formation of AR–AR45 heterodimers. Under conditions where the transcriptional coactivator TIF2 or the oncogene β‐catenin were overexpressed, AR45 stimulated androgen‐dependent promoters in presence of dihydrotestosterone. AR45 activity was triggered additionally by the adrenal androgen androstenedione in presence of exogenous TIF2. Altogether, the data suggest an important role of AR45 in modulating AR function and add a novel level of complexity to the mode of action of androgens.

BackgroundBased on the observation of an increased number of paralogous genes in teleost fishes compared with other vertebrates and on the conserved synteny between duplicated copies, it has been shown that a whole genome duplication (WGD) occurred during the evolution of Actinopterygian fish. Comparative phylogenetic dating of this duplication event suggests that it occurred early on, specifically in teleosts. It has been proposed that this event might have facilitated the evolutionary radiation and the phenotypic diversification of the teleost fish, notably by allowing the sub- or neo-functionalization of many duplicated genes.ResultsIn this paper, we studied in a wide range of Actinopterygians the duplication and fate of the androgen receptor (AR, NR3C4), a nuclear receptor known to play a key role in sex-determination in vertebrates. The pattern of AR gene duplication is consistent with an early WGD event: it has been duplicated into two genes AR-A and AR-B after the split of the Acipenseriformes from the lineage leading to teleost fish but before the divergence of Osteoglossiformes. Genomic and syntenic analyses in addition to lack of PCR amplification show that one of the duplicated copies, AR-B, was lost in several basal Clupeocephala such as Cypriniformes (including the model species zebrafish), Siluriformes, Characiformes and Salmoniformes. Interestingly, we also found that, in basal teleost fish (Osteoglossiformes and Anguilliformes), the two copies remain very similar, whereas, specifically in Percomorphs, one of the copies, AR-B, has accumulated substitutions in both the ligand binding domain (LBD) and the DNA binding domain (DBD).ConclusionThe comparison of the mutations present in these divergent AR-B with those known in human to be implicated in complete, partial or mild androgen insensitivity syndrome suggests that the existence of two distinct AR duplicates may be correlated to specific functional differences that may be connected to the well-known plasticity of sex determination in fish. This suggests that three specific events have shaped the present diversity of ARs in Actinopterygians: (i) early WGD, (ii) parallel loss of one duplicate in several lineages and (iii) putative neofunctionalization of the same duplicate in percomorphs, which occurred a long time after the WGD.

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