RESEARCH ARTICLE Gonadotropin-Activated Androgen- Dependent and Independent Pathways Regulate Aquaporin Expression during

Themediation of fluid homeostasis by multiple classes of aquaporins has been suggested to be essential during spermatogenesis and spermiation. In the marine teleost gilthead seab-ream (Sparus aurata), seven distinct aquaporins, Aqp0a,-1aa,-1ab,-7,-8b,-9b and-10b, are differentially expressed in the somatic and germ cell lineages of the spermiating testis, but the endocrine regulation of these channels during germ cell development is unknown. In this study, we investigated the in vivo developmental expression of aquaporins in the seabream testis together with plasma androgen concentrations.We then examined the in vitro regulatory effects of recombinant piscine gonadotropins, follicle-stimulating (rFsh) and luteinizing (rLh) hormones, and sex steroids on aquaporin mRNA levels during the spermatogenic cycle. Dur-ing the resting phase, when plasma levels of androgens were low, the testis exclusively con-tained proliferating spermatogonia expressing Aqp1ab, whereas Aqp10b and-9b were localized in Sertoli and Leydig cells, respectively. At the onset of spermatogenesis and during spermiation, the increase of androgen plasma levels correlated with the additional appearance of Aqp0a and-7 in Sertoli cells, Aqp0a in spermatogonia and spermatocytes, Aqp1ab,-7 and-10b from spermatogonia to spermatozoa, and Aqp1aa and-8b in spermatids and spermato