RESUMEN
The local gill production of corticotropin releasing hormone (crh) and crh-receptor (crhr) is hypothesized to play important roles during seawater (SW) and freshwater (FW) acclimation in euryhaline black porgy (Acanthopagrus schlegelii). The mRNA expression of crh, crhr, and Na +/K + -ATPase (a-nka) was examined in SW and FW diencephalon (Dien) and in the gills at different exposure time by Q-PCR analysis. The in situ hybridization results indicate that crh mRNA hybridization signals were more abundant in FW fish in the gigantocellular (PMgc) and parvocellular (PMpc) part of the magnocellular preoptic nucleus versus SW fish. The crh and crhr-expressing cells were located in basal cells of gill filament. Furthermore, in vitro dexamethasone (DEX) treatment could increase the crh-system in the gill. Increased transcripts of the crh-system in the gill via in vitro and in vivo CRH treatments suggest that CRH may regulate the system in a local manner. The a-Nka cells were localized in the filament and secondary lamellae mitochondria rich cells (MRCs) of FW fish at 8 h and 1 day. a-Nka cells were seen in both filament and lamellae in the FW but much less in SW fish indicating that gills play key roles in black porgy osmoregulation. Gill crh and crhr play important roles in the response to salinity stress.
RESUMEN
In hermaphroditic fish, the ovotestis can respond to external stimuli so that only one type of gonadal tissue (either ovarian or testicular tissue) will remain reproductively active and the other will recede to a rudimentary stage. However, the molecular mechanism for sexual fate determination is still poorly understood in hermaphroditic fish. In the present study, we examined whether sexual fate determination with respect to testis development is due to differential expression of dmrt1. Expression of dmrt1 was limited to the spermatogonia-surrounding cells (Sertoli cells) throughout testis development. Testicular dmrt1 was differentially expressed in fish (black porgy [Acanthopagrus schlegeli Bleeker]) depending on if fish were destined to be female or male. Expression of dmrt1 in Sertoli cells did not require germ cell factors with busulfan treatment. To examine the role of dmrt1, we used virus-based RNA interference. Deficiency of dmrt1 resulted in a reduced number of germ cells in the testis and stimulated a male-to-female sex change. Higher serum luteinizing hormone levels were detected in 2(+)- to 3-yr-old male fish as compared to sex-changing female fish. Furthermore, we showed that fish treated in vivo with gonadotropin-releasing hormone (Gnrh) and fish treated in vitro with gonadotropin (Gth) had higher dmrt1 expression in the testis, suggesting that these endocrine factors may affect the male-to-female sex change. Therefore, our data suggest that dmrt1 plays a key role in initial testis differentiation and in later maintenance of male development. We show, to our knowledge for the first time, the functions of dmrt1 in hermaphroditic fish, which indicate that male-phase maintenance may be regulated by the brain-pituitary-gonadal axis via the Gnrh-Gth-Dmrt1 axis.
