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Estradiol-17 beta (E2) regulates transcription of estrogen-responsive genes via estrogen receptors (Esr). In many teleost species, choriogenin (chg), vitellogenin (vtg) and esr genes are transactivated by E2 in the liver. This study aimed i) to compare expression properties of all subtypes of these genes (chg: chgH alpha, chgH beta, chgL; vtg: vtgAs, vtgC; esr: esr1a, esr1b, esr2a, esr2b) in response to estrogen stimulation, and ii) to confirm how each of four Esr subtypes is involved in the transcriptional regulation of these estrogen-responsive genes in cutthroat trout hepatocytes. In hepatocytes in primary culture, all chg and vtg subtype mRNA levels, and those of esr1a, were increased by E2 treatment (10(-6) M) at 24 and 72 h post initiation (hpi), but esr1b, esr2a and esr2b mRNA levels were not. Treatment of hepatocytes with various concentrations of E2 (10(-11)-10(-6) M) induced dose-dependent increases in the levels of all chg and vtg subtype mRNAs at 24 and 72 hpi. At both time points, the lowest dose that induced a significant increase in the expression levels of mRNAs (LOEC) for E2 differed among the genes; LOECs were estimated as 10(-11) M for chgHa at 24 hpi, as 10 -9 M for vtgC at 72 hpi, and as 10(-19) M for other mRNAs at both 24 and 72 hpi. Meanwhile, the levels of esrla mRNA exhibited a dose-dependent increase at 24 and 72 hpi, but the LOEC shifted from 10(-9 )M at 24 hpi to 10(-7) M at 72 hpi because of a decrease in mRNA levels at treatment groups exposed to high concentrations of E2. All Esr subtypes transactivated chg, vtg and esrl a promoters in the presence of E2 in vitro. The activation levels indicated that promoter activity of chgHa > vtgAs > chgH5 > chgL > vtgC > esr1a when mediated by Esr1a, chgHO > chgHa > chgHL > vtgAs > vtgC > esr1a by Esr1b, chgHO > chgL > chgHa > vtgAs > vtgC > esr1a by Esr2a, and chgHO > chgHa > vtgAs > chgL > vtgC > esr1a by Esr2b. Collectively, different Esr subtypes were distinctly different in their ability to transactivate estrogen-responsive target genes, resulting in differential expression of chg, vtg and esr1a genes in the estrogen-exposed hepatocytes.

Fifteen radiolarian species were found in a plankton sample collected from surface water shallower than 10 m at the eastern margin of the Japan Sea off Tassha, Aikawa Town, Sado Island, central Japan in late May 2002. The late spring fauna was characterized by Lithomellisa setosa, Tetrapyle octacantha, Stylodictya spp., Spongodiscus spp. and Larcopyle butschlii. It is similar to that reported in late June 2001, but is different from that in early September 2000. Most individuals of warm-water species such as T. octacantha, Didymocyrtis tetrathalamus and Euchitoniafurcata were juveniles.

The early summer radiolarian fauna in surface waters (

Recently, we succeeded in inducing in vitro spermatogenesis in a protogynous hermaphrodite fish, threespotted wrasse (Halichoeres trimaculatus), during organ culture of ovary with a serum-supplemented medium. In the pres- ent study, we further optimized and used this culture system to determine effective steroid doses to induce sex change, and to investigate the importance of apoptosis during sex change in vitro. The results show that the restructuring from ovary to testis in the wrasse could be induced in vitro with a serum-free medium. Gonadal sex change can be triggered during basic in vitro culture due to a lack of endogenous factors (especially, estrogens) for female sexuality, and can be accelerated by androgens. Furthermore, oocyte apoptosis may be an important mechanism effecting gonadal sex change.

Accumulation of oil droplets in previtellogenic oocytes of Japanese eel, Anguilla japonica, could be induced in vitro. Co-treatment with very low-density lipoprotein (VLDL) and 11-ketotestosterone (11-KT) resulted in significant oil droplet accumulation. It is therefore suggested that lipids in oil droplets originate, at least in part, from VLDL, and that 11-KT plays an important role in their transfer and/or accumulation into oocytes.

A cDNA encoding a second type of a progestogen receptor (ePR2) was isolated from the same library as we had previously cloned a functional PR (ePR1) in eel testis. The amino acid sequence of the ePR2 shows low homology with ePR1 (34%), but both PRs showed progestogen-dependent transactivation in transfection experiment. Tissue distribution of ePR2 mRNA was clearly different from that of ePR1. Protein interaction between two PRs was demonstrated in vitro by a glutathione S-transferase pull-down assay. These results indicate that ePR2 is also a functional PR. This is the first isolation of two different functional PR molecules from a vertebrate.

A cDNA encoding a nuclear 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP, spermiation-inducing hormone in fish) receptor (DPR) was, for the first time, isolated from an eel testis cDNA library. The amino acid sequence of DPR shows high homology with those of human and chicken progesterone receptors. The affinity of the bacterial recombinant DPR ligand binding domain protein for 17α,20β-DP is higher than that of progesterone. In transfection experiments using COS7 cells, the DPR showed progestin-dependent activation of transcription. 17α,20β-DP was the most effective activator of transcription. These results indicate that the cDNA encodes a functional eel DPR, and show that 17α,20β-DP has a nuclear receptor-mediated action in eel testes.