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- The swimbladder of the Lusitanian toadfish: sexual dimorphism and hormonal controlPublication . Modesto, Teresa; Canario, Adelino V. M.; Castanõ, J. P.; Malagon, M. M.; Garcia Navarro, S.The members of the family Batrachoididae produce sounds associated with courtship and agonistic interactions. While long mating calls are only produced by nesting males, agonistic short duration grunts have been recorded from toadfishes and midshipmen in both males (nesting or not) and females. Sound production results from the contraction of paired sonic muscles attached to the walls of the swimbladder, which cause a rapid variation in swimbladder volume and internal pressure. Both sonic muscle growth and sonic fibre morphology have been shown to be androgen sensitive in batrachoidids.
- 17a,20ß,21-trihydroxy-4-pregnen-3-one: the probable maturation-inducing steroid of the lusitanian toadfishPublication . Modesto, Teresa; Canario, Adelino V. M.17,20 ,21-Trihydroxy-4-pregnen-3-one (17,20 ,21-P) was identified as the major metabolite of incubations of Lusitanian toadfish Halobatrachus didactylus ovarian follicles with [3H]-17hydroxyprogesterone. The potency of several steroids in inducing germinal vesicle breakdown of follicle-enclosed oocytes of Lusitanian toadfish was systematically examined by using an in vitro germinal vesicle breakdown (GVBD) bioassay. 17,20 -Dihydroxy-4-pregnen-3-one (17,20 -P) and 17,20 ,21-P, two confirmed maturation-inducing steroids (MIS) in teleosts, were the most potent in inducing GVBD with ED50s ranging between 9 and 271 nM. Structure-activity relationships followed similar patterns to what has been observed in similar bioassays, i.e. a vital requirement for 17- and 20 -hydroxyl groups in C21 steroids and a reduction in activity of 14 and 5–6%, respectively, for 5-pregnene and 5 -pregnanes compared to 4-pregnenes. Corticosteroids, testosterone and 17 -oestradiol were ineffective. Folliculated oocytes stimulated by pituitary homogenate produced 17,20 ,21-P from endogenous substrates in amounts one order of magnitude higher than 17,20 -P. These results strongly support the hypothesis that 17,20 ,21-P is the likely MIS in this species.
- Molecular characterization and expression pattern of zona pellucida proteins in gilthead seabream (Sparus aurata)Publication . Modig, Carina; Modesto, Teresa; Canario, Adelino V. M.; Cerda, J.; Hofsten, Jonas von; Olsson, P. E.The developing oocyte is surrounded by an acellular envelope that is composed of 2–4 isoforms of zona pellucida (ZP) proteins. The ZP proteins comprise the ZP1, ZP2, ZP3, and ZPX isoforms. While ZP1 (ZPB) and ZP3 (ZPC) are present in all species, ZP2 (ZPA) is not found in teleost fish and ZPX is not found in mammals. In the present study, we identify and characterize the ZP1, ZP3 and ZPX isoforms of gilthead seabream. Furthermore, by analyzing the conserved domains, which include the external hydrophobic patch and the internal hydrophobic patch, we show that ZP2 and ZPX are closely related isoforms. ZP proteins are synthesized in either the liver or ovary of most teleosts. Only in rainbow trout has it been shown that zp3 has dual transcription sites. In gilthead seabream, all four mRNA isoforms are transcribed in both the liver and ovary, with zp1a, zp1b, and zp3 being highly expressed in the liver, and zpx being primarily expressed in the ovary. However, determination of the ZP proteins in plasma showed high levels of ZP1b, ZP3, and ZPX, with low or non-detectable levels of ZP1a. In similarity to other teleost ZPs, the hepatic transcription of all four ZP isoforms is under estrogenic control. Previously, we have shown that cortisol can potentiate estrogen-induced ZP synthesis in salmonids, and now we show that this is not the case in the gilthead seabream. The present study shows for the first time the endocrine regulation of a teleost ZPX isoform, and demonstrates the dual-organ transcriptional activities of all the ZP proteins in one species.
- Hormonal control of swimbladder sonic muscle dimorphism in the Lusitanian toadfish, Halobatrachus didactylusPublication . Modesto, Teresa; Canario, Adelino V. M.The swimbladder and associated sonic muscle of the Lusitanian toadfish Halobatrachus didactylus increase in size throughout life and are, respectively, 25% and 30% larger in type I (nest-holder) males than females, which may generate sexual differences in sound production. Sexual dimorphism in swimbladder is also evident in the morphological features of sonic muscle fibers. During the breeding season, type I males have smaller myofibril contracting zones surrounded by larger sarcoplasm areas compared with females, possibly an adaptation to speed and fatigue resistance for the production of long mating calls. Type II (floater) males show characteristics that are intermediate, but statistically not significantly different, between type I males and females. Six weeks after castration and androgen (testosterone and 11- ketotestosterone) replacement in type I and type II males there were no alterations either in swimbladder mass or fiber morphology. However, 17b-estradiol induced a significant decrease in swimbladder mass and sarcoplasm area/myofibril area ratio. Six months after castration there was a clear reduction in the seasonal swimbladder hypertrophy in males and induction of sonic fiber morphological characteristics that resemble those occurring in females (low sarcoplasm area/myofibril area ratio). These results suggest that testicular factors are required to initiate sonic muscle hypertrophy and type I sonic fiber phenotype in H. didactylus, but a specific involvement of androgens has not been completely clarified.
- 16.P15. Branchial osmoregulatory response to salinity challenge in the Lusitanian toadfishPublication . Guerreiro, Pedro M; Laiz-Carrión, R.; Haond, Christophe; Modesto, Teresa; Fuentes, Juan; Mancera, J. M.; Canario, Adelino V. M.Halobatrachus didactylus, a marine teleost found in coastal lagoons and river estuaries is often exposed to important salinity changes. Despite its aglomerular kidney, it is able to survive in hypo-osmotic environments, likely via compensatory actions from gills and intestine. We aimed at evaluating the response of the branchial tissue of H. didactylus to salinity changes.
- A PTH/PTHrP receptor antagonist blocks the hypercalcemic response to estradiol-17bPublication . Fuentes, J.; Guerreiro, P. M.; Modesto, Teresa; Rotllant, J.; Canario, Adelino V. M.; Power, DeborahEstradiol (E2) increases circulating calcium and phosphate levels in fish, thus acting as a hypercalcemic and hyperphosphatemic factor during periods of high calcium requirements, such as during vitellogenesis. Since parathyroid hormone (PTH)-related protein (PTHrP) has been shown to be calciotropic in fish, we hypothesized that the two hormones could be mediating the same process. Sea bream (Sparus auratus) juveniles receiving a single intraperitoneal injection of piscine PTHrP(1-34) showed an elevation in calcium plasma levels within 24 h. In contrast, injections of the PTH/PTHrP receptor antagonist PTHrP(7-34) decreased circulating levels of calcium in the same period. Intraperitoneal implants of estradiol-17 (E2; 10 g/g) evoked significant increases of circulating plasma levels of calcium and phosphorus and a sustained increases of circulating plasma levels of PTHrP. However, a combined treatment of E2 and PTHrP(7-34) evoked a markedly lower calcium response compared with E2 alone. We conclude that PTHrP or a related peptide that binds the PTH/PTHrP receptor mediates, at least in part, the hypercalcemic effect of E2 in calcium and phosphate balance in fish.