Kinetic Characterization of Myoglobins from Vertebrates with Vastly Different Body Temperatures

Fish myoglobins are structurally distinct from the previously characterized mammalian myoglobins. Teleost fishes express generally lower levels of myoglobin than those found in mammals. Although the oxygen binding affinity is essentially the same as mammalian myoglobins, oxygen dissociation rates and carbon monoxide combination rates of the teleost myoglobins studied are significantly faster. Thus, the kinetic parameters of myoglobin from two Antarctic teleost species, measured close to their body temperature of −1°C, are comparable to those of mammalian myoglobins with higher body temperatures. These data suggest myoglobins from Antarctic teleosts may function at extreme environmental temperatures.     

Spermiogenesis in the teleost Gambusia affinis with particular reference to the role played by microtubules

Summary During nuclear elongation in spermatids of Gambusia affinis, a deep fossa is formed at the base of the nucleus in which the centriolar complex and proximal portion of the flagellum reside. To stabilize the positional relationship between the nucleus and centriolar complex, while nuclear morphogenesis is taking place, a series of microtubules develop which emanate from the centriolar complex and extend to the nuclear envelope lining the fossa. Buttressing microtubules also develop within the nuclear fossa which both originate and insert along the nuclear envelope. These appear to stabilize nuclear shape prior to the time when chromatin condensation has proceeded to the stage where it could lend structural stability to nuclear form. Microtubules develop only after specific nuclear morphogenic events have taken place. It is therefore concluded that the spermatid nucleus is capable of self-assembly involving microtubules in a supportive role in addition to stabilizing the nuclear-flagellar relationship in G. affinis.The pattern of nuclear fossa-associated microtubules in G. affinis is significantly different from that observed in other poeciliid teleosts indicating a degree of species specificity with regard to both the timing of appearance and total number of microtubules.     

Effects of sublethal exposure to copper on diel activity of sea catfish,Arius felis

The effect of sublethal exposure to copper on the diel activity of sea catfish, Arius felis, was examined after 72 h static exposure to copper (0.0, 0.05, 0.1, or 0.2 mg l^–1 ). The locomotor behavior of 28 individual fish was electronically monitored in a 16-compartment rosette tank. Activity was quantified by the number of entries into compartments per hour. Controls and copper-exposed fish (0.05 mg l^–1) behaved similarly after treatment and displayed no significant effects of handling or copper exposure on diel activity. However, fish exposed to 0.1 and 0.2 mg l^–1 copper were hyperactive immediately following exposure; these fish had significantly greater numbers of entries into compartments per hour for entire 24-h monitoring periods (P < 0.01) and for the 12 h of photophase (P < 0.001) and of scotophase (P < 0.001) than fish in the other two experimental groups. The normal diel activity cycle was abolished. Additionally, exposure of fish to copper at 0.1 and 0.2 mg l^–1 resulted in significantly less variability in activity (P < 0.05) compared to control fish and those exposed to 0.05 mg Cu l^–1.     

Homologous growth hormone (GH) binding in gilthead sea bream (Sparus aurata). Effect of fasting and refeeding on hepatic GH-binding and plasma somatomedin-like immunoreactivity

Specific binding of gilthead sea bream growth hormone (sbGH) to liver membrane preparations was a time and temperature dependent process, and was saturable by increasing amounts of membrane proteins. Scatchard analysis evidenced a single class of high-affinity and lowcapacity binding sites. Ovine prolactin, recombinant tilapia prolactin, carp gonadotropin and chinook salmon gonadotropin did not compete for the¹²⁵I-sbGH binding sites, while recombinant trout GH, bovine GH and human GH displaced iodinated sbGH in a dose dependent-manner. IGF-I-like immunoreactivity was detected after acidification of plasma and removal of IGF-I binding activity. A parallel displacement to the rhIGF-1 standard was observed with extracted plasma samples. Free and total hepatic GH-binding decreased during long-term starvation (3–9 weeks), returning to control values during the refeeding period. Plasma IGF-I-like immunoreactivity showed a similar trend. To our knowledge, this is the first report that indicates a coordinated regulation of GH-binding and plasma somatomedin-like activity in a typical marine fish.     

The fates of zebrafish Hox gene duplicates

In his 1970 book, Susumu Ohno stressed the importance of gene duplication in the evolution of the vertebrate genome and body plan. He elaborated the idea that duplication events provide novel genetic material on which evolution may act. Data are accumulating to show that extensive duplication events, perhaps incorporating the duplication of entire genomes, occurred in the lineage leading to teleost fishes. These duplications may have been pivotal in the explosive radiation of this highly successful vertebrate group. Thus, the teleosts provide us with an ideal opportunity to investigate the fates and functions of duplicated genes. A convenient system for these studies is the zebrafish, Danio rerio, which has become a popular genetic and embryological model.     

Gonadotropin-releasing hormone (GnRH): from fish to mammalian brains

1. This work deals with a family of neuropeptides, gonadotropin-releasing hormone (GnRH), that play a key role in the development and maintenance of reproductive function in vertebrates.2. Until now, a total of 16 GnRH structural variants have been isolated and characterized from vertebrate and protochordate nervous tissue. All vertebrate species already investigated have at least two GnRH forms coexisting in the central nervous system. However, it is now well accepted that three forms of GnRH in early and late evolved bony fishes are present.3. In these cases, cGnRH-II is expressed by midbrain neurons, a species-specific GnRH is present mainly in the preoptic area and the hypothalamus, and sGnRH is localized in the terminal nerve ganglion (TNG). In this context it is possible to think that three GnRH forms and three GnRH receptor (GnRH-R) subtypes are expressed in the central nervous system of a given species.4. Then it is possible to propose three different GnRH lineages expressed by distinct brain areas in vertebrates: (1) the conserved cGnRH-II or mesencephalic lineage; or (2) the hypothalamic or releasing lineage whose primary structure has diverged by point mutations (mGnRH and its orthologous forms: hrGnRH, wfGnRH, cfGnRH, sbGnRH, and pjGnRH); and (3) the telencephalic sGnRH form. Also different GnRH nomenclatures are discussed.