Wiley

Fully grown oocytes of the frog (Rana pipiens) undergo cytoplasmic and nuclear maturation when treated with progesterone after the follicular envelopes have been removed. The mechanism of this maturation was investigated by injection of cytoplasm from progesterone‐treated oocytes at various stages of maturation into fully grown but immature oocytes. The injected cytoplasm becomes effective in inducing maturation by 12 hours after progesterone administration, reaches a maximum effectiveness around 20 hours, and then declines after the donor oocytes complete maturation. However, even cytoplasm from early embryos retains some capacity to induce oocyte maturation. The frequency with which maturation is induced is proportional to the volume of the injected cytoplasm. Progesterone itself is not directly responsible for the maturation‐producing effect of injected cytoplasm since injected progesterone does not promote maturation. However, externally applied progesterone does induce the completion of the first meiotic division, presumably by releasing a cytoplasmic “maturation promoting factor.” The production of this cytoplasmic factor was not affected by removal of the nucleus.

After completion of the first meiotic division, oocytes cease further development at the metaphase of the second meiotic division, where they remain until fertilized or activated to develop. Cytoplasm from such secondary oocytes when injected into one of the blastomeres at the two‐cell stage of development suppresses mitosis as well as cleavage. Mitosis is usually arrested at metaphase. No such inhibition was brought about by injection of cytoplasm from cleaving blastomeres. Thus, the arrest of mitosis and cleavage can be attributed to a specific “cytostatic factor” in the cytoplasm of the secondary oocyte. Activation of donor secondary oocytes by insemination or pricking with a glass needle soon destroys the cytostatic factor. Likewise, addition of cortical cytoplasm to endoplasm from the secondary oocyte rapidly destroys the cytostatic capacity. This result implies that cortical material is involved in the process of removing the cytostatic factor at the time of normal activation or fertilization. Enucleation of oocytes demonstrated that production and removal of the cytostatic factor is independent of the nucleus.

The larval shells of the marine bivalves Mercenaria mercenaria and Crassostrea gigas are investigated by polarized light microscopy, infrared spectroscopy, Raman imaging spectroscopy, and scanning electron microscopy. Both species contain similar shell ultrastructures. We show that larval shells contain amorphous calcium carbonate (ACC), in addition to aragonite. The aragonite is much less crystalline than nonbiogenic aragonite. We further show that the initially deposited mineral phase is predominantly ACC that subsequently partially transforms into aragonite. The postset juvenile shell, as well as the adult shell of Mercenaria also contains aragonite that is less crystalline than nonbiogenic aragonite. We conclude that ACC fulfills an important function in mollusc larval shell formation. It is conceivable that ACC may also be involved in adult shell formation. J. Exp. Zool. 293:478–491, 2002. © 2002 Wiley‐Liss, Inc.

Representatives of 30 species of fish were examined for their content of LDH isozymes. One major isozyme system was found in all fish. In addition, two minor systems restricted to eyes and to gonads were found in many fish. Fish may be classified into four groups on the basis of their possession of one, two, three, or five major isozymes of LDH. The major isozyme patterns can be attributed to the polymers of two protein subunits under the control of two genes, as in mammals and birds, but the variety of heteropolymers produced varies in different species. The fluke and other flatfish are exceptional in that they synthesize only one kind of subunit which polymerizes to form a single variety of LDH. All other fish produced at least two major isozymes presumably the homopolymers of A and B subunits. The three‐isozyme fish produce, in addition, a single heteropolymer. A few fish produce three heteropolymers and two homopolymers to produce the characteristic pattern of five isozymes seen in mammals.

In populations of the whiting, which has five major isozymes, two mutant alleles at the B locus were discovered. Each of these alleles produced polypeptides with characteristic electrophoretic mobilities. Consequently, heterozygous individuals contained more than 15 isozymes.

A variety of minor isozymes that appear on zymograms may represent modifications of the major isozymes. However, the minor isozyme systems of the gonad and the eye seem to be genetically distinct molecular systems, separate from and in addition to the major isozyme system.

The secondary active Cl⁻ secretion in seawater (SW) teleost fish gills and elasmobranch rectal gland involves basolateral Na⁺,K⁺‐ATPase and NKCC, apical membrane CFTR anion channels, and a paracellular Na⁺‐selective conductance. In freshwater (FW) teleost gill, the mechanism of NaCl uptake is more controversial and involves apical V‐type H⁺‐ATPase linked to an apical Na⁺ channel, apical Cl⁻–HCO exchange and basolateral Na⁺,K⁺‐ATPase. Ca²⁺ uptake (in FW and SW) is via Ca²⁺ channels in the apical membrane and Ca²⁺‐ATPase in the basolateral membrane. Mainly this transport occurs in mitochondria rich (MR) chloride cells, but there is a role for the pavement cells also. Future research will likely expand in two major directions, molded by methodology: first in physiological genomics of all the transporters, including their expression, trafficking, operation, and regulation at the molecular level, and second in biotelemetry to examine multivariable components in behavioral physiological ecology, thus widening the integration of physiology from the molecular to the environmental levels while deepening understanding at all levels. © 2002 Wiley‐Liss, Inc.

A triple‐stain technique has been developed to score normal acrosome‐reacted human sperm in fixed smears. Live and dead sperm are first differentiated using the vital stain trypan blue. Sperm are then fixed in glutar‐aldehyde, dried onto slides, and the postacrosomal region and acrosome are differentiated using Bismark brown and Rose Bengal. Slides are examined at 1,000 × with a bright‐field microscope and assessed for (1) the percentage of sperm that were alive at the time of fixation and (2) the percentage of sperm that had undergone normal acrosome reactions. Experiments are included that show that trypan blue is a reliable stain for dead sperm and that Rose Bengal stains only sperm having intact acrosomes. This technique may have applications in experimental and clinical studies on sperm capacitation, acrosome reactions, and fertilization in laboratory and domestic animals as well as in man.

In this short review of fish gill morphology we cover some basic gross anatomy as well as in some more detail the microscopic anatomy of the branchial epithelia from representatives of the major extant groups of fishes (Agnathans, Elasmobranchs, and Teleosts). The agnathan hagfishes have primitive gill pouches, while the lampreys have arch‐like gills similar to the higher fishes. In the lampreys and elasmobranchs, the gill filaments are supported by a complete interbranchial septum and water exits via external branchial slits or pores. In contrast, the teleost interbranchial septum is much reduced, leaving the ends of the filaments unattached, and the multiple gill openings are replaced by the single caudal opening of the operculum. The basic functional unit of the gill is the filament, which supports rows of plate‐like lamellae. The lamellae are designed for gas exchange with a large surface area and a thin epithelium surrounding a well‐vascularized core of pillar cell capillaries. The lamellae are positioned for the blood flow to be counter‐current to the water flow over the gills. Despite marked differences in the gross anatomy of the gill among the various groups, the cellular constituents of the epithelium are remarkably similar. The lamellar gas‐exchange surface is covered by squamous pavement cells, while large, mitochondria‐rich, ionocytes and mucocytes are found in greatest frequency in the filament epithelium. Demands for ionoregulation can often upset this balance. There has been much study of the structure and function of the branchial mitochondria‐rich cells. These cells are generally characterized by a high mitochondrial density and an amplification of the basolateral membrane through folding or the presence of an intracellular tubular system. Morphological subtypes of MRCs as well as some methods of MRC detection are discussed. © 2002 Wiley‐Liss, Inc.

Half of the 22 extant crocodilians show evidence of temperature‐dependent sex determination (TSD). We examine evidence for TSD in 11 species by reviewing reports on five and presenting new data for six. The female‐male pattern (FM; females at low temperature, males at high temperature) attributed to Alligator mississippiensis and Caiman crocodilus are here revised to be female‐male‐female (FMF; males at intermediate temperature, females at low and high temperatures). A similar pattern characterizes Crocodylus palustris, C. moreletii, C. siamensis, and Gavialis gangeticus based on new data; published accounts establish a FMF pattern in Crocodylus porosus, C. johnstoni, and C. niloticus. TSD apparently occurs in Paleosuchus trigonatus and Alligator sinensis, but patterns are not yet documented. In the well‐studied species, the incubation temperatures for FM transitions are congruent, but MF transition temperatures differ among species. In A. mississippiensis, 100% males are produced over a range of constant incubation temperatures, whereas in C. johnstoni, only low proportions of males are produced at any constant temperature.

The thermosensitive period (TSP) for A. mississippiensis occurs during stages 21 to 24 (days 30–45 at intermediate temperatures) and coincides with gonadal differentiation. A similar scenario is suggested in other species. The TSP in A. mississippiensis (and possibly other crocodilians) encompasses the third quarter of development and occurs later than in turtles and a lizard. In A. mississippiensis as in turtles, the duration (cumulative effect) and/or the magnitude (potency effect) of incubation temperatures during the TSP predictably alter sex ratios. TSP chronologies and features which are shared among TSD reptiles suggest common, underlying mechanisms; A. mississippiensis is an appropriate model for further study. In crocodilians, clutch effects are a significant source of variation in TSD response. Hatchling sex ratios previously reported for A. mississippiensis are reconsidered in light of our new data. © 1994 Wiley‐Liss, Inc.

Among reptiles that show temperature‐dependent sex determination, sex ratios vary across constant incubation temperatures in ways sufficiently predictable to allow classification into patterns. One common pattern shows low temperatures yielding only males and high temperatures yielding only females. Another common pattern has low as well as high temperatures yielding only or mostly females and some intermediate temperatures yielding mostly males. Patterns tend to be associated with the direction of sexual dimorphism in adult size, especially for species with strong dimorphism.

Pivotal temperatures (those yielding 1:1 sex ratios) within the best‐documented species and genera tend to increase with both latitude and longitude across central and southern North America. These geographic trends probably reflect factors that affect nest temperatures (duration of growing season, insolation, and prevailing amounts of shading by vegetation).

Data from a population of the alligator snapping turtle (Macroclemys temminckii) suggest that some embryos are temperature‐independent females because these individuals become females even when they are shifted among male‐producing temperatures during development. These individuals are also more frequent in clutches of small eggs. In this and several other species, no constant incubation temperatures yield more than 75% males. © 1994 Wiley‐Liss, Inc.