Maturation of mammalian spermatozoa: modifications of the acrosome and plasma membrane leading to fertilization

The mammalian spermatozoon is a terminally differentiated cell. Its surface is covered by a continuous plasma membrane that is divided into distinct domains in which functional molecules are distributed. The acrosome is an internal organelle located at the anterior head and contains hydrolytic enzymes. The anterior acrosome participates in the acrosome reaction, which is an indispensable event during fertilization. These surface domains and the acrosome are formed during spermiogenesis, during which associated molecules are transported and organized. Many of the molecules thus arranged are functionally immature but gradually become mature during epididymal maturation. Some of them are further altered and redistributed during the fertilization process and play various roles. Here, the sequential changes in the acrosome and plasma membrane during spermatozoan maturation are reviewed, particular attention being paid to molecules derived from the testis.     

Functional Compartments During Sporangium Development in the Pteridophyte Cyrtomium falcatum (L.f.) Presl as Expressed in Tapetum Function

Abstract: The tapetum surrounds the developing sporogenous tissue, and therefore is suggested to have an important role during sporogerlesis. In pteridophytes details about tapetum development and function during sporangium development are poorly known. The current article analyses the leptospor-angiate development of the pteridophyte Cyrtomium falcatum in terms of functional compartmentalization related to tapetum function. Morphology, development and localization of different compounds during sporangium development are studied. Dur ing C. falcatum leptosporangiate development phases of initia tion, division, differentiation, and maturation are identified. Functional compartments are distinguished by the presence of a callose culture sac during the division and differentiation phase, and a callose spore sac during the differentiation and ma turation phase.     

A quantitative analysis of mitotic gradients during early development in Calliphora erythrocephala Meig. (Diptera)

Mitotic waves during superficial cleavage and early gastrulation were analyzed quantitatively in Calliphora. Three consecutive patterns are present: (1) a monotonic anterioposterior mitotic gradient during early superficial cleavage; (2) a double mitotic gradient from the anterior and posterior poles during superficial cleavage, especially toward the end of the period; and (3) more complicated patterns with intermediate mitotic centers during the last superficial cleavage division and during early gastrulation. Mitotic gradients are absent in many eggs during early superficial cleavage, but they then become ubiquitous. The gradients are longitudinal; no transverse component was detected before gastrulation. Anterior and posterior gradient patterns are not mirror images of each other; mitotic activity always starts earlier anteriorly. The gradients are accompanied by a pronounced increase in interphase length. The mitotic gradients are compared with the morphogenetic gradients predicted in a current model for pattern specification in insect eggs.     

Sleep and pregnancy

Sleep disturbances are frequent during pregnancy and are currently regarded as one of the most important factors determining pregnancy outcome. Detailed research of sleep features during pregnancy is obviously essential. In the present review recent data concerning changes in sleep structure and regulation in pregnant women and rats - main subjects of experimental sleep research, are given, including surmised mechanisms underlying such changes. The importance of women's sleep integrity preservation during pregnancy for the viability and normal development of the fetus is emphasized and possible ways of pathological influence of sleep disorders during this period are discussed.     

Some aspects of the ecology of the desert snail Sphincterochila prophetarum in relation to energy and water flow

Summary Between 1976–1978, we studied the ecology of the Sphincterochila prophetarum, the most common snail, on stony slopes in Northern Negev. Energy and water flow determinations were made at the individual and population levels on a field observation basis and metabolic data were derived from laboratory simulations.The snails are active during 5–7% of the time during the year, while the remaining 95% of the time, the snails are in aestivation under stones. The energy and water inputs during the short feeding periods are very fast. Only 8% of the total energy in the eaten food are assimilated. Eighty-nine percent of the total assimilated energy are utilized in respiration during the various periods of activity and dormancy.The water loss during the feeding and activity period is about 37% of the total annual input. The snails lose twice as much the amount of water during the winter dormancy periods than in the summer dormancy period.Dedicated to Prof. Evenari and Dr. Springer     

Proteomic analysis of day-night variations in protein levels in the rat pineal gland

The pineal gland secretes the hormone melatonin. This secretion exhibits a circadian rhythm with a zenith during night and a nadir during day. We have performed proteome analysis of the superficial pineal gland in rats during daytime and nighttime. The proteins were extracted and subjected to 2-DE. Of 1747 protein spots revealed by electrophoresis, densitometric analysis showed the up-regulation of 25 proteins during nighttime and of 35 proteins during daytime. Thirty-seven of the proteins were identified by MALDI-TOF MS. The proteins up-regulated during the night are involved in the Krebs cycle, energy transduction, calcium binding, and intracellular transport. During the daytime, enzymes involved in glycolysis, electron transport, and also the Krebs cycle were up-regulated as well as proteins taking part in RNA binding and RNA processing. Our data show a prominent day-night variation of the protein levels in the rat pineal gland. Some proteins are up-regulated during the night concomitant with the melatonin secretion of the gland. Other proteins are up-regulated during the day indicating a pineal metabolism not related to the melatonin synthesis.     

Are spatial memories strengthened in the human hippocampus during slow wave sleep?

In rats, the firing sequences observed in hippocampal ensembles during spatial learning are replayed during subsequent sleep, suggesting a role for posttraining sleep periods in the offline processing of spatial memories. Here, using regional cerebral blood flow measurements, we show that, in humans, hippocampal areas that are activated during route learning in a virtual town are likewise activated during subsequent slow wave sleep. Most importantly, we found that the amount of hippocampal activity expressed during slow wave sleep positively correlates with the improvement of performance in route retrieval on the next day. These findings suggest that learning-dependent modulation in hippocampal activity during human sleep reflects the offline processing of recent episodic and spatial memory traces, which eventually leads to the plastic changes underlying the subsequent improvement in performance.     

Immunity and reproduction during colony foundation in the dampwood termite, Zootermopsis angusticollis

Abstract.  Termite primary reproductives may be exposed to pathogens when dispersing from their parental nest and establishing a new colony. Immunity and reproduction are investigated during colony foundation by implanting a nylon filament into the abdomen of mated and unmated female and male primary reproductives of the dampwood termite Zootermopsis angusticollis. Primary reproductives are paired in combinations of female/male, female/female and male/male and, using confocal microscopy, immune defence is assessed by measuring the degree of encapsulation of nylon implants during three periods of colony foundation: (I) shortly after pairing; (II) during copulation/oocyte maturation; and (III) during oviposition. There are differences in the encapsulation response of mated and unmated termites that are contingent on the period of colony foundation when termites are challenged. Mated females and males have significantly greater encapsulation responses than their unmated counterparts shortly after pairing, perhaps as a prophylactic measure against exposure to disease. The encapsulation response of mated and unmated males does not differ significantly during periods II and III. The onset of oviposition is significantly delayed in mated females that received implants during periods I and II. Mated females have a significantly reduced encapsulation response during the time of copulation and oocyte maturation, but not during oviposition. Overall, males have a significantly greater ability than females to encapsulate a nylon implant. The findings suggest that reproduction can reduce the immune response in female primary reproductives. The results are discussed in light of trade-offs between immunity and reproduction during the critical life-history phase of colony establishment in termites.     

A Three-Dimensional Musculoskeletal Model of the Human Knee Joint. Part 2: Analysis of Ligament Function

A three-dimensional model of the knee is used to study ligament function during anterior-posterior (a-p) draw, axial rotation, and isometric contractions of the extensor and flexor muscles. The geometry of the model bones is based on cadaver data. The contacting surfaces of the femur and tibia are modeled as deformable; those of the femur and patella are assumed to be rigid. Twelve elastic elements are used to describe the geometry and mechanical properties of the cruciate ligaments, the collateral ligaments, and the posterior capsule. The model is actuated by thirteen musculotendinous units, each unit represented as a three-element muscle in series with tendon. The calculations show that the forces applied during a-p draw are substantially different from those applied by the muscles during activity. Principles of knee-ligament function based on the results of in vitro experiments may therefore be overstated. Knee-ligament forces during straight a-p draw are determined solely by the changing geometry of the ligaments relative to the bones: ACL force decreases with increasing flexion during anterior draw because the angle between the ACL and the tibial plateau decreases as knee flexion increases; PCL force increases with increasing flexion during posterior draw because the angle between the PCL and the tibial plateau increases. The pattern of ligament loading during activity is governed by the geometry of the muscles spanning the knee: the resultant force in the ACL during isometric knee extension is determined mainly by the changing orientation of the patellar tendon relative to the tibia in the sagittal plane; the resultant force in the PCL during isometric knee flexion is dominated by the angle at which the hamstrings meet the tibia in the sagittal plane.     

Possible mechanism of the reorganization of the cardiomyocyte plasma membrane in the suslik in the hibernation-arousal-wakefulness cycle

Studies have been made on the ultrastructure of cardiomyocytes during hibernation and arousal of the ground squirrel C. undulatus. It was found that the number of elements of the rough endoplasmic reticulum, Golgi complex, vesicles and ribosomes increases in the perinuclear areas of cardiomyocytes during arousal of animals. These areas are saturated with lipid inclusions and mitochondria. Numerous vesicles and fringed bubbles were found near the plasma membrane which has many caveolae. These findings may indicate the intense metabolism of the membrane material between plasmalemma and cytoplasmic vesicles. Possible mode of rapid reorganization of the sarcolemma and changes in its functional properties during hibernation-arousal stages are suggested. It is concluded that apart from structural and functional properties which are acquired by cells during preparation of animals to hibernation and which exhibit only small changes during the whole period of hibernation, cyclic changes in plasmalemma structure and function occur during arousal of the ground squirrels.     

Haemolymph levels of juvenile hormone,ecdysteroids and protein during the last two larval instars of Locusta migratoria

The radioimmunoassay of ecdysteroids and juvenile hormone has enabled us to relate hormone levels to haemolymph protein concentrations and weight increase during the 4th and 5th instar of the migratory locust. The two hormones are never present in high concentrations in the blood simultaneously. The levels of ecdysteroids are high on the 5th day during the 4th larval stage: they show a small peak on the 3rd day, and then a large peak on the 8th day during the 5th instar. JHI-immunoreactive substances are high during the first 4 days of the 4th instar, and during the first 5 hr during the 5th instar. Protein concentrations in the haemolymph begin to rise when ecdysteroid levels increase during stage 4, and immediately after the small peak (on day 3) in the 4th stage larva. The rise in protein levels is correlated with an increase in weight.     

Small RNAs in early mammalian development: from gametes to gastrulation

Small non-coding RNAs, including microRNAs (miRNAs), endogenous small interfering RNAs (endo-siRNAs) and Piwi-interacting RNAs (piRNAs), play essential roles in mammalian development. The function and timing of expression of these three classes of small RNAs differ greatly. piRNAs are expressed and play a crucial role during male gametogenesis, whereas endo-siRNAs are essential for oocyte meiosis. By contrast, miRNAs are ubiquitously expressed in somatic tissues and function throughout post-implantation development. Surprisingly, however, miRNAs are non-essential during pre-implantation embryonic development and their function is suppressed during oocyte meiosis. Here, we review the roles of small non-coding RNAs during the early stages of mammalian development, from gamete maturation through to gastrulation.     

The Seasonal Succession of Biotic Communities in Wetlands of the Tropical Wet-and-Dry Climatic Zone: I. Physical and Chemical Causes and Biological Effects in the Pantanal of Mato Grosso,Brazil

The tropical wet-and-dry climatic zone is characterized by aquatic environments that cover extensive areas during part of the year and shrink to small standing water bodies or rivers with minimal water levels during the dry seasons. Even in the small permanent water bodies, the conditions fluctuate radically during each annual cycle. While there are often strong currents in the water courses during the high water periods, most aquatic habitats are strictly lentic during the dry seasons. Studies conducted in the Pantanal of Mato Grosso, one of the largest wetlands of the world, revealed major features of changes in physical and chemical parameters during the annual cycle. The general features of the climate include a hot, rainy period usually lasting from late October through late April, a cool, dry period from late April through late August, and a hot, dry period from late August through late October. Considerable year to year variations are encountered in the dates of onset and end of the various seasons, however. Four annual periods are recognized according to the water level in the Pantanal. Generally, the concentrations of dissolved inorganic substances are very low and stable during the high water period and variable and usually high in the remaining standing water bodies when much of the region has dried out. The amount of mineral nutrients increases as the water level rises during the early rainy season but decreases again as the aquatic macrophyte populations develop. Some of the reasons for the many short-term changes in mineral nutrient concentrations and the roles of the various aquatic communities are discussed. The results presented will serve as a basis for subsequent studies on the seasonal succession of the flora and fauna.     

A Three-Dimensional Musculoskeletal Model of the Human Knee Joint. Part 2: Analysis of Ligament Function

A three-dimensional model of the knee is used to study ligament function during anterior-posterior (a-p) draw, axial rotation, and isometric contractions of the extensor and flexor muscles. The geometry of the model bones is based on cadaver data. The contacting surfaces of the femur and tibia are modeled as deformable; those of the femur and patella are assumed to be rigid. Twelve elastic elements are used to describe the geometry and mechanical properties of the cruciate ligaments, the collateral ligaments, and the posterior capsule. The model is actuated by thirteen musculotendinous units, each unit represented as a three-element muscle in series with tendon. The calculations show that the forces applied during a-p draw are substantially different from those applied by the muscles during activity. Principles of knee-ligament function based on the results of in vitro experiments may therefore be overstated. Knee-ligament forces during straight a-p draw are determined solely by the changing geometry of the ligaments relative to the bones: ACL force decreases with increasing flexion during anterior draw because the angle between the ACL and the tibial plateau decreases as knee flexion increases; PCL force increases with increasing flexion during posterior draw because the angle between the PCL and the tibial plateau increases. The pattern of ligament loading during activity is governed by the geometry of the muscles spanning the knee: the resultant force in the ACL during isometric knee extension is determined mainly by the changing orientation of the patellar tendon relative to the tibia in the sagittal plane; the resultant force in the PCL during isometric knee flexion is dominated by the angle at which the hamstrings meet the tibia in the sagittal plane.     

Respiratory-related activity of upper airway muscles in anesthetized rabbit

The electromyographic activity of the glossal, suprahyoid, infrahyoid, and pharyngeal muscles was examined during spontaneous respiration in rabbits anesthetized with ketamine hydrochloride. This activity was then correlated with phases of the respiratory cycle. Our findings indicate that the overwhelming majority of the muscles comprising these groups show activity that increased during inspiration and returns to the background level during expiration and the end-expiratory pause. The exceptions are the inferior pharyngeal constrictor muscle, which demonstrates increased activity during expiration and the end-expiratory pause, and the stylohyoid major and digastric muscles, whose activity was not modulated with respiration. In general, the results obtained under ketamine anesthesia are in agreement with the studies on a more limited number of muscles in humans during sleep or in animal studies utilizing light anesthesia. Furthermore, the use of ketamine avoids the central suppressant effects produced by barbituate anesthesia. It has been argued that the upper airway muscles are rhythmically active during respiration to maintain the patency of the upper airway. Both the number of muscles that are rhythmically active and their strict correlation with specific phases of the respiratory cycle suggest that the forces exerted on the upper airway are complex and that peak tension is generated during inspiration. Further studies are required to evaluate the effects of ketamine anesthesia on these upper airway muscles before this rabbit model can be utilized to examine respiratory disorders of the upper airway.     

Acoustic communication in an electric fish,Pollimyrus isidori (Mormyridae)

It has been known since von Frisch's work in the 1930's that mormyrid electric fishes are quite sensitive to sound. We now describe a repertoire of natural sounds produced by the mormyrid, Pollimyrus isidori, during breeding and aggression; reception of communication sounds is probably a major function for mormyrid audition. In aquaria, Pollimyrus isidori produce 'grunts', 'moans', 'growls', 'pops' and 'hoots' at various phases during nesting, courtship, and territory defense. All five sounds are produced primarily at night. Territorial males produce grunts, moans and growls during courtship. Vocalizing is stimulated by the presence of a gravid female on the male's territory and decreases with the onset of spawning. Hoots and pops are given during agonistic behavior. Grunts are bursts of acoustic pulses, stereotyped for an individual, with the potential as individual signatures. The electric organ is silent during grunts and moans and is discharged at a reduced rate during growls. The courtship and spawning of Pollimyrus isidori is described.     

Reproductive cycles of male and female tuatara (Sphenodon punctatus) on Stephens Island, New Zealand

Cycles in gonadal activity and plasma sex steroid concentrations were investigated in wild female and male tuatara on Stephens Island, New Zealand. Females nest once every four years on average. Vitellogenesis is spread over the first three years, and mating, ovulation and nesting occur in the fourth. Oviducal eggs are carried for6–8 months before nesting. Although the length of this ovarian cycle is unparalleled among oviparous reptiles, the associated cycles in plasma concentrations of sex steroids are similar to those in other reptiles. Mean plasma concentrations of oestradiol increase during vitellogenesis, peak at mating, fall rapidly before or around ovulation, are low during most of gravidity, and rise slightly during late gravidity-nesting. Plasma concentrations of testosterone show a similarcycle. Mean plasma concentrations of progesterone are low during vitellogenesis and peak around ovulation. This periovulatory surge falls within1–2 months, and mean concentrations are low during the final 5–6 months of gravidity. Male tuatara show an annual, pre-nuptial reproductive cycle. Mean plasma concentrations of testosterone are low during winter, rise during spring, peak during midsummer-early autumn, when pre-nuptial displays and mating occur, and fall in mid autumn. Limited histological data indicate that spermiogenesis occurs during midsummer-early autumn, and also support a previous study suggesting that there may be no period of complete testicular and epididymal regression. In comparison with the pre-nuptial cycles of other temperate-zone reptiles, the cycle in male tuatara shows a more prolonged duration of testicular activity and of rising or elevated plasma testosterone concentrations. The prolonged reproductive cycles of male and female tuatara may be adaptations to a temperate environment with cool summers and cool, but not freezing, winters.     

Persistent discontinuities in late replicating DNA during meiosis inLilium

DNA regions of chromosomes that are replicated during zygotene are not ligated to the body of nuclear DNA on completion of replication. The discontinuities are present only in the strands that are synthesized during premeiotic S and they persist through prophase until the interval of chromosome disjunction. The discontinuities are gaps rather than nicks, and must be shielded in vivo from repair activity during pachytene when gaps elsewhere in the DNA are being repaired. The gaps can nevertheless be cured in isolated prophase nuclei in the presence of added polymerase and ligase.     

Seasonal differences in the hormonal control of territorial aggression in free-living European stonechats

In birds, territorial aggression during the breeding season is regulated by testosterone (T). However, many bird species also express aggressive behavior during the nonbreeding season, when plasma levels of T are low. It has been suggested that during this period estrogens might play a major role in regulating territorial aggression. In the present study we compared the effects of simultaneous blockage of androgenic and estrogenic actions on territorial aggression during the breeding and nonbreeding seasons in free-living male European stonechats (Saxicola torquata rubicola). European stonechats are of particular interest since they establish territories and form pairs during both the breeding and the nonbreeding seasons. Thus territorial aggression and its endocrine control can be compared between reproductive and non-reproductive contexts. Inhibition of androgenic and estrogenic actions by simultaneous application of Flutamide and ATD reduced territorial aggression during the breeding season, but not during the nonbreeding season. Our results show that androgens and/or estrogens are involved in the endocrine control of territorial aggression in stonechats only in a reproductive context, but not in a non-reproductive one.     

Membrane fusion proteins are required for oskar mRNA localization in the Drosophila egg chamber

We used a genetic screen in Drosophila to identify mutations which disrupt the localization of oskar mRNA during oogenesis. Based on the hypothesis that some cytoskeletal components which are required during the mitotic divisions will also be required for oskar mRNA localization during oogenesis, we designed the following genetic screen. We screened for P-element insertions in genes which slow down the blastoderm mitotic divisions. A secondary genetic screen was to generate female germ-line clones of these potential cell division cycle genes and to identify those which cause the mislocalization of oskar mRNA. We identified mutations in ter94 which disrupt the localization of oskar mRNA to the posterior pole of the oocyte. Ter94 is a member of the CDC48p/VCP subfamily of AAA proteins which are involved in homotypic fusion of the endoplasmic reticulum during mitosis. Consistent with the function of the yeast ortholog, ter94-mutant egg chambers are defective in the assembly of the endoplasmic reticulum. We tested whether other membrane biosynthesis genes are required for localizing oskar mRNA during oogenesis. We found that ovaries that are mutant for syntaxin-1a, rop, and synaptotagmin are also defective in oskar mRNA localization during oogenesis. We suggest a pathway for the role of membrane assembly proteins on oskar mRNA localization.