Laser scanning fluorescence microscopic measurement of the movement of cleaving egg surface of Rana Amurensis

By laser scanning fluorescence microscopy for quantitative measurement of fluorescence intensity changes on egg surface stained with fluorescein isothiocyanate during cleavage furrow extending forward,it was found that in area of presumptive cleavage furrow the scanning curve became ∨ shape,indicating dark stripe appeared in that place.Then the fluorescence intensity increased at the place where the bottom of ∨ shape had located,and the scanning curve turned to ∧ shape,indicating single stripe was formed.While enhanced fluorescence appeared on the borders of ∧ shape,an M shape curve was found,showing double stripe occurred.During the distance between two borders of M shape incresing from 50μm to 100μm,a fluorescence peak came to sight in the middle of the M shape,which being the cleavge furrow bottom.The two lateral sides of furrow bottom with decreasing fluorescence were nascent membrane.At that time the curve became W shape.By the sides of cleavage furrow the the stress folds became conspicous after double stripe stage,showing the stretching of the egg surface being increased.With our[31,33]and others[32] reports that polylysine could induce the appearance of nascent membrane and phytohemagglutinins could decrease or prevent the appearance of nascent membrane,we believed the idea of Schroeder[25] that increasing mechanical stress could initiate nascent membrane formation and thought that the stresslay to the outsides of cleavage furrow.     

Modeling the cuckoo’s brood parasitic behavior in the presence of egg polymorphism

The common cuckoo Cuculus canorus is a brood parasite that utilizes many host species. These have evolved defense against parasitism to reject cuckoo eggs that look unlike their own and some cuckoos have evolved egg mimicry to counter this defense. Egg phenotype indeed plays a key role for both the cuckoo and its hosts to successfully reproduce. It has been argued that cuckoos should parasitize host nests where egg phenotype matches because this makes parasitism more successful. Details of the cuckoo’s parasitic behavior, however, largely remains unknown if they really parasitize hosts depending on “egg matching”. In this paper, we model a time sequence of parasitic events in which a cuckoo finds host nests and decides to parasitize them or not in the presence of egg polymorphism. We evaluate which strategy is optimal: (1) opportunistic parasitism where cuckoos parasitize hosts irrespective of the phenotype, or (2) non-opportunistic parasitism where cuckoos parasitize hosts where egg phenotype matches. The analysis showed that either of the two strategies can be optimal. Factors not considered in the model, e.g., ecological and evolutionary changes both in the cuckoo and the host side, are discussed to explain apparent contrasts observed in some cuckoo–host interactions.     

Could the egg itself be the source of the oviposition deterrent marker in the ectoparasitoid Dinarmus basalis?

Females of Dinarmus basalis, a solitary ectoparasitoid, strongly avoid superparasitising hosts bearing eggs which are 20 or more hours old. Our objective was to determine the mechanism by which the factors inducing host discrimination and such an oviposition deterring effect act, and the origin of the deterrent. This study showed that the information is carried by the parasitised host. It is acquired by a transfer of molecules from the wasp egg onto the host and it requires contact between egg and host for at least 4 h. The factors transferred do not, as commonly reported in other species, come from the female's genital apparatus but from the live egg itself. Consequently, the D. basalis egg directly participates in the success of parasitism by releasing factors which elicit the oviposition host deterring effect. The originality and the ecological importance of these results are discussed.     

Is there a role for the Ca influx during fertilization of the sea urchin egg?

Both isotopic and microelectrode studies reveal a significant Ca²⁺ influx at fertilization which if freely distributed in the cytoplasm would equal 1–2 × 10⁻⁵ M. The role, if any, of this influx is disputed. We have attempted to reevaluate contradictory findings by others on this role. Our results with Strongylocentrotus purpuratus and Lytechinus pictus eggs, assessing fertilization with acrosome-reacted sperm in EGTA-buffered media (free [Ca²⁺], 4.4 × 10⁻⁸ M) indicate that exogenous Ca²⁺ is not required for fertilization and subsequent cleavage. The contradictory findings by others may have resulted from reduced fertilizability in Ca²⁺-free seawater, which can be circumvented by higher sperm concentration and by a sensitivity to temperature in Ca²⁺-free medium, which can be bypassed by carrying out fertilization at lower temperature. Also consistent with the absence of a requirement for this Ca²⁺ influx, we found that Ca²⁺ uptake can be induced in eggs by depolarizing the membrane with high [K⁺], but there is no resultant activation of egg metabolism. Under our conditions for fertilization in Ca²⁺-free media, there is no effect on the block to polyspermy but the initiation of the cortical reaction may be delayed. The data support the hypothesis that sperm induce release of Ca²⁺ from intracellular stores, perhaps by affecting an equilibrium between Ca²⁺ sequestration and Ca²⁺ release.     

Differential investment in the Banggai cardinalfish: can females adjust egg size close to egg maturation to match the attractiveness of a new partner?

To test whether females can change their egg investment according to the different attractiveness (  i.e . size as measured by standard length, L _s) of a new mate after eggs have already matured in response to an earlier mate, female Banggai cardinalfish Pterapogon kauderni were first allowed to produce eggs for small (unattractive) or large (attractive) males. Then, when spawning was initiated, but prior to actual spawning, their partner was switched to either a significantly larger or a significantly smaller partner, respectively. A strong positive correlation between egg size and days until spawning with the second male was found for the females initially paired to a small and then a large male. Within a few days, these females apparently increased their egg size to match the attractiveness of their new male. No correlation between days until spawning and egg size in females initially paired to a large and then a small male, however was found, so apparently females were unable to adjust egg size in response to a decrease in mate attractiveness. Consequently, it is suggested that females can increase their egg size investment even after the onset of egg maturation and that this change can be quite rapid.     

Exosomes and retroviruses: the chicken or the egg?

Retroviruses appropriate pre‐existing cellular machineries to propagate. In the last decade, impressive similarities have been observed in the generation and dissemination in the host cells of retroviruses and small cellular vesicles known as exosomes. These cellular vesicles are thought to facilitate intercellular communication processes and mediate immune functions. However, their link to the retroviral life cycle has given rise to distinct hypotheses and puzzling dilemmas. Are exosomes the antecessors of retroviruses or do retroviruses merely exploit the same cellular machinery designated for exosome biosynthesis? Here, we address these fascinating evolutionary questions by reviewing recent discoveries and analysing the controversies surrounding them.     

Intrinsic chiral properties of the Xenopus egg cortex: an early indicator of left-right asymmetry?

Vertebrate embryos define an anatomic plane of bilateral symmetry by establishing rudimentary anteroposterior and dorsoventral (DV) axes. A left-right (LR) axis also emerges, presaging eventual morphological asymmetries of the heart and other viscera. In the radially symmetric egg of Xenopus laevis, the earliest steps in DV axis determination are driven by microtubule-dependent localization of maternal components toward the prospective dorsal side. LR axis determination is linked in time to this DV-determining process, but the earliest steps are unclear. Significantly, no cytoskeletal polarization has been identified in early embryos capable of lateral displacement of maternal components. Cleaving Xenopus embryos and parthenogenetically activated eggs treated with 2,3-butanedione monoxime (BDM) undergo a dramatic large-scale torsion, with the cortex of the animal hemisphere shearing in an exclusively counterclockwise direction past the vegetal cortex. Long actin fibers develop in a shear zone paralleling the equator. Drug experiments indicate that the actin is not organized by microtubules, and depends on the reorganization of preexisting f-actin fibers rather than new actin polymerization. The invariant chirality of this drug response suggests a maternally inherited, microfilament-dependent organization within the egg cortex that could play an early role in LR axis determination during the first cell cycle. Consistent with this hypothesis, brief disruption of cortical actin during the first cell cycle randomizes the LR orientation of tadpole heart and gut.     

Do cuckoos choose nests of great reed warblers on the basis of host egg appearance?

Prevailing theory assumes cuckoos lay at random among host nests within a population, although it has been suggested that cuckoos could choose large nests and relatively active pairs within host populations. We tested the hypothesis that egg matching could be improved by cuckoos choosing nests in which host eggs more closely match their own, by assessing matching and monitoring nest fate in great reed warblers naturally or experimentally parasitized by eggs of European cuckoos. A positive correlation between cuckoo and host egg visual features suggests that cuckoos do not lay at random within a population, but choose nests and this improves egg matching: naturally parasitized cuckoo eggs were more similar to host eggs as perceived by humans and as measured by spectrophotometry. Our results suggest a hitherto overlooked step in cuckoo-host evolutionary arms races, and have nontrivial implications for the common experimental practice of artificially parasitizing clutches.     

A study on the interaction of the amyloid fibrils of α-synuclein and hen egg white lysozyme with biological membranes

Alpha-synuclein (α-syn) aggregation and mitochondrial dysfunction are considered as two of the main factors associated with Parkinson's disease (PD). In the present investigation, the effectiveness of the amyloid fibrils obtained from α-syn with those of hen egg white lysozyme (HEWL), as disease-related and-unrelated proteins, to damage rat brain and rat liver mitochondria have been investigated. This was extended by looking at SH-SY5Y human neuroblastoma cells and erythrocytes, thereby investigating the significance of structural characteristics of amyloid fibrils related to their interactions with biomembranes obtained from various sources. Results presented clearly demonstrate substantial differences in the response of tested biomembranes to toxicity induced by α-syn/HEWL amyloid fibrils, highlighting a structure-function relationship. We found that fibrillar aggregates of α-syn, but not HEWL, caused a significant increase in mitochondrial ROS, loss of membrane potential, and mitochondrial swelling, in a dose-dependent manner. Toxicity was found to be more pronounced in brain mitochondria, as compared to liver mitochondria. For SH-SY5Y cells and erythrocytes, however, both α-syn and HEWL amyloid fibrils showed the capacity to induce toxicity. Taken together, these results may suggest selective toxicity of α-syn amyloid fibrils to mitochondria mediated likely by their direct interaction with the outer mitochondrial membrane, indicating a correlation between specific structural characteristics of α-syn fibrils and an organelle strongly implicated in PD pathology.     

Mammalian development: Axes in the egg?

An enduring but erroneous belief is that the post-fertilisation period is irrelevant for axis development in mammals. Two recent studies further undermine this belief. Is information for axial developmental encoded in the egg cortex?     

The serpent and the egg: unidirectional evolution of reproductive mode in vipers?

Dollo’s law, that complex characters are not regained in evolution, is a pattern applied to many systems. Recent work has evaluated unidirectional evolution in a number of contexts, and several violations of this law have been documented. These methods have also been criticized for potentially overestimating reversals. We test the hypothesis that the ancestral reproductive mode of oviparity can be regained in vipers, in opposition to Dollo’s law. We use model comparison and ancestral character state reconstruction methods that address recent criticisms, and find evidence both supporting and refuting Dollo’s predictions from different analyses. We discuss our results in the context of unidirectional evolution and review factors required for strong inference of violations of Dollo’s law.     

Somatic mutations in mitochondria: the chicken or the egg?

Somatic mutations of mitochondrial DNA have been detected in various pathologies such as cancer, neurodegenerative diseases, cardiac disorders and aging in general. Now it has been found that patients with rheumatoid arthritis also have a higher incidence of mitochondrial mutations in synoviocytes and synovial tissue compared with patients with osteoarthritis. Furthermore, it has been shown that these mutations possibly result in changed peptides that are presented by major histocompatibility complex II and thus might be recognized as non-self by the immune system. Further studies will show whether these mutations are actually able to trigger autoimmune inflammation in rheumatoid arthritis or whether they must be considered epiphenomena of cellular damage in chronic inflammation.     

Uncommon mechanism of egg incubation in the endemic Southern hermit crab Loxopagurus loxochelis: how is this phenomenon related to egg production?

The aim of the present work was to characterize the egg production of Loxopagurus loxochelis. A total of 71 ovigerous females were obtained, 28% of which were simultaneously incubating eggs at different developmental stages. This phenomenon can be the result of incomplete fertilization, or may represent a rapid gonadal cycle by this species in this area, which is, to our understanding, the best explanation of this phenomenon. Egg volume decreased 25.6% during the incubation period. The reproductive output based on dry and wet weight was 6.8 and 19.3%, respectively. Water was the prevailing component of the eggs, representing 86.0% of the total weight at initial stage, increasing to 95.1% at the final stage. Ash content increased at the same time as a decrease in the organic content occurred, indicating the consumption of yolk and absorption of salts from the water medium. In conclusion, we hypothesized that this population has the capacity to copulate and deposit another brood even before the release of the larvae from the previous one, intensifying the reproductive effort of these hermit crabs as a strategy of adaptation in a region considered the northern limit of the geographical distribution of this species.     

Getting rid of the cuckoo Cuculus canorus egg: why do hosts delay rejection?

Egg discrimination is well documented in many hosts of avianbrood parasites, but the proximate mechanisms of egg recognitionand rejection decisions are poorly understood. Relevant in thisrespect is the observation that rejectors of parasite eggs oftendelay their response. This delay has implications for understandingmechanisms important for egg recognition and is the main focusof the present study. We investigated experimentally the relativeeffects of egg mimicry and eggshell strength of common cuckooCuculus canorus eggs on the delay in rejection in marsh warblersAcrocephalus palustris. In addition, by video recording hostresponses, we elucidate the proximate mechanisms behind thedelayed rejections. Host nests were experimentally parasitizedwith 3 types of real eggs differing in mimicry and/or eggshellstrength. Both egg mimicry and eggshell strength significantlyaffected the time to rejection, but the effect of mimicry wasdominant. The delayed rejection of mimetic eggs was explainedby the existence of latency to the release of rejection behaviorbecause of recognition problems. Second, when rejection responsetowards mimetic eggs was initiated, it was less intense comparedwith hosts experiencing nonmimetic eggs. Our results are consistentwith the hypothesis that host motivation when confronted withmimetic eggs needs to increase above a certain threshold beforerejection behavior is released, which likely minimizes the riskof recognition errors. An additional component of the delayin rejection as shown by hosts facing nonmimetic eggs was theseemingly inefficient host rejection behavior, probably reflectinglack of previous experience.     

Panic attacks and supraventricular tachycardias: the chicken or the egg?

Panic attacks occur in about 2 % of the population. Symptoms include a racing or pounding heart beat, chest pain, dizziness, light-headedness, nausea, difficulty in breathing, tingling or numbness in the hands, flushes or chills, dreamlike sensations or perceptual distortions. The symptoms of paroxysmal supraventricular tachycardia (PSVT) may be similar. A PSVT is often difficult to document on the ECG since it has often ceased before the patient comes to medical attention. Besides, a tachycardia may still be present and even be documented but interpreted as a phenomenon secondary to the panic attack. In addition, ECG abnormalities between episodes can often not be identified. The evidence that in some patients paroxysmal SVT is the cause, but not the consequence of a panic attack, is based on observations that catheter ablation was able to cure patients presenting with panic disorders. To better establish the prevalence of SVT as the underlying mechanism of a panic attack, there is a need for prospective studies and/or registries. Whereas gastric ulcer has in some patients changed from a psychosomatic disorder to an infectious disease, we may hypothesise that a certain proportion of panic disorders may mutate into an underlying arrhythmia rather than a primary psychiatric disorder.     

Is juvenile hormone involved in the maternal regulation of egg size and progeny characteristics in the desert locust?

The role of juvenile hormone (JH) in the maternal regulation of progeny characteristics was examined in the desert locust, Schistocerca gregaria. Female adults of this species are known to produce smaller but more eggs when reared in isolation than do those reared in a group. Eggs laid by isolated females develop green hatchlings typical of solitarious forms, whereas those laid by the latter produce black hatchlings typical of gregarious forms. Topical application of a juvenile hormone analog (JHA), fenoxycarb, or implantation of corpora allata (CA) taken from the migratory locust, Locusta migratoria, caused crowded S. gregaria females to deposit smaller eggs, but did not have a significant effect on the number of eggs per egg pod except at high doses of JHA. The production of smaller eggs by treated and untreated crowded females was closely associated with earlier deposition of the egg pods and shorter oviposition intervals. However, neither JHA application nor CA implantation influenced the progeny characteristics in actively reproducing aged females under crowded conditions, while untreated control females started producing smaller and more eggs upon transfer to isolated conditions. These results may suggest that JH is not directly involved in the maternal regulation of phase-dependent progeny characteristics.