Egg Envelope Research Articles

Some Data on Reproductive Biology of Spotted Ghoul Inimicus sinensis (Synanceiidae)

Gonadal structure, cytological condition of oocytes, ultrastructure of egg envelope, and spermatozoa morphology are studied in the individuals of Inimicus sinensis 120–230 mm TL with the gonads mainly at maturity stage IV. The males possess hypertrophied urinary bladders. Based on oocytes’ size distribution in the ovaries, the oogenesis is continuous and the spawning is multiple. Oocytes of the maturation period are 600–700 µm in diameter. The batch fecundity is 15 380 oocytes on average. The zona radiata of oocytes that have completed growth is 10.2 µm in width on average and it consists of two layers. The narrow outermost layer of the egg envelope approximately 0.34 µm width is most likely chorion. Spermatozoon ultrastructure of I. sinensis does not notably differ from that in other representatives of the suborder Scorpaenoidei with external insemination. The centriolar complex is characterized by orthogonal position of centrioles. Based on ovarian structure, the representatives of the genus Inimicus do not differ from the majority of teleost fishes and viviparous species of the genera Sebastes and Sebastiscus. However, many representatives of the suborder Scorpaenoidei have unique ovarian structure with the central ovigerous stroma attached to the anterior part of the ovary. Based on the current phylogenetic schemes, this ovarian type evolved independently in several evolutionary lineages.

Ovocidal action of glutaraldehyde and benzalkonium chloride mixture on Aonchotheca bovis (Nematoda, Capillariidae) embryogenesis

Deinvasion, aimed at elimination of environmental exogenic stages of invasion agents and avoidance of their invasion to host organism, occupies an important place in the complex of sanitary and prophylactic activities against animal helminthosis diseases. Application of glutaraldehyde and benzalkonium chloride at vital activity and embryogenesis of Aonchotheca bovis (Schnyder, 1906) obtained from nematode female gonads was investigated with different concentration and exposures. Two test-cultures were used in the experiment. The first culture contained non-invasive eggs of A. bovis, the second contained invasive ones, obtained by the laboratory culturing of gonadic eggs until mobile larva maturing. It was established that glutaraldehyde and benzalkonium chloride mixture has a deinvasive capacity against A. bovis eggs, parasitizing on sheep. Ovocidal efficiency indexes appeared higher with use of the test culture against the non-invasive capillaria eggs’ test-culture. So, the high level of ovocidal efficiency of glutaraldehyde and benzalkonium chloride mixture against non-invasive A. bovis eggs culture was established at the concentration of 0.5% and exposure of 10–60 min (93.6–100.0%), and against the invasive A. bovis egg culture – at the concentration of 0.5% and exposure of 30 and 60 min (90.3–94.6%) and 1.0% at all exposures (100.0%). Ovocidal activity of the examined mixture was accompanied by specific morphological changes of nematode eggs structure. Destruction of the egg envelope, embryo loosening and decay and its dissolution were observed. Such changes are proved by metric indexes of width and length of capillaria eggs, envelope thickness and cap length, indicating the violation of embryogenesis of A. bovis. Thus, glutaraldehyde and benzalkonium chloride mixture of 1.0% concentration is a promising deinvasive agent suitable for effective fight against and prophylaxis of sheep-breeding nematodosis.

Mammalian egg coat modifications and the block to polyspermy.

Fertilization by more than one sperm causes polyploidy, a condition that is generally lethal to the embryo in the majority of animal species. To prevent this occurrence, eggs have developed a series of mechanisms that block polyspermy at the level of the plasma membrane or their extracellular coat. In this review, we first introduce the mammalian egg coat, the zona pellucida (ZP), and summarize what is currently known about its composition, structure, and biological functions. We then describe how this specialized extracellular matrix is modified by the contents of cortical granules (CG), secretory organelles that are exocytosed by the egg after gamete fusion. This process releases proteases, glycosidases, lectins and zinc onto the ZP, resulting in a series of changes in the properties of the egg coat that are collectively referred to as hardening. By drawing parallels with comparable modifications of the vitelline envelope of nonmammalian eggs, we discuss how CG‐dependent modifications of the ZP are thought to contribute to the block to polyspermy. Moreover, we argue for the importance of obtaining more information on the architecture of the ZP, as well as systematically investigating the many facets of ZP hardening.

Ultrastructure of the fertilized egg envelopes in Hemigrammus erythrozonus, Characidae, Teleostei

We examined the morphology and ultrastructures of fertilized egg envelopes of glowlight tetra (Hemigrammus erythrozonus) belong to Characidae using light and electron microscopes.The fertilized eggs were spherical, transparent, demersal, adhesive, and have no oil droplet. The perivitelline space was well-developed and the micropyle was surrounded by 15–20 uplifted lines of egg envelope in a spoke like pattern. The outer surface of egg envelope was rough side with grooves. Also, the total thickness of the fertilized egg envelope was about 2.1–2.3 μm, and the fertilized egg envelope consisted of two layers, an outer adhesive electron-dense layer with grooves and three feather-like lamellae layers. Collectively, these morphological characteristics of fertilized egg and micropyle with spoke-like structure showed family Characidae specificity, and ultrastructures of outer surface and section of fertilized egg envelope showed species specificity.

Conjoined twins in Aegla uruguayana Schmitt, 1942 (Decapoda: Anomura: Aeglidae)

AbstractThe first instance of a pair of conjoined embryos in Aegla uruguayanaSchmitt, 1942 is reported. Collected in a stream in Entre Ríos province, Argentina, the embryos were detected among 550 eggs containing embryos with normal morphological development, and constitute the second observed case of twins in AeglaLeach, 1820. The twins were joined together by their dorsum and lived for a few days in the laboratory; however, they did not hatch, dying inside the egg envelope.

Ultrastructural Studies of Oogenesis in the Fern Diplopterygium glaucum

The present investigation examines the oogenesis of the gleichenioid fern, Diplopterygium glaucum (Thunb. ex Houtt.) Nakai using transmission electron microscopy. The results demonstrate that the oogenesis of D. glaucum is similar to the core leptosporangiate ferns. The egg cell of D. glaucum was progressively isolated from the adjacent cells by forming a separation cavity and an egg envelope during maturation. However, during this process, a pore region consistently connected the egg and the ventral canal cell. Ultimately, a fertilization pore formed at the pore region when the egg matured. The nucleus produced conspicuous evaginations during later stages of egg development. The cytological features during oogenesis in D. glaucum more closely resembled the core leptosporangiate ferns rather than the basal leptosporangiate ferns (Lygodium and Osmunda), which possess no egg envelope or fertilization pore. The results provide new characteristics for interpreting the evolutionary history of the gleichenioid ferns.

Annual killifish: an approach to the choriogenins of Austrolebias charrua egg envelope

Annual killifish are freshwater teleosts that have a short lifespan and inhabit shallow temporal ponds in regions of the Americas and Africa. During the dry season, adults die while embryos survive by being buried in the bottom mud and hatching during the next rainy season. Juveniles reach sexual maturity within few weeks. Hence, species survival is entirely embryo-dependent, and killifish exhibit a set of unique developmental features. Epiboly is temporarily and spatially detached from axis formation (dispersion-reaggregation phase) and embryos undergo reversible arrests or diapauses. Furthermore, the egg envelope is a notably strong structure and protects the embryos during the long development that they undergo. The present study reports the identification and characterization of two egg envelope proteins and the involved genes, achzpL and achzpH, both expressed in the liver under hormone regulation. This study’s results help to elucidate the function of the embryo egg envelope. Moreover, the oestrogen-regulated liver expression of these genes allows us to suggest components of the annual killifish egg envelope as possible biomarkers to monitor water contamination.

Male parental assistance in embryo hatching of barred-chin blenny Rhabdoblennius nitidus.

Most teleostean embryos develop and hatch without parental assistance, though some receive parental care. We focused on a paternal brood-care species, the barred-chin blenny (Rhabdoblennius nitidus [Günther, 1861]). As hatching approached, fanning behavior by the male parent drastically increased and then embryos hatch. In the absence of the male parent, most embryos failed to hatch. However, the hatching rate was greatly assisted by introducing an artificial water current, suggesting that paternal assistance other than for aeration is required for successful embryo hatching. Next, we analyzed genes for the hatching enzyme and egg-envelope protein, which were successfully cloned from barred-chin blenny, and found the expression patterns differed from those of other euteleosts. Generally, high choriolytic enzyme swells the intact egg envelope, and then low choriolytic enzyme solubilizes the swollen envelope. The expression levels of both the enzymes, but especially the latter, were much lower in barred-chin blenny that is known in most other oviparous species. In addition, the main component of the egg envelope was changed into ChgHm and choriogenin L (ChgL) in barred-chin blenny, whereas ChgH and ChgL for other euteleosts. These in barred-chin blenny would result in ineffective egg-envelope digestion because the posthatching egg envelopes were observed to be swollen but not solubilized. Male parental assistance by fanning until hatching may compensate for this insufficiency. Our study illustrates an example of the evolution of parent-embryo interaction built on a novel relationship: Degradation of the hatching enzyme/egg-envelope digestion system, accompanied by male parental hatching assistance.

Previtellogenic oocytes of South African largemouth bass Micropterus salmoides Lacépède 1802 (Actinopterygii, Perciformes) - the Balbiani body, cortical alveoli and developing eggshell.

The ovaries of the largemouth bass Micropterus salmoides, an alien and invasive species in South Africa, contain a germinal epithelium which consists of germline and somatic cells, as well as previtellogenic and late vitellogenic ovarian follicles. The ovarian follicle consists of an oocyte surrounded by follicular cells and a basal lamina; thecal cells adjacent to this lamina are covered by an extracellular matrix. In this article, we describe the Balbiani body and the polarization and ultrastructure of the cytoplasm (ooplasm) in previtellogenic oocytes. The nucleoplasm in all examined oocytes contains lampbrush chromosomes, nuclear bodies and several nucleoli near the nuclear envelope. The ultrastructure of the nucleoli is described. Numerous nuage aggregations are present in the perinuclear cytoplasm in germline cells as well as in the ooplasm. Possible roles of these aggregations are discussed. The ooplasm contains the Balbiani body, which defines the future vegetal region in early previtellogenic oocytes. It is comprised of nuage aggregations, rough endoplasmic reticulum, Golgi apparatus, mitochondria, complexes of mitochondria with nuage-like material, and lysosome-like organelles. In mid-previtellogenic oocytes, the Balbiani body surrounds the nucleus and later disperses in the ooplasm. The lysosome-like organelles fuse and transform into vesicles containing material which is highly electron dense. As a result of the fusion of the vesicles of Golgi and rough endoplasmic reticulum, the cortical alveoli arise and distribute uniformly throughout the ooplasm of late previtellogenic oocytes. During this stage, the deposition of the eggshell (zona radiata) begins. The eggshell is penetrated by canals containing microvilli and consists of the following: the internal and the external egg envelope. In the external envelope three sublayers can be distinguished.

Embryonic and Larval Development and Some Reproductive-Biology Features of Dendrochirus zebra (Scorpaenidae)

Embryonic and larval development of zebra turkeyfish Dendrochirus zebra is described to the transition of the larvae to exogenous feeding. Mature sex products are obtained after double hormonal injections of the fish. A detailed, illustrated morphological description of developmental stages is presented. The changes of body pigmentation and number of muscular segments after hatching of the embryo from the egg envelope are recorded. Fertilized eggs are characterized by slightly irregular spherical shape; narrow perivitelline space; smooth, transparent, and unstructured egg envelope; and homogenous, transparent, and colorless yolk ~0.79 (0.74−0.81) mm in diameter. A single lipid droplet 0.15 (0.146−0.153) mm in diameter is located in the yolk. The droplet is colorless or with a yellowish pink tinge. The duration of the cellular cycle during the period of synchronous cleavage is approximately 27 min, and the duration of the incubation period is 25.5 h. At hatching, the prelarvae body length is 1.6–1.7 mm. The transition of the larvae to the exogenous feeding occurs at 2.33–2.42 mm body length by the fifth day after hatching.

Analysis of sperm chemotaxis.

In many species, sperm must locate the female gamete to achieve fertilization. Molecules diffusing from the egg envelope, or the female genital tract, guide the sperm toward the oocyte through a process called chemotaxis. Sperm chemotaxis has been studied for more than 100 years being a widespread phenomenon present from lower plants to mammals. This process has been mostly studied in external fertilizers where gametes undergo a significant dilution, as compared to internal fertilizers where the encounter is more defined by the topology of the female tract and only a small fraction of sperm appear to chemotactically respond. Here, we summarize the main methods to measure sperm swimming responses to a chemoattractant, both in populations and in individual sperm. We discuss a novel chemotactic index (CI) to score sperm chemotaxis in external fertilizers having circular trajectories. This CI is based on the sperm progressive displacement and its orientation angle to the chemoattractant source.

The Molecular Mechanisms of Gametic Incompatibility in Invertebrates.

Fertilization (gamete fusion followed by zygote formation) is a multistage process. Each stage is mediated by ligand-receptor recognition of gamete interaction molecules. This recognition includes the movement of sperm in the gradient of egg chemoattractants, destruction of the egg envelope by acrosomal proteins, etc. Gametic incompatibility is one of the mechanisms of reproductive isolation. It is based on species-specific molecular interactions that prevent heterospecific fertilization. Although gametic incompatibility may occur in any sexually reproducing organism, it has been studied only in a few model species. Gamete interactions in different taxa involve generally similar processes, but they often employ non-homologous molecules. Gamete recognition proteins evolve rapidly, like immunity proteins, and include many taxon-specific families. In fact, recently appeared proteins particularly contribute to reproductive isolation via gametic incompatibility. Thus, we can assume a multiple, independent origin of this type of reproductive isolation throughout animal evolution. Gametic incompatibility can be achieved at any fertilization stage and entails different consequences at different taxonomic levels and ranges, from complete incompatibility between closely related species to partial incompatibility between distantly related taxa.

Morphogenesis of serial abdominal outgrowths during development of the viviparous dermapteran, Arixenia esau (Insecta, Dermaptera)

The embryos and first instar larvae of the epizoic earwig, Arixenia esau, develop sequentially in two different compartments of the female reproductive system, that is ovarian follicles and the lateral oviducts (the uterus). Here we show that the second (intrauterine) phase of development consists of three physiologically disparate stages: early embryos (before dorsal closure, surrounded by an egg envelope), late embryos (after dorsal closure, surrounded by an egg envelope) and the first instar larvae (after “hatching” from an egg envelope). Early and late embryos float in the fluid filling the uterus, whereas the first instar larvae develop attached to the uterus wall. Our analyses revealed also that in Arixenia serial multilobed outgrowths develop on dorso-lateral aspects of all abdominal segments. At the onset of the third developmental stage and after liberation from an egg envelope, these outgrowths (or more precisely their lobes) adhere to the epithelium lining the uterus, forming a series of small contact sites, where the mother and embryo tissues are separated only by a thin, presumably permeable, embryonic cuticle. We suggest that all these contact sites collectively constitute a dispersed placenta-like organ involved in the nourishment of the embryo.

High Fecundity, Rapid Development and Selfing Ability in Three Species of Viviparous Land Snails Phaedusinae (Gastropoda: Stylommatophora: Clausiliidae) from East Asia.

Anna Sulikowska-Drozd, Takahiro Hirano, Shu-Ping Wu, and Barna Páll-Gergely (2018) Life history traits are important yet understudied aspects of ecological diversification in land snail faunas. To acquire information for comparative analysis of gastropod life cycles, we conducted experimental breeding of three viviparous clausiliids from Japan and Taiwan. Under laboratory conditions, Tauphaedusa sheridani (Pfeiffer, 1866), T. tau (O. Boettger, 1877) and Stereophaedusa (Breviphaedusa) jacobiana (Pilsbry, 1902) featured similar times to complete shell growth (12-16 weeks), age of first reproduction (23-24 weeks) and annual fecundity (143- 173 neonates per pair of snails). The maximum number of eggs retained in genital tract reaches nine for T. sheridani, 11 for T. tau, and seven for S. jacobiana. The ratio between average shell height of neonate and adult varied between 13.5% for T. tau, 13.9% for T. sheridani, and 16.7% for S. jacobiana. All species were able to self-fertilize. Exposure to long drought affects intrauterine embryo development in all species; additionally, it results in parent and embryo mortality in S. jacobiana. Observed differences in the structure of the egg envelope among studied species point to greater than expected differentiation of developmental processes in viviparous Phaedusinae of East Asia.

Oocyte Development and Staging in the Florida Bass,Micropterus floridanus(LeSueur, 1822), with Comments on the Evolution of Pelagic and Demersal Eggs in Bony Fishes

Oocyte development and staging is described from histological preparation of the ovaries of field collected specimens of the Florida Bass, Micropterus floridanus. Oocyte development in Florida Bass progresses through six stages beginning with oogonial proliferation and ending with ovulation, the release of eggs. The stages are based on mitosis and meiosis, the core processes of Adaptable Oocyte Staging. After ovulation, the postovulatory follicle complex produces a mucus-like fluid with unknown function; we speculate that it protects the eggs immediately upon ovulation and upon their release into freshwater during spawning. Atresia is rare in the ovaries of reproductive Florida Bass. The release of cortical alveoli after fertilization follows a unique, extended time-release sequence. Oocyte development in the freshwater perciform Florida Bass follows precisely a pattern that has been documented for marine perciform fishes that produce positively buoyant, pelagic, non-adhesive eggs. The eggs of Florida Bass are morphologically like these pelagic eggs in that they have a single large oil globule and no attachment filaments. Yet Florida Bass eggs have small, clear yolk globules and an adhesive egg envelope and are functionally demersal. Thus, classification of an egg as pelagic or demersal should consider its morphology as well as its function, especially if egg type is to be used to interpret phylogenetic relationships or evolutionary patterns. The clearing of yolk due to the uptake of water during the development of actinopterygian eggs, as they progress from a demersal to a potentially pelagic phase, may be a general mechanism of oocyte maturation in teleost fishes.

Comparative ultrastructure of the fertilized egg envelope in Corydoras adolfoi and Corydoras sterbai, Callichthyidae, Teleostei.

In teleost, the structural characteristics of fertilized egg and egg envelope are very important for classification of genus or species. The structures of fertilized egg and egg envelope from Corydoras adolfoi and Corydoras sterbai, Callichthyidae, Siluriformes in teleost were examined by scanning and transmission electron microscopes to confirm whether these morphological structures have specificities of species and family or not. The fertilized eggs of C. adolfoi and C. sterbai were non-transparent, spherical, demersal, and strong adhesive. There were no structural differences between two species through the light microscope. The size of the fertilized eggs of C. adolfoi was 1.95 ± 0.03 mm (n = 20), and that of C. sterbai was 1.92 ± 0.03 mm (n = 20). The perivitelline space was almost not developed in both species. In both species, the adhesive protuberances structures were on the outer surface of egg envelope. And fibrous structures were specially located at attachment part of spawning bed. And the egg envelope consisted of two layers, an inner lamellae layer and an outer strong adhesive layer with high electron dense protuberances structures in cross section. Consequentially, the fertilized eggs, outer surface on the egg envelope and cross section of egg envelope have identical structure. So, these structural characteristics of fertilized eggs and egg envelope show genus Corydoras specificity.

Early development of the longsnout seahorse Hippocampus reidi (Syngnathidae) within the male brood pouch.

Fertilized and unfertilized eggs and embryos of the longsnout seahorse Hippocampus reidi were collected at different stages of development and provided the basis for a description of morphological development from fertilization until release from the paternal pouch. Images of fertilized eggs, as well as their rupture after a few minutes in seawater are reported for the first time. The yolk sac transitioned from ovoid to spherical shape and was reabsorbed progressively until release. The tail began rising from the surface of the deuteroplasm while embryos were in the egg envelope. Embryos lacked a primordial fin fold and developed some species characteristics, such as rays in the dorsal fin, before resorption of the yolk sac. At release, juvenile seahorses were in an advanced stage of development even if they lacked important adult characteristics, such as ring plates and coronet. The tail was not prehensile in juveniles at release; a small caudal fin was present, although this fin is lost in adults.

Gamet Ultrastructure in Some Species of the Genus Icelus (Pisces: Cottidae)

With the help of scanning and transmission electron microscopy, the morphology of spermatozoa of Icelus spiniger and egg envelopes of I. spiniger and I. spatula has been studied. Spermatozoa have an elongated head flattened on one side, an insignificant centriolar fossa, and numerous mitochondria in the middle section. The axoneme has a structure described by the formula 9 + 2. The envelopes of oocytes of both species have a follicular membrane, chorion, and zona radiata.

Reproductive biology of annual killifishes and its relationship with embryonic survival during diapause: Millerichthys robustus (Cyprinodontiformes: Cynolebiidae) as an integrative model

Diapause is a metabolic arrest expressed by annual killifish embryos as an extreme adaptation to persist in environments that show alternate periods of favourable-hostile conditions along the annual cycle. Survival under deteriorated condition can be considered as the final consequence of a previous set of complementary morphophysiological and behavioral processes in adult fishes. Millerichthys robustus is the only annual fish that has developed an annual life history in North America wherewith allow us to consider it as an emerging model for annual killifishes to review, analyze and integrate the knowledge about its reproductive biology involved in allowing the embryos in diapause to survive face the hostile environmental condition. First, we review developmental ecology of Millerichthys embryos throughout different periods (flood, drought and humid) of the annual life cycle showing the possible developmental trajectories in situ. We then analyze: (i) the way in which embryos achieve survive drought from protective cortical structures (perivitelline space and egg envelope) that present dynamic changes according to the conditions to which they are exposed buffering the harmful effects of high temperatures and water loss. (ii) The nature and origin of these protective structures during the ovogenesis (cortical alveoli and zona pellucida give rise to the perivitelline space and egg envelope respectively and oil droplets represent an emergency nutritional reserve). (iii) Sexual synchronization through secretion of pheromones and the reproductive behavior that allows them to spawn under the substrate. Embryonic survival is achieved by success of simplest interactions between reproductive biology elements prior to embryo development.

Scrambled eggs: Proteomic portraits and novel biomarkers of egg quality in zebrafish (Danio rerio).

Egg quality is a complex biological trait and a major determinant of reproductive fitness in all animals. This study delivered the first proteomic portraits of egg quality in zebrafish, a leading biomedical model for early development. Egg batches of good and poor quality, evidenced by embryo survival for 24 h, were sampled immediately after spawning and used to create pooled or replicated sample sets whose protein extracts were subjected to different levels of fractionation before liquid chromatography and tandem mass spectrometry. Obtained spectra were searched against a zebrafish proteome database and detected proteins were annotated, categorized and quantified based on normalized spectral counts. Manually curated and automated enrichment analyses revealed poor quality eggs to be deficient of proteins involved in protein synthesis and energy and lipid metabolism, and of some vitellogenin products and lectins, and to have a surfeit of proteins involved in endo-lysosomal activities, autophagy, and apoptosis, and of some oncogene products, lectins and egg envelope proteins. Results of pathway and network analyses suggest that this aberrant proteomic profile results from failure of oocytes giving rise to poor quality eggs to properly transit through final maturation, and implicated Wnt signaling in the etiology of this defect. Quantitative comparisons of abundant proteins in good versus poor quality eggs revealed 17 candidate egg quality markers. Thus, the zebrafish egg proteome is clearly linked to embryo developmental potential, a phenomenon that begs further investigation to elucidate the root causes of poor egg quality, presently a serious and intractable problem in livestock and human reproductive medicine.