尖唇散白蚁胚胎发育激光共聚焦扫描显微镜观察

【目的】本研究旨在探究尖唇散白蚁Reticulitermes aculabialis胚胎在不同发育阶段的变化特征。【方法】每日收集尖唇散白蚁的卵,并固定其胚胎发育状态,采用DAPI染剂对白蚁胚胎进行染色,通过激光共聚焦扫描显微镜观察记录尖唇散白蚁胚胎在不同发育阶段的形态特征。【结果】在25℃下尖唇散白蚁胚胎发育过程历经25~30 d,按照发育特征将其划分为12个阶段。胚胎发育早期,卵黄细胞均匀分布在卵内部,卵内细胞核向卵的中间浓缩,在细胞到达卵的后表面时形成浓缩的囊胚细胞作为胚盘;胚胎发育中期,胚胎开始进行“反转型”的囊胚运动,头部和前后轴从后极到前极反转,胚带出现明显的“双弯”结构。胚胎发育中后期,胚胎变宽,内部器官逐渐开始发育,出现明显的伸长与分节;胚胎发育后期,附肢发育明显,内部器官发育成熟。【结论】尖唇散白蚁胚胎发育过程历经12个阶段,属于短胚带型,胚带出现“双弯”结构,发育中期经历两次囊胚反转。本研究为真社会性昆虫白蚁的胚胎发育过程提供了形态学和生物学依据。     

Expression patterns of twist and snail in Tribolium (Coleoptera) suggest a homologous formation of mesoderm in long and short germ band insects

The mesodermal region in Drosophila is determined by a maternally derived morphogenetic gradient system which specifies the different cell fates along the dorsoventral axis, including the prospective mesodermal cells at the ventral side of the embryo. There are at least two zygotic target genes, twist and snail, which are required for mesoderm formation in Drosophila. To analyze whether a similar mode of mesoderm specification might also apply to short germ band insect embryos, we have cloned twist and snail- related gene fragments from the flour beetle Tri-bolium and have analyzed their expression pattern. Both genes are expressed in a ventral stripe at early blastoderm stage, which is restricted to the region of the developing germ rudiment. The cells expressing the two genes are those that invaginate during gastrulation, indicating that the early stages of mesoderm specification are indeed very similar between the two species. Interestingly, both genes are also expressed during germband extension in a subregion of the growth zone of the embryo which forms the mesodermal cells. This suggests that the expression of the two genes is required for mesoderm formation both at early blastoderm stage and during germband elongation until the end of the segmental growth process. © 1994 Wiley-Liss, Inc.     

Crumbs Affects Protein Dynamics In Anterior Regions Of The Developing Drosophila Embryo

Maintenance of apico-basal polarity is essential for epithelial integrity and requires particular reinforcement during tissue morphogenesis, when cells are reorganised, undergo shape changes and remodel their junctions. It is well established that epithelial integrity during morphogenetic processes depends on the dynamic exchange of adherens junction components, but our knowledge on the dynamics of other proteins and their dynamics during these processes is still limited. The early Drosophila embryo is an ideal system to study membrane dynamics during morphogenesis. Here, morphogenetic activities differ along the anterior-posterior axis, with the extending germband showing a high degree of epithelial remodelling. We developed a Fluorescence Recovery After Photobleaching (FRAP) assay with a higher temporal resolution, which allowed the distinction between a fast and a slow component of recovery of membrane proteins during the germband extension stage. We show for the first time that the recovery kinetics of a general membrane marker, SpiderGFP, differs in the anterior and posterior parts of the embryo, which correlates well with the different morphogenetic activities of the respective embryonic regions. Interestingly, absence of crumbs, a polarity regulator essential for epithelial integrity in the Drosophila embryo, decreases the fast component of SpiderGFP and of the apical marker Stranded at Second-Venus specifically in the anterior region. We suggest that the defects in kinetics observed in crumbs mutant embryos are the first signs of tissue instability in this region, explaining the earlier breakdown of the head epidermis in comparison to that of the trunk, and that diffusion in the plasma membrane is affected by the absence of Crumbs.     

Topological determination of early morphogenesis in Metazoa

This paper presents a topological interpretation of some developmental events through the use of well-known concepts and theorems of combinatorial geometry. The organization of early embryo using a simulation of cleavage considering only blastomere contacts is examined. Each blastomere is modeled as a topological cell and whole embryo—as cell packing. The egg cleavage results in a pattern of cellular contacts on the surface of each blastomere and whole embryo, a discrete morphogenetic field. We find topological distinctions between different types of early egg cleavage and suggest a topological classification of cleavage. Blastulation and gastrulation may be related to an inevitable emergence of discrete curvature that directs development in three-dimensional space. The relationship between local and global orders in metazoan development, i.e., between local morphogenetic processes and integral developmental patterns, is established. Thus, this methodology reveals a topological imperative: a certain set of topological rules that constrains and directs biological morphogenesis.     

Cellular mechanics of germ band retraction in Drosophila

Germ band retraction involves a dramatic rearrangement of the tissues on the surface of the Drosophila embryo. As germ band retraction commences, one tissue, the germ band, wraps around another, the amnioserosa. Through retraction the two tissues move cohesively as the highly elongated cells of the amnioserosa contract and the germ band moves so it is only on one side of the embryo. To understand the mechanical drivers of this process, we designed a series of laser ablations that suggest a mechanical role for the amnioserosa. First, we find that during mid retraction, segments in the curve of the germ band are under anisotropic tension. The largest tensions are in the direction in which the amnioserosa contracts. Second, ablating one lateral flank of the amnioserosa reduces the observed force anisotropy and leads to retraction failures. The other intact flank of amnioserosa is insufficient to drive retraction, but can support some germ band cell elongation and is thus not a full phenocopy of ush mutants. Another ablation-induced failure in retraction can phenocopy mys mutants, and does so by targeting amnioserosa cells in the same region where the mutant fails to adhere to the germ band. We conclude that the amnioserosa must play a key, but assistive, mechanical role that aids uncurling of the germ band.     

Ultrastructure of the Developing and Fertilized Embryo Sac of Amaranthus hypochondriacus L.

Amaranthus hypochondriacus embryo sac development was investigatedbefore and after fertilization. During the early stages of development,the young embryo sac displays three antipodal cells at the chalazalpole that degenerate very early in the maturation process, beforethe synergids and egg cell are completely differentiated. Themature embryo sac is composed only of the female germ unit.The synergid cells organize a filiform apparatus accompaniedby the presence of mitochondria and dictyosomes with numerousvesicles. The involvement of the synergids in transport andsecretory functions related to pollen tube attraction and guidance,are discussed. The egg cell is located at the micropylar polenear the synergids and displays exposed plasma membranes atthe chalazal pole. The fertilized egg cell does not exhibitmarked changes after fertilization except for the closure ofthe cell wall. The central cell is the largest cell of thisvery long embryo sac. The fused nucleus is close to the eggapparatus before fertilization and displays a remarkable chalazalmigration after gamete delivery. The ultrastructure of the centralcell cytoplasm and the numerous wall ingrowths around this cellsuggest an important role in nutrient transportation. Aftergamete delivery, the embryo sac displays electron dense bodiesthat aggregate within the intercellular space between the synergids,egg cell and central cell. These bodies, that appear in theembryo sac of several plants, are probably involved in gametedelivery for double fertilization. The possibility of biparentalinheritance of mitochondria in this plant is also discussed.Copyright 1999 Annals of Botany Company Amaranthus hypochondriacus, grain amaranth, embryo sac, fertilization.     

Attractive internuclear force drives the collective behavior of nuclear arrays in Drosophila embryos

The collective behavior of the nuclear array in Drosophila embryos during nuclear cycle (NC) 11 to NC14 is crucial in controlling cell size, establishing developmental patterns, and coordinating morphogenesis. After live imaging on Drosophila embryos with light sheet microscopy, we extract the nuclear trajectory, speed, and internuclear distance with an automatic nuclear tracing method. We find that the nuclear speed shows a period of standing waves along the anterior-posterior (AP) axis after each metaphase as the nuclei collectively migrate towards the embryo poles and partially move back. And the maximum nuclear speed dampens by 28-45% in the second half of the standing wave. Moreover, the nuclear density is 22–42% lower in the pole region than the middle of the embryo during the interphase of NC12-14. To find mechanical rules controlling the collective motion and packing patterns of the nuclear array, we use a deep neural network (DNN) to learn the underlying force field from data. We apply the learned spatiotemporal attractive force field in the simulations with a particle-based model. And the simulations recapitulate nearly all the observed characteristic collective behaviors of nuclear arrays in Drosophila embryos.     

Reduced cul-5 Activity Causes Aberrant Follicular Morphogenesis and Germ Cell Loss in Drosophila Oogenesis

Drosophila oogenesis is especially well suited for studying stem cell biology, cellular differentiation, and morphogenesis. The small modifier protein ubiquitin regulates many cellular pathways. Ubiquitin is conjugated to target proteins by a diverse class of enzymes called ubiquitin E3 ligases. Here we characterize the requirement of Cul-5, a key component of a subgroup of Cullin-RING-type ubiquitin E3 ligases, in Drosophila oogenesis. We find that reduced cul-5 activity causes the formation of aberrant follicles that are characterized by excess germ cells. We show that germ line cells overproliferate in cul-5 mutant females, causing the formation of abnormally large germ line cysts. Also, the follicular epithelium that normally encapsulates single germ line cysts develops aberrantly in cul-5 mutant, leading to defects in cyst formation. We additionally found that Cul-5 is required for germ cell maintenance, as germ cells are depleted in a substantial fraction of cul-5 mutant ovaries. All of these cul-5 phenotypes are strongly enhanced by reduced activity of gustavus (gus), which encodes a substrate receptor of Cul-5-based ubiquitin E3 ligases. Taken together, our results implicate Cul-5/Gus ubiquitin E3 ligases in ovarian tissue morphogenesis, germ cell proliferation and maintenance of the ovarian germ cell population.     

Fertilization and embryogeny in Agapanthus praecox ssp. orientalis (Leighton) Leighton

Fertilization and embryogeny in Agapanthus praecox ssp. orientalis are described for the first time, and embryogenic characters of Agapanthus are discussed. The main results are: (1) The pollen tube enters the embryo sac and discharges two sperm 44?C48?h after pollination. (2) The sperm fuse with the egg cell and polar nuclei, forming zygote and primary endosperm nucleus, approximately 50?h after pollination. The zygote then enters a short period of dormancy. (3) Seven days after pollination, the zygote starts division. The first division of the zygote is transversal. (4) The embryo undergoes globular stage, rod-shaped stage, and finally forms a monocotyledonous embryo. (5) The suspensor cells are ephemeral and degenerate at the globular embryo stage. (6) Endosperm cells contain massive starch grains as nutrition for embryo development. (7) Embryogeny conforms to the Onagrad type, and endosperm formation is of the nuclear type; the whole process of embryogeny and endosperm development needs approximately 60?days in A. praecox ssp. orientalis. (8) Dicotyledonous together with monocotyledonous forms of embryo morphogenesis in Agapanthus supports the concept of homology of monocots and dicot cotyledons.     

STRUCTURE AND HISTOGENESIS OF THE EMBRYO OF ACER SACCHARINUM. I. EMBRYO SAC AND PROEMBRYO

Structure of the embryo sac and development of the proembryo of Acer saccharinum L. are described from paraffin sections. The embryo sac is monosporic and identical to the 8-nucleate Polygonum type in all respects. Cell, nuclear, and nucleolar sizes are constant within a narrow range and sharply distinctive for all components of the mature sac. Polar nuclei fuse before double fertilization. The longitudinal axis of symmetry of the egg, zygote, and proembryo is variously oriented with respect to the longitudinal axis of the embryo sac and is determined by the point of attachment of the presumptive egg cell to the sac wall. Subsequent development of the young embryo is responsive to aligning factors within the embryo sac and is collateral with the longitudinal axis of the sac. The first segmentation is transverse to the longitudinal axis of the zygote; the second and third are transverse in the basal cell and longitudinal in the apical cell. Descendants of ci form a short irregular suspensor; ca and m give rise to the apical and basal halves respectively of the embryo proper. The contribution of the proembryonic tiers to the older embryo differs in embryos of different initial orientation. Distribution and orientation of mitosis in the proembryo are shown in two accumulation maps.     

Egg structure and outline of embryonic development of the basal mantodean, Metallyticus splendidus Westwood, 1835 (Insecta,Mantodea, Metallyticidae)

The egg structure and outline of the embryonic development of Metallyticus splendidus of one of the basal Mantodea representatives, Metallyticidae, were described in the present study. The results obtained were compared with those from the previous studies, to reconstruct and discuss the groundplan of Mantodea and Dictyoptera. In M. splendidus, the egg is spheroidal, it has a convex ventral side at the center in which numerous micropyles are grouped, and it possesses a conspicuous hatching line in its anterior half. These are the groundplan features of mantodean eggs and the “grouped micropyles in the ventral side of the egg” are regarded as an apomorphic groundplan feature of Dictyoptera. A small circular embryo is formed by a simple concentration of blastoderm cells, which then undergoes embryogenesis of the typical short germ band type. Blastokinesis is of the “non-reversion type” and the embryo keeps its original superficial position and original orientation throughout embryonic development. During the middle stages of development, the embryo undergoes rotation around the egg's anteroposterior axis. These features are a part of the groundplan of Mantodea. It is uncertain whether sharing of the “non-reversion type” of blastokinesis by Mantodea and blaberoidean Blattodea can be regarded as homology or homoplasy.     

Embryonic expression of the engrailed homologue of Rhynchosciara americana

The segment polarity gene engrailed is involved in the determination of segment posterior identity in Drosophila. engrailed has been largely used for comparative developmental studies due to its evolutionary conservation from nematodes to humans. By in situ hybridization of an engrailed cDNA probe from Drosophila to polytene chromosomes of fourth instar larvae of Rhynchosciara americana we have shown that engrailed-like sequences must be localized in band 6 of chromosome A in this species. The pattern of engrailed protein expression during R. americana embryo development is diffuse at first evolving into a nuclear striped pattern after quite a length of time. In addition, our results suggest a possible developmentally regulated molecular modification of engrailed protein in R. americana embryos.     

A Candida albicans Temperature-Sensitive cdc12-6 Mutant Identifies Roles for Septins in Selection of Sites of Germ Tube Formation and Hyphal Morphogenesis

Septins were identified for their role in septation in Saccharomyces cerevisiae and were subsequently implicated in other morphogenic processes. To study septins in Candida albicans hyphal morphogenesis, a temperature-sensitive mutation was created that altered the C terminus of the essential Cdc12 septin. The cdc12-6 cells grew well at room temperature, but at 37°C they displayed expected defects in septation, nuclear localization, and bud morphogenesis. Although serum stimulated the cdc12-6 cells at 37°C to form germ tube outgrowths, the mutant could not maintain polarized hyphal growth and instead formed chains of elongated cell compartments. Serum also stimulated the cdc12-6 mutant to induce a hyphal reporter gene (HWP1-GFP) and a characteristic zone of filipin staining at the leading edge of growth. Interestingly, cdc12-6 cells shifted to 37°C in the absence of serum gradually displayed enriched filipin staining at the tip, which may be due to the altered cell cycle regulation. A striking difference from the wild type was that the cdc12-6 cells frequently formed a second germ tube in close proximity to the first. The mutant cells also failed to form the diffuse band of septins at the base of germ tubes and hyphae, indicating that this septin band plays a role in preventing proximal formation of germ tubes in a manner analogous to bud site selection. These studies demonstrate that not only are septins important for cytokinesis, but they also promote polarized morphogenesis and selection of germ tube sites that may help disseminate an infection in host tissues.     

Metabolome Analysis of Drosophila melanogaster during Embryogenesis

The Drosophila melanogaster embryo has been widely utilized as a model for genetics and developmental biology due to its small size, short generation time, and large brood size. Information on embryonic metabolism during developmental progression is important for further understanding the mechanisms of Drosophila embryogenesis. Therefore, the aim of this study is to assess the changes in embryos’ metabolome that occur at different stages of the Drosophila embryonic development. Time course samples of Drosophila embryos were subjected to GC/MS-based metabolome analysis for profiling of low molecular weight hydrophilic metabolites, including sugars, amino acids, and organic acids. The results showed that the metabolic profiles of Drosophila embryo varied during the course of development and there was a strong correlation between the metabolome and different embryonic stages. Using the metabolome information, we were able to establish a prediction model for developmental stages of embryos starting from their high-resolution quantitative metabolite composition. Among the important metabolites revealed from our model, we suggest that different amino acids appear to play distinct roles in different developmental stages and an appropriate balance in trehalose-glucose ratio is crucial to supply the carbohydrate source for the development of Drosophila embryo.     

Symplastic communication between the central cell and the egg apparatus cells in the embryo sac of Torenia fournieri Lind. before and during fertilization

 Various membrane-impermeable, water-soluble fluorescent tracers with different molecular weights were microinjected into the central cell of the embryo sac of Torenia fournieri Lind. before and during fertilization. Before anthesis, there was high symplastic permeability between the central cell and the egg apparatus cells. In this stage, fluorescent tracers up to 10 kDa could pass from the central cell into the egg apparatus cells, whereas those with larger molecular weight remained in the central cell. As the embryo sac matured, symplastic permeability decreased such that 2 d after anthesis only tracers less than 3 kDa could spread from the central cell into the egg cell. There appeared to be no symplastic permeability between the primary endosperm and zygote after fertilization, since tracers as small as 521 Da could not pass into the zygote in about half of the microinjected embryo sacs. This is the first report of a change in cell-to-cell communication among the cells of the female germ unit before and after fertilization. Received: 16 December 1999 / Accepted: 4 February 2000     

External features of the developing embryo of the stonefly,Kamimuria tibialis (pictet) (plecoptera,perlidae)

External features of the egg, developing embryo, and first instar nymph of Kamimuria tibialis are described. The embryonic development from the germ disc to the full-grown embryo is divided into 12 stages. The saclike embryonic rudiment is formed by the bending and folding of the germ disc. The embryo first elongates at the egg surface and then sinks into the yolk due to caudal flexure. In the head, four paired protocerebral lobes differentiate and the fourth lobes are thought to be the rudiments of preantennal ganglia. The columnar serosal cells appear at the posterior pole of the egg and they disappear before katatrepsis. The coniform chloride cells occur at the hind margins of the first nine abdominal segments in the full-grown embryo and first instar nymph. Amnion formation in K. tibialis is very similar to that of Allonarcys proteus and the Isoptera. It is proposed that the immersed type of growth pattern of embryos is divided into two subtypes in hemimetabolous insects; one is in the Palaeoptera and Paraneoptera, and the other is in the Plecoptera, Orthoptera, Notoptera, Isoptera, Embioptera, and the blattarian, Periplaneta americana.     

Embryogenesis of Heliconius erato (Lepidoptera,Nymphalidae): A contribution to the anatomical development of an evo‐devo model organism

This study reports on the embryogenesis of Heliconius erato phyllis between blastoderm formation and the prehatching larval stage. Syncytial blastoderm formation occurred approximately 2 h after egg laying (AEL) and at about 4 h, the cellular blastoderm was formed. The germ band arose from the entire length of the blastoderm, and rapidly became compacted occupying approximately two‐thirds of the egg length. At about 7 h AEL, protocephalon and protocorm differentiation occurred. Continued proliferation of the germ band was followed by penetration into the yolk mass, forming a C‐shaped embryo at about 10 h. Approximately 12 h AEL, the gnathal, thoracic and abdominal segments became visible. The primordium of the mouthparts and thoracic legs formed as paired evaginations, while the prolegs formed as paired lobes. At about 30 h, the embryo reversed dorsoventrally. Approximately 32 h AEL, the protocephalon and gnathal segments fused, shifting the relative position of the rudimentary appendages in this region. At about 52 h, the embryo was U‐shaped in lateral view and at approximately 56 h, the bristles began evagination from the larval cuticle. Larvae hatched at about 72 h. We found that H. erato phyllis followed an embryonic pattern consistent with long‐germ embryogenesis. Thus, we believe that H. erato phyllis should be classified as a long‐germ lepidopteran. The study of H. erato phyllis embryogenesis provided a structural glimpse into the morphogenetic events that occur in the Heliconius egg period. This study could help future molecular approaches to understanding the evolution of Heliconius development.