Oogenesis in the viviparous phoronid,Phoronis embryolabi

The study of gametogenesis is useful for phylogenetic analysis and can also provide insight into the physiology and biology of species. This report describes oogenesis in the Phoronis embryolabi, a newly described species, which has an unusual type of development, that is, a viviparity of larvae. Phoronid oogonia are described here for the first time. Yolk formation is autoheterosynthetic. Heterosynthesis occurs in the peripheral cytoplasm via fusion of endocytosic vesicles. Simultaneously, the yolk is formed autosynthetically by rough endoplasmic reticulum in the central cytoplasm. Each developing oocyte is surrounded by the follicle of vasoperitoneal cells, whose cytoplasm is filled with glycogen particles and various inclusions. Cytoplasmic bridges connect developing oocytes and vasoperitoneal cells. These bridges and the presence of the numerous glycogen particles in the vasoperitoneal cells suggest that nutrients are transported from the follicle to oocytes. Phoronis embryolabi is just the second phoronid species in which the ultrastructure of oogenesis has been studied, and I discuss the data obtained comparing them with those in Phoronopsis harmeri. Finally, I discuss the distribution of reproductive patterns across both, molecular and morphological phylogenetic trees in Phoronida proving that parental care has evolved independently several times in this phylum.     

Ultrastructure of oogenesis in imposex females of <Emphasis Type="Italic">Babylonia areolata</Emphasis> (Caenogastropoda: Buccinidae)

During a tributyltin (TBT)-exposure experiment, the ultrastructural features of oogenesis have been examined in TBT-induced imposex females of Babylonia areolata and compared with those of the normal female. The results obtained from such experiment demonstrates that B. areolata exhibits a low to moderate intensity of imposex because all VDSI values are never higher than 3. Ultrastructures of germ cell development including oogonia, pre-vitellogenic, early vitellogenic, late vitellogenic and mature oocytes show that oogenesis in imposex female is similar to that of normal females except for the presence of numerous lipid droplets in the cytoplasm of the oocytes and the follicle cells in imposex females, indicating the degeneration of their oocytes. Vitellogenesis in B. areolata involves both auto- and heterosynthetic processes that resemble those of the basal gastropods and the pulmonates. In addition, the presence of cortical granules and microvilli are unique structures of this species.     

泥螺卵子发生的超微结构研究

利用透射电镜观察了泥螺卵子发生过程。结果表明 ,泥螺的卵子发生可划分为卵原细胞、卵黄发生早期、卵黄发生中期及卵黄发生后期卵母细胞 4个时期。卵原细胞核大而圆 ,胞质内分布有少量的线粒体和高尔基囊泡 ,细胞表面具微绒毛。卵黄发生早期的卵母细胞 ,胞质中各类细胞器发达 ,并出现数量较多的类朦胧子。卵黄发生中期的卵母细胞胞体迅速增大 ,核伸出伪足状突起 ,卵质中各种细胞器活动活跃 ,并参与形成卵黄粒和脂滴。此期还可观察到卵母细胞与滤泡细胞间的物质交换现象。卵黄发生后期的卵母细胞体积增至最大 ,细胞器数量减少。本文就卵黄发生前后卵母细胞内部构造的变化、意义及滤泡细胞与卵母细胞蛋白来源间的关系作了探讨     

Ultrastructure of the Blood System in the Phoronid Phoronopsis harmeri Pixell, 1912: 1. Capillaries

Four types of blood capillaries of the phoronid Phoronopsis harmeri are described. These are capillaries of the tentacles, of the body, of the stomach plexus, and of the vasoperitoneal tissue. The wall of capillary consists of cells of the coelomic lining, a layer of extracellular matrix, and separate endothelial cells. Myoepithelial coelomic cells of tentacle capillaries contain cross-striated fibers. In capillaries of the body and the stomach plexus, the myofilaments are smooth. In the cells of the wall of vasoperitoneal tissue capillaries, myofilaments are lacking. The cells of the vessel wall of the tentacles, the body, and the vasoperitoneal tissue bear a single cilium. The cells of capillaries of the stomach plexus lack a cilium. The ultrastructure of erythrocytes and amebocytes is described. In the cytoplasm of erythrocytes, there is a basal body. It is assumed that erythrocytes originated from the ciliary cells of the wall of the blood vessels.     

东方扁虾卵子发生的超微结构

根据卵细胞的形态、内部结构特征及卵母细胞与滤泡细胞之间的关系,东方扁虾的卵子发生可划分为卵原细胞、卵黄发生前卵母细胞、卵黄发生卵母细胞和成熟卵母细胞等四个时期。卵原细胞胞质稀少,胞器以滑面内质网为主。卵黄发生前卵母细胞核明显膨大,特称为生发泡;在靠近核外膜的胞质中可观察到核仁外排物。卵黄发生卵母细胞逐渐为滤泡细胞所包围;卵黄合成旺盛,胞质中因而形成并积累了越来越多的卵黄粒。东方扁虾卵母细胞的卵黄发生是二源的。游离型核糖体率先参与内源性卵黄合成形成无膜卵黄粒。粗面内质网是内源性卵黄形成的主要胞器。滑面内质网、线粒体和溶酶体以多种方式活跃地参与卵黄粒形成。卵周隙内的外源性物质有两个来源:滤泡细胞的合成产物和血淋巴携带、转运的卵黄蛋白前体物。这些外源性物质主要通过质膜的微吞饮作用和微绒毛的吸收作用这两种方式进入卵母细胞,进而形成外源性卵黄。内源性和外源性的卵黄物质共同参与成熟卵母细胞中富含髓样小体的卵黄粒的形成。卵壳的形成和微绒毛的回缩被认为是东方扁虾卵母细胞成熟的形态学标志。       

A comparative histochemical study of fish (Channa maruleus) and amphibian (Bufo stomaticus) oogenesis

Summary Comparative histochemical studies on the fish (Channa maruleus) and amphibian (Bufo stomaticus) oogenesis demonstrate a great similarity in the growth and differentiation of their egg follicle. The ooplasm, germinal vesicle and egg-membranes show distinct morphological and cytochemical changes during previtellogenesis and vitellogenesis.During previtellogenesis the various components of the follicle are engaged in the synthesis of protoplasm as shown by the proliferation of yolk nucleus substance, mitochondria and some lipid bodies in the ooplasm and of nucleoli in the germinal vesicle. The substance of the yolk nucleus consisting of proteins, lipoproteins and RNA first appears adjacent to the nuclear membrane. Numerous mitochondria of lipoprotein composition, and some lipid bodies consisting of unsaturated phospholipids lie in association with the yolk nucleus which forms substratum for the former. The lipid bodies, present inside the germinal vesicle, follicular epithelium, and adjacent to the plasma membrane in association with some pinocytotic vacuoles, have been considered to play a significant role in the active transport of some substances from the environment into the ooplasm and from the latter into the germinal vesicle. The follicular epithelium itself is very poorly developed, negating its appreciable role in the contribution of specific substances into the oocyte, which seem to be contributed by the germinal vesicle showing a considerable development of nuclear sap, basophilic granules and nucleoli consisting of RNA and proteins; many large nucleoli bodily pass into the cytoplasm during the previtellogenesis of Channa, where their substance is gradually dissolved. The intense, diffuse, basophilic substance of the cytoplasm is believed due to free ribosomes described in many previous ultrastructural studies.During vitellogenesis, the various deutoplasmic inclusions, namely carbohydrate yolk, proteid yolk and fatty yolk, are deposited in the ooplasm. The carbohydrate yolk bodies rich in carbohydrates originate in association with the plasma membrane and correspond to vesicles and cortical granules of previous studies. The proteid yolk consisting of proteins and some lipoproteins, and fatty yolk containing first phospholipids and some triglycerides and then triglycerides only are deposited under the influence of yolk nucleus substance, mitochondria and cytoplasm. The mitochondria and yolk nucleus substance foreshadow in some way the pattern of these two deutoplasmic inclusions and persist at the animal pole of mature egg while the other inclusions of previtellogenesis disappear from view. The pigment granules, which also show a gradient from the animal to vegetal pole in Bufo, are also formed in association with yolk nucleus substance and mitochondria. Some glycogen also appears in both the species. The nuclear membrane becomes irregular due to the formation of lobes. The lipid bodies of the germinal vesicle come to lie outside the nuclear membrane, suggesting active transport of some substances into the ooplasm; many nucleoli bodily pass into the ooplasm of Bufo, where they are gradually absorbed. The amount of basophilic granules is considerably increased in the germinal vesicle during vitellogenesis. Various egg-membranes such as outer epithelium, thin theca, single-layered follicular epithelium, zona pellucida or vitelline membrane surround the vitellogenic oocytes. The zona pellucida formed between the oocyte and follicle cells consists of a carbohydrate-protein complex. The follicle cells show lipid droplets, mitochondria and basophilic substance in their cytoplasm. The various changes that occur in the components of the follicle during vitellogenesis seem to be initiated by gonadrotrophins formed under the influence of specific environmental conditions.The author wishes to express sincere appreciation and gratitude to Dr. Gilbert S. Greenwald, who has made the completion of this investigation possible.Ph. D. Population Council Post-doctoral Fellow.     

凡纳滨对虾卵母细胞卵黄发生的超微结构

利用电镜研究凡纳滨对虾卵母细胞卵黄发生的全过程。结果表明 :凡纳滨对虾卵黄的发生是双源性的。卵黄发生早、中期是内源性卵黄大量合成的阶段 ,卵黄发生中、后期则以外源性卵黄的合成为主。内源性卵黄主要由内质网、线粒体、核糖体、溶酶体、高尔基器等多种胞器活跃参与形成。其中数量众多的囊泡状粗面内质网是形成内源性卵黄粒的最主要的细胞器 ;部分线粒体参与卵黄粒的合成并自身最终演变为卵黄粒 ;丰富的游离核糖体合成了大量致密的蛋白质颗粒并在卵质中直接聚集融合成无膜的卵黄粒 ;溶酶体通过吞噬、消化内含物来形成卵黄粒和脂滴 ,且方式多样 ;高尔基器不直接参与形成卵黄粒。外源性卵黄主要通过卵质膜的微吞饮活动从卵周隙或卵泡细胞中摄取外源物质来形成     

Oogenesis in Actinoposthia beklemischevi (Platyhelminthes, Acoela): an ultrastructural and cytochemical study

The oogenesis of the acoel Actinoposthia beklemischevi can be divided into a previtellogenic and a vitellogenic stage. Maturing oocytes are surrounded by accessory cells (a.c.) that produce electrondense granules, the content of which is released into the space between the oocyte and a.c. and gives rise to a thin primary egg envelope. The a.c. may also contribute to yolk synthesis by transferring low molecular weight precursors to the oocyte. Two types of inclusion are produced in maturing oocytes. Type I inclusions are small, roundish granules produced by the Golgi complex. They have a proteinaceous non-polyphenolic content which is discharged in the intercellular space and produce a thicker secondary egg envelope. Type I inclusions represent eggshell-forming granules (EFGs). Type II inclusions are variably sized globules progressively changing their shape from round to crescent. They appear to be produced by the ER, contain glycoproteins and remain scattered throughout the cytoplasm in large oocytes. Type II inclusions represent yolk. The main features of oogenesis in Actinoposthia are: (a) EFGs have a non-polyphenolic composition; (b) the egg envelope has a double origin and is not sclerotinized; (c) yolk production appears to be autosynthetic. The present ultrastructural findings are compared with those from other Acoelomorpha and Turbellaria.     

Carbohydrate and protein histochemistry during oogenesis inHalobatrachus didactylus (Schneider, 1801) from the Bay of Cadiz (Spain)

Summary Histological and histochemical characteristics were studied inHalobatrachus didactylus (Schneider, 1801) during oogenesis. Three phases could be differentiated: previtellogenesis (oogonia and basophilic oocytes), vitellogenesis (yolk synthesis) and maturation-spawning. Glycogen, glycoproteins and proteins rich in certain amino acids were present in the previtellogenic as well as in the vitellogenic cytoplasm oocytes. No acid mucosubstances were detected. Three types of yolk (vesicles, vacuoles and granules) contained different types of organic reserves; granules were essentially proteic whereas globules were lipidic. Carbohydrates and proteins were present in vesicles.     

Ultrastructural aspects of the germovitellarium of two prorhynchids (Platyhelminthes,Lecithoepitheliata)

Summary

The female gonad of two fresh-water prorhynchids, Geocentrophora baltica and Prorhynchus stagnalis, has been investigated by means of conventional electron microscopy and cytochemical techniques. Both species have an unpaired germovitellarium located under the gut; accessory cells surround the germovitellarium of G. baltica. The germovitellarium consists of a restricted germinative area where early differentiating oocytes and vitellocytes are randomly associated, and an extensive growth area with follicular organization. Each follicle consists of a single alecithal oocyte surrounded by numerous vitellocytes. The main features of oocyte differentiation are the accumulation of lipid droplets and the appearance of Golgi complexes and small bodies possibly representing secondary lysosomes. Vitellocytes show features typical of secretory cells, including well-developed rough endoplasmic reticulum (RER) and Golgi complexes which are involved in the production of type A and type B inclusions, hi both species, type A inclusions appear first, have a glycoprotein content, do not contain polyphenols, and become localized in the peripheral cytoplasm of mature vitellocytes; they have been interpreted as eggshell forming granules. Type B inclusions are larger, have a proteinaceous content with a different structure in the two species examined, and remain scattered in the cytoplasm of mature vitellocytes; they are considered to be yolk. The finding of eggshell forming granules without polyphenols in prorhynchids contrasts with the condition in most platyhelminths that have a sclerotized eggshell formed through a tanning process of polyphenolic substances. The small bodies in the oocytes and the eggshell granules in the vitellocytes of Lecithoepitheliata differ from those observed in prolecithophorans, which have oocyte and vitellocyte inclusions similar to those of the Rhabdocoela.     

Oogenesis in the leech Glossiphonia heteroclita (Annelida, Hirudinea, Glossiphoniidae) II. Vitellogenesis, follicle cell structure and egg shell formation

By the end of previtellogenesis, the oocytes of Glossiphonia heteroclita gradually protrude into the ovary cavity. As a result they lose contact with the ovary cord (which begins to degenerate) and float freely within the hemocoelomic fluid. The oocyte's ooplasm is rich in numerous well-developed Golgi complexes showing high secretory activity, normal and transforming mitochondria, cisternae of rER and vast amounts of ribosomes. The transforming mitochondria become small lipid droplets as vitellogenesis progresses. The oolemma forms microvilli, numerous coated pits and vesicles occur at the base of the microvilli, and the first yolk spheres appear in the peripheral ooplasm. A mixed mechanism of vitellogenesis is suggested. The eggs are covered by a thin vitelline envelope with microvilli projecting through it. The envelope is formed by the oocyte. The vitelline envelope is produced by exocytosis of vesicles containing two kinds of material, one of which is electron-dense and seems not to participate in envelope formation. The cortical ooplasm of fully grown oocytes contains many cytoskeletal elements (F-actin) and numerous membrane-bound vesicles filled with stratified content. Those vesicles probably are cortical granules. The follicle cells surrounding growing oocytes have the following features: (1) they do not lie on a basal lamina; (2) their plasma membrane folds deeply, forming invaginations which eventually seem to form channels throughout their cytoplasm; (3) the plasma membrane facing the ovary lumen is lined with a layer of dense material; and (4) the plasma membrane facing the oocyte forms thin projections which intermingle with the oocyte microvilli. In late oogenesis, the follicle cells detach from the oocytes and degenerate in the ovary lumen.     

Do fast increasing food conditions promote the midsummer decline of Daphnia galeata?

Ovaries from mature giant red shrimp Aristaeomorpha foliacea were investigated histochemically and ultrastructurally. Four growing stages of the oocytes were distinguished: premeiosis stage, previtellogenetic stage, early vitellogenic stage and late vitellogenic stage. In addition, occasional resorptive oocytes were found. Oogonia and premeiotic oocytes were found in germinative zones. Previtellogenic and vitellogenic oocytes were localized in maturative zones. As vitellogenesis proceeded, oocytes showed a progressive development in the number of lipid droplets as well as in the extension of RER, constituted of dilated cisternae, uniformely scattered throughout the cytoplasm. The RER produced yolk granules and a lampbrush-like substance. The latter was released under the oolemma and constituted a characteristic cortical zone. The oolemma did not develop microvilli or micropinocytotic vesicles to incorporate yolk precursors. Thus, the protein yolk appeared to be of endogenous origin. Few somatic cells were found around the oocytes, but they never gave place to a continuous epithelial layer around oocytes, thus it is not possible to speak of ovarian follicle. The cytoplasm of these mesodermal-oocyte associated cells (MOAC) was characterized by a typical steroidogenic apparatus. Few resorptive immature oocytes were found inside late vitellogenic oocytes. Since the ovaries were packed with late vitellogenic oocytes and the few immature oocytes were hardly detectable, oocyte maturation occurred in a synchronous way.     

Ovarian maturation and oogenesis in the blue swimmer crab,Portunus pelagicus (Decapoda: Portunidae)

The study was aimed at understanding the process of reproduction and the changes happening in the ovary of Portunus pelagicus during maturation, which would be useful for its broodstock development for hatchery purposes. For that, tissue samples from different regions of the ovary at various stages of maturation were subjected to light and electron microscopy, and based on the changes revealed and the differences in ovarian morphology, the ovary was divided into five stages such as immature (previtellogenic oocytes), early maturing (early vitellogenic oocytes), late maturing (late vitellogenic oocytes), mature (vitellogenic oocytes), and spent (resorbing oocytes). The ovarian wall comprised of an outermost thin pavement epithelium, a middle layer of connective tissue, and an innermost layer of germinal epithelium. The oocytes matured as they moved from the centrally placed germinal zone toward the ovarian wall. The peripheral arrangement of nucleolar materials and the high incidence of cell organelles during the initial stages indicated vitellogenesis I. Movement of follicle cells toward oocytes in the early maturing stage and low incidence of mitochondria and endoplasmic reticulum in the ooplasm during late vitellogenic stage marked the commencement and end of vitellogenesis II, respectively. Yolk granules at various stages of development were seen in the ooplasm from late vitellogenic stage onwards. The spent ovary had an area with resorbing oocytes and empty follicle cells denoting the end of one reproductive cycle and another area with oogonial cells and previtellogenic oocytes indicating the beginning of the next.     

Immunolocalization of estrogen receptor α in Neomysis japonica oocytes and follicle cells during ovarian development

Estrogen induces oocytes development and vitellogenesis in crustacean by interacting with estrogen receptor (ER) subtypes. In the present study, we detect for the first time the ERα in oocytes and follicle cells and hepatopancreas cells of mysis by immunohistochemistry using a specific ERα antibody. ERα was mainly localized in the nuclei of oocytes and follicle cells, while mainly detected in nuclei of oogonia (OG), previtellogenic oocyte (PR) and endogenous vitellogenic oocyte (EN) at previtellogenic and early vitellogenic stage (I-early III). Follicle cells in all stages of ovary (all vitellogenic stages) showed strong ERα positive reaction, and they were able to gradually move to oocytes during the development of oocytes. In addition, ERα was also localized in the nuclei and cytoplasm of four hepatopancreas cells (including E-, R-, F- and B-cell) in all ovary stages. These findings suggest, for the first time to our knowledge, that there could be a close link between oogenesis, follicle cells, hepatopancreas cells and endocrine regulation, and estrogens might be involved in the regulation of oocytes at early ovarian stage in mysis.     

An ultrastructural study of oogenesis in a marine triclad

The ultrastructural features of oocyte differentiation were studied in the marine triclad Cercyra hastata. Oocytes at several stages of maturation, each surrounded by follicle cell projections, are present within each of the two ovaries. A pre-vitellogenic and a vitellogenic stage have been detected in the oogenesis of C. hastata. The pre-vitellogenic stage is mainly characterized by an increase in the nuclear and nucleolar volume and activity, and the appearance and development of cortical granule precursors which are elaborated by the Golgi complex. In early phases of the vitellogenic stage, intense delamination and blebbing of the nuclear envelope occurs which probably contributes to an increase in number of cytoplasmic membranes and to transfer of nuclear material to the cytoplasm. The rough endoplasmic reticulum is extensively developed and often assumes a ‘whorl’ array. Several areas of yolk precursor formation appear in the whorls. Numerous 2–5 μm protein yolk globules are subsequently formed which appear surrounded by a double membrane (cisternae of the smooth endoplasmic reticulum) and become randomly distributed throughout the cytoplasm of mature oocytes. The peripheral ooplasm is occupied by a monolayer of electron-dense cortical granules. Finally, the evolutionary significance of the autosynthetic mechanism of yolk production is discussed.     

Oogenesls in the terrestrial hermit crab,coenobita clypeatus (decapoda,anomura): II. Vitellogenesis

Oocytes from the land hermit crab, Coenobita clypeatus, in various stages of vitellogenesis were examined by light and electron microscopy. Early vitellogenic oocytes are characterized by accumulations of discrete vesicles of endoplasmic reticulum in the perinuclear cytoplasm. As oocytes develop, the endoplasmic reticulum becomes abundant, and numerous Golgi complexes are seen. There is a well developed Golgi-endoplasmic reticulum interaction. Within the confines of the reticulum are discrete intracisternal granules, which can be seen coalescing into electron-dense yolk bodies. Lipid accumulation is seen throughout the cytoplasm. Coincident with the burst of intra-oocytic metabolism are oolemma modifications and micropinocytosis, which provide ultrastructural evidence for extra-oocytic yolk production. The mature oocyte contains numerous yolk and lipid vesicles of varying electron density that comprise both intra- and extra-oocytic substrates.     

Comparative Spiralian Oogenesis--Structural Aspects: An Overview

Considerable variety exists in ovarian structure and cellularinteraction in spiralians. During their development the eggsof Dwpatra cuprea, are associated with nurse cells; there areno follicle cells in this species. The nurse cells have prominentnuclei and connect to oocytes via cytoplasmic bridges throughwhich ribosomes, mitochondria and other inclusions pass. Morecommonly, follicle cells surround a portion of, or entire, oocytesin many species of spiralians. Usually, as in Ilyanassa, theyhave a well developed compliment of organelles. The structureand distribution of organelles within follicle cells impliesthat they are functionally active, but precisely in what mannerduring oogenesis is poorly understood. Other cell types, suchas Leydig and interstitial cells also seem to play a role inoogenesis. Within the oocyte, a host of components includingyolk, lipid, mitochondria, ribosomes, membranous cisternae,cortical granules, etc. are accumulated. Autosynthetic yolkformation is prevalent among spiralians. Surface differentiationincludes microvillar development. This may be uniform in someeggs or restricted to certain regions (e.g., the animal hemisphere)in other oocytes. Oocyte-follicle cell interactions change duringoogenesis. The topographical association of the oocyte withother ovarian cells influences subsequent animal-vegetal polarityand other ooplasmic differences. Examples of ooplasmic localizationsare discussed. Conventional EM has revealed no unusual corticalstructure in many oocytes although occasionally microtubulesand microfilaments are present.     

Previtellogenic and vitellogenic oocytes in ovarian follicles of cultured siberian sturgeon Acipenser baerii (Chondrostei,Acipenseriformes)

Previtellogenic and vitellogenic oocytes in ovarian follicles from cultured Siberian sturgeon Acipenser baerii were examined. In previtellogenic oocytes, granular and homogeneous zones in the cytoplasm (the ooplasm) are distinguished. Material of nuclear origin, rough endoplasmic reticulum, Golgi complexes, complexes of mitochondria with cement and round bodies are numerous in the granular ooplasm. In vitellogenic oocytes, the ooplasm comprises three zones: perinuclear area, endoplasm and periplasm. The endoplasm contains yolk platelets, lipid droplets, and aggregations of mitochondria and granules immersed in amorphous material. In the nucleoplasm, lampbrush chromosomes, nucleoli, and two types of nuclear bodies are present. The first type of nuclear bodies is initially composed of fibrillar threads only. Their ultrastructure subsequently changes and they contain threads and medium electron dense material. The second type of nuclear bodies is only composed of electron dense particles. All nuclear bodies impregnate with silver, stain with propidium iodide, and are DAPI‐negative. Their possible role is discussed. All oocytes are surrounded by follicular cells and a basal lamina which is covered by thecal cells. Egg envelopes are not present in previtellogenic oocytes. In vitellogenic oocytes, the plasma membrane (the oolemma) is covered by three envelopes: vitelline envelope, chorion, and extrachorion. Vitelline envelope comprises four sublayers: filamentous layer, trabecular layer 2 (t2), homogeneous layer, and trabecular layer 1 (t1). In the chorion, porous layer 1 and porous layer 2 are distinguished in most voluminous examined oocytes. Three micropylar cells that are necessary for the formation of micropyles are present between follicular cells at the animal hemisphere. J. Morphol. 278:50–61, 2017. ©© 2016 Wiley Periodicals,Inc.     

黄胫小车蝗卵子发生及卵母细胞凋亡的显微观察

对黄胫小车蝗(Oedaleus infernalis)卵子发生过程和卵母细胞凋亡进行显微观察。结果表明,黄胫小车蝗卵子发生可明显分为3个时期10个阶段,即卵黄发生前期、卵黄发生期和卵壳形成期。第1阶段,卵母细胞位于卵原区,经历减数第一次分裂;第2阶段,卵母细胞核内染色体解体成网状,滤泡细胞稀疏地排列在卵母细胞周围;第3阶段,滤泡细胞扁平状,在卵母细胞周围排成一层;第4阶段,滤泡细胞呈立方形排在卵母细胞周围;第5阶段,滤泡细胞呈长柱形排在卵母细胞周围,滤泡细胞之间、滤泡细胞与卵母细胞之间出现空隙;第6阶段,卵母细胞边缘开始出现卵黄颗粒;第7阶段,卵母细胞中沉积大量卵黄,胚泡破裂;第8阶段,滤泡细胞分泌卵黄膜包围卵黄物质;第9阶段,滤泡细胞分泌卵壳;第10阶段,卵壳分泌结束,卵子发育成熟。卵母细胞发育过程中的凋亡发生在卵黄发生前期,主要表现为滤泡细胞向卵母细胞内折叠,胞质呈团块状等特征。     

Development of the nervous system in Phoronopsis harmeri (Lophotrochozoa, Phoronida) reveals both deuterostome- and trochozoan-like features

Background

Inferences concerning the evolution of invertebrate nervous systems are often hampered by the lack of a solid data base for little known but phylogenetically crucial taxa. In order to contribute to the discussion concerning the ancestral neural pattern of the Lophotrochozoa (a major clade that includes a number of phyla that exhibit a ciliated larva in their life cycle), we investigated neurogenesis in Phoronopsis harmeri, a member of the poorly studied Phoronida, by using antibody staining against serotonin and FMRFamide in combination with confocal microscopy and 3D reconstruction software.

Results

The larva of Phoronopsis harmeri exhibits a highly complex nervous system, including an apical organ that consists of four different neural cell types, such as numerous serotonin-like immunoreactive flask-shaped cells. In addition, serotonin- and FMRFamide-like immunoreactive bi- or multipolar perikarya that give rise to a tentacular neurite bundle which innervates the postoral ciliated band are found. The preoral ciliated band is innervated by marginal serotonin-like as well as FMRFamide-like immunoreactive neurite bundles. The telotroch is innervated by two neurite bundles. The oral field is the most densely innervated area and contains ventral and ventro-lateral neurite bundles as well as several groups of perikarya. The digestive system is innervated by both serotonin- and FMRFamide-like immunoreactive neurites and perikarya. Importantly, older larvae of P. harmeri show a paired ventral neurite bundle with serial commissures and perikarya.

Conclusions

Serotonin-like flask-shaped cells such as the ones described herein for Phoronopsis harmeri are found in the majority of lophotrochozoan larvae and therefore most likely belong to the ground pattern of the last common lophotrochozoan ancestor. The finding of a transitory paired ventral neurite bundle with serially repeated commissures that disappears during metamorphosis suggests that such a structure was part of the ??ur-phoronid?? nervous system, but was lost in the adult stage, probably due to its acquired sessile benthic lifestyle.