Stages of oocyte development in the zebrafish,Brachydanio rerio

Oocyte development has been divided into five stages in the zebrafish Brachydanio rerio, based on morphological criteria and on physiological and biochemical events. In stage I (primary growth stage), oocytes reside in nests with other oocytes (Stage IA) and then within a definitive follicle (Stage IB), where they greatly increase in size. In stage II (cortical alveolus stage), oocytes are distinguished by the appearance of variably sized cortical alveoli and the vitelline envelope becomes prominent. In stage III (vitellogenesis), yolk proteins appear in oocytes and yolk bodies with crystalline yolk accrue during this major growth stage. Ooctes develop the capacity to respond in vitro to the steroid 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) by undergoing oocyte maturation. In stage IV (oocyte maturation), oocytes increase slightly in size, become translucent, and their yolk becomes non-crystalline as they undergo final meiotic maturation in vivo (and in response to DHP in vitro). In stage V (mature egg), eggs (approx. 0.75 mm) are ovulated into the ovarian lumen and are capable of fertilization. This staging series lays the foundation for future studies on the cellular processes occurring during oocyte development in zebrafish and should be useful for experimentation that requires an understanding of stage-specific events. © 1993 Wiley-Liss, Inc.     

Ultrastructural observation of oogenesis in the crustacea amphipoda Orchestia gammarellus (Pallas)

The oogenesis of the Crustacea Amphipoda Orchestia gammarellus can be divided in five stages taking into consideration both the oocyte ultrastructure and the physiology of the ovary. The primary oogonium (12 μm in diameter) is lodged within the germinative zone: after division, the daughter cell (or secondary oogonium) leaves this area and enters meiotic prophase. Stage I is represented by the oocyte with visible chromosomes (12–18 μm in diameter) the cytoplasmic ultrastructure of which is comparable to that of the oogonium. Stage II or previtellogenesis is characterized by a considerable growth of the oocyte (18–80 μm in diameter) which becomes enriched in ribosomes and vesicles of the rough endoplasmic reticulum; the oocyte does not yet contain any vitelline reserve (proteinaceous and lipid). Stage III or primary vitello-genesis (80–160 μm in diameter) is typified by the synthetic activity of the rough endoplasmic reticulum, corresponding to an endogenous accumulation of proteinaceous yolk. Stage IV or secondary vitellogenesis (160–800 μm in diameter) only appears during the period of reproduction; by means of endocytosis the oocyte accumulates yolk spheres in addition to lipid droplets, the origin of which is uncertain; towards the end of vitellogenesis, cortical granules become a feature that is noted for the first time in Crustacea. The last stage or maturation (800 μm in diameter) starts right before or immediately after the exuviation of the female and ends with fertilization.     

The stage of ovarian development affects organ expression of vitellogenin as well as the morphometry and ultrastructure of germ cells in the freshwater prawn Macrobrachium amazonicum (Heller, 1862)

The objective was to characterize vitellogenin expression in the ovary and hepatopancreas, and to describe the morphometry and ultrastructure of oocytes, in the freshwater prawn Macrobrachium amazonicum at various stages of ovarian development. Five ovarian stages were defined: (I) immature, (II) maturing, (III) mature, (IV) spawned, and (V) reorganized. Ovaries and hepatopancreas were analyzed by immunohistochemistry for vitellogenin expression. Vitellogenin expression in both ovary and hepatopancreas was predominantly widespread, beginning at Stage I, peaking at Stage III, and decreasing in Stages IV and V. Characterization of the ovary included measurement of the following germ cell types: oogonia (OG), and previtellogenic (PV), early vitellogenesis (EV), advanced vitellogenesis (AV), and mature (M) oocytes. Mean ± SD diameter of OG and EV oocytes in Stages I (14.2 ± 5.5 and 119.8 ± 15.7 μm) and II (17.9 ± 4.8 and 114.3 ± 34.6 μm), respectively, were significantly different from that in Stages IV (16.6 ± 4.7 and 107.0 ± 24.6 μm) and V (14.4 ± 4.1 and 101.0 ± 25.2 μm). Both scanning and transmission electron microscopy enabled identification of EV, AV and M oocytes based on the presence of a nucleus, and the organization and distribution of yolk in the cytoplasm. In summary, vitellogenesis occurred both in the hepatopancreas and ovary, with the ovary expressing vitellogenin starting as early as Stage I. This process promoted accumulation of yolk and growth of oocytes, thus favoring sexual maturation of females. This knowledge may be applied to improve production of farmed M. amazonicum.     

The development of oocytes in the ovary of a parthenogenetic tick, Haemaphysalis longicornis

Haemaphysalis longicornis is an important vector of various pathogens in domestic animals and humans. The tick is a unique species with bisexual and parthenogenetic races. Although mating induces oocyte development, it is possible in the parthenogenetic race to complete oogenesis without copulation. Here we examined the developmental process of oocytes from unfed to the oviposition period in parthenogenetic H. longicornis. We classified the developmental stages of oocytes into five stages: stage I, germinal vesicle occupies more than half of the cytoplasm; stage II, germinal vesicle occupies less than half of the cytoplasm; stage III, germinal vesicle migrates from the center in the oocyte to the vicinity of the pedicel cells; stage IV, the cytoplasm is filled with yolk granules of various sizes; stage V, the cytoplasm is occupied by large yolk granules. Oocytes at the unfed period were undeveloped and classified as stage I. Stage I and II oocytes were observed at the rapid feeding period, indicating that oocyte development began after the initiation of blood feeding. All developmental stages of oocytes were observed at the pre-oviposition period. At 10?days after the beginning of the oviposition period, the ratios of stage I and II oocytes were higher than those of the previous period, suggesting that the ovarian development and activity may be continuing. Based on these findings, we propose classification criteria for the oocyte development in the parthenogenetic H. longicornis. The criteria will be useful for understanding the mechanisms of tick reproduction and transovarial transmission of pathogens.     

Studies on the ovotestis of the slug Agriolimax reticulatus (Müller)

Summary The ovarian oocytes of Agriolimax reticulatus (Müller) have been studied by light and electron microscopy and electron cytochemistry. The development of the oocyte in the ovotestis may be divided into three stages.During Stage I the oocyte cytoplasm contains mainly ribosomes and also strands of endoplasmic reticulum, scattered mitochondria and Golgi systems. The nucleus contains both a paranucleolus and an eunucleolus. By Stage II the oocyte has enlarged, especially in a plane parallel to the basement membrane. In addition to the above mentioned organelles, the cytoplasm contains lipid, glycogen and early yolk platelets. During Stage III, the oocyte continues to enlarge, but mainly in a plane perpendicular to the basement membrane. A considerable degree of cytoplasmic differentiation has also taken place. The plasma membrane of the oocyte has become specialized with the appearance of a polysaccharide-rich glycocalyx, microvilli and pinocytotic tubules. Elsewhere, much of the background cytoplasm, containing Golgi-derived, polysaccharide and acid phosphatase-rich multivesiculate bodies, lipid and glycogen, is sequestered by smooth membranes and ultimately fuses with the growing yolk platelets. The nucleus contains an amphinucleolus, characteristic of many gastropods.The findings of this study are discussed in relation to results from other studies on oogenesis.     

Development of the follicle complex and oocyte staging in red drum,sciaenops ocellatus linnaeus, 1776 (perciformes,sciaenidae)

Pelagic egg development in red drum, Sciaenops ocellatus, is described using tiered staging. Based on mitosis and meiosis, there are five periods: Mitosis of Oogonia, Active Meiosis I, Arrested Meiosis I, Active Meiosis II, and Arrested Meiosis II. The Periods are divided into six stages: Mitotic Division of Oogonia, Chromatin Nucleolus, Primary Growth, Secondary Growth, Oocyte Maturation and Ovulation. The Chromatin Nucleolus Stage is divided into four steps: Leptotene, Zygotene, Pachytene, and Early Diplotene. Oocytes in the last step possess one nucleolus, dispersed chromatin with forming lampbrush chromosomes and lack basophilic ooplasm. The Primary Growth Stage, characterized by basophilic ooplasm and absence of yolk in oocytes, is divided into five steps: One‐Nucleolus, Multiple Nucleoli, Perinucleolar, Oil Droplets, and Cortical Alveolar. During primary growth, the Balbiani body develops from nuage, enlarges and disperses throughout the ooplasm as both endoplasmic reticulum and Golgi develop within it. Secondary growth or vitellogenesis has three steps: Early Secondary Growth, Late Secondary Growth and Full‐Grown. The Oocyte Maturation Stage, including ooplasmic and germinal vesicle maturation, has four steps: Eccentric Germinal Vesicle, Germinal Vesicle Migration, Germinal Vesicle Breakdown and Resumption of Meiosis when complete yolk hydration occurs. The period is Arrested Meiosis II. When folliculogenesis is completed, the ovarian follicle, an oocyte and encompassing follicle cells, is surrounded by a basement membrane and developing theca, all forming a follicle complex. After ovulation, a newly defined postovulatory follicle complex remains attached to the germinal epithelium. It is composed of a basement membrane that separates the postovulatory follicle from the postovulatory theca. Arrested Meiosis I encompasses primary and secondary growth (vitellogenesis) and includes most of oocyte maturation until the resumption of meiosis (Active Meiosis II). The last stage, Ovulation, is the emergence of the oocyte from the follicle when it becomes an egg or ovum. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Ultrastructural and cytochemical studies on the germarium of Dicrocoelium dendriticum (Plathelminthes,Digenea)

Summary The unpaired germarium of Dicrocoelium dendriticum contains many female germ cells at different stages of maturation and is enveloped by a fibrous basal lamina-like structure and a multilayered cytoplasmic sheath whose origins and functions are discussed. The maturation process of primary oocytes occurs completely within the prophase of the first meiotic division. It has been divided into three stages, as previously suggested for monogeneans. Stage I corresponds to oogonia and early oocytes which are located in the distal germinative area of the gonad. These cells are characterized by a high nucleo/cytoplasmic ratio and a poorly differentiated cytoplasm. Stage II corresponds to maturing oocytes grouped in the central area of the gonad and exhibiting long synaptonemal complexes and a prominent nucleolus. The main feature of cytoplasmic differentiation is the increase in the number of RER and Golgi complex which are involved in the production of small electron-dense granules. Stage III corresponds to mature oocytes located in the proximal area of the germarium near the origin of the oviduct. In this stage, the granules become regularly distributed in a monolayer in the peripheral ooplasm and make contact with the oolemma. They show a distinctive complex structure, are composed of proteins and glycoproteins and do not contain polyphenols. Their possible role as cortical granules is discussed in relation to chemical composition and previous studies on other Plathelminthes. Neither yolk globules nor glycogen are present in the oocytes.Abbreviations I oogonium and early oocyte - II growing oocyte - III mature oocyte - cg cortical granule - cs cytoplasmic sheath - db dense body - ecm extra cellular matrix - ER endoplasmic reticulum - fl fibrous extracellular layer - gc Golgi complex - m mitochondria - N nucleus - nu nucleolus - RER rough endoplasmic reticulum - sc synaptonemal complex     

FINE STRUCTURE OF LOACH OOCYTES DURING MATURATION IN VITRO

The morphological changes during in vitro maturation of Misgurnus anguillicaudatus oocyte are described. The process of oocyte maturation can be divided into three provisional stages based on morphological events. Fully-grown, immature oocytes are opaque yellowish-white. The morphological characteristics of their ooplasm are the existence of annulate lamellae, a mass of long mitochondria and an electron dense layer beneath the vitelline surface. Three hr after a 1 hr exposure to corticosterone, these structures disappear and the cortical ooplasm becomes semi-transparent. In this stage of the maturation process (Stage I), the germinal vesicle, without a nucleolus, moves toward the animal pole, and scattered cytoplasmic inclusions approach the vitelline surface. Six hr after exposure to the hormone (Stage II), the whole ooplasm becomes semi-transparent and large yolk platelets are seen in the animal pole region. Tubular endoplasmic reticula develop throughout the ooplasm and some cortical alveoli (CA) become aligned beneath the vitelline surface. Nine hr after exposure to the hormone (Stage III), the oocyte chorion separates from the follicle cells. Most CA align beneath the vitelline surface and cytoplasm accumulates in the cortical region of the animal hemisphere.     

Oogenesis of microlecithal oocytes in the viviparous teleost Heterandria formosa

Viviparous teleosts exhibit two patterns of embryonic nutrition: lecithotrophy (when nutrients are derived from yolk that is deposited in the oocyte during oogenesis) and matrotrophy (when nutrients are derived from the maternal blood stream during gestation). Nutrients contained in oocytes of matrotrophic species are not sufficient to support embryonic development until term. The smallest oocytes formed among the viviparous poeciliid fish occur in the least killifish, Heterandria formosa, these having diameters of only 400 μm. Accordingly, H. formosa presents the highest level of matrotrophy among poeciliids. This study provides histological details occurring during development of its microlecithal oocytes. Five stages occur during oogenesis: oogonial proliferation, chromatin nucleolus, primary growth (previtellogenesis), secondary growth (vitellogenesis), and oocyte maturation. H. formosa, as in all viviparous poeciliids, has intrafollicular fertilization and gestation. Therefore, there is no ovulation stage. The full‐grown oocyte of H. formosa contains a large oil globule, which occupies most of the cell volume. The oocyte periphery contains the germinal vesicle, and ooplasm that includes cortical alveoli, small oil droplets and only a few yolk globules. The follicular cell layer is initially composed of a single layer of squamous cells during early previtellogenesis, but these become columnar during early vitellogenesis. They are pseudostratified during late vitellogenesis and reduce their height becoming almost squamous in full‐grown oocytes. The microlecithal oocytes of H. formosa represent an extreme in fish oogenesis typified by scarce yolk deposition, a characteristic directly related to matrotrophy. J. Morphol., 2011. © 2010 Wiley‐Liss, Inc.     

莫桑比克非鲫卵黄形成的电镜观察

运用透射电镜观察了莫桑比克非鲫卵母细胞的生长.根据卵母细胞的大小和内部结构特征,将其分为四个时期:卵母细胞生长早期:卵黄泡形成期:卵黄积累期:卵黄积累完成期.本文着重研究了主要卵黄成分--卵黄球的形成过程.卵黄球属外源性卵黄,由卵母细胞通过微胞饮作用吸收肝脏合成的卵黄蛋白原后形成的.在卵黄大量积累前,卵母细胞内的线粒体和多泡体聚集成团,构成卵黄核,继而线粒体大量增殖,线粒体形状发生改变,形成同心多层膜结构,为大量的卵黄物质积累提供场所.最终形成的卵黄球由被膜、卵黄结晶体和两者之间的非结晶区三部分组成.       

Retinal-tectal connections in the embryonic chick: evidence for regionally specific cell surface components which mimic the pattern of innervation.

The chorion surface in the eggs of the annual fishes Cynolebias melanotaenia and C. ladigesi contains an elaborate, three-dimensional species-specific pattern. Two concentric layers form the chorion. The pattern resides in the outer layer, the secondary envelope. It consists of closely packed tubules about 250 Å in diameter. A coat of electron dense “fuzzy” material increases this to 475 Å. The inner layer, the primary envelope, of uniformly low electron density possesses no obvious substructure. Oogenesis is divided into six stages. The oocyte increases in size from 10–20 μm in Stage 1 to 250 μm in Stage 3, 600 μm in Stage 4, and attains maximal size of 900 μm by Stage 6. Massive inclusions of protein and lipid yolk accumulate during Stages 4 and 5. Zone 1, one of the three zones of the primary envelope, first appears late in Stage 2. During Stage 3, Zone 1 is completed and Zone 2 appears between the oocyte surface and Zone 1. The oocyte cytoplasm increases in complexity. Material similar to Zone 1 (light, fibrillar) and Zone 2 (dark, compact) is present in the RER, Golgi, derivative vesicles, and apical pits. Micropyle formation also commences. The oocyte secretes Zone 3 during Stage 4 as thin filaments which consolidate into a highly ordered, transitional structure composed of tangentially oriented bundles of interwoven filaments. These partially fuse during Stage 5 except for fenestrations through which oocyte and follicle cell microvilli pass. Complete fusion during Stage 6 produces a continuous layer. Follicle cells retain an unspecialized structure from Stages 1 through 4. Secondary envelope material accumulates in the RER of the follicle cells during Stage 5. It is secreted and deposited during Stage 6.     

Daytime changes in oocyte development with relation to the tide for the Hawaiian saddleback wrasse, Thalassoma duperrey

Hourly variations in oocyte stages were characterized by size class and histological examination inassociation to the daytime tidal cycle for the Hawaiian saddleback wrasse, Thalassoma duperrey . Stage I (previtellogenic), stage II (vitellogenic) and stage III (hydrated) oocytes were identified as distinct clutches. During the autumn the profiles of oocytes stages showed rapid, group-synchronous development from stage I to stage III. Concurrent increases in percentages of both stage III oocytes and the gonadosomatic index (GSI) were positively correlated to and occurred I h before the high tide. Increases in stage I and stage II oocytes 1 h after high tide indicated development of new clutches following a decline in stage III oocytes, and the appearance of post-ovulatory follicles. The profile of stage II oocytes always exceeded 30% of the ovary. Lower GSI and percentages of stage III oocytes reflect significantly reduced reproduction in the summer: as in the autumn, both factors were significantly correlated, but neither variable showed a statistical relationship to the tide. Nevertheless, hydrated oocytes were found almost exclusively within 2 h of the high tide. The association of developmental changes with changes in tidal heights points to the importance of the tidal cycle or its underlying lunar influence as a predominant reproductive cue. These data show that developmental changes in oocytes occur more rapidly than observed in some more commonly studied temperate species which reproduce annually.     

An autoradiographic and cytophotometric study of oogenesis in a pulmonate snail,Planorbarius corneus

Summary The spatial and temporal patterns of macromolecular syntheses in oocytes and somatic auxiliary cells of the snail Planorbarius corneus have been investigated by autoradiography and cytophotometry. Oogenesis has been divided into three stages, comprising early meiosis up to diplotene (stage I), previtellogenetic growth phase (stage II), and vitellogenesis (stage III). No DNA synthesis was found in any oocyte stage. In stage-I oocytes, only nucleoli were found labelled with ³H-uridine. Oocyte nuclei of stage II and III actively synthesize RNA in nucleoli and chromosomes. The most intense incorporation of uridine in chromatin probably occurs during the previtellogenesis — vitellogenesis transition period during which cytological findings suggest well developed lampbrush chromosomes. RNA synthesis in amphinucleoli of stage-III oocytes is restricted to basophilic nucleolar parts, whereas acidophilic parts (protein bodies) neither synthesize nor store RNA. During vitellogenesis oocytes incorporate amino acids into yolk platelet proteins. Radioactive proteins are found in yolk platelet precursors 5 h after injection of the tracer and in yolk platelets 3 h thereafter. The labelling pattern suggests that oocytes synthesize certain hitherto unidentified yolk components. No evidence for the participation of follicle cells in synthesis and transport of vitellogenic proteins has been obtained from autoradiography. Cytological findings suggest an important role for these cells in oogenesis. They are highly active in RNA and protein synthesis. Cellular differentiation is accompanied by polyploidization of the nuclei which attain a highest DNA content of 256 c. Polyploidization probably occurs in incremental steps as indicated by complete endomitotic chromosomal cycles. Autoradiographs show that, during vitellogenesis, oocytes do not incorporate significant amounts of glucose, and only certain follicle cells were labelled with glucose, probably indicating the synthesis of glycogen.     

Ovarian morphology of the Japanese eel in Mikawa Bay

Annual changes in gonadal maturation of female Japanese eel Anguilla japonica in sea water were investigated histologically over 5 years in the Mikawa Bay, Japan, where they occurred throughout the year except in March. Almost all immature Japanese eels (yellow eels) occurred mainly from April to September, and they were rare after November. In contrast, maturing Japanese eels (silver eels) occurred from October to February. The gonado‐somatic index ( I _G) and oocyte diameters of yellow eels were <1·0 and 150 μm, respectively, and oocytes were at the peri‐nucleolus or the oil droplet stages. The I _G and oocyte diameters of silver eels were greater than those of yellow eels and most oocytes developed to the primary yolk globule stage. The numbers of silver eels lacking oocytes at the primary yolk globule stage increased after January in Mikawa Bay, although I _G and oocyte diameters remained unchanged. In contrast, silver eels caught at the mouth of the bay in January possessed oocytes that had advanced to the secondary yolk globule stage. These observations indicate that oocyte development changes seasonally, especially after winter in Mikawa Bay.     

Ripening of the oocyte of the river lamprey (Lampetra fluviatilis L.) after river entry

River lampreys (Lampetra fluviatilis L.) enter rivers for spawning with their gonads in the final stages of maturation, however the oocytes continue to develop until the spawn. This study was undertaken to depict detailed changes in the oocytes in the period approaching the spawn, using metric analysis and to look for atresia to determine if the time period influences the final fecundity. The study was performed on 37 females caught between October and May in the Rega River, north‐western Poland. Mid‐part sections of fixed ovaries were stained with Heidenhain haematoxylin and PAS. Ten cell structures of the oocytes were measured under light microscope with the aid of a computer image analysis programme. In the autumn, when the first lampreys entered the river, the nuclei of the oocytes were in the polar position. With the approaching mating season many oocyte structures changed significantly. Statistically significant (P < 0.001, Mann–Whitney U‐test) was the increase in oocyte size (up to 1.06 × 0.78 mm in morphometric measurement), enlargement of the yolk platelets (f.a. 8.0 × 5.1 μm), elevation of theca over the chorion followed by the accumulation of glycoconjugates (f. a. 29.2 μm), growth of the zona granulosa at the vegetative pole (f. a. 24.2 μm), and increase in the thickness of the chorion at the animal pole (f. a. 11.1 μm). Other statistically significant changes (P < 0.05 and P < 0.01, Mann–Whitney U‐test) included a decrease in the width of the cortical cytoplasm band (f. a. 20.5 μm), decrease in the ratio of the distance between the nucleus and cell membrane and the long axis of the oocyte (f. a. 7.6 μm), and increase in the thickness of the chorion at the vegetative pole (f. a. 6.0 μm). No statistically significant changes in the area of the nucleus and diameter of the cortical alveoles were noted. Beginning with the lamprey entering the river until the spawn, the oocytes undergo significant growth and maturation. In this period the fecundity of the lamprey decreased only slightly, as atresia was observed sporadically in the ovaries.     

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.     

Biochemical studies of mammalian oogenesis: kinetics of accumulation of total and poly(A)-containing RNA during growth of the mouse oocyte

Kinetics of accumulation of total and poly(A)-containing RNA have been measured during growth of the mouse oocyte. Total RNA from oocytes isolated at discrete stages of growth was determined by two independent microassays. The full-grown oocyte contained about 0.60 ng of RNA. Kinetics of accumulation of total RNA with respect to oocyte volume were biphasic. Small, growing oocytes (about 30 pl) contained about 0.20 ng of RNA/oocyte. The amount of RNA increased in a quasi-linear fashion until oocyte volume was about 160 pl, at which point there was about 0.57 ng of RNA/oocyte. Thus oocytes about 65% of their final volume had accumulated about 95% of the total amount of RNA present in the fully-grown oocyte. The relative amount of poly (A)-containing RNA in oocytes of various size was determined by in situ hybridization of [3H] poly (U) to ovarian sections from juvenile mice of known age, followed by autoradiography. The kinetics of accumulation of poly (A)-containing RNA were similar to those of total RNA; oocytes about 70% of their final volume had accumulated about 95% of the amount of poly (A)-containing RNA present in the fully-grown oocyte. The poly(A)-containing RNA resided predominantly in the cytoplasm and no obvious cytoplasmic localization was observed. Kinetics of accumulation of total RNA, which is mainly ribosomal, and poly (A)-containing RNA were consistent with levels of RNA polymerases I and II measured by others during oocyte growth (Moore and Lintern-Moore, '78). The number of ribosomes that could be made from the amount of rRNA present at various stages of growth was compared to the actual number of ribosomes calculated from a published morphometric study (Garcia et al., '79). Kinetic differences in accumulation between the theoretical and actual number of ribosomes suggested oocyte ribosomes are recruited into cytoplasmic lattice structures. These structures accumulate during oocyte growth and have been postulated to be a ribosomal storage form. In addition, the results from this study are compared to results derived from lower species.     

Oogenesis and the ovarian cycle in Salamandra salamandra infraimmaculata Mertens (Amphibia; Urodela; Salamandridae) in fringe areas of the taxon's distribution

Reproductive cycle and oogenesis were studied in specimens of Salamandra salamandra infraimmaculata Mertens that inhabit fringe areas of the taxon's distribution in the Mediterranean region. Both ovarian mass and length are correlated significantly with body mass and length. Ovarian length is also correlated with the number of oocytes. During the oogenetic cycle six stages in oocyte development were recognized. Three occur during previtellogenesis: stage 1, in which oogonia divide and form cell nests; stage 2 in which oogonia differentiate into oocytes; and stage 3, in which the oocyte cytoplasm increases in volume. In the vitellogenic phase two additional stages, 4 and 5, were recognized: stage 4, in which lipid accumulates in vacuoles in the periphery followed by the appearance of yolk platelets near the cytoplasmic margin; and stage 5, in which oocyte volume increases rapidly due to increased number of yolk platelets until it reaches its maximal size. During postvitellogenesis one stage was recognized: stage 6, in which the beginning of maturation is characterized by movement of the nucleus toward the animal pole. Oogenesis continues year-round. The first four stages were seen in all ovaries examined. The ovarian cycle is independent of season and reproductive stage apart from the number of mature, postvitellogenic oocytes that increases following gestation toward the beginning of spring (March-April). J. Morphol 231:149–160, 1997. © 1997 Wiley-Liss, Inc.     

Ultrastructural detection of proteins, lipids and carbohydrates in oocytes of Amblyomma triste (Koch, 1844) (Acari; Ixodidae) during the vitellogenesis process

The ovary of the tick Amblyomma triste is classified as panoistic, which is characterized by the presence of oogonia without nurse and follicular cells. The present study has demonstrated that the oocytes in all developmental stages (I-IV) are attached to the ovary through a pedicel, a cellular structure that synthesizes and provides carbohydrate, lipids and proteins supplies for the oocytes during the vitellogenesis process. The lipids are deposited during all oocyte stages; they are freely distributed as observed in stages II, III and IV or they form complexes with other elements. The proteins are also deposited in all stages of the oocytes, however, in lower concentration in the stage IV. There is carbohydrate deposition from oocytes in the stage II as well as in stages III and IV. In addition, the present work has demonstrated that the oocyte yolk of A. triste has a glycolipoprotein nature and the elements are deposited in the following sequence: firstly the lipids and proteins, and finally the carbohydrates.