Ultrastructural investigations of the ovary and oogenesis in the pycnogonids Cilunculus armatus and Ammothella biunguiculata (Pycnogonida, Ammotheidae)

Abstract. Ovarian ultrastructure and oogenesis in two pycnogonid species, Cilunculus armatus and Ammothella biunguiculata , were investigated. The ovary is morphologically and functionally divided into trunk and pedal parts. The former represents the germarium and contains very young germ cells in a pachytene or postpachytene phase, whereas the latter houses developing previtellogenic and vitellogenic oocytes and represents the vitellarium. Intercellular bridges were occasionally found between young (trunk) germ cells. This indicates that in pycnogonids, as in other animal groups, at the onset of oogenesis clusters of germ cells are generated. As nurse cells are absent in the ovaries of investigated species, the clusters must secondarily split into individual oocytes. In the vitellarium, the oocytes are located outside the ovary. Each oocyte is connected to the ovarian tissue by a stalk composed of several somatic cells. The stalk cells directly associated with the oocyte are equipped with irregular projections that reach the oocyte plasma membrane. This observation suggests that the stalk cells may play a nutritive role. The ooplasm of vitellogenic oocytes comprises mitochondria, free ribosomes, stacks of annulate lamellae, active Golgi complexes, and vesicles derived from these complexes. Within the latter, numerous electron-dense bodies are present. We suggest that these bodies contribute to yolk formation.     

Precocene-induced sterility in F1 generation of Glossina morsitans morsitans

Precocene treatment does not disrupt the events of reproduction in Glossina morsitans morsitans or induce any apparent changes in treated tsetse. However, some females of the F₁ generation are either sterile or show retardations in follicle development. Sterility is not reversed spontaneously or with juvenile hormone analogues. The critical period for precocene action is related to each ovulation. The corpora allata of precocene-treated tsetse are normal, but those of F₁ sterile females are degenerate. The occurrence of retardation has enabled the characterisation of stages in follicle development in G. m. morsitans.     

The germarium of panoistic ovarioles of Bacillus rossius (Insecta Phasmatodea): Structure and function during imaginal life

Summary

In adult females of Bacillus rossius (Insecta Phasmatodea) the germarium, localized at the ovariole tip just below the terminal filament and above the vitellarium, progressively reduces in size and eventually disappears at the end of the ovulatory period. The observations with light and electron microscopes show that in the end-chamber most germ cells are arrested in a post-pachytenic diffuse stage, which just precedes diplotenic oocyte growth. These observations also indicate that the reduction in size of the germarium of ovulating females should probably be ascribed to a progressive and extensive activation of the resting germ cells. The average number of ovulated eggs per ovariole (6.7±0.9) is consistent with this view. However, occasional findings of lepto-zygotenic germ cells in some preovulatory ovarioles of adult females do not completely rule out the persistence of scarce undifferentiated germ elements (oogonia) in the larval germarium at the onset of adult life. Furthermore, the reduction of the germarium in ovulating females and its subsequent disappearance in post-ovulating ones also includes the somatic cells, which are always present among the germ cells in previous stages. Since each early growing oocyte becomes surrounded by a thin monolayer of follicle cells, the diminution of end-chamber somatic cells supports the view that they actually represent prefollicular cells, which are progressively utilized from the onset of imaginal life onwards.     

Novel Tools for Genetic Manipulation of Follicle Stem Cells in the Drosophila Ovary Reveal an Integrin-Dependent Transition from Quiescence to Proliferation

In many tissues, the presence of stem cells is inferred by the capacity of the tissue to maintain homeostasis and undergo repair after injury. Isolation of self-renewing cells with the ability to generate the full array of cells within a given tissue strongly supports this idea, but the identification and genetic manipulation of individual stem cells within their niche remain a challenge. Here we present novel methods for marking and genetically altering epithelial follicle stem cells (FSCs) within the Drosophila ovary. Using these new tools, we define a sequential multistep process that comprises transitioning of FSCs from quiescence to proliferation. We further demonstrate that integrins are cell-autonomously required within FSCs to provide directional signals that are necessary at each step of this process. These methods may be used to define precise roles for specific genes in the sequential events that occur during FSC division after a period of quiescence.     

Histological and ultrastructural investigation of the female reproductive system of Argulus bengalensis Ramakrishna, 1951 (Crustacea: Branchiura)

In order to understand branchiuran reproductive biology, it is imperative to know the sites of oogenesis and oocyte maturation, locate the accessory reproductive glands, and identify the fertilization site with the present knowledge of the sperm transfer mechanism of the genus Argulus. With these objectives, we attempted to describe the female reproductive system of Argulus bengalensis using serial histological sections through the ovaries and associated ducts in the transverse, longitudinal, and sagittal planes. The reproductive organs include a median ovary, one pair of ovarian lumina, a median oviduct, and a pair of collateral accessory glands. A duct from each of the collateral accessory glands leads into the proximal part of the median oviduct, which opens to the exterior through a genital opening at the distal end. The glandular secretion presumably contributes to the jelly coat of the egg. The ovary is bound with a tunica propria which extends further diametrically inside the ovary forming the paired lumina. The lumina are confluent into the median oviduct. Two distinct areas, the germarium and differentiating zones, are clearly distinguishable within the ovary. The tunica propria itself houses the oogonia within a matrix, serving as the germarium. Transmission electron micrograph reveals that the matrix is made of collagen. The collagen matrix confers elasticity to the tunica propria to accommodate the postvitellogenic oocytes within the ovarian lumen. The differentiating zone is situated in between the germarium: dorsally it is covered with a chromatophore layer. The ovary is ensheathed by a circum ovarian striated muscle. The presence of spermatophores in the ovarian lumen indicates the fertilization site. J. Morphol. 277:707–716, 2016. © 2016 Wiley Periodicals, Inc.