Ultrahistology of oogenesis and vitellogenesis in the spider mite Tetranychus urticae

An overview of chelicerate ovaries, with special reference to mites - myths and facts

In arthropods of the subphylum Chelicerata a panoistic ovary, in which all germline cells differentiate into oocytes, prevails. Among the chelicerates, mites are believed to show a great variety of the structure of the female gonads. In general, the knowledge of the ovarian structure in mites is fragmentary and patchy. In both evolutionary lines, Acariformes and Parasitiformes, apart from the panoistic ovary, the meroistic ovary, in which the oocytes grow supported by their sibling cells, the nurse cells, occurs. The presence of the meroistic ovary is considered an apomorphic state. Previous studies revealed a various structure of the meroistic ovary in different mite taxa, and the differences came down, inter alia, to a different number and location of the nurse cells in relation to the oocytes. Here we provide a comprehensive review of the structure of the Chelicerata ovary, with special reference to the mite ovary. We also provide our preliminary results of the analysis of ovarian structure in two representatives of terrestrial Parasitengona (Acariformes), Allothrombium fuliginosum (Trombidiidae) and Erythraeus cinereus (Erythraeidae), performed using light, confocal and electron transmission microscopy. The analyses allowed for verification of data published before. In A. fuliginosum we showed the presence of the nurse cells in the ovarian wall, so the ovary should be classified as meroistic. In meroistic ovary of E. cinereus we found that each oocyte is connected to several mononucleated nurse cells. The verification of literature data and broadening the knowledge of the structure of the female gonad in mites, will result in estimating the usefulness of the ovary traits in phylogenetic analyses and will provide the basis for inference about the directions of evolutionary changes of female gonad at lower systematic levels.

Molecular characterization, expression, and function of Vitellogenin genes in Phytoseiulus persimilis

Vitellogenin (Vg) is an important factor that impacts oocyte maturation, egg formation and embryonic development in Arthropoda. Two orthologs of Vg gene were obtained from the genome of Phytoseiulus persimilis and termed as PpVg1 and PpVg2. Both orthologs belong to the large lipid transfer protein superfamily. The expression of PpVg1 and PpVg2 was low in immatures and male adults, and increased rapidly in female adults after mating, and reached a peak before the first egg was laid (168×  and 20.5×  the level in virgin females, respectively). When PpVg1 and PpVg2 were interfered with dsRNA, the relative expression decreased by 81.0 and 30.9%, respectively, and 7.8 and 31.4% interfered individuals died within 24 h. Among surviving individuals, ca. 51.1 and 44.8% are infertile. Factors that might be related to expression of Vg genes are also discussed.

The involvement of cyclotides in mutual interactions of violets and the two-spotted spider mite

Plants employ different chemicals to protect themselves from herbivory. These defenses may be constitutive or triggered by stress. The chemicals can be toxic, act as repellents, phagosuppressants and/or phago-deterrents. The two-spotted spider mite (Tetranychus urticae) is a generalist arthropod herbivorous pest and its feeding causes extensive damage both to crops and wild plants. Cyclotides are cyclic peptides involved in host-plant defenses. A single Viola sp. can produce more than a hundred cyclotides with different biological activities and roles. The organ and tissue specific cyclotide patterns change over the seasons and/or with environment, but the role of biotic/abiotic stress in shaping them remains unclear. Here, we demonstrate the involvement of cyclotides in mutual interactions between violets and mites. We used immunohistochemistry and mass spectrometry imaging to show the ingested cyclotides in T. urticae and assess the Viola odorata response to mite feeding. Moreover, to assess how mites are affected by feeding on violets, acceptance and reproductive performance was compared between Viola uliginosa, V. odorata and Phaseolus vulgaris. We demonstrate that cyclotides had been taken in by mites feeding on the violets. The ingested peptides were found in contact with epithelial cells of the mite digestive system, in the fecal matter, feces, ovary and eggs. Mites preferred common bean plants (P. vulgaris) to any of the violet species; the latter affected their reproductive performance. The production of particular cyclotides in V. odorata (denoted by molecular weights: 2979, 3001, 3017, 3068, 3084, 3123) was activated by mite feeding and their levels were significantly elevated compared to the control after 5 and 21 days of infestation. Specific cyclotides may affect mites by being indigestible or through direct interaction with cells in the mite digestive tract and reproductive organs. A group of particular peptides in V. odorata appears to be involved in defense response against herbivores.

Female reproductive system and oogenesis in the mite Bakericheyla chanayi

The fine structure of the female reproductive system of a cheyletid mite Bakericheyla chanayi (Trombidiformes: Cheyletidae) is investigated for the first time. This system consists of an unpaired ovary, glandular oviduct, receptaculum seminis, long cuticle-lined vagina, and genital atrium terminating in the genital opening. A separate sperm access system has not been found. The receptaculum seminis opens into the distal oviduct region, where fertilization apparently takes place. The ovary contains clusters of oogonia (cystocytes), clustered early meiotic cells, a few growing previtellogenic oocytes, and 3 large nurse cells. The dorsal ovarian region is occupied by the clusters of bacteriocytes which harbor symbiotic bacteria. Oocytes undergo vitellogenesis in individual ovarian pouches, each connected to the corresponding nurse cell by an intercellular bridge. The fine structure of the bridge suggests transport between the interconnected cells in the course of vitellogenesis. The population of cystocytes was shown to be heterogenic. The electron-light cells enter meiosis and develop into the oocytes or nurse cells. The electron-dense cystocytes do not show meiotic transformation and probably give rise to the bacteriocytes. The early development of the nurse cells and oocytes is similar and accompanied by the blebbing of the nuclear envelope, appearance of nuage material and Balbiani bodies.

Regulation of female reproduction in mites: a unifying model for the Acari

It is well established in the literature that circulating high levels of juvenile hormone (JH) are responsible for the initiation of vitellogenesis and female reproduction in most insects studied so far. Exceptions include some Diptera, Lepidoptera and Hymenoptera. The current view is that JH also regulates yolk protein (vitellogenin, Vg) synthesis and female reproduction in mites. However, there is no published evidence that mites have the common insect JHs at any stage of their development. Also, research on the effects of exogenous applications of JH and JH analogs on the reproduction of mites is contradictory. Significant information is available on the life history of mite reproduction, and new information has become available on mite storage proteins including Vg. Although initial studies suggested that ticks may respond to exogenously applied juvenile hormone or anti-JHs, current research shows that ticks cannot synthesize the common insect JHs and have no detectable levels of these hormones in their hemolymph during female reproduction. In ticks, it appears that ecdysteroids, and not JH, regulate expression of the Vg gene and the synthesis and release of Vg protein into the hemolymph. In fact within the Arthropoda, JH has been found only in insects. Methyl farnesoate and not JH regulates Vg synthesis in the Crustacea, the sister group to the insects. Based on this evidence, a new working hypothesis is proposed, i.e., that ecdysteroids and not the JHs regulate vitellogenesis in the Acari including both ticks and mites. To the present, the role of neuropeptides in the regulation of female reproduction in mites is not known.

Characterization of vitellin protein in the twospotted spider mite, Tetranychus urticae (Acari: Tetranychidae)

In mites, vitellogenin synthesis, regulation and uptake by the oocytes as vitellin remain practically unknown. Although a partial sequence of the gene is now available, no previous studies have been conducted that describe the native vitellin protein in mites. The objective of this study was to characterize vitellin in the twospotted spider mite, Tetranychus urticae. The native twospotted spider mite vitellin migrated as a single major band with a molecular weight of 476+/-14.5 kDa as compared to 590+/-25.5 kDa for vitellin from the American dog tick, Dermacentor variabilis. However, isoelectric focusing analysis of native spider mite vitellin showed five bands with pI values slightly acidic to neutral (pH 5.8, 6.2, 6.7, 7.0 and 7.2), as is the case for insect and tick vitellins. Reducing conditions (SDS-PAGE) also revealed multiple subunits ranging from 290.9 to 3.6 kDa and was similar to that found in D. variabilis. Spider mite vitellin weakly bound lipids and carbohydrates compared to the tick. Unlike D. variabilis, the spider mite egg yolk protein does not bind heme. The significance of non-heme binding in mites is discussed.

Suppression of ovarian development and vitellogenin gene expression in the adult diapause of the two-spotted spider mite Tetranychus urticae

Tetranychus urticae (Acari: Tetranychidae) possesses a sac-like ovary with characteristic oocytes that protrude from the ovarian surface. In nondiapause females, transparent oocytes became opaque with yolk deposition between days 0 and 1 in the adult stage at 20 degrees C. In diapause females, however, ovarian development ceased at a stage having transparent oocytes without yolk deposition; this stage corresponded to the day-0 stage of the nondiapause females. Four partial fragments of the vitellogenin (Vg) genes of T. urticae were isolated. This is the first report on the Vg genes of mites. The deduced amino acid sequences of these four Vg gene fragments contained the von Willebrand factor D domain and the GLCG motif, which were reported to be the common features of Vg sequences in insects and ticks. Northern blot analysis did not detect Vg mRNA in the diapause adult females of T. urticae. It is, therefore, suggested that diapause mites do not synthesize Vg mRNA and that vitellogenesis is regulated at the transcriptional level in diapause.

The annulate lamellae--from obscurity to spotlight

This review aims to provide a comprehensive and in-depth survey of a cell organelle, the annulate lamellae, that is widely distributed and especially prevalent in both female and male sex cells as well as tumor and cancer cells. The organelle is also present in many somatic cells and plant cells. Emphasis is placed on the contributions that electron microscopy and associated experimental approaches have made in providing information about the distribution, ultrastructure, morphogenesis and relationships of annulate lamellae to other cellular organelles, especially the nuclear envelope and endoplasmic reticulum, as well as cell product. An increasing number of experimental manipulations have recently been shown to alter, either increase or decrease, the amount of annulate lamellae and these studies are explored in depth. Information about the origin and morphogenesis of annulate lamellae in different cells is summarized and extensive coverage is given to several hypotheses about possible annulate lamellae function. A detailed bibliography provides a thorough compilation of research dealing with annulate lamellae. A major goal of this extensive review is to generate increased awareness of, and interest in, this cell organelle for students and investigators of the cell who, by bringing current techniques in cell and molecular biology to bear, might focus and intensify studies on the function of an organelle whose precise role in the cell is presently enigmatic.