No description available.

No description available.

No description available.

No description available.

Mosquito reproduction is tightly regulated by the endocrine system. The sesquiterpenoid insect hormone, Juvenile hormone (JH), plays a crucial role in mosquito reproductive maturation. JH signaling pathways consist of a hierarchy of transcriptional regulators that modulate the transcriptional responses to this hormone. Genomic action of JH is mediated through the intracellular receptor Methoprene tolerant (Met) and Krüppel homolog 1 (Kr-h1), an intermediate effector that acts downstream of Met. Kr-h1 is an essential transcription factor for proper oogenesis and egg production in several insects. However, the regulatory mechanism of Kr-h1 in mosquito reproduction has not been well studied. In the current study, we performed global analyses of the Kr-h1 binding sites at multiple time points before and after a blood meal. In addition to known JH-regulated genes, we identified the binding of Kr-h1 to several genes that are controlled by the insect steroid hormone 20-hydroxyecdysone (20E). Kr-h1 seemed to have different roles in regulating the 20E-responsive genes before and after the blood-feeding. RNAi mediated Kr-h1 silencing demonstrated the activator role of Kr-h1 on several 20E-regulated genes in the previtellogenic stage, while Kr-h1 mostly repressed those genes after blood feeding. On the genes that were activated by Kr-h1 in the previtellogenic stage, the binding of Kr-h1 was associated with an increase of the histone marker H3K27ac. For the first time, we demonstrated that the regulatory action of Kr-h1 involves histone modification on the 20E-responsive genes. This study significantly extends our understanding of the regulatory mechanism of Kr-h1, and the cross-talk of JH and 20E in coordinating mosquito reproduction. JH analogs are commonly used as mosquito larvicides. Recent studies reported that the application of a JH analog, pyriproxyfen (PPF), on adult female mosquitoes substantially reduces their reproduction. A big knowledge gap was the poor understanding of the mechanism underlying this sterilizing effect of PPF. Here, with our customized laboratory setup that mimics the bed net intervention, we established a dose-dependent effect of PPF in compromising mosquito fecundity and fertility. We carefully assessed the effects of PPF exposure on mosquito physiology and follicular development. PPF induced excessive growth of primary follicles during the previtellogenic stage. However, the follicular development in the PPF-treated mosquitoes was severely impaired after blood feeding. The primary follicles were much smaller than their counterparts in the control groups and their development stopped at Christopher's stage III. Moreover, PPF triggered the atypical premature growth of secondary follicles at ~36 h PBM. In addition to the follicular developmental reprogramming, PPF also altered the levels of storage metabolites, enhancing the accumulation of glycogen and triglyceride (TAG) before a blood meal and speeding their depletion after blood-feeding. Consistent with the observed phenotypical changes and relevant metabolic genes, several 20E-responsive genes were significantly altered in their expression as a result of PPF exposure. Furthermore, RNAi experiments demonstrated that the JH receptor Met is required in the PPF-induced sterilization. In summary, we evaluated the sterilizing effects of PPF on mosquito reproduction, investigated the molecular action of PPF in regulating mosquito gene expression, and determined the signaling pathway involved in the PPF-induced sterilization of female mosquitoes. / Doctor of Philosophy / Among different insect-borne diseases, mosquito causes the highest disease burden with almost 700 million infections and over a million deaths every year. Aedes aegypti mosquitoes are the major vehicle to transmit several viral diseases including dengue, yellow fever, chikungunya, and Zika fever. They pose a global threat to public health and economic sectors. Different mosquito control strategies are used, and a very quick, powerful, and popular strategy is using chemical insecticides to decrease mosquito populations. However, insecticide resistance in mosquitoes and non-specific toxicity to other animals are great challenges associated with the commonly used insecticides. To resolve this problem, new insecticides are urgently needed. If we can broaden our understanding of mosquito reproductive biology, new targets will be identified and can be exploited to develop new insecticides. In our study, we investigated an insect-specific hormone, Juvenile hormone (JH), to understand its regulatory action in mosquito reproduction. Also, this study improved our knowledge of the molecular understanding of the insecticide (synthetic JH-like compound) in decreasing mosquito egg numbers and reducing the hatching rate. Overall, we gained a significant understanding of the hormonal regulation of mosquito reproduction. This knowledge can be used in the future to develop new insecticides with better efficiency to decrease the mosquito population and mosquito-borne disease burden.

Egg activation is a series of highly coordinated processes that prepare the mature oocyte for embryogenesis. Typically associated with fertilisation, egg activation results in the resumption of the cell cycle, expression of maternal mRNAs and cross-linking of the vitelline membrane. While some aspects of egg activation, such as initiation factors in mammals and environmental cues in sea animals, have been well-documented, the mechanics of egg activation in many animals are still not well understood. This is especially true for animals where fertilisation and egg activation are unlinked. In order to elucidate how egg activation is regulated independently of fertilisation, I use Drosophila melanogaster as a model system. This insect provides extensive genetic tools, ease of manipulation for experimentation and is amenable for imaging. Through visualisation of calcium, Processing bodies and meiotic spindles, I show that osmotic pressure acts as an initiation cue for the calcium wave and downstream processes, including the resumption of cell cycle and the dispersion of the translational repression sites. I further show that aquaporin channels, together with external sodium ions, play a role in coordinating swelling of the oocyte in response to the osmotic pressure. I proceed to identify the requirement of internal calcium sources together with a dynamic actin cytoskeleton for a calcium wave to occur. Through co-visualisation of calcium and actin, I provide the first evidence that the calcium wave is followed by a wavefront of non-cortical F-actin at egg activation, which requires the calcium wave. Genetic analysis supports a model where changes in osmotic pressure trigger the calcium wave via stretch sensitive calcium channels in the oocyte membrane and the calcium wave is relayed by nearby channels via the actin cytoskeleton. My work concludes that the mechanism of egg activation in Drosophila is more similar to plants, compared to most vertebrates.

Fetal germ cell development is a key stage of female reproductive life. The DAZ family proteins (DAZ, DAZL and BOLL) are RNA-binding proteins with critical roles in murine germ cell development but their expression and potential targets in the human are largely unknown. The studies in this Thesis investigated the expression and function of DAZL and BOLL in human fetal ovary. Both DAZL and BOLL mRNA are increased dramatically at the time of entry into meiosis. Immunohistochemical analysis with specific meiotic markers suggested that DAZL and BOLL have distinct spatial-temporal expression patterns, with minimal co-expression – BOLL expression was transient prior to follicle formation. This pattern was shown not to be present in the mouse fetal ovary, where Dazl and Boll are co-expressed, indicating a limitation of the mouse for exploring the function of Boll. Two human cell lines, embryonic kidney derived HEK293 cells and germ cell tumour derived TCam-2 cells were used as models to identify the mRNA targets of DAZL and BOLL after transfection of DAZL or BOLL vectors. In HEK293 cells, TEX19 and TEX14 were confirmed as potential targets of both DAZL and BOLL, and CDC25A as a potential DAZL target. Further experiments indicated that DAZL and BOLL did not increase target mRNA transcription but increased stabilisation. A DAZL/GFP co-transfection-FACS system for TCam-2 cells was established as this cell line has very low transfection efficiency. TEX14 and SYCP3 significantly increased in GFP+ve-DAZL+ve cells when compare to the GFP-ve-DAZL-ve cells, whilst SOX17 and DNMT3L significantly decreased in the GFP+ve-DAZL+ve cells. A 3'-UTR luciferase assay confirmed regulation of TEX14 and SOX17 by DAZL through their 3'-UTR. RNA immunoprecipitation further demonstrated direct binding between human TEX14, TEX19, SYCP3, SOX17 mRNA and DAZL protein, and that TEX14 binding is through its 3'-UTR. Dual fluorescence immunohistochemistry showed that SOX17 and DMNT3L are expressed in early germ cells with DAZL, and are later down-regulated co-incident with that of DAZL, consistent with the novel repressive effect of human DAZL on these two potential targets. These studies indicate that DAZL and BOLL are associated with different key meiotic stages of germ cell development in human fetal ovary. Several potential mRNA targets of DAZL and BOLL, and a novel repression function of human DAZL on its mRNA targets were identified giving further insight into the role of these factors in human ovarian development.

O objetivo, deste estudo foi investigar o comportamento dos hormônios esteróides 17β-Estradiol (E2), 17α-hidroxiprogesterona (17α-OHP), Testosterona (T) e 11-Ketotestosterona (11-KT), em piracanjuba Brycon orbignyanus de diferentes sexos e idades, na estação reprodutiva, e nas fêmeas submetidas à reprodução induzida. Os animais utilizados no trabalho, eram criados em piscicultura comercial, mantidos em 3 viveiros, separados por lotes de diferentes idades. A coleta dos animais, consistiu de quatro machos e cinco fêmeas (48 meses), identificados através do dimorfismo sexual da espécie, e as demais idades, (12 e 24 meses), coletaram-se, 20 peixes de cada idade, para identificação do sexo através de histologia. Já o experimento de caracterização dos esteróides sexuais na reprodução induzida, foram coletadas cinco fêmeas, selecionadas através das características com: abdome abaulado, papila urogenital, saliente e avermelhada. Após captura, os peixes foram transportados ao laboratório, onde houve coleta de sangue, para quantificação do perfil plasmático de E2, 17α-OHP, T e 11-KT. Posteriormente, os animais foram abatidos e suas gônadas coletadas e fixadas, a fim de que fosse realizada análise histológica para identificação do sexo. Na reprodução induzida, foi coletado sangue em dois momentos: pré-indução (PI) e pós-extrusão (PE). O nível plasmático de E2 nos machos de 12 meses destaca sua ação no processo de proliferação e renovação das espermatogônia observado em machos imaturos. Nas fêmeas o E2 apresentou os maiores níveis (P<0,05) nos animais de 48 meses, confirmando assim, sua principal função na estimulação do processo de vitelogênese, e maturação final do oócito. Quanto aos andrógenos T e 11-KT, os maiores níveis (p<0,05) foram observados nos peixes adultos (48 meses), permitindo afirmar que estes atuam como feedback negativo, do FSH e feedback positivo do LH, fundamental no processo de maturação final e liberação dos gametas, além de regular o comportamento reprodutivo. O resultado da 17α-OHP, sugere que, nas idades estudadas, é indispensável por participar como precursor dos principais esteróides (T, E2 e 11-KT), além da 17α,20β dihydroxy-4-pregnen-3-one (17α,20β-DHP), essencial no estágio final de maturação, e desova na reprodução induzida. / The objective of this study was to investigate the physiological behavior of steroid hormones 17β-Estradiol (E2), 17α-hydroxyprogesterone (17α-OHP), testosterone (T) and 11-Ketotestosterone (11-KT) in Brycon orbignyanus with different sex and ages on the reproductive season and in females submitted to induced reproduction. The animals used in the study were kept in three ponds on a commercial fish farming, separated by lots with different ages. The sampling of animals consisted of the collection of four males and five females (48 months) identified by the sexual dimorphism of the specie. In the other groups (12 and 24 months), 20 fish of each age were collected for identification of sex through histology. In the experiment with characterization of the sexual steroids in the induced reproduction, were collected five females selected through the following characteristics: bulging abdomen and prominent reddish genital papilla. After capture, the fish were transported to the laboratory, where blood was collected for quantification of the plasma profile of E2, 17α-OHP, T and 11-KT Subsequently, the animals were slaughtered and their gonads were collected and fixed for histological analysis. In the induced females, blood was collected at two moments: pre-induction (PI) and post-extrusion (PE). The plasma profile of E2 is fundamental in immature males, highlighting its action in the process of proliferation and renewal of spermatogonia, observed in males of 12 months. In females E2 presented the highest levels (P <0.05) in animals at 48 months, thus confirming its main function in the stimulation of the vitellogenesis process and final oocyte maturation. The highest levels (p <0.05) of T and 11-KT androgens were observed in adult fish (48 months), allowing to affirm that they are acting as FSH negative feedback and LH positive feedback, fundamental in the final maturation and release of the gametes, besides regulating the reproductive behavior of the fish. The results of 17α-OHP suggest this hormon is fundamental in the studied ages because it is a precursor of the main steroids (T, E2 and 11-KT) and 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-DHP), essential in the final stage of maturation and spawning in induced reproduction.

While actin was discovered in the nucleus over 50 years ago, research lagged for decades due to strong skepticism. The revitalization of research into nuclear actin occurred after it was found that cellular stresses both induce the nuclear localization and alter the structure of nuclear actin. These studies provided the first hints that actin has a nuclear function. Subsequently, it was established that the nuclear import and export of actin is highly regulated. While the structures of nuclear actin remain unclear, it can function as monomers, polymers, and even rods. Furthermore, even within a given structure, distinct pools of nuclear actin that can be differentially labeled have been identified. Numerous mechanistic studies have uncovered an array of functions for nuclear actin. It regulates the activity of RNA polymerases, as well as specific transcription factors. Actin also modulates the activity of several chromatin remodeling complexes and histone deacetylases, to ultimately impinge on transcriptional programing and DNA damage repair. Further, nuclear actin mediates chromatin movement and organization. It has roles in meiosis and mitosis, and these functions may be functionally conserved from ancient bacterial actin homologs. The structure and integrity of the nuclear envelope and sub-nuclear compartments are also regulated by nuclear actin. Furthermore, nuclear actin contributes to human diseases like cancer, neurodegeneration, and myopathies. The work presented in this thesis aims to describe the nuclear localization and functions of actin during Drosophila oogenesis. Drosophila oogenesis, i.e. follicle development, provides a developmental system with which to study nuclear actin. Follicles are composed of roughly 1000 somatic follicle cells and 16 germline cells, including 15 nurse or support cells and a single oocyte. Follicles progress through a series of 14 morphological stages, from the germanium to Stage 14 (S14). Ovary staining using the anti-actin C4 antibody reveals one pool of nuclear actin during early oogenesis (germarium through S9), including in the germline and somatic stem cells, a subset of mitotic follicles cells, and a subset of nurse cells during S5-S9. Cofilin and Profilin, which regulate the nuclear import and export of actin, also localize to the nuclei. Expression of GFP-tagged actin results in nuclear actin rod formation. These findings indicate that nuclear actin is tightly regulated during oogenesis. One factor mediating this regulation is Fascin. Overexpression of Fascin enhances nuclear GFP-Actin rod formation, and Fascin colocalizes with the rods. Loss of Fascin reduces, whereas overexpression of Fascin increases, the frequency of nurse cells with high levels of C4 nuclear actin, but does not alter the overall nuclear level of actin within the ovary. These data suggest that Fascin regulates the ability of specific cells to accumulate C4 nuclear actin. Evidence indicates that Fascin positively regulates C4 nuclear actin through Cofilin. Indeed, loss of Fascin results in decreased nuclear Cofilin. In addition, Fascin and Cofilin genetically interact, as double heterozygotes exhibit a reduction in the number of nurse cells with high C4 nuclear actin levels. Thus, through Cofilin, Fascin positively regulates C4 nuclear actin. These studies identified Fascin as a novel means of nuclear actin regulation. Having established Drosophila oogenesis as an in vivo, developmental system to study nuclear actin, I sought to identify the functions of nuclear actin. To uncover the functions of nuclear actin, I manipulate nuclear actin levels by blocking its nuclear import (Importin 9) and export (Exportin 6). Knockdown of Importin 9, results in female sterility and defects within the germarium, supporting a role for nuclear actin in stemness. Additionally, reduced Importin 9 levels cause chromatin organization defects. Loss or knockdown of Exportin 6 causes reduced female fertility, abnormal nucleolar morphology, alterations in the nuclear envelope, and aberrant heterochromatin status. These data suggest several functions for nuclear actin in the ovary: nuclear actin is essential for stem cell differentiation, proper chromatin organization and dispersal, nucleolar structure and likely function, nuclear envelope morphology, heterochromatin status and likely gene expression. Ultimately, nuclear actin is absolutely required for the highly conserved process of follicle development. These studies provide insight into the regulation and function of nuclear actin in Drosophila oogenesis. The data presented here indicate that nuclear actin is critical for chromatin organization, nucleolar morphology, nuclear envelope shape, and heterochromatin status and suggest that nuclear actin ultimately impacts transcription, a process essential for all cells. Considering the high level of sequence and functional conservation of actin, studies in Drosophila oogenesis will provide insight into the conserved functions of nuclear actin in follicle development across higher organisms. The study of nuclear actin in the many cell types of the Drosophila ovary provide insight into the functions of nuclear actin for all cell types across evolution. Further, aberrant nuclear actin regulation has been implicated in several disease states. The studies in Drosophila provide insight into the regulation of nuclear actin and how misregulation contributes to disease states. Together, the data presented in this thesis advance our understanding of the nuclear localization and functions of actin.

Abstract not available