Dissertations / Theses on the topic 'Oocyte Maturation Factors'

Maternally supplied mRNAs encode for necessary developmental regulators that pattern early embryos in many species until zygotic transcription is activated. In Caenorhabditis elegans, post-transcriptional regulatory mechanisms guide early development during embryogenesis. Maternal transcripts remain in a translationally silenced state until fertilization. A suite of RNA-binding proteins (RBP’s) regulate these maternally supplied mRNAs during oogenesis, the oocyte-to-embryo transition, and early embryogenesis. Identifying the target specificity of these RNA-binding proteins will reveal their contribution to patterning of the embryo. We are studying post-transcriptional regulation of maternal mRNAs during oocyte maturation, which is an essential part of meiosis that prepares oocytes for fertilization. Although the physiological events taking place during oocyte maturation have been well studied, the molecular mechanisms that regulate oocyte maturation are not well understood. OMA-1 and OMA-2 are essential CCCH-type tandem zinc finger (TZF) RBP’s that function redundantly during oocyte maturation. This dissertation shows that I defined the RNA-binding specificity of OMA-1, and demonstrated that OMA-1/2 are required to repress the expression of 3ʹUTR reporters in developing oocytes. The recovered sequences from in vitro selection demonstrated that OMA-1 binds UAA and UAU repeats in a cooperative fashion. Interestingly, OMA-1 binds with high affinity to a conserved region of the glp-1 3ʹUTR that is rich in UAA and UAU repeats. Multiple RNA-binding proteins regulate translation of GLP-1 protein, a homolog of Notch receptor. In addition to previously identified RBP’s, we showed that OMA-1 and OMA-2 repress glp-1 reporter expression in C. elegans oocytes. Mapping the OMA-1 dependent regulatory sites in the glp-1 mRNA and characterizing the interplay between OMA-1 and other factors will help reveal how multiple regulatory signals coordinate the transition from oocyte to embryo but the abundance of OMA-1 binding motifs within the glp-1 3ʹUTR makes it infeasible to identify sites with a functional consequence. I therefore first developed a strategy that allowed us to generate transgenic strains efficiently using a library adaptation of MosSCI transgenesis in combination with rapid RNAi screening to identify RBP-mRNA interactions with a functional consequence. This allowed me to identify five novel mRNA targets of OMA-1 with an in vivo regulatory connection. In conclusion, the findings in this dissertation provide new insights into OMA-1 mediated mRNA regulation and provide new tools for C. elegans transgenesis. Development of library MosSCI will advance functional mapping of OMA-1 dependent regulatory sites in the target mRNAs. Extending this strategy to map functional interactions between mRNA targets and RNAbinding proteins in will help reveal how multiple regulatory binding events coordinate complex cellular events such as oocyte to embryo transition and cell-fate specification.

Maternally supplied mRNAs encode for necessary developmental regulators that pattern early embryos in many species until zygotic transcription is activated. In Caenorhabditis elegans, post-transcriptional regulatory mechanisms guide early development during embryogenesis. Maternal transcripts remain in a translationally silenced state until fertilization. A suite of RNA-binding proteins (RBP’s) regulate these maternally supplied mRNAs during oogenesis, the oocyte-to-embryo transition, and early embryogenesis. Identifying the target specificity of these RNA-binding proteins will reveal their contribution to patterning of the embryo. We are studying post-transcriptional regulation of maternal mRNAs during oocyte maturation, which is an essential part of meiosis that prepares oocytes for fertilization. Although the physiological events taking place during oocyte maturation have been well studied, the molecular mechanisms that regulate oocyte maturation are not well understood. OMA-1 and OMA-2 are essential CCCH-type tandem zinc finger (TZF) RBP’s that function redundantly during oocyte maturation. This dissertation shows that I defined the RNA-binding specificity of OMA-1, and demonstrated that OMA-1/2 are required to repress the expression of 3ʹUTR reporters in developing oocytes. The recovered sequences from in vitro selection demonstrated that OMA-1 binds UAA and UAU repeats in a cooperative fashion. Interestingly, OMA-1 binds with high affinity to a conserved region of the glp-1 3ʹUTR that is rich in UAA and UAU repeats. Multiple RNA-binding proteins regulate translation of GLP-1 protein, a homolog of Notch receptor. In addition to previously identified RBP’s, we showed that OMA-1 and OMA-2 repress glp-1 reporter expression in C. elegans oocytes. Mapping the OMA-1 dependent regulatory sites in the glp-1 mRNA and characterizing the interplay between OMA-1 and other factors will help reveal how multiple regulatory signals coordinate the transition from oocyte to embryo but the abundance of OMA-1 binding motifs within the glp-1 3ʹUTR makes it infeasible to identify sites with a functional consequence. I therefore first developed a strategy that allowed us to generate transgenic strains efficiently using a library adaptation of MosSCI transgenesis in combination with rapid RNAi screening to identify RBP-mRNA interactions with a functional consequence. This allowed me to identify five novel mRNA targets of OMA-1 with an in vivo regulatory connection. In conclusion, the findings in this dissertation provide new insights into OMA-1 mediated mRNA regulation and provide new tools for C. elegans transgenesis. Development of library MosSCI will advance functional mapping of OMA-1 dependent regulatory sites in the target mRNAs. Extending this strategy to map functional interactions between mRNA targets and RNAbinding proteins in will help reveal how multiple regulatory binding events coordinate complex cellular events such as oocyte to embryo transition and cell-fate specification.

A resposta da produção in vitro de embriões (PIVE) é reduzida quando comparada à in vivo. O aprimoramento do conhecimento dos mecanismos de maturação de oócitos bovinos permite fornecer embasamento para incrementar os sistemas in vitro, aproximando-os do ideal fisiológico. O presente estudo visou investigar os efeitos da suplementação dos meios de maturação com FGF16 (10 ng/ml), BMP15 (100 ng/ml) e a interação de ambos sobre parâmetros relevantes ao desenvolvimento do complexo cumulus oócito (COC), tais como: expansão as células do cumulus (CC), fragmentação de DNA em CC e oócito, maturação nuclear oocitária, metabolismo energético e produção de progesterona. Os COC foram maturados em meios de tratamento (controle, FGF16, BMP15 e FGF16+BMP15) e avaliados em diferentes momentos da MIV (0 e 22 horas). A análise da expansão das CC demonstrou efeito positivo (p=0,0071) da BMP15 (11,34±1,09 unidade arbitrária/UA) e da combinação FGF16+BMP15 (11,34±0,61 UA) em relação ao grupo controle (8,73±0,44 UA) e ao suplementado com FGF16 (9,42±0,65 UA). A presença de fragmentação de DNA em CC (p=0,0015) e oócitos (p=0,036) foi significativamente menor em COC tratados com BMP15 (11,73±1,24 % e 3,81±2,76 %, respectivamente) em comparação ao grupo FGF16 (22,54±2,80 % e 31,13±7,81 %, respectivamente). Ainda, o FGF16 causou aumento na incidência de fragmentação de DNA em CC, quando relacionado ao controle (16,04±1,45 %). A taxa de maturação nuclear oocitária foi superior (p=0,014) no grupo suplementado com BMP15 (93,60±4,03 %) em comparação aos grupos controle (80,80±2,49 %) e FGF16 (76,75±2,28 %), aproximando-se da totalidade. De forma inédita, descrevemos ação da BMP15 (10,79±0,72 ng/ml) no incremento da produção de progesterona, sendo maior (p=0,0113) do que a produzida nos grupos controle (8,38±0,39 ng/ml) e FGF16 (8,84±0,45 ng/ml). Não foi evidenciado efeito dos tratamentos sobre o consumo de glicose e a produção de lactato. O presente estudo reforça o envolvimento da BMP15 na foliculogênese e na diferenciação do COC. Deste modo, a adição da BMP15 (100ng/ml) aos convencionais protocolos de PIVE pode ser de grande valia para elevar a efetividade desta biotecnologia. A suplementação de FGF16 (10ng/ml) se mostrou indiferente ao processo de maturação, permitindo inferir que o FGF16 não tenha envolvimento nas etapas da maturação compreendidas pelo presente estudo in vitro. Não foi observada ação sinérgica entre o FGF16 e a BMP15.
In vitro embryo production (IVEP) efficiency is reduced when compared to in vivo. Gaining knowledge of bovine oocyte maturation mechanisms will provide bases to improve in vitro systems. The present study assessed the in vitro effects of fibroblast growth factor 16 (FGF16), bone morphogenetic protein 15 (BMP15) and their interaction on relevant parameters to cumulus oocyte complex (COC) development, such as: cumulus cells (CC) expansion, oocyte and CC DNA fragmentation, nuclear maturation, energetic metabolism and progesterone production. COCs were matured in control or supplemented media containing, FGF16 (10ng/ml), BMP15 (100ng/ml), FGF16±BMP15 and analyzed at different times of IVM (0 and 22 hours). CC expansion evaluation demonstrated a positive effect (p=0.0071) of BMP15 (11.34±1.09 arbitrary unit/AU) and FGF16+BMP15 (11.34±0,61 AU) when compared to control (8.73±0.44 AU) and FGF16 groups (9.42±0.65 UA). The presence of DNA fragmentation in CC (p=0.0015) and oocytes (p=0.036) were lower in COCs treated in media supplemented with BMP15 (11.73±1.24 % and 3.81±2.76 %, respectively) in comparison to FGF16 group (22.54±2.80 % and 31.13±7.81 %, respectively). Moreover, FGF16 caused an increase in CC DNA fragmentation, when related to control (16.04±1.45 %). Oocyte nuclear maturation rate was higher (p=0.014) in groups supplemented with BMP15 (93.60±4.03 %) compared to control (80.80±2.49 %) and FGF16 treatments (76.75±2.28 %), almost reaching the totality of COCs. In an unprecedented way, we described the BMP15 increasing action on progesterone production (10.79±0,72 ng/ml; p=0.0113) when compared to control (8.38±0.39 ng/ml) and FGF16 groups (8.84±0.45 ng/ml). There were no differences in glucose consumption and lactate production. The present study reinforces BMP15 involvement in folliculogenesis and COC differentiation. FGF16 (10 ng/ml) media supplementation did not improve any of the outcomes measured, suggesting that FGF16 is not involved in the maturation steps analyzed in the present in vitro study. Thus, the inclusion of BMP15 (100 ng/ml) to conventional IVEP protocols can be valuable to increase the effectiveness of this biotechnology. Synergistic action between FGF16 and BMP15 was not observed.

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第6915号
農博第933号
新制||農||742(附属図書館)
学位論文||H9||N3039(農学部図書室)
16032
UT51-97-H299
京都大学大学院農学研究科畜産学専攻
(主査)教授 宮本 元, 教授 佐々木 義之, 教授 矢野 秀雄
学位規則第4条第1項該当

During vertebrate oocyte maturation, the chromosomes progress to and arrest at metaphase of meiosis II in preparation for fertilization. This process includes emission of the first polar body. The second polar body is emitted after fertilization. A number of proteins are accumulated during oocyte maturation. Inhibition of this de novo translation does not appear to affect the progression of meiosis during oocyte maturation. The role of these pools of proteins has yet to be elucidated. Curiously, several of the upregulated proteins are key players in mitosis, including INCENP, a subunit of the chromosome passenger complex implicated in chromosome segregation and cytokinesis. During early stages of development in Xenopus laevis, the embryo cycles through mitosis, also known as embryo cleavage, every 30min with little to no time for transcription/translation. Our goal is to determine if the de novo translation of these mitotic proteins during oocyte maturation has a role in early embryogenesis. We used morpholino oligonucleotides antisense to INCENP mRNA (INCENPmorpho) to inhibit de novo translation during oocyte maturation. Using confocal imaging and the host transfer technique, these injected oocytes were matured, fertilized and assessed for developmental competency. INCENPmorpho and a control morpholino (ctrlmorpho) had no discernable effect on 1st or 2nd polar body emission. Whereas ctrlmorpho embryos developed normally, INCENPmorpho embryos did not cleave. Thus, de novo translation of INCENP during oocyte maturation is necessary for embryogenesis. Specifically, accumulation of INCENP and other mitotic proteins during oocyte maturation may be a common strategy in this species to prepare for the rapid and synchronous mitoses during early embryogenesis.

Thesis advisor: Laura E. Hake
Metazoan development depends on cytoplasmic polyadenylation, a key mechanism that controls the translation of maternally deposited mRNAs. In Xenopus laevis oocytes, CPEB regulates the translation of several developmentally important mRNAs, which drive meiotic progression and the production of fertilizable eggs. Most of our current knowledge of this process, also referred to as oocyte maturation, has been acquired from experiments conducted in Xenopus laevis oocytes. Despite over 30 years of research devoted to the exploration of progesterone signaling during maturation, the very early events that occur from progesterone receptor engagement to CPEB activation are not well understood. XGef, a putative Rho family guanine nucleotide exchange factor (GEF), interacts with CPEB and facilitates CPEB activation and timely meiotic progression. To further our understanding of XGef function during meiotic progression, the requirement for exchange factor activity and the activities of several Rho GTPases during maturation were examined. Despite previous reports of XGef activation of Cdc42 in mammalian cell culture, XGef does not stimulate the activation of Cdc42 in maturing Xenopus oocytes. Further, Cdc42 activity does not affect CPEB phosphorylation and overexpression of a dominant negative Cdc42 mutant does not affect maturation. Inhibition of Toxin B sensitive Rho GTPases, including Cdc42, Rac1 and Rho A-C, also fails to affect CPEB activation or meiotic progression. Lastly, the overexpression of XGef exchange deficient point mutants did not affect maturation compared to oocytes overexpressing wildtype XGef. Together, these results suggest that as a facilitator of CPEB activation and meiotic progression, XGef functions independently of exchange factor activity and Rho GTPase activation. Additionally, we found that XGef activity influences the function of RINGO/CDK1, a novel component of the progesterone signaling pathway. XGef inhibition depresses RINGO-induced GVBD, whereas XGef overexpression enhances this process. XGef interacts with RINGO in oocyte extracts and the interaction is direct in vitro. Our protein interaction data, in total, suggest that a XGef/RINGO/MAPK/CPEB complex forms in ovo to facilitate CPEB activation. Lastly, inhibition of RINGO activity directly compromises CPEB phosphorylation during early maturation, which suggests that RINGO/CDK1 directly mediates CPEB-activation
Thesis (PhD) — Boston College, 2009
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Biology

Les marqueurs épigénétiques, en particulier la méthylation de l’ADN des gènes soumis à empreinte parentale, sont sensibles aux changements environnementaux. Les techniques de l’aide médicalisée à la procréation (AMP) nécessitant la manipulation des gamètes et des embryons in vitro et dans la plupart des cas la stimulation hormonale de l’ovulation des patientes, peuvent interférer avec la reprogrammation et/ou le maintien de la méthylation des gènes soumis à empreinte. Afin d’évaluer ce risque nous avons analysé le profil de méthylation de KvDMR1, qui régule l’expression de KCNQ1OT1, dans des ovocytes humains mûris in vivo ou in vitro, provenant de patientes stimulées ou non. Nos résultats montrent que la mise en place de la méthylation au niveau de KvDMR1 se poursuit au cours de la maturation de l’ovocyte après reprise de la méiose, in vivo et in vitro et que la superovulation des patientes en AMP génère des ovocytes épigénétiquement immatures. Par ailleurs, l’étude de la méthylation de KvDMR1 et de H19 DMR (qui régule l’expression d’Igf2 et H19) dans des embryons issus d’ICSI, évolutifs ou présentant un défaut de développement, n’établit pas de lien entre les dérégulations de l’empreinte et l’arrêt du développement embryonnaire au stade blastocyste
Epigenetic modifications, particularly DNA methylation of imprinted genes are sensible to environment. Techniques of assisted reproduction require in vitro manipulation of gamete and embryos and currently superovulation of patients. These technologies may interfere with eprogramming and maintenance of methylation at imprinted genes. To evaluate such a risk, we have determined the methylation profile of KvDMR1, the region that regulates KCNQ1OT1 imprinted gene, in human oocytes retrieved from stimulated or unstimulated cycles, at different phases of their maturation in vivo or in vitro. Our results show that the timing of establishment of the methylation profile of KvDMR1 covers the maturation phase of 199 oocyte growth, in vivo and in vitro, and that hyperstimulation likely recruits young follicles epigenetically immature. Analysis of the methylation profile of KvDMR1 and H19DMR (DMR of IGF2/H19) in ICSI embryos suggests that imprinting disorders are not responsible of embryo developmental failure prior the blastocyst stage

Thesis (M.Sc.)--York University, 2009. Graduate Programme in Biology.
Typescript. Includes bibliographical references (leaves 53-57). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR51603

Thesis (M.Sc.)--York University, 2005. Graduate Programme in Biology.
Typescript. Includes bibliographical references (leaves 56-62). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss &rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR11827

Oocyte maturation (OM) in teleosts is under precise hormonal control by estrogens and progestins. We show here that estrogens activate an epidermal growth factor receptor (EGFR) signaling pathway through the G protein-coupled estrogen receptor (GPER) to maintain meiotic arrest of full-grown zebrafish (Danio rerio) oocytes in an in vitro germinal vesicle breakdown (GVBD) bioassay. A GPER- specific agonist decreased OM and a GPER-specific antagonist increased spontaneous OM, whereas specific nuclear estrogen receptor (ERα and ERβ) agonists did not affect OM, which suggests the inhibitory action of estrogens on OM are solely mediated through GPER. Furthermore, a peptide-bound estrogen, which cannot enter the oocyte, decreased GVBD, showing that these estrogen actions are mediated through a membrane receptor. Treatment of oocytes with actinomycin D, a transcription inhibitor, did not block the inhibitory effects of estrogens on OM, indicating that estrogens act via a nongenomic mechanism to maintain oocyte meiotic arrest. EGFR mRNA was detected in denuded zebrafish oocytes by reverse transcription polymerase chain reaction (RT-PCR). Therefore, the potential role of transactivation of EGFR in estrogen inhibition of OM was investigated. The matrix metalloproteinase inhibitor, ilomastat, which prevents the release of heparin-bound epidermal growth factor (HB-EGF), increased spontaneous OM. Moreover, specific EGFR1 (ErbB1) inhibitors and inhibitors of extracellular-related kinase 1 and 2 (ERK1/2) increased spontaneous OM. Previously, estrogens have been shown to increase 3’-5’-cyclic adenosine mono phosphate (cAMP) levels through GPER in zebrafish oocytes during meiotic arrest. Taken together these present results suggest that estrogens also act through GPER to maintain meiotic arrest through a second signaling pathway involving transactivation of EGFR and activation of ERK 1 and 2.
text

Pre-pubertal pig oocytes possess lower developmental competence than those from adult pigs following in vitro maturation (IVM). Previous studies have demonstrated that exposure of pre-pubertal oocytes to 1 mM dibutyryl cAMP (dbcAMP), a membrane permeable cyclic adenosine monophosphate (cAMP) analogue, for the first 20 h of IVM improves the rate of blastocyst development. Developmental competence of in vitro matured pig oocytes has been reported to increase with increasing follicle size. In this thesis, experiments were carried out using pre-pubertal and adult pig oocytes to investigate the relationship between donor age, intra-oocyte cAMP level and follicle size in terms of oocyte maturation and developmental competence. These experiments demonstrated that, while ovarian, follicular and oocyte morphology are immediately altered with the onset of puberty, pre-pubertal oocytes must be exposed to more than the first oestrous cycle to achieve improved developmental competence in vitro. Later experiments demonstrated that pre-pubertal oocytes accumulate less cAMP during IVM, undergo more rapid meiotic progression and display reduced rates of blastocyst development compared to in vitro matured adult oocytes. Treatment with dbcAMP for 22 h IVM increased the cAMP content of pre-pubertal oocytes, slowed meiotic progression during IVM and improved the rate of blastocyst formation. While the cAMP concentration of pre-pubertal oocytes was increased to levels similar to that of adult oocytes, rates of blastocyst formation remained lower, suggesting that additional factor(s) are required for oocyte maturation. This thesis also examined the follicle size cohorts that make up the 3-8 mm aspiration range on pig ovaries. The surface of pre-pubertal ovaries contained around double the number of 3 mm follicles compared with adult ovaries. Blastocyst development of pre-pubertal oocytes increased with increasing follicle size and was highest using oocytes from 5-8 mm follicles, while adult oocytes from all follicle size cohorts displayed similar high rates of blastocyst formation. The interaction between follicle size and cAMP content in pre-pubertal oocytes was examined next. Cumulus-oocyte complexes (COCs) from 3 mm follicles accumulated less intra-oocyte and inter-COC cAMP and displayed reduced cumulus expansion compared with COCs from 5-8 mm follicles. While dbcAMP treatment increased the cAMP content of oocytes from 3 mm follicles, it had no effect on the cAMP content of the whole COC. These findings suggest that inadequate levels of intra-oocyte cAMP during IVM contribute to the low developmental competence of pre-pubertal oocytes from 3 mm follicles, suggesting that cAMP transfer, production or degradation processes are incomplete. Analysis of steroid content from different follicle size cohorts revealed that the progesterone content of prepubertal follicular fluid (FF) increased with increasing follicle size, yet overall was lower than that of adults. This suggests that differences may exist in the gonadotropinstimulated steroidogenic activity of granulosa cells of pre-pubertal COCs from different follicle sizes. Since progesterone secretion did not differ between pre-pubertal and adult COCs, it appears that the downstream pathway from the granulosa cell response rather than the actual quantity of progesterone is important for subsequent maturation processes. These studies then examined gap junction communication (GJC) within the pre-pubertal COC during IVM to examine whether the positive effects of increasing follicle size and dbcAMP on intra-oocyte cAMP levels relates to improved cAMP transfer between the cumulus cell layer and oocyte. Cumulus cell-oocyte GJC during IVM was maintained for a longer period in pre-pubertal COCs from 3 mm follicles than in those from 5-8 mm follicles. Treatment with dbcAMP had minimal effect on GJC in either COC type, thus the dbcAMP-induced increase in intra-oocyte cAMP levels appears independent of GJC. Differences in GJC during IVM together with the COCs ability to increase intraoocyte cAMP levels during IVM, suggests that differences may exist in the quantity of gonadotropin receptors, which are responsible for cAMP production, within the cumulus layer of COCs from 3 mm compared with 5-8 mm follicles. In conclusion, this thesis has demonstrated that an increase in intra-oocyte cAMP is necessary during maturation for completion and synchronisation of maturation and high developmental competence of the pig oocyte. Comparison of 3, 4 and 5-8 mm follicle sizes in the pre-pubertal pig, as described here, provides an excellent model for further investigation into the role of cAMP and the other factors required for co-ordination of oocyte nuclear and cytoplasmic maturation and subsequent embryo production.
http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297309
Thesis (Ph.D.) -- School of Paediatrics and Reproductive Health, 2007

As a functional unit involved in both maintaining endocrine homeostasis and also producing mature eggs, the ovary plays a central role in female reproduction. The development and function of the ovarian follicles are controlled by gonadotropins released from the pituitary. It is widely accepted that the action of gonadotropins on ovarian follicles is mediated by paracrine/autocrine factors produced by the somatic cells surrounding the oocyte. Increasing evidence indicates that the Igf system is involved in mediating the action of gonadotropins in the ovary. Previously, we identified a gonad-specific Igf subtype (Igf3) distinct from Igf1 and Igf2. This fmding further highlights the importance of the Igf system in the fish ovary. In this thesis, efforts were made to understand the role of the Igf system in ovary using zebrafish as the model organism, and attention was focused on Igf3.
Because the expression of Igf3 is correlated with the LH receptor in zebrafish follicles, the regulation of igf3 by gonadotropins was subsequently studied in the ovary. The expression of igf3 was significantly up-regulated in both ovarian fragments and isolated follicles upon treatment with hCG in dose- and time-dependent manners. Treatment with 8-Br-cAMP or IBMX mimicked the effects of hCG on the expression of igf3 in follicles of different stages.
Four Igfs are present in zebrafish, and our results show that all four igfs are expressed in the ovary of zebrafish and exhibit the differential expression profiles during folliculogenesis. Using a primary culture of zebrafish follicle cells, we demonstrated that hCG stimulated igf2b and igf3 expression but suppressed igf2a expression. Moreover, the effect of gonadotropin could be mimicked by IBMX, which increased the intracellular levels of cAMP, suggesting the possible involvement of cAMP in the gonadotropin-based regulation and differential expression of igf2a, igf2b and igf3. These results also show that the Igf3 is the Igf subtype most sensitive to gonadatropin and cAMP.
In addition, the expression patterns of igf1, igf2a, igf2b, igf3, igf1ra and igf1rb were also studied during zebrafish embryogenesis. The unique temporal and spatial expression patterns of igf1, igf2a, igf2b, igf3, igf1ra and igf1rb were revealed by both real-time PCR and whole mount in situ hybridization, the results suggest divergent functions for these Igfs in early zebrafish development.
Taken together, the present studies provide substantial information about the Igf system, especially that of Igf3 in the zebrafish ovary. Data were gathered regarding Igf3 expression, regulation and functions, which is not only helpful for the understanding of the role of the Igf system in fish reproduction, but also contributes toward uncovering the ovarian signaling network involved in oocyte maturation across vertebrates. This study of igfs gene expression provides direct information to the study of Igf signaling in zebrafish.
To study the function of Igf3, bioactive recombinant Igf3 proteins were prepared using a bacterial expression system. Incubation of follicles with recombinant zebrafish Igf3 significantly enhanced oocyte maturation in time-, dose- and stage-dependent manners. The potential mechanisms of Igf3-induced oocyte maturation were then investigated. Igf3 stimulated oocyte maturation via a steroid-independent manner. Igf3 induced oocyte maturation through Igf1rs and the PI3 kinase, PDE3 and MAP kinase were necessary for Igf3-mediated oocyte maturation in zebrafish.
We first examined the gene expression patterns of Igf3 in the ovary. The igf3 gene in zebrafish was found to be alternatively spliced into two transcripts, with transcript variant 1 exclusively expressed in the gonads and transcript variant 2 only expressed during early development. Using specific antibodies developed for zebrafish Igf3, both the prepropeptide and the mature peptide forms of Igf3 were found to be predominantly expressed in the zebrafish ovary. Real-time PCR and in situ hybridization revealed that igf3 mRNA levels were relatively low in the early follicles but significantly increased after the mid vitellogenic stage (midstage III) and were high in the full grown follicles. In the full grown follicles, igf3 mRNA was detected primarily in the somatic follicular cells, with a low level of expression in the oocytes. Igf3 immunoreactivity was confined to the follicular cells alone.
Li, Jianzhen.
Advisers: Hui Zhao; Hon Ki Christopher Cheng.
Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: .
Thesis (Ph.D.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references (leaves 122-150).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.