In silico identification and molecular characterization of genes predominantly expressed in the fish oocyte

Background: In fish, molecular mechanisms that control follicle-enclosed oocyte progression throughout oogenesis and oocyte developmental competence acquisition remain poorly understood. Existing data in mammals have indicated that the so called "oocyte-specific" genes play an important role in oogenesis, fertilization, and early embryo development. In teleost species, very little is known about "oocyte-specific" genes. The present study therefore aimed at identifying and characterizing oocyte-specific genes in fish. Results: Using digital differential display PCR, mouse ESTs exhibiting an oocyte-predominant expression were identified. Those murine ESTs were subsequently used to identify cognate rainbow trout (Oncorhynchus mykiss) ESTs using a reciprocal Blast search strategy. In the present study we report the identification of five previously uncharacterized rainbow trout cDNAs exhibiting a oocyte-specific, oocyte-predominant, or gonad-specific expression: zygote arrest 1 (zar1), v-mos Moloney murine sarcoma viral oncogene-like protein (mos), B-cell translocation gene (btg3), growth differentiation factor 9 (gdf9), and mutS homolog 4 (msh4). The orthology relationship of each of these genes with vertebrate counterparts was verified by phylogenetic analysis. Among those five genes, three had never been characterized in any fish species. In addition, we report the oocyte-predominant expression of btg3 for the first time in any vertebrate species. Finally, those five genes are present in unfertilized eggs as maternally-inherited mRNAs thus suggesting that they could participate in ovarian folliculogenesis as well as early embryonic development. Conclusion: The expression patterns of zar1, mos, btg3, gdf9 and msh4 in rainbow trout and the functions of their orthologs in higher vertebrates strongly suggest that they might play an important role in follicle-enclosed oocyte development, meiosis control and early embryonic development in fish. Future investigations are however required to unravel the participation of those strong candidates in the molecular processes that control folliculogenesis and/or oocyte developmental competence in fish

Two unrelated putative membrane-bound progestin receptors, progesterone membrane receptor component 1 (PGMRC1) and membrane progestin receptor (mPR) beta, are expressed in the rainbow trout oocyte and exhibit similar ovarian expression patterns

BACKGROUND: In lower vertebrates, steroid-induced oocyte maturation is considered to involve membrane-bound progestin receptors. Two totally distinct classes of putative membrane-bound progestin receptors have been reported in vertebrates. A first class of receptors, now termed progesterone membrane receptor component (PGMRC; subtypes 1 and 2) has been studied since 1996 but never studied in a fish species nor in the oocyte of any animal species. A second class of receptors, termed membrane progestin receptors (mPR; subtypes alpha, beta and gamma), was recently described in vertebrates and implicated in the progestin-initiated induction of oocyte maturation in fish. METHODS: In the present study, we report the characterization of the full coding sequence of rainbow trout PGMRC1 and mPR beta cDNAs, their tissue distribution, their ovarian expression profiles during oogenesis, their hormonal regulation in the full grown ovary and the in situ localization of PGMRC1 mRNA in the ovary. RESULTS: Our results clearly show, for the first time in any animal species, that rainbow trout PGMRC1 mRNA is present in the oocyte and has a strong expression in ovarian tissue. In addition, we show that both mPR beta and PGMRC1, two members of distinct membrane-bound progestin receptor classes, exhibit highly similar ovarian expression profiles during the reproductive cycle with maximum levels during vitellogenesis and a down-expression during late vitellogenesis. In addition, the mRNA abundance of both genes is not increased after in vitro hormonal stimulation of full grown follicles by maturation inducing hormones. CONCLUSION: Together, our findings suggest that PGMRC1 is a new possible participant in the progestin-induced oocyte maturation in fish. However, its participation in the process of oocyte maturation, which remains to be confirmed, would occur at post-transcriptional levels

In silico identification and molecular characterization of genes predominantly expressed in the fish oocyte

<p>Abstract</p> <p>Background</p> <p>In fish, molecular mechanisms that control follicle-enclosed oocyte progression throughout oogenesis and oocyte developmental competence acquisition remain poorly understood. Existing data in mammals have indicated that the so called "oocyte-specific" genes play an important role in oogenesis, fertilization, and early embryo development. In teleost species, very little is known about "oocyte-specific" genes. The present study therefore aimed at identifying and characterizing oocyte-specific genes in fish.</p> <p>Results</p> <p>Using digital differential display PCR, mouse ESTs exhibiting an oocyte-predominant expression were identified. Those murine ESTs were subsequently used to identify cognate rainbow trout (<it>Oncorhynchus mykiss</it>) ESTs using a reciprocal Blast search strategy. In the present study we report the identification of five previously uncharacterized rainbow trout cDNAs exhibiting a oocyte-specific, oocyte-predominant, or gonad-specific expression: zygote arrest 1 (<it>zar1</it>), v-mos Moloney murine sarcoma viral oncogene-like protein (<it>mos</it>), B-cell translocation gene (<it>btg3</it>), growth differentiation factor 9 (<it>gdf9</it>), and mutS homolog 4 (<it>msh4</it>). The orthology relationship of each of these genes with vertebrate counterparts was verified by phylogenetic analysis. Among those five genes, three had never been characterized in any fish species. In addition, we report the oocyte-predominant expression of <it>btg3 </it>for the first time in any vertebrate species. Finally, those five genes are present in unfertilized eggs as maternally-inherited mRNAs thus suggesting that they could participate in ovarian folliculogenesis as well as early embryonic development.</p> <p>Conclusion</p> <p>The expression patterns of <it>zar1</it>, <it>mos</it>, <it>btg3</it>, <it>gdf9 </it>and <it>msh4 </it>in rainbow trout and the functions of their orthologs in higher vertebrates strongly suggest that they might play an important role in follicle-enclosed oocyte development, meiosis control and early embryonic development in fish. Future investigations are however required to unravel the participation of those strong candidates in the molecular processes that control folliculogenesis and/or oocyte developmental competence in fish.</p

Maternal temperature exposure impairs emotional and cognitive responses and triggers dysregulation of neurodevelopment genes in fish

Fish are sensitive to temperature, but the intergenerational consequences of maternal exposure to high temperature on offspring behavioural plasticity and underlying mechanisms are unknown. Here we show that a thermal maternal stress induces impaired emotional and cognitive responses in offspring rainbow trout (Oncorhynchus mykiss). Thermal stress in mothers triggered the inhibition of locomotor fear-related responses upon exposure to a novel environment and decreased spatial learning abilities in progeny. Impaired behavioural phenotypes were associated with the dysregulation of several genes known to play major roles in neurodevelopment, including auts2 (autism susceptibility candidate 2), a key gene for neurodevelopment, more specifically neuronal migration and neurite extension, and critical for the acquisition of neurocognitive function. In addition, our analysis revealed the dysregulation of another neurodevelopment gene (dpysl5) as well as genes associated with human cognitive disorders (arv1, plp2). We observed major differences in maternal mRNA abundance in the eggs following maternal exposure to high temperature indicating that some of the observed intergenerational effects are mediated by maternally-inherited mRNAs accumulated in the egg. Together, our observations shed new light on the intergenerational determinism of fish behaviour and associated underlying mechanisms. They also stress the importance of maternal history on fish behavioural plasticity

Oocyte-somatic cells interactions, lessons from evolution

BACKGROUND: Despite the known importance of somatic cells for oocyte developmental competence acquisition, the overall mechanisms underlying the acquisition of full developmental competence are far from being understood, especially in non-mammalian species. The present work aimed at identifying key molecular signals from somatic origin that would be shared by vertebrates. RESULTS: Using a parallel transcriptomic analysis in 4 vertebrate species - a teleost fish, an amphibian, and two mammals - at similar key steps of developmental competence acquisition, we identified a large number of species-specific differentially expressed genes and a surprisingly high number of orthologous genes exhibiting similar expression profiles in the 3 tetrapods and in the 4 vertebrates. Among the evolutionary conserved players participating in developmental competence acquisition are genes involved in key processes such as cellular energy metabolism, cell-to-cell communications, and meiosis control. In addition, we report many novel molecular actors from somatic origin that have never been studied in the vertebrate ovary. Interestingly, a significant number of these new players actively participate in Drosophila oogenesis. CONCLUSIONS: Our study provides a comprehensive overview of evolutionary-conserved mechanisms from somatic origin participating in oocyte developmental competence acquisition in 4 vertebrates. Together our results indicate that despite major differences in ovarian follicular structure, some of the key players from somatic origin involved in oocyte developmental competence acquisition would be shared, not only by vertebrates, but also by metazoans. The conservation of these mechanisms during vertebrate evolution further emphasizes the important contribution of the somatic compartment to oocyte quality and paves the way for future investigations aiming at better understanding what makes a good egg

Identification of new participants in the rainbow trout (Oncorhynchus mykiss) oocyte maturation and ovulation processes using cDNA microarrays

BACKGROUND: The hormonal control of oocyte maturation and ovulation as well as the molecular mechanisms of nuclear maturation have been thoroughly studied in fish. In contrast, the other molecular events occurring in the ovary during post-vitellogenesis have received far less attention. METHODS: Nylon microarrays displaying 9152 rainbow trout cDNAs were hybridized using RNA samples originating from ovarian tissue collected during late vitellogenesis, post-vitellogenesis and oocyte maturation. Differentially expressed genes were identified using a statistical analysis. A supervised clustering analysis was performed using only differentially expressed genes in order to identify gene clusters exhibiting similar expression profiles. In addition, specific genes were selected and their preovulatory ovarian expression was analyzed using real-time PCR. RESULTS: From the statistical analysis, 310 differentially expressed genes were identified. Among those genes, 90 were up-regulated at the time of oocyte maturation while 220 exhibited an opposite pattern. After clustering analysis, 90 clones belonging to 3 gene clusters exhibiting the most remarkable expression patterns were kept for further analysis. Using real-time PCR analysis, we observed a strong up-regulation of ion and water transport genes such as aquaporin 4 (aqp4) and pendrin (slc26). In addition, a dramatic up-regulation of vasotocin (avt) gene was observed. Furthermore, angiotensin-converting-enzyme 2 (ace2), coagulation factor V (cf5), adam 22, and the chemokine cxcl14 genes exhibited a sharp up-regulation at the time of oocyte maturation. Finally, ovarian aromatase (cyp19a1) exhibited a dramatic down-regulation over the post-vitellogenic period while a down-regulation of Cytidine monophosphate-N-acetylneuraminic acid hydroxylase (cmah) was observed at the time of oocyte maturation. CONCLUSION: We showed the over or under expression of more that 300 genes, most of them being previously unstudied or unknown in the fish preovulatory ovary. Our data confirmed the down-regulation of estrogen synthesis genes during the preovulatory period. In addition, the strong up-regulation of aqp4 and slc26 genes prior to ovulation suggests their participation in the oocyte hydration process occurring at that time. Furthermore, among the most up-regulated clones, several genes such as cxcl14, ace2, adam22, cf5 have pro-inflammatory, vasodilatory, proteolytics and coagulatory functions. The identity and expression patterns of those genes support the theory comparing ovulation to an inflammatory-like reaction

Multiple vitellogenins in zebrafish (Danio rerio): quantitative inventory of genes, transcripts and proteins, and relation to egg quality

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