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Comparative transcriptomic analysis of follicle-enclosed oocyte maturational and developmental competence acquisition in two non-mammalian vertebrates.

Gohin M, Bobe J, Chesnel F - BMC Genomics (2010)

Bottom Line: We have successfully identified orthologous genes exhibiting conserved expression profiles in the ovarian follicle during late oogenesis in both trout and Xenopus.While some identified genes were previously uncharacterized during Xenopus late oogenesis, the nature of these genes has pointed out molecular mechanisms possibly conserved in amphibians and teleosts.It should also be stressed that in addition to the already suspected importance of steroidogenesis in maturational competence acquisition, our approach has shed light on other regulatory pathways which may be involved in maturational and developmental competence acquisitions that will require further studies.

View Article: PubMed Central - HTML - PubMed

Affiliation: CNRS/IGDR (UMR 6061), IFR140 GFAS, Université de Rennes I, 2, Avenue du Pr, Léon Bernard, 35043 Rennes Cedex, France. Julien.bobe@rennes.inra.fr.

ABSTRACT

Background: In vertebrates, late oogenesis is a key period during which the oocyte acquires its ability to resume meiosis (i.e. maturational competence) and to develop, once fertilized, into a normal embryo (i.e. developmental competence). However, the molecular mechanisms involved in these key biological processes are far from being fully understood. In order to identify key mechanisms conserved among teleosts and amphibians, we performed a comparative analysis using ovarian tissue sampled at successive steps of the maturational competence acquisition process in the rainbow trout (Oncorhynchus mykiss) and in the clawed toad (Xenopus laevis). Our study aimed at identifying common differentially expressed genes during late oogenesis in both species. Using an existing transcriptomic analysis that had previously been carried out in rainbow trout, candidate genes were selected for subsequent quantitative PCR-based comparative analysis.

Results: Among the 1200 differentially expressed clones in rainbow trout, twenty-six candidate genes were selected for further analysis by real-time PCR in both species during late oogenesis. Among these genes, eight had similar expression profiles in trout and Xenopus. Six genes were down-regulated during oocyte maturation (cyp19a1, cyp17a1, tescalcin, tfr1, cmah, hsd11b3) while two genes exhibited an opposite pattern (apoc1, star). In order to document possibly conserved molecular mechanisms, four genes (star, cyp19a1, cyp17a1 and hsd11b3) were further studied due to their known or suspected role in steroidogenesis after characterization of the orthology relationships between rainbow trout and Xenopus genes. Apoc1 was also selected for further analysis because of its reported function in cholesterol transport, which may modulate steroidogenesis by regulating cholesterol bioavailability in the steroidogenic cells.

Conclusions: We have successfully identified orthologous genes exhibiting conserved expression profiles in the ovarian follicle during late oogenesis in both trout and Xenopus. While some identified genes were previously uncharacterized during Xenopus late oogenesis, the nature of these genes has pointed out molecular mechanisms possibly conserved in amphibians and teleosts. It should also be stressed that in addition to the already suspected importance of steroidogenesis in maturational competence acquisition, our approach has shed light on other regulatory pathways which may be involved in maturational and developmental competence acquisitions that will require further studies.

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star expression profiles during late oogenesis and tissue expression profiles. Expression profiles of star in rainbow trout ovary sampled from females during late vitellogenesis (LV, n = 6), post-vitellogenesis (PV, n = 14) and during maturation (Mat., n = 8) (A), in Xenopus laevis ovarian follicles sampled from six females, at stage IV, stage VI and after in vitro maturation (st VI MII) (B). Expression of star mRNA in rainbow trout tissues: brain (Br), heart (He), stomach (St), liver (Li), intestine (In), muscle (Mu), skin (Sk), post-vitellogenic ovary (Ov), and testis (Te) (C) and in Xenopus laevis tissues: brain (Br), heart (He), stomach (St), liver (Li), intestine (In), muscle (Mu), skin (Sk), ovary (Ov), testis (Te). Data were normalized to the abundance of 18S. Mean and SEM are shown. Bars sharing the same letter(s) are not significantly different (p > 0.05). In tissue, expression levels which are not significantly different from background signal are indicated with #.
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Figure 6: star expression profiles during late oogenesis and tissue expression profiles. Expression profiles of star in rainbow trout ovary sampled from females during late vitellogenesis (LV, n = 6), post-vitellogenesis (PV, n = 14) and during maturation (Mat., n = 8) (A), in Xenopus laevis ovarian follicles sampled from six females, at stage IV, stage VI and after in vitro maturation (st VI MII) (B). Expression of star mRNA in rainbow trout tissues: brain (Br), heart (He), stomach (St), liver (Li), intestine (In), muscle (Mu), skin (Sk), post-vitellogenic ovary (Ov), and testis (Te) (C) and in Xenopus laevis tissues: brain (Br), heart (He), stomach (St), liver (Li), intestine (In), muscle (Mu), skin (Sk), ovary (Ov), testis (Te). Data were normalized to the abundance of 18S. Mean and SEM are shown. Bars sharing the same letter(s) are not significantly different (p > 0.05). In tissue, expression levels which are not significantly different from background signal are indicated with #.

Mentions: Star mRNA expression shows a progressive increase during late and/or post-vitellogenesis and a sharp increase during maturation in both species (Fig. 6A and 6B). In rainbow trout, star mRNA abundance is two times higher during post-vitellogenesis than during late vitellogenesis and six times higher during maturation than during late vitellogenesis. In Xenopus laevis, star mRNA abundance is four times higher at prophase I of stage VI and 40 times higher at metaphase II of stage VI, when compared to stage IV follicles. Tissue analysis revealed a predominant expression in gonads of trout and Xenopus (Fig. 6C and 6D). The expression of star in Xenopus testis was 60 times higher than in ovary. In contrast, expression of star in trout testis was six times lower than in ovary. Low expression levels were also evidenced in trout intestine and to a less extent in other tissues. Star mRNA expression was also detected in Xenopus stomach.


Comparative transcriptomic analysis of follicle-enclosed oocyte maturational and developmental competence acquisition in two non-mammalian vertebrates.

Gohin M, Bobe J, Chesnel F - BMC Genomics (2010)

star expression profiles during late oogenesis and tissue expression profiles. Expression profiles of star in rainbow trout ovary sampled from females during late vitellogenesis (LV, n = 6), post-vitellogenesis (PV, n = 14) and during maturation (Mat., n = 8) (A), in Xenopus laevis ovarian follicles sampled from six females, at stage IV, stage VI and after in vitro maturation (st VI MII) (B). Expression of star mRNA in rainbow trout tissues: brain (Br), heart (He), stomach (St), liver (Li), intestine (In), muscle (Mu), skin (Sk), post-vitellogenic ovary (Ov), and testis (Te) (C) and in Xenopus laevis tissues: brain (Br), heart (He), stomach (St), liver (Li), intestine (In), muscle (Mu), skin (Sk), ovary (Ov), testis (Te). Data were normalized to the abundance of 18S. Mean and SEM are shown. Bars sharing the same letter(s) are not significantly different (p > 0.05). In tissue, expression levels which are not significantly different from background signal are indicated with #.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2821372&req=5

Figure 6: star expression profiles during late oogenesis and tissue expression profiles. Expression profiles of star in rainbow trout ovary sampled from females during late vitellogenesis (LV, n = 6), post-vitellogenesis (PV, n = 14) and during maturation (Mat., n = 8) (A), in Xenopus laevis ovarian follicles sampled from six females, at stage IV, stage VI and after in vitro maturation (st VI MII) (B). Expression of star mRNA in rainbow trout tissues: brain (Br), heart (He), stomach (St), liver (Li), intestine (In), muscle (Mu), skin (Sk), post-vitellogenic ovary (Ov), and testis (Te) (C) and in Xenopus laevis tissues: brain (Br), heart (He), stomach (St), liver (Li), intestine (In), muscle (Mu), skin (Sk), ovary (Ov), testis (Te). Data were normalized to the abundance of 18S. Mean and SEM are shown. Bars sharing the same letter(s) are not significantly different (p > 0.05). In tissue, expression levels which are not significantly different from background signal are indicated with #.
Mentions: Star mRNA expression shows a progressive increase during late and/or post-vitellogenesis and a sharp increase during maturation in both species (Fig. 6A and 6B). In rainbow trout, star mRNA abundance is two times higher during post-vitellogenesis than during late vitellogenesis and six times higher during maturation than during late vitellogenesis. In Xenopus laevis, star mRNA abundance is four times higher at prophase I of stage VI and 40 times higher at metaphase II of stage VI, when compared to stage IV follicles. Tissue analysis revealed a predominant expression in gonads of trout and Xenopus (Fig. 6C and 6D). The expression of star in Xenopus testis was 60 times higher than in ovary. In contrast, expression of star in trout testis was six times lower than in ovary. Low expression levels were also evidenced in trout intestine and to a less extent in other tissues. Star mRNA expression was also detected in Xenopus stomach.

Bottom Line: We have successfully identified orthologous genes exhibiting conserved expression profiles in the ovarian follicle during late oogenesis in both trout and Xenopus.While some identified genes were previously uncharacterized during Xenopus late oogenesis, the nature of these genes has pointed out molecular mechanisms possibly conserved in amphibians and teleosts.It should also be stressed that in addition to the already suspected importance of steroidogenesis in maturational competence acquisition, our approach has shed light on other regulatory pathways which may be involved in maturational and developmental competence acquisitions that will require further studies.

View Article: PubMed Central - HTML - PubMed

Affiliation: CNRS/IGDR (UMR 6061), IFR140 GFAS, Université de Rennes I, 2, Avenue du Pr, Léon Bernard, 35043 Rennes Cedex, France. Julien.bobe@rennes.inra.fr.

ABSTRACT

Background: In vertebrates, late oogenesis is a key period during which the oocyte acquires its ability to resume meiosis (i.e. maturational competence) and to develop, once fertilized, into a normal embryo (i.e. developmental competence). However, the molecular mechanisms involved in these key biological processes are far from being fully understood. In order to identify key mechanisms conserved among teleosts and amphibians, we performed a comparative analysis using ovarian tissue sampled at successive steps of the maturational competence acquisition process in the rainbow trout (Oncorhynchus mykiss) and in the clawed toad (Xenopus laevis). Our study aimed at identifying common differentially expressed genes during late oogenesis in both species. Using an existing transcriptomic analysis that had previously been carried out in rainbow trout, candidate genes were selected for subsequent quantitative PCR-based comparative analysis.

Results: Among the 1200 differentially expressed clones in rainbow trout, twenty-six candidate genes were selected for further analysis by real-time PCR in both species during late oogenesis. Among these genes, eight had similar expression profiles in trout and Xenopus. Six genes were down-regulated during oocyte maturation (cyp19a1, cyp17a1, tescalcin, tfr1, cmah, hsd11b3) while two genes exhibited an opposite pattern (apoc1, star). In order to document possibly conserved molecular mechanisms, four genes (star, cyp19a1, cyp17a1 and hsd11b3) were further studied due to their known or suspected role in steroidogenesis after characterization of the orthology relationships between rainbow trout and Xenopus genes. Apoc1 was also selected for further analysis because of its reported function in cholesterol transport, which may modulate steroidogenesis by regulating cholesterol bioavailability in the steroidogenic cells.

Conclusions: We have successfully identified orthologous genes exhibiting conserved expression profiles in the ovarian follicle during late oogenesis in both trout and Xenopus. While some identified genes were previously uncharacterized during Xenopus late oogenesis, the nature of these genes has pointed out molecular mechanisms possibly conserved in amphibians and teleosts. It should also be stressed that in addition to the already suspected importance of steroidogenesis in maturational competence acquisition, our approach has shed light on other regulatory pathways which may be involved in maturational and developmental competence acquisitions that will require further studies.

Show MeSH
Related in: MedlinePlus