Limits...
Discovering genes associated with dormancy in the monogonont rotifer Brachionus plicatilis.

Denekamp NY, Thorne MA, Clark MS, Kube M, Reinhardt R, Lubzens E - BMC Genomics (2009)

Bottom Line: Real-time PCR confirmed that LEA transcripts, small heat-shock proteins and some antioxidant genes were upregulated in resting eggs, therefore suggesting that desiccation tolerance is a characteristic feature of resting eggs even though they do not necessarily fully desiccate during dormancy.The 47,926 ESTs expand significantly the current sequence resource of B. plicatilis.It describes, for the first time, genes putatively associated with resting eggs and will serve as a database for future global expression experiments, particularly for the further identification of dormancy related genes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Israel Oceanographic and Limnological Research, Haifa 31080, Israel. nadavd@ocean.org.il

ABSTRACT

Background: Microscopic monogonont rotifers, including the euryhaline species Brachionus plicatilis, are typically found in water bodies where environmental factors restrict population growth to short periods lasting days or months. The survival of the population is ensured via the production of resting eggs that show a remarkable tolerance to unfavorable conditions and remain viable for decades. The aim of this study was to generate Expressed Sequence Tags (ESTs) for molecular characterisation of processes associated with the formation of resting eggs, their survival during dormancy and hatching.

Results: Four normalized and four subtractive libraries were constructed to provide a resource for rotifer transcriptomics associated with resting-egg formation, storage and hatching. A total of 47,926 sequences were assembled into 18,000 putative transcripts and analyzed using both Blast and GO annotation. About 28-55% (depending on the library) of the clones produced significant matches against the Swissprot and Trembl databases. Genes known to be associated with desiccation tolerance during dormancy in other organisms were identified in the EST libraries. These included genes associated with antioxidant activity, low molecular weight heat shock proteins and Late Embryonic Abundant (LEA) proteins. Real-time PCR confirmed that LEA transcripts, small heat-shock proteins and some antioxidant genes were upregulated in resting eggs, therefore suggesting that desiccation tolerance is a characteristic feature of resting eggs even though they do not necessarily fully desiccate during dormancy. The role of trehalose in resting-egg formation and survival remains unclear since there was no significant difference between resting-egg producing females and amictic females in the expression of the tps-1 gene. In view of the absence of vitellogenin transcripts, matches to lipoprotein lipase proteins suggest that, similar to the situation in dipterans, these proteins may serve as the yolk proteins in rotifers.

Conclusion: The 47,926 ESTs expand significantly the current sequence resource of B. plicatilis. It describes, for the first time, genes putatively associated with resting eggs and will serve as a database for future global expression experiments, particularly for the further identification of dormancy related genes.

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The life cycle of Brachionus plicatilis showing asexual and sexual reproduction and formation of resting eggs. In the asexual life cycle, diploid amictic females produce parthenogenetic diploid amictic eggs. A mixis signal initiates the occurrence of a sexual cycle, whereby, diploid mictic females produce haploid eggs via meiosis. The haploid eggs develop into either haploid males or, if fertilized, they form diploid dormant (or diapausing) resting eggs. The internal insemination of diploid mictic females carrying haploid eggs, is possible for only a few hours after birth. Mictic females are shaded in grey and include mictic females producing male eggs or mictic females that form diploid resting eggs. All females are diploid while males are haploid.
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Figure 1: The life cycle of Brachionus plicatilis showing asexual and sexual reproduction and formation of resting eggs. In the asexual life cycle, diploid amictic females produce parthenogenetic diploid amictic eggs. A mixis signal initiates the occurrence of a sexual cycle, whereby, diploid mictic females produce haploid eggs via meiosis. The haploid eggs develop into either haploid males or, if fertilized, they form diploid dormant (or diapausing) resting eggs. The internal insemination of diploid mictic females carrying haploid eggs, is possible for only a few hours after birth. Mictic females are shaded in grey and include mictic females producing male eggs or mictic females that form diploid resting eggs. All females are diploid while males are haploid.

Mentions: Brachionus plicatilis shows periodic parthenogenesis, where asexual reproduction is prevalent but under certain circumstances sexual reproduction occurs (Figure 1). Parthenogenesis dominates (amictic phase) the monogonont life cycle in the absence of males, but following certain environmental cues, sexual reproduction (mictic phase) takes place. Females that reproduce asexually are termed "amictic" and females that reproduce sexually are "mictic". Amictic females produce diploid eggs that develop by ameiotic pathenogenesis into females. Mictic females are morphologically similar to amictic females but produce haploid (mictic) eggs via meiosis. These eggs will develop parthenogenetically into haploid males but if these mictic females are fertilized they will produce diploid resting eggs. The haploid males are significantly smaller than the females and move faster. The mictic females produce resting eggs only if they are inseminated at a young age. Resting-egg production is therefore a consequence of switching from an asexual type of reproduction to sexual reproduction. Resting eggs then undergo obligatory diapause or dormancy, eventually hatching as amictic females [2,5-8]. It has also been suggested that certain clones show a higher tendency for sexual reproduction and resting-egg production than others, within the same population [9,10]. The factors inducing the mixis signal are largely unknown, although population density and environmental factors such as salinity, presence of pheromones and food availability have been shown to play a role [11-15].


Discovering genes associated with dormancy in the monogonont rotifer Brachionus plicatilis.

Denekamp NY, Thorne MA, Clark MS, Kube M, Reinhardt R, Lubzens E - BMC Genomics (2009)

The life cycle of Brachionus plicatilis showing asexual and sexual reproduction and formation of resting eggs. In the asexual life cycle, diploid amictic females produce parthenogenetic diploid amictic eggs. A mixis signal initiates the occurrence of a sexual cycle, whereby, diploid mictic females produce haploid eggs via meiosis. The haploid eggs develop into either haploid males or, if fertilized, they form diploid dormant (or diapausing) resting eggs. The internal insemination of diploid mictic females carrying haploid eggs, is possible for only a few hours after birth. Mictic females are shaded in grey and include mictic females producing male eggs or mictic females that form diploid resting eggs. All females are diploid while males are haploid.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2667189&req=5

Figure 1: The life cycle of Brachionus plicatilis showing asexual and sexual reproduction and formation of resting eggs. In the asexual life cycle, diploid amictic females produce parthenogenetic diploid amictic eggs. A mixis signal initiates the occurrence of a sexual cycle, whereby, diploid mictic females produce haploid eggs via meiosis. The haploid eggs develop into either haploid males or, if fertilized, they form diploid dormant (or diapausing) resting eggs. The internal insemination of diploid mictic females carrying haploid eggs, is possible for only a few hours after birth. Mictic females are shaded in grey and include mictic females producing male eggs or mictic females that form diploid resting eggs. All females are diploid while males are haploid.
Mentions: Brachionus plicatilis shows periodic parthenogenesis, where asexual reproduction is prevalent but under certain circumstances sexual reproduction occurs (Figure 1). Parthenogenesis dominates (amictic phase) the monogonont life cycle in the absence of males, but following certain environmental cues, sexual reproduction (mictic phase) takes place. Females that reproduce asexually are termed "amictic" and females that reproduce sexually are "mictic". Amictic females produce diploid eggs that develop by ameiotic pathenogenesis into females. Mictic females are morphologically similar to amictic females but produce haploid (mictic) eggs via meiosis. These eggs will develop parthenogenetically into haploid males but if these mictic females are fertilized they will produce diploid resting eggs. The haploid males are significantly smaller than the females and move faster. The mictic females produce resting eggs only if they are inseminated at a young age. Resting-egg production is therefore a consequence of switching from an asexual type of reproduction to sexual reproduction. Resting eggs then undergo obligatory diapause or dormancy, eventually hatching as amictic females [2,5-8]. It has also been suggested that certain clones show a higher tendency for sexual reproduction and resting-egg production than others, within the same population [9,10]. The factors inducing the mixis signal are largely unknown, although population density and environmental factors such as salinity, presence of pheromones and food availability have been shown to play a role [11-15].

Bottom Line: Real-time PCR confirmed that LEA transcripts, small heat-shock proteins and some antioxidant genes were upregulated in resting eggs, therefore suggesting that desiccation tolerance is a characteristic feature of resting eggs even though they do not necessarily fully desiccate during dormancy.The 47,926 ESTs expand significantly the current sequence resource of B. plicatilis.It describes, for the first time, genes putatively associated with resting eggs and will serve as a database for future global expression experiments, particularly for the further identification of dormancy related genes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Israel Oceanographic and Limnological Research, Haifa 31080, Israel. nadavd@ocean.org.il

ABSTRACT

Background: Microscopic monogonont rotifers, including the euryhaline species Brachionus plicatilis, are typically found in water bodies where environmental factors restrict population growth to short periods lasting days or months. The survival of the population is ensured via the production of resting eggs that show a remarkable tolerance to unfavorable conditions and remain viable for decades. The aim of this study was to generate Expressed Sequence Tags (ESTs) for molecular characterisation of processes associated with the formation of resting eggs, their survival during dormancy and hatching.

Results: Four normalized and four subtractive libraries were constructed to provide a resource for rotifer transcriptomics associated with resting-egg formation, storage and hatching. A total of 47,926 sequences were assembled into 18,000 putative transcripts and analyzed using both Blast and GO annotation. About 28-55% (depending on the library) of the clones produced significant matches against the Swissprot and Trembl databases. Genes known to be associated with desiccation tolerance during dormancy in other organisms were identified in the EST libraries. These included genes associated with antioxidant activity, low molecular weight heat shock proteins and Late Embryonic Abundant (LEA) proteins. Real-time PCR confirmed that LEA transcripts, small heat-shock proteins and some antioxidant genes were upregulated in resting eggs, therefore suggesting that desiccation tolerance is a characteristic feature of resting eggs even though they do not necessarily fully desiccate during dormancy. The role of trehalose in resting-egg formation and survival remains unclear since there was no significant difference between resting-egg producing females and amictic females in the expression of the tps-1 gene. In view of the absence of vitellogenin transcripts, matches to lipoprotein lipase proteins suggest that, similar to the situation in dipterans, these proteins may serve as the yolk proteins in rotifers.

Conclusion: The 47,926 ESTs expand significantly the current sequence resource of B. plicatilis. It describes, for the first time, genes putatively associated with resting eggs and will serve as a database for future global expression experiments, particularly for the further identification of dormancy related genes.

Show MeSH
Related in: MedlinePlus