Dormancy in embryos: insight from hydrated encysted embryos of an aquatic invertebrate [Research]

Numerous aquatic invertebrates remain dormant for decades in a hydrated state as encysted embryos. In search for functional pathways associated with this form of dormancy, we used label-free quantitative proteomics to compare the proteomes of hydrated encysted dormant embryos (resting eggs; RE) with non-dormant embryos (amictic eggs; AM) of the rotifer Brachionus plicatilis.</p> <p>A total of 2,631 proteins were identified in rotifer eggs. About 62% proteins showed higher abundance in AM relative to RE (Fold Change>3; p=0.05). Proteins belonging to numerous putative functional pathways showed differences in abundance in RE, demonstrating the dramatic changes during dormancy. Most striking were changes in the mitochondria, including a lower abundance of ribosomal, citrate (TCA) cycle and oxidative phosphorylation proteins. ATP was not detected in RE and TCA cycle metabolites were significantly lower in RE, indicating an impeded metabolism.</p> <p>A comparison between the abundance of proteins and their corresponding transcript levels, revealed higher concordance for RE than for AM. Surprisingly, numerous highly abundant dormancy related proteins show corresponding high mRNA levels in RE, raising a question on the role of mRNAs in metabolically inactive REs, as these mRNAs and proteins degrade at the time of exit from dormancy. It is proposed that these highly abundant mRNAs and proteins, may serve as a source of nucleotides and amino acids with the resumption of transcription and translation, during the exit from dormancy. Since proteome analyses point to a similarity in functional pathways of hydrated RE and desiccated life forms, REs were dried. Similar hatching levels and reproductive rates were found for wet and dried REs, suggesting analogous pathways for long-term survival in wet or dry forms. Analyses by KEGG pathways revealed a few general strategies for dormancy, proposing an explanation for the low transcriptional similarity among dormancies across species, despite the resemblance in physiological phenotypes.

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