Masked mRNA is stored with aggregated nuclear speckles and its asymmetric redistribution requires a homolog of mago nashi

Abstract

BackgroundMany rapidly developing systems rely on the regulated translation of stored transcripts for the formation of new proteins essential for morphogenesis. The microspores of the water fern Marsilea vestita dehydrate as they mature. During this process both mRNA and proteins required for subsequent development are stored within the microspores as they become fully desiccated and enter into senescence. At this point microspores become transcriptionally silent and remain so upon rehydration and for the remainder of spermatogenesis. Transcriptional silencing coupled with the translation of preformed RNA makes the microspore of M. vestita a useful system in which to study post-transcriptional regulation of RNA.ResultsWe have characterized the distribution of mRNA as well as several conserved markers of subnuclear bodies within the nuclei of desiccating spores. During this period, nuclear speckles containing RNA were seen to aggregate forming a single large coalescence. We found that aggregated speckles contain several masked mRNA species known to be essential for spermatogenesis. During spermatogenesis masked mRNA and associated speckle proteins were shown to fragment and asymmetrically localize to spermatogenous but not sterile cells. This asymmetric localization was disrupted by RNAi knockdown of the Marsilea homolog of the Exon Junction Complex core component Mago nashi.ConclusionsA subset of masked mRNA is stored in association with nuclear speckles during the dormant phase of microspore development in M. vestita. The asymmetric distribution of specific mRNAs to spermatogenous but not sterile cells mirrors their translational activities and appears to require the EJC or EJC components. This suggests a novel role for nuclear speckles in the post-transcriptional regulation of transcripts.

Uncovering Divergence of Rice Exon Junction Complex Core Heterodimer Gene Duplication Reveals Their Essential Role in Growth, Development, and Reproduction

“…The cytohistological assays we conducted revealed that normal degradation and absorption of both endothecium and tapetum were inhibited, thus leading to defects in pollen maturation and morphology. Defects in pollen development were also observed in hapless1 (atmago) and AtMAGO-RNAi plants in Arabidopsis (Johnson et al, 2004;Park et al, 2009) and in the knockdowns of MvMAGO in M. vestita (van der Weele et al, 2007;Boothby and Wolniak, 2011). However, the transgenic rice plants in our study did not show any defects in floral meristem and seed development, as were observed in Arabidopsis (Park et al, 2009).…”

“…The Arabidopsis (Arabidopsis thaliana) AtMAGO gene is required for pollen grain development, and its knockout is lethal (Johnson et al, 2004;Park et al, 2009). Mutation of MvMAGO disrupts spermatogenesis in Marsilea vestita (van der Weele et al, 2007;Boothby and Wolniak, 2011). Besides, plant MAGO genes also seem to have broad roles in the growth and development of other plant organs.…”

Evidence for extensive horizontal gene transfer from the draft genome of a tardigrade

“…S6): When desiccated membranes are rehydrated, they become transiently leaky, making the uptake of large macromolecules possible (29), which has been exploited previously to introduce large nucleic acids and drugs into the cytoplasm of rehydrating anhydrobiotic cells (30)(31)(32). In addition, when tardigrades, rotifers, and other anhydrobionts desiccate, genomic double-stranded breakages and other damage are induced (19,33,34), and there appear to be robust mechanisms for repairing this damage (19,34).…”

Transcriptome analysis reveals a diverse family of kinesins essential for spermatogenesis in the fern Marsilea

“…Our early work showed that at most a small amount of new transcription might be required for late stages of development when mature spermatozoids emerge from the spore wall [Hart and Wolniak, ; Klink and Wolniak, ]. The transcripts are stored in the dry spore within nuclear speckles as partially processed pre‐mRNAs [Boothby and Wolniak, ]. During gametophyte development, the stored pre‐mRNAs become unmasked, spliced, polyadenylated, and translated in a precise spatio‐temporal relationship to form motile spermatozoids [Tsai et al, ; Boothby and Wolniak, ; Boothby et al, ].…”

“…The transcripts are stored in the dry spore within nuclear speckles as partially processed pre‐mRNAs [Boothby and Wolniak, ]. During gametophyte development, the stored pre‐mRNAs become unmasked, spliced, polyadenylated, and translated in a precise spatio‐temporal relationship to form motile spermatozoids [Tsai et al, ; Boothby and Wolniak, ; Boothby et al, ]. Since development is post‐transcriptionally regulated, we suspected that transcripts encoding proteins required for cell division would be available early in development, when the mitotic division cycles are occurring, and that those involved in spermatid differentiation and ciliogenesis would become available during later phases of spermiogenesis.…”