Moravec, C. | Search bioRxiv

bioRxiv2024

A maternally inherited Chromosomal Passenger Complex regulates germ plasm ribonucleoparticle aggregation in Zebrafish

In zebrafish, the formation of primordial germ cells depends on the inheritance of a compartmentalized membrane-less subcellular structure containing a pool of maternally expressed germ plasm ribonucleoparticles (gpRNPs) and proteins. Interactions between cytoskeletal components and gpRNPs are crucial for the movement and collection of gpRNPs into the furrows during the first few cellular division of the early embryo. Previous work has identified motley/ birc5b, a maternally-expressed homolog of a known Chromosomal Passenger Complex (CPC) component, Survivin, as a linker between gpRNPs and microtubules during gpRNP aggregation. However, Survivin can also function independent of the CPC in other cellular contexts. Here we investigated whether a maternally inherited CPC is necessary for gpRNP aggregation. We identified cdca9 as a maternally-expressed duplicated homolog of Borealin, another member of the CPC. Similar to motley, embryos from homozygous cdca9 mutant females exhibit defects in chromosome segregation and cytokinesis during meiosis and mitosis, phenotypes associated with mutations in CPC members. Additionally, embryos lacking Cdca9 displayed decreased gpRNP aggregation prior to furrow formation in the early embryo, a phenotype indistinguishable from that observed in motley mutants. As previously shown for Birc5b, Cdca9 and other CPC components INCENP and Aurora B kinase colocalize at the tips of astral microtubules as gpRNPs are transported to the forming furrow. Unexpectedly, Birc5b, but not other CPC components, accumulates within the growing gpRNP aggregate prior to and during furrow formation. The association of Birc5b with germ plasm masses continues during their asymmetric segregation in the cleavage stages, ceasing only when gpRNPs undergo cytoplasmic dispersal during gastrulation. Our studies reveal a role for a non-conventional, maternally-inherited CPC for spindle and furrow formation, and, unexpectedly, gpRNP aggregation during early development. Additionally, we find that Birc5b, but not other CPC proteins, remains a component of zebrafish germ plasm during and after its aggregation. Author SummaryMaternal products are necessary for early development across species, and the removal of these products from the embryo can cause developmental defects or death. The zebrafish has been widely used to discover the role of maternal products during early development. Using zebrafish, we discovered that a mutation in a maternal-specific duplicated borealin gene not only affects early development but also the aggregation of germ cell determinants. We also find that this duplicated Borealin interacts within a specialized Chromosomal Passenger Complex, a complex that traditionally regulates multiple steps of cellular division. This specialized Chromosomal Passenger Complex acts as a linker between germ cell determinants and the cytoskeleton during early development. These results highlight a unique role for the Chromosomal Passenger Complex outside of cellular division during early development. Further, these findings underscore the intricate mechanisms by which gene duplications contribute to the regulation of early developmental processes, providing valuable insight into the molecular events of embryogenesis.

developmental biology↗

bioRxiv2022

The midbody and midbody remnant are assembly sites for RNA and active translation

The midbody (MB) is a transient structure at the spindle midzone that is required for cytokinesis, the terminal stage of cell division. Long ignored as a vestigial remnant of cytokinesis, we now know MBs are released post-abscission as extracellular vesicles called MB remnants (MBRs) and can modulate cell proliferation, fate decisions, tissue polarity, neuronal architecture, and tumorigenic behavior. Here, we demonstrate that the MB matrix--the structurally amorphous MB core of unknown composition--is the site of ribonucleoprotein assembly and is enriched in mRNAs that encode proteins involved in cell fate, oncogenesis, and pluripotency, that we are calling the MB granule. Using a quantitative transcriptomic approach, we identified a population of mRNAs enriched in mitotic MBs and confirmed their presence in signaling MBR vesicles released by abscission. The MB granule is unique in that it is translationally active, contains both small and large ribosomal subunits, and has both membrane-less and membrane-bound states. Both MBs and post-abscission MBRs are sites of spatiotemporally regulated translation, which is initiated when nascent daughter cells re-enter G1 and continues after extracellular release. We demonstrate that the MB is the assembly site of an RNP granule. MKLP1 and ARC are necessary for the localization and translation of RNA in the MB dark zone, whereas ESCRT-III was necessary to maintain translation levels in the MB. Our data suggest a model in which the MB functions as a novel RNA-based organelle with a uniquely complex life cycle. We present a model in which the assembly and transfer of RNP complexes are central to post-mitotic MBR function and suggest the MBR serves as a novel mode of RNA-based intercellular communication with a defined biogenesis that is coupled to abscission, and inherently links cell division status with signaling capacity. To our knowledge, this is the first example of an autonomous extracellular vesicle with active translation activity. HighlightsO_LIThe MB, the center region of the intercellular bridge, is the assembly site of a ribonucleoprotein granule, we call the MB granule C_LIO_LIDistinct oncogenic and pluripotent transcription factor RNAs, including Jun/Fos and KLF4, are packaged in MBs and MBRs C_LIO_LIThe MB granule is coincident with the MB matrix, or dark zone, of the MB C_LIO_LIThe Kif23/MKLP1 kinesin is a core hexanediol-sensitive MB granule component C_LIO_LIThe MB and MBR are site of active translation that begins in early G1 and continues post-mitotically C_LIO_LIMKLP1 and ARC are necessary for RNA targeting/maintenance and translation at the MB C_LIO_LIDepletion of ESCRT-III increases the levels of translation during abscission C_LIO_LIAbscission releases MBRs as MB granule-harboring, translating extracellular vesicles C_LIO_LIMultiple cell types including cancer, stem, neural stem, all have actively translating MBRs C_LIO_LIMBRs are proposed as a novel mode of intercellular communication by extracellular vesicle-mediated direct transfer of RNA C_LI

cell biology↗