Biology subjects

Capelson, M.

Publications and source records attributed to Capelson, M..

5 recordsLinked to original sources

bioRxiv2026

Nup98 regulates the G1/S transition

Nuclear pore complexes (NPCs) are embedded throughout the nuclear envelope of all eukaryotic cells and are composed of 30 unique proteins called nucleoporins (Nups). While Nups primarily function at NPCs, multiple Nups function in the nucleoplasm independent of the NPC. We previously found that Nup98-96 is necessary for entry into S phase in Drosophila cells, however, the mechanism is unknown. Here, we demonstrate that Nup98-96 is one of only a subset of Nup genes that can promote entry into S phase. We identify that transcripts dependent on Nup98-96 in Drosophila cells are enriched in cell cycle processes and that many of these transcripts are also dependent on the cell cycle regulator, E2f1. Importantly, we find that entry into S phase can be rescued by co-depleting the CycE/CDK2 inhibitor, dacapo, in Nup98-96-depleted cells. Furthermore, Nup96-98 promotes S phase entry across multiple cell and tissue types and cell cycle contexts. Critically, overexpression of Nup98 has a dominant-negative effect on entry into S phase in larval salivary glands, suggesting that Nup98, not Nup96, promotes entry into S phase. Our work identifies Nup98 as a key regulator of the G1/S transition in metazoans.

molecular biology↗

bioRxiv2026

Distinct functions of Nup93 paralogs in tumor growth and Polycomb-mediated repression of JAK/STAT signaling

Nuclear pore complexes (NPCs) are nuclear envelope (NE)-embedded protein assemblies that mediate nucleocytoplasmic exchange and interact with the genome, including binding of an NPC component Nup93 to Polycomb chromatin domains. Here, we investigated the in vivo relevance of this relationship in Drosophila, which unusually contains two distinct paralogs of Nup93. Interestingly, we identified a Nup93-2-specific tumorigenic phenotype in larval wings, where depletion of Nup93-2, but not Nup93-1, led to tumor-like overgrowth, reminiscent of Polycomb mutations. Consistently, our transcriptomic analysis revealed a wide-spread loss of gene silencing in Nup93-2-depleted wings, particularly in a Nup93-bound Polycomb domain spanning genes for activators of JAK/STAT signaling. Nup93 paralogs were not found to differ in their effect on NPC biogenesis but strikingly, showed differences in subnuclear localization patterns. While Nup93-1 co-localized exclusively with fully assembled NPCs, Nup93-2 exhibited only partial co-localization and was found at additional NE locations in a tissue-specific manner. Together, our results identify an in vivo silencing role of a Nup93 paralog and suggest that Nup93-2 may form a unique NE-associated complex that targets a subset of Polycomb domains containing growth-promoting genes.

developmental biology↗

bioRxiv2026

Developmentally programmed nuclear pore complex replacement enables oocyte specification

Oocytes endow embryos with molecular machinery essential for development, but not all maternal components are inherited indiscriminately. In Drosophila, surveillance pathways eliminate defective mitochondria and aberrant RNAs from the maternal pool. Whether stable nuclear structures, like nuclear pore complexes (NPCs), are similarly curated remains unknown. Here, we uncover a developmentally programmed NPC turnover pathway that renews NPCs during oocyte specification. NPC levels decline through a combination of passive dilution, driven by deferred nucleoporin expression, and active degradation mediated by the ESCRT-III/Vps4 pathway. This clearance is counterbalanced by subsequent de novo NPC synthesis. Failure to turn over NPCs results in aberrantly persistent germ cell gene expression and defective oocyte specification. These findings establish NPC renewal as a critical step in oocyte identity establishment and maternal provisioning.

developmental biology↗

bioRxiv2023

'Off-pore' nucleoporins relocalize heterochromatic breaks through phase separation

Phase separation forms membraneless compartments in the nuclei, including by establishing heterochromatin "domains" and repair foci. Pericentromeric heterochromatin mostly comprises repeated sequences prone to aberrant recombination, and "safe" homologous recombination (HR) repair of these sequences requires the movement of repair sites to the nuclear periphery before Rad51 recruitment and strand invasion. How this mobilization initiates is unknown, and the contribution of phase separation to these dynamics is unclear. Here, we show that Nup98 nucleoporin is recruited to heterochromatic repair sites before relocalization through Sec13 or Nup88 nucleoporins, and downstream from the Smc5/6 complex and SUMOylation. Remarkably, the phase separation properties of Nup98 are required and sufficient to mobilize repair sites and exclude Rad51, thus preventing aberrant recombination while promoting HR repair. Disrupting this pathway results in heterochromatin repair defects and widespread chromosome rearrangements, revealing a novel "off-pore" role for nucleoporins and phase separation in nuclear dynamics and genome integrity in a multicellular eukaryote. HighlightsO_LINup88 and Sec13 recruit Nup98 to heterochromatic DSBs downstream from Smc5/6 C_LIO_LINup88, Sec13 and Nup98 promote repair focus mobilization in heterochromatin off-pore C_LIO_LINup98 excludes Rad51 from repair sites inside the heterochromatin domain C_LIO_LIPhase separation by Nup98 is required and sufficient for relocalization and Rad51 exclusion C_LI

cell biology↗

bioRxiv2020

Nup98-dependent transcriptional memory is established independently of transcription

Cellular ability to mount an enhanced transcriptional response upon repeated exposure to external cues has been termed transcriptional memory, which can be maintained epigenetically through cell divisions. The majority of mechanistic knowledge on transcriptional memory has been derived from bulk molecular assays, and this phenomenon has been found to depend on a nuclear pore component Nup98 in multiple species. To gain an alternative perspective on the mechanism and on the contribution of Nup98, we set out to examine single-cell population dynamics of transcriptional memory by monitoring transcriptional behavior of individual Drosophila cells upon initial and subsequent exposures to steroid hormone ecdysone. To this end, we combined single-molecule RNA FISH with mathematical modeling, and found that upon hormone exposure, cells rapidly activate a low-level transcriptional response, but simultaneously, begin a slow transitioning into a specialized memory state, characterized by a high rate of expression. Strikingly, our modeling predicted that this transition between non-memory and memory states is independent of the transcription stemming from initial activation, and we were able to confirm this prediction experimentally by showing that inhibiting transcription during initial ecdysone exposure did not interfere with memory establishment. Together, our findings reveal that Nup98s role in transcriptional memory is to stabilize the forward rate of conversion from low to high expressing state, and that induced genes engage in two separate behaviors - transcription itself and the establishment of epigenetically propagated transcriptional memory.

molecular biology↗