Zaytseva, Y. | Search bioRxiv

bioRxiv2026

GRAF1-dependent endocytotic processes and the Golgi apparatus contribute to novel intermediate stages of early ciliogenesis

The intracellular cilia assembly pathway is a complex, multistep process that requires the continuous and coordinated incorporation of membrane material. However, how membrane remodeling occurs during early ciliogenesis is not yet understood. Moreover, the identity of the organelle(s) that supply membrane material for the nascent cilium has yet to be determined. Here, we extend the current model of primary cilia formation by showing that randomly attached distal appendage vesicles and tubules fuse laterally to generate a doughnut-shaped membrane structure. Centripetal fusion events follow to close the central hole. Our data demonstrate that both the Golgi apparatus and endocytotic pathways independently contribute to ciliogenesis. We identify the endocytotic protein GRAF1 as being essential during the early stages of ciliogenesis and for the delivery of plasma membrane-derived material to the developing ciliary membrane. Our three-dimensional ultrastructural analysis uncovers previously unrecognized intermediate stages in the intracellular cilia assembly pathway with GRAF1 as a novel regulator of ciliogenesis.

cell biology↗

bioRxiv2025

PUM2 binds SARS-CoV-2 RNA and PUM1 mildly reduces viral RNA levels, but neither protein affects progeny virus production

Pumilio proteins (PUM1 and PUM2) are essential post-transcriptional regulators of gene expression found across plants, animals, and yeast. They bind Pumilio Response Elements (PREs) on messenger RNAs (mRNAs) to modulate mRNA stability and translation. PUMs have been implicated in diverse cellular processes, including stem cell maintenance, neurogenesis, and cell cycle regulation. They have also been reported to negatively regulate innate immunity genes and to participate in viral RNA sensing. Previous high-throughput interactome studies revealed that PUMs bind SARS-CoV-2 RNA. We found that SARS-CoV-2 transcripts contain multiple conserved PREs, some of which are preferentially bound by PUM2. Surprisingly, altering PUM levels does not affect the production of progeny virions. However, depletion of PUM1 slightly increases intracellular viral RNA levels, suggesting that PUM1 either plays a mild antiviral role against SARS-CoV-2 or regulates a host factor that promotes viral replication. Notably, PUM1 also negatively regulates innate immunity gene expression both at steady state and during SARS-CoV-2 infection. Our findings support a complex immunomodulatory role for PUM1, acting both as a negative regulator of innate immunity genes and a mild inhibitor of SARS-CoV-2 RNA accumulation. However, in cell culture, these roles appear negligible based on viral progeny output. Whether the multiple PREs found in the SARS-CoV-2 genome contribute to evasion of PUM1 activity remains an open question.

microbiology↗