Ribonucleoproteins (RNP) condensates often contain intrinsically disordered proteins (IDPs) able to confer an exceptional multifunctionality necessary for gene expression, a process that defines cell types and enables cellular adaptation in metazoans. Centosomes, the microtubule-organizing centers of animal cells, are particularly enriched in disordered proteins but the role of RNPs surrounding the centrosome and the ciliary basal body remains largely unknown. By refining and integrating the existing protein-protein interaction network, spatial proteomics and transcriptomic data, we here report the subcellular and genomic proximity between the spliceosome, a huge nuclear RNP complex that removes introns from a transcribed pre-mRNA, and centrosome/cilia components. We present a comprehensive map of pre-RNA processing factors and other RNA-binding proteins playing a role in the regulation of splicing but localized to the centrosome and cilia. Protein-protein interactions studies reveal that a large number of spliceosome components interact with both centrosome linker and centriolar satellites elements, necessary for cellular division and ciliogenesis. RNAseq data from mouse Embryonic Stem Cells (mESC) and human tissues revealed a co-transcriptional coordination program of splicing and centrosome-related genes with relevance to tissue-specific neurosensory disorders and cancer types. Additionally, we found that centrosome and spliceosome genes form linearly and spatially colocalized genomic loci (CEP250, RBBM39, DHX35, and CTNNBL1) conserved in human and mouse genome, then explaining similarities in co-modification and subcellular distribution. Our results suggest that centrosome and cilia constitute cytoplasmic sites for the exchange of molecular machinery with nucleus, storage of RNA splicing and spliceosome condensates previously unrecognized. These complexes in response to external signals, could play an integral part in ciliogenesis and nuclear division to establish and maintain cellular identity in metazoans.

Recent data suggest that K-Ras4B (hereafter K-Ras) can drive cancer cell stemness via calmodulin (CaM)-dependent, non-canonical Wnt-signalling. Here we examined whether another Ca2+-binding protein, the CaM-related centrin1, binds to K-Ras and could mediate some K-Ras functions that were previously ascribed to CaM. While CaM and centrin1 appear to distinguish between peptides that were derived from their classical targets, they both bind to K-Ras in cells. Cellular BRET-data suggest that CaM engages more with K-Ras than centrin1 and that the interaction with the C-terminal membrane anchor of K-Ras is sufficient for this. Surprisingly, binding of neither K-Ras nor its membrane anchor alone to CaM or centrin1 is sensitive to inhibition of prenylation. In support of an involvement of the G-domain of K-Ras in cellular complexes with these Ca2+-binding proteins, we find that oncogenic K-RasG12V displays increased engagement with both CaM and centrin1. This is abrogated by addition of the D38A effector-site mutation, suggesting that K-RasG12V is held together with CaM or centrin1 in complexes with effectors. When treated with CaM-inhibitors the BRET-interaction of K-RasG12V with centrin1 was also disrupted in the low micromolar range, comparable to that with CaM. While CaM predominates in regulating functional membrane anchorage of K-Ras, it has a very similar co-distribution with centrin1 on mitotic organelles. Given these results, a significant overlap of the CaM- and centrin1-dependent functions of K-Ras is suggested.

Genetic activation of the class I PI3K pathway is very common in cancer. This mostly results from oncogenic mutations in PIK3CA, the gene encoding the ubiquitously expressed PI3Kα catalytic subunit, or from inactivation of the PTEN tumour suppressor, a lipid phosphatase which opposes class I PI3K signalling. The clinical impact of PI3K inhibitors in solid tumours, aimed at dampening cancer-cell-intrinsic PI3K activity, has thus far been limited. Challenges include poor drug tolerance, incomplete pathway inhibition and pre-existing or inhibitor-induced resistance. The principle of pharmacologically targeting cancer-cell-intrinsic PI3K activity also assumes that all cancer-promoting effects of PI3K activation are reversible, which might not be the case. Emerging evidence suggests that genetic PI3K pathway activation can induce and/or allow cells to tolerate chromosomal instability, which – even if occurring in a low fraction of the cell population – might help to facilitate and/or drive tumour evolution. While it is clear that such genomic events cannot be reverted pharmacologically, a role for PI3K in the regulation of chromosomal instability could be exploited by using PI3K pathway inhibitors to prevent those genomic events from happening and/or reduce the pace at which they are occurring, thereby dampening cancer development or progression. Such an impact might be most effective in tumours with clonal PI3K activation and achievable at lower drug doses than the maximum-tolerated doses of PI3K inhibitors currently used in the clinic.

Microtubule organizing centers (MTOCs) perform critical cellular tasks by nucleating, stabilizing and anchoring microtubule’s minus ends. These capacities impact tremendously a wide array of cellular functions ranging from ascribing cell shape to orchestrating cell division and generating motile structures, among others. The phylum Apicomplexa comprises over 6000 single-celled obligate intracellular parasitic species. Many of the apicomplexan are well known pathogens such as Toxoplasma gondii and the Plasmodium species, causative agents of toxoplasmosis and malaria, respectively. Microtubule organization in these parasites is critical for organizing the cortical cytoskeleton, enabling host cell penetration and the positioning of large organelles, drive cell division and direct the formation of flagella in sexual life stages. Apicomplexans are a prime example of MTOC diversity displaying multiple functional and structural MTOCs combinations within a single species. This diversity can only be fully understood in light of each organism's specific MT nucleation requirements and their evolutionary history. Insight into apicomplexan MTOCs had traditionally been limited to classical ultrastructural work by transmission electron microscopy. However, in the past few years, a large body of molecular insight has emerged. In this work we describe the latest insights into nuclear MTOC biology in two major human and animal disease causing Apicomplexans; Toxoplasma gondii and Plasmodium spp.

In zebrafish inner ear, hair cell orientation in anterior and posterior maculae of the embryonic otic vesicle is different (about 30–40 degrees): this is rather unusual in planar polarity mechanism of action, instead suggests that kinocilia may be rotationally polarized. In mice node, the innermost monociliated cells generate a left-ward fluid flow sensed by the immotile primary cilia of Left peri-nodal cells: the Nodal signaling pathway is then expressed asymmetrically, in the Left lateral plate mesoderm, breaking symmetry in visceral organs (situs solitus); however, Right peri-nodal cells also, if artificially excited by a right-ward flow, break symmetry and activate the Nodal cascade, though inverting visceral organ asymmetry (situs inversus); surprisingly, peri-nodal cells prove to be adept at distinguishing flow directionality. Recently, in the Kupffer vesicle (the zebrafish laterality organ), chiral primary cilia orientation has been described: primary cilia, in the left and right side, are symmetrically oriented, showing a mirror average divergence of about 15–20 degrees from the midline. This finding, taken together with the mirror behavior of mouse perinodal cells and zebrafish hair cells, champions the idea of primary cilia enantiomerism.