Chromosome alignment at the equator of the mitotic spindle is a highly conserved step during cell division; however, its importance to genomic stability and cellular fitness is not understood. Normal mammalian somatic cells lacking KIF18A function complete cell division without aligning chromosomes. These alignment-deficient cells display normal chromosome copy numbers in vitro and in vivo, suggesting that chromosome alignment is largely dispensable for maintenance of euploidy. However, we find that loss of chromosome alignment leads to interchromosomal compaction defects during anaphase, abnormal organization of chromosomes into a single nucleus at mitotic exit, and the formation of micronuclei in vitro and in vivo. These defects slow cell proliferation and are associated with impaired postnatal growth and survival in mice. Our studies support a model in which the alignment of mitotic chromosomes promotes proper organization of chromosomes into a single nucleus and continued proliferation by ensuring that chromosomes segregate as a compact mass during anaphase.

Dendritic cells (DCs) activated via TLR ligation experience metabolic reprogramming, in which the cells are heavily dependent on glucose and glycolysis for the synthesis of molecular building blocks essential for maturation, cytokine production, and the ability to stimulate T cells. Although the TLR-driven metabolic reprogramming events are well documented, fungal-mediated metabolic regulation via C-type Lectin Receptors such as Dectin-1 and Dectin-2 is not clearly understood. Here, we show that activation of DCs with fungal-associated β-glucan ligands induces acute glycolytic reprogramming that supports the production of IL-1β and its secretion subsequent to NLRP3 inflammasome activation. This acute glycolytic induction in response to β-glucan ligands requires Syk signaling in a TLR-independent manner, suggesting now that different classes of innate immune receptors functionally induce conserved metabolic responses to support immune cell activation. These studies provide new insight into the complexities of metabolic regulation of DCs immune effector function regarding cellular activation associated with protection against fungal microbes.

Micronuclei, whole or fragmented chromosomes spatially separated from the main nucleus, are associated with genomic instability and have been identified as drivers of tumorigenesis. Paradoxically, Kif18a mutant mice produce micronuclei due to asynchronous segregation of unaligned chromosomes in vivo but do not develop spontaneous tumors. We report here that micronuclei in Kif18a mutant mice form stable nuclear envelopes. Challenging Kif18a mutant mice via deletion of the Trp53 gene led to formation of thymic lymphoma with elevated levels of micronuclei. However, loss of Kif18a had modest or no effect on survival of Trp53 homozygotes and heterozygotes, respectively. Micronuclei in cultured KIF18A KO cells form stable nuclear envelopes characterized by increased recruitment of nuclear envelope components and successful expansion of decondensing chromatin compared with those induced by nocodazole washout or radiation. Lagging chromosomes were also positioned closer to the main chromatin masses in KIF18A KO cells. These data suggest that not all micronuclei actively promote tumorigenesis.

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During the cell cycle, differential phosphorylation of select histone H3 serine/threonine residues regulates chromatin structure, necessary for both dynamic transcriptional control and proper chromosome segregation1-2. Histone H3.3 contains a highly conserved serine residue (Ser31) within its N-terminal tail that is unique to this variant. During interphase phosphorylation of Ser31 amplifies stimulation-induced transcription and is required for early metazoan development3-6. During mitosis Ser31 phosphorylation at the pericentromere supports proper chromosome segregation, albeit by unknown mechanisms7-10. H3.3 Ser31 is flanked by mutational sites that drive several human cancers, including pediatric gliomas5-8. This is typified by the H3.3K27M mutation found in ∼80% of diffuse midline gliomas, which undergo epigenetic reprogramming in proliferative cells coordinate with loss of global H3 lysine 27 trimethylation (H3K27Me3)11-14. However, whether the K27M mutation influences the neighboring Ser31 phosphorylation and whether disrupting Ser31 phosphorylation plays a distinct role in driving gliomagenesis has not been tested. Here we show that H3.3K27M mutant cells have reduced capacity for H3.3 Ser31 phosphorylation at the mitotic pericentromere, increased rates of chromosome missegregation, and impaired G1 checkpoint responses to chromosome instability. CRISPR-reversion of K27M to wild-type restores phospho-Ser31 levels and suppresses chromosome segregation defects. CRISPR editing to introduce a non-phosphorylatable H3.3S31A alone is sufficient to increase the frequency of chromosome missegregations. Finally, expression of H3.3S31A in a PDGFβ-driven RCAS/TVA mouse model is sufficient to drive high grade gliomagenesis, generating diffuse tumors morphologically indistinguishable from those generated by H3.3K27M expression. Importantly, this occurs without the loss of H3K27 triple methylation that is the hallmark of K27M tumors. Our results reveal that the H3.3 K27M mutation alters the neighboring Ser31 phosphorylation, and loss of proper H3.3 Ser31 phosphorylation contributes to the formation of diffuse midline gliomas.