Nuclear assembly shaped by microtubule dynamics.

Maintenance of nuclear architecture is crucial for gene regulation, cell proliferation and tissue development. However, during every open mitosis and meiosis, chromosomes are exposed to cytoskeletal forces until they are fully reassembled into mature nuclei. Here we discuss our recent study of nuclear assembly in Xenopus egg extracts, where we showed that the DNA binding protein Developmental pluripotency associated 2 (Dppa2) directly inhibits microtubule polymerization during nuclear formation, and that this is essential for normal nuclear shape and replication. We explore mechanisms by which microtubule dynamics could regulate nuclear formation and morphology, and discuss the importance of both spatial and temporal regulation of microtubules in this process. Moreover, expression of Dppa2 is limited to the early embryo and pluripotent tissues, and we highlight the specific demands of mitosis in these often rapidly dividing cells, in which telophase nuclear assembly must be expedited and may facilitate developmental changes in nuclear architecture.

Adiponectin receptor signaling on dendritic cells blunts antitumor immunity.

Immune escape is a fundamental trait of cancer. Dendritic cells (DC) that interact with T cells represent a crucial site for the development of tolerance to tumor antigens, but there remains incomplete knowledge about how DC-tolerizing signals evolve during tumorigenesis. In this study, we show that DCs isolated from patients with metastatic or locally advanced breast cancer express high levels of the adiponectin receptors AdipoR1 and AdipoR2, which are sufficient to blunt antitumor immunity. Mechanistic investigations of ligand-receptor interactions on DCs revealed novel signaling pathways for each receptor. AdipoR1 stimulated IL10 production by activating the AMPK and MAPKp38 pathways, whereas AdipoR2 modified inflammatory processes by activating the COX-2 and PPARγ pathways. Stimulation of these pathways was sufficient to block activation of NF-κB in DC, thereby attenuating their ability to stimulate antigen-specific T-cell responses. Together, our findings reveal novel insights into how DC-tolerizing signals evolve in cancer to promote immune escape. Furthermore, by defining a critical role for adiponectin signaling in this process, our work suggests new and broadly applicable strategies for immunometabolic therapy in patients with cancer.

Chromatin-bound Xenopus Dppa2 shapes the nucleus by locally inhibiting microtubule assembly.

Nuclear shape and size vary between species, during development, and in many tissue pathologies, but the causes and effects of these differences remain poorly understood. During fertilization, sperm nuclei undergo a dramatic conversion from a heavily compacted form into decondensed, spherical pronuclei, accompanied by rapid nucleation of microtubules from centrosomes. Here we report that the assembly of the spherical nucleus depends on a critical balance of microtubule dynamics, which is regulated by the chromatin-binding protein Developmental pluripotency-associated 2 (Dppa2). Whereas microtubules normally promote sperm pronuclear expansion, in Dppa2-depleted Xenopus egg extracts excess microtubules cause pronuclear assembly defects, leading to abnormal morphology and disorganized DNA replication. Dppa2 inhibits microtubule polymerization in vitro, and Dppa2 activity is needed at a precise time and location during nascent pronuclear formation. This demonstrates a strict spatiotemporal requirement for local suppression of microtubules during nuclear formation, fulfilled by chromatin-bound microtubule regulators.

Survivin reads phosphorylated histone H3 threonine 3 to activate the mitotic kinase Aurora B.

A hallmark of mitosis is the appearance of high levels of histone phosphorylation, yet the roles of these modifications remain largely unknown. Here, we demonstrate that histone H3 phosphorylated at threonine 3 is directly recognized by an evolutionarily conserved binding pocket in the BIR domain of Survivin, which is a member of the chromosomal passenger complex (CPC). This binding mediates recruitment of the CPC to chromosomes and the resulting activation of its kinase subunit Aurora B. Consistently, modulation of the kinase activity of Haspin, which phosphorylates H3T3, leads to defects in the Aurora B-dependent processes of spindle assembly and inhibition of nuclear reformation. These findings establish a direct cellular role for mitotic histone H3T3 phosphorylation, which is read and translated by the CPC to ensure accurate cell division.