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Symmetric cell division requires the even partitioning of genetic information and cytoplasmic contents between daughter cells. Whereas the mechanisms coordinating the segregation of the genome are well known, the processes that ensure organelle segregation between daughter cells remain less well understood1. Here we identify multiple actin assemblies with distinct but complementary roles in mitochondrial organization and inheritance in mitosis. First, we find a dense meshwork of subcortical actin cables assembled throughout the mitotic cytoplasm. This network scaffolds the endoplasmic reticulum and organizes three-dimensional mitochondrial positioning to ensure the equal segregation of mitochondrial mass at cytokinesis. Second, we identify a dynamic wave of actin filaments reversibly assembling on the surface of mitochondria during mitosis. Mitochondria sampled by this wave are enveloped within actin clouds that can spontaneously break symmetry to form elongated comet tails. Mitochondrial comet tails promote randomly directed bursts of movement that shuffle mitochondrial position within the mother cell to randomize inheritance of healthy and damaged mitochondria between daughter cells. Thus, parallel mechanisms mediated by the actin cytoskeleton ensure both equal and random inheritance of mitochondria in symmetrically dividing cells.During mitosis, complementary actin-based mechanisms ensure equal and random distributions of mitochondria among daughter cells following symmetrical cell division. [ABSTRACT FROM AUTHOR]

Parkinson disease (PD)-causing mutations in the LRRK2 (leucine rich repeat kinase 2) gene hyperactivate LRRK2 kinase activity. Here, we discuss our recent work linking LRRK2 hyperactivation to defective axonal autophagosome transport in neurons. In three different models, we observed that expression of the most common causative mutation for PD, LRRK2G2019S, disrupts processive autophagosome transport in a kinase-dependent manner. Mechanistically, we found that hyperactive LRRK2 recruits SPAG9/JIP4, a motor adaptor known to bind to LRRK2-phosphorylated RAB proteins, to the autophagosomal membrane. Increased SPAG9/JIP4 levels induce abnormal recruitment and activation of kinesin-1, which we propose results in an unproductive tug-of-war between anterograde and retrograde motors bound to autophagosomes. Disruption of autophagosome transport correlates with defective autophagosome maturation, suggesting that hyperactive LRRK2 may impair efficient degradation of autophagosomal cargo. Our work demonstrates that LRRK2 hyperactivation is sufficient to induce defects in autophagosome transport and maturation, further establishing a role of defective autophagy in the pathogenesis of PD. [ABSTRACT FROM AUTHOR]

Gain-of-function mutations in the LRRK2 gene cause Parkinson's disease (PD), increasing phosphorylation of RAB GTPases through hyperactive kinase activity. We find that LRRK2-hyperphosphorylated RABs disrupt the axonal transport of autophagosomes by perturbing the coordinated regulation of cytoplasmic dynein and kinesin. In iPSC-derived human neurons, knockin of the strongly hyperactive LRRK2 -p.R1441H mutation causes striking impairments in autophagosome transport, inducing frequent directional reversals and pauses. Knockout of the opposing protein phosphatase 1H (PPM1H) phenocopies the effect of hyperactive LRRK2. Overexpression of ADP-ribosylation factor 6 (ARF6), a GTPase that acts as a switch for selective activation of dynein or kinesin, attenuates transport defects in both p.R1441H knockin and PPM1H knockout neurons. Together, these findings support a model where a regulatory imbalance between LRRK2-hyperphosphorylated RABs and ARF6 induces an unproductive "tug-of-war" between dynein and kinesin, disrupting processive autophagosome transport. This disruption may contribute to PD pathogenesis by impairing the essential homeostatic functions of axonal autophagy. [Display omitted] • Parkinson's-associated LRRK2 -p.R1441H impairs axonal autophagosomal transport • Knockout of LRRK2-opposing phosphatase PPM1H phenocopies hyperactive LRRK2 • Transport deficits are linked to regulatory imbalance between ARF6 and phospho-RABs Dou et al. find that the opposing activities of LRRK2 kinase and PPM1H phosphatase dictate a regulatory balance for the motors that drive axonal autophagosome transport. Hyperactive LRRK2, which is associated with Parkinson's disease (PD), is predicted to contribute to PD pathogenesis by disrupting the essential homeostatic pathway of autophagy. [ABSTRACT FROM AUTHOR]

The presence. phenotype. and functional characteristics of peripheral blood penicillin-specific T lymphocytes in individuals with cutaneous allergic reactions to penicillin were investigated using in vitro long-term culture techniques. Peripheral blood mononuclear cells from two penicillin-allergic patients were stimulated in vitro with penicillin, and `F-cell blasts were clonally expanded by limiting dilution. Seven T-cell clones were derived, all of which were CD3+ CD4&mn; CD8+ HLA-DR4+, and produced IL-2 and IFN-γ upon stimulation. T-cell proliferation required the presence of antigen and autologous. but not allogeneic. antigen-presenting cells. In addition to the parent compound. the T- cell clones also developed a proliferative response to penicilloyl. the major metabolite of penicillin. The cloned T-cell lines were found to exhibit marked suppressor activity for Con A mitogenesis. The observed suppressor activity required cell-to-cell contact, as supernatants from these T-cell clones had no comparable inhibitory effect. These findings indicate that there is a predominance of penicillin- specific CD8&mn; T cells in the peripheral blood of individuals sensitized to beta-lactam antibiotics. [ABSTRACT FROM AUTHOR]