The carboxyl-terminal tail of the stalk of Arabidopsis NACK1/HINKEL kinesin is required for its localization to the cell plate formation site.

Plant cytokinesis is achieved by formation of cell plates in the phragmoplast, a plant-specific cytokinetic apparatus, which consists of microtubules (MTs) and microfilaments. During cytokinesis, the cell plate is expanded centrifugally outward from the inside of cells in a process that is supported by dynamic turnover of MTs. M-phase-specific kinesin NACK1, which comprises the motor domain at the amino-terminal half to move on MT bundles and the stalk region in the carboxyl-terminal half, is a key player in the process of MT turnover. That is, the specific region in the stalk binds the MAP kinase kinase kinase to activate the whole MAP kinase cascade, which stimulates depolymerization of MTs for the MT turnover. The stalk is also responsible for recruiting the activated kinase cascade to the mid-zone of the phragmoplast, which corresponds to the cell-plate formation site. It should be crucial to uncover roles of the NACK1 kinesin stalk as well as the motor domain in the formation of cell plates in order to understand the mechanisms of cell plate formation. Using dissected Arabidopsis NACK1 (AtNACK1/HINKEL) molecules and AtNACK1-fused GFP, we showed that the C-terminal tail of the stalk in addition to the motor domain is critical for its proper localization to the site of cell plate formation in the phragmoplast, probably by affecting its motility activity.

Carnitine deficiency is associated with late-onset hypogonadism and depression in uremic men with hemodialysis.

Late-onset hypogonadism (LOH) and depression contribute to cardiovascular disease (CVD) in male hemodialysis (HD) patients. Carnitine deficiency is frequently observed in HD patients, playing a role in CVD. We examined whether carnitine deficiency was independently associated with LOH and depression in these patients. Twenty-six male HD patients underwent determinations of serum levels of free carnitine and testosterone. Status of LOH and depression were evaluated by questionnaires using aging male symptoms' (AMS) scale and self-rating depression scale (SDS), respectively. Free carnitine and testosterone levels in male HD patients were significantly lower than those in age-matched healthy male subjects. Linear regression analysis showed that AMS scale was positively associated with SDS. Univariate regression analysis revealed that total carnitine (inversely), free carnitine (inversely) and HD duration were correlated with AMS scale. Multiple stepwise regression analysis revealed that free carnitine was an independent determinant of AMS scale. Furthermore, free carnitine was also independently correlated with SDS in male HD patients. This study demonstrated that decreased free carnitine levels were independently associated with AMS scale and SDS in male HD patients. The observations suggest that decreased free carnitine levels could be a marker and therapeutic target of LOH and depression in uremic men with HD.