Drosophila Condensin II subunit Chromosome-associated protein D3 regulates cell fate determination through non-cell-autonomous signaling

Condensin I is required for faithful meiosis in Drosophila males

The heteropentameric condensin complexes play vital roles in the formation and faithful segregation of mitotic chromosomes in eukaryotes. While the different contributions of the two common condensin complexes, condensin I and condensin II, to chromosome morphology and behavior in mitosis have been thoroughly investigated, much less is known about the specific roles of the two complexes during meiotic divisions. In Drosophila melanogaster, faithful mitotic divisions depend on functional condensin I, but not on condensin II. However, meiotic divisions in Drosophila males require functional condensin II subunits. The role of condensin I during male meiosis in Drosophila has been unresolved. Here, we show that condensin I-specific subunits localize to meiotic chromatin in both meiosis I and II during Drosophila spermatogenesis. Live cell imaging reveals defects during meiotic divisions after RNAi-mediated knockdown of condensin I-specific mRNAs. This phenotype correlates with reduced male fertility and an increase in nondisjunction events both in meiosis I and meiosis II. Consistently, a reduction in male fertility was also observed after proteasome-mediated degradation of the condensin I subunit Barren. Taken together, our results demonstrate an essential role of condensin I during male meiosis in Drosophila melanogaster.

Condensin II protein dysfunction impacts mitochondrial respiration and mitochondrial oxidative stress responses

The maintenance of mitochondrial respiratory function and homeostasis is essential to human health. Here, we identify condensin II subunits as novel regulators of mitochondrial respiration and mitochondrial stress responses. Condensin II is present in the nucleus and cytoplasm. While the effects of condensin II depletion on nuclear genome organization are well studied, the effects on essential cytoplasmic and metabolic processes are not as well understood. Excitingly, we observe that condensin II chromosome-associated protein (CAP) subunits individually localize to different regions of mitochondria, suggesting possible mitochondrial-specific functions independent from those mediated by the canonical condensin II holocomplex. Changes in cellular ATP levels and mitochondrial respiration are observed in condensin II CAP subunit-deficient cells. Surprisingly, we find that loss of NCAPD3 also sensitizes cells to oxidative stress. Together, these studies identify new, and possibly independent, roles for condensin II CAP subunits in preventing mitochondrial damage and dysfunction. These findings reveal a new area of condensin protein research that could contribute to the identification of targets to treat diseases where aberrant function of condensin II proteins is implicated.

Comparing and Contrasting the Effects of Drosophila Condensin II Subunit dCAP-D3 Overexpression and Depletion in Vivo

The Condensin II complex plays important, conserved roles in genome organization throughout the cell cycle and in the regulation of gene expression. Previous studies have linked decreased Condensin II subunit expression with a variety of diseases. Here, we show that elevated levels of Condensin II subunits are detected in somatic cancers. To evaluate potential biological effects of elevated Condensin II levels, we overexpressed the Condensin II subunit, dCAP-D3 in Drosophila melanogaster larval tissues and examined the effects on the mitotic- and interphase-specific functions of Condensin II. Interestingly, while ubiquitous overexpression resulted in pupal lethality, tissue specific overexpression of dCAP-D3 caused formation of nucleoplasmic protein aggregates which slowed mitotic prophase progression, mimicking results observed when dCAP-D3 levels are depleted. Surprisingly, dCAP-D3 aggregate formation resulted in faster transitions from metaphase to anaphase. Overexpressed dCAP-D3 protein failed to precipitate other Condensin II subunits in nondividing tissues, but did cause changes to gene expression which occurred in a manner opposite of what was observed when dCAP-D3 levels were depleted in both dividing and nondividing tissues. Our findings show that altering dCAP-D3 levels in either direction has detrimental effects on mitotic timing, the regulation of gene expression, and organism development. Taken together, these data suggest that the different roles for Condensin II throughout the cell cycle may be independent of each other and/or that dCAP-D3 may possess functions that are separate from those involving its association with the Condensin II complex. If conserved, these findings could have implications for tumors harboring elevated CAP-D3 levels.

In Favor of Establishment: Regulation of Chromatid Cohesion in Plants

In eukaryotic organisms, the correct regulation of sister chromatid cohesion, whereby sister chromatids are paired and held together, is essential for accurate segregation of the sister chromatids and homologous chromosomes into daughter cells during mitosis and meiosis, respectively. Sister chromatid cohesion requires a cohesin complex comprised of structural maintenance of chromosome adenosine triphosphatases and accessory proteins that regulate the association of the complex with chromosomes or that are involved in the establishment or release of cohesion. The cohesin complex also plays important roles in the repair of DNA double-strand breaks, regulation of gene expression and chromosome condensation. In this review, we summarize progress in understanding cohesion dynamics in plants, with the aim of uncovering differences at specific stages. We also highlight dissimilarities between plants and other eukaryotes with respect to the key players involved in the achievement of cohesion, pointing out areas that require further study.