Asymmetric spindle pole formation in CPAP-depleted mitotic cells

Aberrant centrosome biogenesis disrupts nephron and collecting duct progenitor growth and fate resulting in fibrocystic kidney disease

Mutations that disrupt centrosome biogenesis or function cause congenital kidney developmental defects and fibrocystic pathologies. Yet how centrosome dysfunction results in the kidney disease phenotypes remains unknown. Here, we examined the consequences of conditional knockout of the ciliopathy gene Cep120, essential for centrosome duplication, in the nephron and collecting duct progenitor niches of the mouse embryonic kidney. Cep120 loss led to reduced abundance of both cap mesenchyme and ureteric bud populations, due to a combination of delayed mitosis, increased apoptosis and premature differentiation of progenitor cells. These defects resulted in dysplastic kidneys at birth, which rapidly formed cysts, displayed increased interstitial fibrosis and decline in kidney function. RNA sequencing of embryonic and postnatal kidneys from Cep120-null mice identified changes in the pathways essential for development, fibrosis and cystogenesis. Our study defines the cellular and developmental defects caused by centrosome dysfunction during kidney morphogenesis and identifies new therapeutic targets for patients with renal centrosomopathies.

Aberrant centrosome biogenesis disrupts nephron progenitor cell renewal and fate resulting in fibrocystic kidney disease

Mutations that disrupt centrosome structure or function cause congenital kidney developmental defects and fibrocystic pathologies. Yet, it remains unclear how mutations in proteins essential for centrosome biogenesis impact embryonic kidney development. Here, we examined the consequences of conditional deletion of a ciliopathy gene, Cep120 , in the two nephron progenitor niches of the embryonic kidney. Cep120 loss led to reduced abundance of both metanephric mesenchyme and ureteric bud progenitor populations. This was due to a combination of delayed mitosis, increased apoptosis, and premature differentiation of progenitor cells. These defects resulted in dysplastic kidneys at birth, which rapidly formed cysts, displayed increased interstitial fibrosis, and decline in filtration function. RNA sequencing of embryonic and postnatal kidneys from Cep120-null mice identified changes in pathways essential for branching morphogenesis, cystogenesis and fibrosis. Our study defines the cellular and developmental defects caused by centrosome dysfunction during kidney development, and identifies new therapeutic targets for renal centrosomopathies.

Highlights

Defective centrosome biogenesis in nephron progenitors causes:Reduced abundance of metanephric mesenchyme and premature differentiation into tubular structuresAbnormal branching morphogenesis leading to reduced nephron endowment and smaller kidneysChanges in cell-autonomous and paracrine signaling that drive cystogenesis and fibrosisUnique cellular and developmental defects when compared to Pkd1 knockout models.

Gene transcriptional profiles in gonads of Bacillus taxa (Phasmida) with different cytological mechanisms of automictic parthenogenesis

The evolution of automixis - i.e., meiotic parthenogenesis - requires several features, including ploidy restoration after meiosis and maintenance of fertility. Characterizing the relative contribution of novel versus pre-existing genes and the similarities in their expression and sequence evolution is fundamental to understand the evolution of reproductive novelties. Here we identify gonads-biased genes in two Bacillus automictic stick-insects and compare their expression profile and sequence evolution with a bisexual congeneric species. The two parthenogens restore ploidy through different cytological mechanisms: in Bacillus atticus, nuclei derived from the first meiotic division fuse to restore a diploid egg nucleus, while in Bacillus rossius, diploidization occurs in some cells of the haploid blastula through anaphase restitution. Parthenogens' gonads transcriptional program is found to be largely assembled from genes that were already present before the establishment of automixis. The three species transcriptional profiles largely reflect their phyletic relationships, yet we identify a shared core of genes with gonad-biased patterns of expression in parthenogens which are either male gonads-biased in the sexual species or are not differentially expressed there. At the sequence level, just a handful of gonads-biased genes were inferred to have undergone instances of positive selection exclusively in the parthenogen species. This work is the first to explore the molecular underpinnings of automixis in a comparative framework: it delineates how reproductive novelties can be sustained by genes whose origin precedes the establishment of the novelty itself and shows that different meiotic mechanisms of reproduction can be associated with a shared molecular ground plan.

CPAP insufficiency leads to incomplete centrioles that duplicate but fragment

Centrioles are structures that assemble centrosomes. CPAP is critical for centrosome assembly, and its mutations are found in patients with diseases such as primary microcephaly. CPAP’s centrosomal localization, its dynamics, and the consequences of its insufficiency in human cells are poorly understood. Here we use human cells genetically engineered for fast degradation of CPAP, in combination with superresolution microscopy, to address these uncertainties. We show that three independent centrosomal CPAP populations are dynamically regulated during the cell cycle. We confirm that CPAP is critical for assembly of human centrioles, but not for recruitment of pericentriolar material on already assembled centrioles. Further, we reveal that CPAP insufficiency leads to centrioles with incomplete microtubule triplets that can convert to centrosomes, duplicate, and form mitotic spindle poles, but fragment owing to loss of cohesion between microtubule blades. These findings further our basic understanding of the role of CPAP in centrosome biogenesis and help understand how CPAP aberrations can lead to human diseases.

Loss of CPAP causes sustained EGFR signaling and epithelial-mesenchymal transition in oral cancer

Higher epidermal growth factor receptor (EGFR) signaling can contribute to tumor metastasis and resistance to therapies in oral squamous cell carcinoma (OSCC). EGFR signaling can promote epithelial-mesenchymal transition (EMT) in OSCC. EMT is a process by which epithelial cells acquire invasive properties and it can contribute to tumor metastasis. Not only do the abnormal functions of microtubule and microtubule-organizing centers (MTOC) such as centrosomes lead to cancers, but also the malignant tissues are characterized by aberrant centriolar features and amplified centrosomes. Microtubule inhibition therapies increase the sensitivity to EGFR targeting drugs in various cancers. In this study, we show that the loss of expression of a microtubule/tubulin binding protein, centrosomal protein 4.1-associated protein (CPAP), which is critical for centriole biogenesis and normal functioning of the centrosome, caused an increase in the EGFR levels and its signaling and, enhanced the EMT features and invasiveness of OSCC cells. Further, depletion of CPAP enhanced the tumorigenicity of these cells in a xeno-transplant model. Importantly, CPAP loss-associated EMT features and invasiveness of multiple OSCC cells were attenuated upon depletion of EGFR in them. On the other hand, we found that CPAP protein levels were higher in EGF treated OSCC cells as well as in oral cancer tissues, suggesting that the frequently reported aberrant centriolar features of tumors are potentially a consequence, but not the cause, of tumor progression. Overall, our novel observations show that, in addition to its known indispensable role in centrosome biogenesis, CPAP also plays a vital role in suppressing tumorigenesis in OSCC by facilitating EGFR homeostasis.

Alcohol inhibits the proliferation of Neuro2a cells via promoting the asymmetric cell division through down-regulation of the expression of centrosome protein-J

Alcohol can decrease cell proliferation in neural cells. The proliferation of neural cells can be inhibited by the asymmetric division of neural progenitor cells. However, whether alcohol inhibits cell proliferation through inducing cell asymmetric division is not yet clear. Here, we reported that the percentage of asymmetric division was increased in alcohol-treated Neuro2a cells owing to the impaired-spindle orientation. Meanwhile, the expression of Centrosome protein-J (CPAP) which plays an important role in spindle orientation was reduced in Neuro2a cells. The overexpression of GFP-CPAP in Neuro2a cells rescued the disorder of spindle orientation and the asymmetric cell division induced by alcohol. Taken together, the results demonstrate that alcohol exposure diminished the pool of proliferative Neuro2a cells through disordering the spindle orientation and promoting the asymmetric division. And these abnormal orientation and division were due to the reduced CPAP protein level.

Phosphorylation of CPAP by Aurora-A Maintains Spindle Pole Integrity during Mitosis

CPAP is required for centriole elongation during S/G2 phase, but the role of CPAP in mitosis is incompletely understood. Here, we show that CPAP maintains spindle pole integrity through its phosphorylation by Aurora-A during mitosis. Depletion of CPAP induced a prolonged delay in mitosis, pericentriolar material (PCM) dispersion, and multiple mitotic abnormalities. Further studies demonstrated that CPAP directly interacts with and is phosphorylated by Aurora-A at serine 467 during mitosis. Interestingly, the dispersal of the PCM was effectively rescued by ectopic expression of wild-type CPAP or a phospho-mimic CPAP-S467D mutant, but not a non-phosphorylated CPAP-S467A mutant. Finally, we found that CPAP-S467D has a low affinity for microtubule binding but a high affinity for PCM proteins. Together, our results support a model wherein CPAP is required for proper mitotic progression, and phosphorylation of CPAP by Aurora-A is essential for maintaining spindle pole integrity.

Determination of Mother Centriole Maturation in CPAP-Depleted Cells Using the Ninein Antibody

BACKGROUND

Mutations in centrosomal protein genes have been identified in a number of genetic diseases in brain development, including microcephaly. Centrosomal P4.1-associated protein (CPAP) is one of the causal genes implicated in primary microcephaly. We previously proposed that CPAP is essential for mother centriole maturation during mitosis.

METHODS

We immunostained CPAP-depleted cells using the ninein antibody, which selectively detects subdistal appendages in mature mother centrioles.

RESULTS

Ninein signals were significantly impaired in CPAP-depleted cells.

CONCLUSION

The results suggest that CPAP is required for mother centriole maturation in mammalian cells. The selective absence of centriolar appendages in young mother centrioles may be responsible for asymmetric spindle pole formation in CPAP-depleted cells.