Central Spindle Self-Organization and Cytokinesis in Artificially Activated Sea Urchin Eggs

KIFC1 promotes proliferation and pseudo-bipolar division of ESCC through the transportation of Aurora B kinase

Esophageal squamous cell carcinoma (ESCC) accounts for over 90% of total in China, and the five-year survival rate for patients is less than 30%. Accordingly, the identification of novel, effective early diagnosis markers and therapeutic targets for ESCC is of paramount importance. KIFC1 has been identified as highly expressed in several types of cancer, although its prognostic value is inconsistent, and no research has been conducted specifically on its effect on ESCC. To investigate the expression and function of KIFC1 in ESCC, we conducted immunohistochemical staining on 30 pairs of para-carcinoma tissue and cancerous tissues, revealing a significant increase in KIFC1 expression in ESCC tissues. Using siRNA to knock down KIFC1 significantly reduced the proliferation of EC109 ESCC cells both in vitro and in vivo. Bioinformatics analysis revealed a highly significant positive correlation between KIFC1 overexpression and signaling pathways associated with tumor proliferation pathways. In EC109 cells, overexpression of KIFC1 significantly increased the rate of centrosome amplification and the likelihood of pseudo-bipolar division. Furthermore, the expression of KIFC1 and the rate of centrosome amplification in ESCC tissues were also positively correlated. In order to explore the underline molecular mechanisms, we identified, through proteomics, that KIFC1 binds to the protein Aurora B. The knockdown of KIFC1 significantly reduced the distribution of Aurora B on the metaphase plate and substantially inhibited the phosphorylation of its classical substrate, Histone H3. In conclusion, these findings indicate the potential utility of KIFC1 as both a tumor marker and a promising target for therapeutic interventions.

Prc1E and Kif4A control microtubule organization within and between large Xenopus egg asters

The cleavage furrow in Xenopus zygotes is positioned by two large microtubule asters that grow out from the poles of the first mitotic spindle. Where these asters meet at the midplane, they assemble a disk-shaped interaction zone consisting of anti-parallel microtubule bundles coated with chromosome passenger complex (CPC) and centralspindlin that instructs the cleavage furrow. Here we investigate the mechanism that keeps the two asters separate and forms a distinct boundary between them, focusing on the conserved cytokinesis midzone proteins Prc1 and Kif4A. Prc1E, the egg orthologue of Prc1, and Kif4A were recruited to anti-parallel bundles at interaction zones between asters in Xenopus egg extracts. Prc1E was required for Kif4A recruitment but not vice versa. Microtubule plus-end growth slowed and terminated preferentially within interaction zones, resulting in a block to interpenetration that depended on both Prc1E and Kif4A. Unexpectedly, Prc1E and Kif4A were also required for radial order of large asters growing in isolation, apparently to compensate for the direction-randomizing influence of nucleation away from centrosomes. We propose that Prc1E and Kif4, together with catastrophe factors, promote "anti-parallel pruning" that enforces radial organization within asters and generates boundaries to microtubule growth between asters.

Parthenogenesis in Insects: The Centriole Renaissance

Building a new organism usually requires the contribution of two differently shaped haploid cells, the male and female gametes, each providing its genetic material to restore diploidy of the new born zygote. The successful execution of this process requires defined sequential steps that must be completed in space and time. Otherwise, development fails. Relevant among the earlier steps are pronuclear migration and formation of the first mitotic spindle that promote the mixing of parental chromosomes and the formation of the zygotic nucleus. A complex microtubule network ensures the proper execution of these processes. Instrumental to microtubule organization and bipolar spindle assembly is a distinct non-membranous organelle, the centrosome. Centrosome inheritance during fertilization is biparental, since both gametes provide essential components to build a functional centrosome. This model does not explain, however, centrosome formation during parthenogenetic development, a special mode of sexual reproduction in which the unfertilized egg develops without the contribution of the male gamete. Moreover, whereas fertilization is a relevant example in which the cells actively check the presence of only one centrosome, to avoid multipolar spindle formation, the development of parthenogenetic eggs is ensured, at least in insects, by the de novo assembly of multiple centrosomes.Here, we will focus our attention on the assembly of functional centrosomes following fertilization and during parthenogenetic development in insects. Parthenogenetic development in which unfertilized eggs are naturally depleted of centrosomes would provide a useful experimental system to investigate centriole assembly and duplication together with centrosome formation and maturation.