Entrainment of mammalian motile cilia in the brain with hydrodynamic forces.

Motile cilia are widespread across the animal and plant kingdoms, displaying complex collective dynamics central to their physiology. Their coordination mechanism is not generally understood, with previous work mainly focusing on algae and protists. We study here the entrainment of cilia beat in multiciliated cells from brain ventricles. The response to controlled oscillatory external flows shows that flows at a similar frequency to the actively beating cilia can entrain cilia oscillations. We find that the hydrodynamic forces required for this entrainment strongly depend on the number of cilia per cell. Cells with few cilia (up to five) can be entrained at flows comparable to cilia-driven flows, in contrast with what was recently observed in Chlamydomonas Experimental trends are quantitatively described by a model that accounts for hydrodynamic screening of packed cilia and the chemomechanical energy efficiency of the flagellar beat. Simulations of a minimal model of cilia interacting hydrodynamically show the same trends observed in cilia

Klp10A, a Microtubule-Depolymerizing Kinesin-13, Cooperates with CP110 to Control Drosophila Centriole Length

Klp10A is a kinesin-13 of Drosophila melanogaster that depolymerizes cytoplasmic microtubules [1]. In interphase, it promotes microtubule catastrophe [2, 3, 4]; in mitosis, it contributes to anaphase chromosome movement by enabling tubulin flux [1, 5]. Here we show that Klp10A also acts as a microtubule depolymerase on centriolar microtubules to regulate centriole length. Thus, in both cultured cell lines and the testes, absence of Klp10A leads to longer centrioles that show incomplete 9-fold symmetry at their ends. These structures and associated pericentriolar material undergo fragmentation. We also show that in contrast to mammalian cells where depletion of CP110 leads to centriole elongation [6], in Drosophila cells it results in centriole length diminution that is overcome by codepletion of Klp10A to give longer centrioles than usual. We discuss how loss of centriole capping by CP110 might have different consequences for centriole length in mammalian [6, 7, 8] and insect cells and also relate these findings to the functional interactions between mammalian CP110 and another kinesin-13, Kif24, that in mammalian cells regulates cilium formation

Drosophila Mgr, a Prefoldin subunit cooperating with von Hippel Lindau to regulate tubulin stability

Mutations in Drosophila merry-go-round (mgr) have been known for over two decades to lead to circular mitotic figures and loss of meiotic spindle integrity. However, the identity of its gene product has remained undiscovered. We now show that mgr encodes the Prefoldin subunit counterpart of human von Hippel Lindau binding-protein 1. Depletion of Mgr from cultured cells also leads to formation of monopolar and abnormal spindles and centrosome loss. These phenotypes are associated with reductions of tubulin levels in both mgr flies and mgr RNAi-treated cultured cells. Moreover, mgr spindle defects can be phenocopied by depleting β-tubulin, suggesting Mgr function is required for tubulin stability. Instability of β-tubulin in the mgr larval brain is less pronounced than in either mgr testes or in cultured cells. However, expression of transgenic β-tubulin in the larval brain leads to increased tubulin instability, indicating that Prefoldin might only be required when tubulins are synthesized at high levels. Mgr interacts with Drosophila von Hippel Lindau protein (Vhl). Both proteins interact with unpolymerized tubulins, suggesting they cooperate in regulating tubulin functions. Accordingly, codepletion of Vhl with Mgr gives partial rescue of tubulin instability, monopolar spindle formation, and loss of centrosomes, leading us to propose a requirement for Vhl to promote degradation of incorrectly folded tubulin in the absence of functional Prefoldin. Thus, Vhl may play a pivotal role: promoting microtubule stabilization when tubulins are correctly folded by Prefoldin and tubulin destruction when they are not

Stem cell decisions:A twist of fate or a niche market?

AbstractEstablishing and maintaining cell fate in the right place at the right time is a key requirement for normal tissue maintenance. Stem cells are at the core of this process. Understanding how stem cells balance self-renewal and production of differentiating cells is key for understanding the defects that underpin many diseases. Both, external cues from the environment and cell intrinsic mechanisms can control the outcome of stem cell division. The role of the orientation of stem cell division has emerged as an important mechanism for specifying cell fate decisions. Although, the alignment of cell divisions can dependent on spatial cues from the environment, maintaining stemness is not always linked to positioning of stem cells in a particular microenvironment or `niche'. Alternate mechanisms that could contribute to cellular memory include differential segregation of centrosomes in asymmetrically dividing cells

Lis1 is essential for cortical microtubule organization and desmosome stability in the epidermis

Desmoplakin recruits the centrosomal protein Lis1 to the epidermal cell cortex, where it regulates cortical microtubule organization and desmosome stability

Parts list for a microtubule depolymerising kinesin

The Kinesin superfamily is a large group of molecular motors that use the turnover of ATP to regulate their interaction with the microtubule cytoskeleton. The coupled relationship between nucleotide turnover and microtubule binding is harnessed in various ways by these motors allowing them to carry out a variety of cellular functions. The Kinesin-13 family is a group of specialist microtubule depolymerising motors. Members of this family use their microtubule destabilising activity to regulate processes such as chromosome segregation, maintenance of cilia and neuronal development. Here, we describe the current understanding of the structure of this family of kinesins and the role different parts of these proteins play in their microtubule depolymerisation activity and in the wider function of this family of kinesins

CDK5RAP2 functions in centrosome to spindle pole attachment and DNA damage response

Two domains of centrosomal protein CDK5RAP2, CNN1 and CNN2, link centrosomes to mitotic spindle poles. CNN1 lacking centrosomes are unable to recruit pericentriolar matrix components that mediate attachment to spindle poles

Conserved molecular interactions in centriole-to-centrosome conversion.

Centrioles are required to assemble centrosomes for cell division and cilia for motility and signalling. New centrioles assemble perpendicularly to pre-existing ones in G1-S and elongate throughout S and G2. Fully elongated daughter centrioles are converted into centrosomes during mitosis to be able to duplicate and organize pericentriolar material in the next cell cycle. Here we show that centriole-to-centrosome conversion requires sequential loading of Cep135, Ana1 (Cep295) and Asterless (Cep152) onto daughter centrioles during mitotic progression in both Drosophila melanogaster and human. This generates a molecular network spanning from the inner- to outermost parts of the centriole. Ana1 forms a molecular strut within the network, and its essential role can be substituted by an engineered fragment providing an alternative linkage between Asterless and Cep135. This conserved architectural framework is essential for loading Asterless or Cep152, the partner of the master regulator of centriole duplication, Plk4. Our study thus uncovers the molecular basis for centriole-to-centrosome conversion that renders daughter centrioles competent for motherhood.J.F., Z.L., S.S. and N.S.D. are supported from Programme Grant to D.M.G. from Cancer Research UK. H.R. is supported from MRC Programme Grant to D.M.G. J.F. thank the British Academy and the Royal Society for Newton International Fellowship and Z.L. thanks the Federation of European Biochemical Societies for the Long-Term postdoctoral Fellowship. The authors thank Nicola Lawrence and Alex Sossick for assistance with 3D-SIM.This is the author accepted manuscript. The final version is available from NPG via http://dx.doi.org/10.1038/ncb327

Comparative Live-Cell Imaging Analyses of SPA-2, BUD-6 and BNI-1 in Neurospora crassa Reveal Novel Features of the Filamentous Fungal Polarisome

A key multiprotein complex involved in regulating the actin cytoskeleton and secretory machinery required for polarized growth in fungi, is the polarisome. Recognized core constituents in budding yeast are the proteins Spa2, Pea2, Aip3/Bud6, and the key effector Bni1. Multicellular fungi display a more complex polarized morphogenesis than yeasts, suggesting that the filamentous fungal polarisome might fulfill additional functions. In this study, we compared the subcellular organization and dynamics of the putative polarisome components BUD-6 and BNI-1 with those of the bona fide polarisome marker SPA-2 at various developmental stages of Neurospora crassa. All three proteins exhibited a yeast-like polarisome configuration during polarized germ tube growth, cell fusion, septal pore plugging and tip repolarization. However, the localization patterns of all three proteins showed spatiotemporally distinct characteristics during the establishment of new polar axes, septum formation and cytokinesis, and maintained hyphal tip growth. Most notably, in vegetative hyphal tips BUD-6 accumulated as a subapical cloud excluded from the Spitzenkörper (Spk), whereas BNI-1 and SPA-2 partially colocalized with the Spk and the tip apex. Novel roles during septal plugging and cytokinesis, connected to the reinitiation of tip growth upon physical injury and conidial maturation, were identified for BUD-6 and BNI-1, respectively. Phenotypic analyses of gene deletion mutants revealed additional functions for BUD-6 and BNI-1 in cell fusion regulation, and the maintenance of Spk integrity. Considered together, our findings reveal novel polarisome-independent functions of BUD-6 and BNI-1 in Neurospora, but also suggest that all three proteins cooperate at plugged septal pores, and their complex arrangement within the apical dome of mature hypha might represent a novel aspect of filamentous fungal polarisome architecture