A family of carboxypeptidases catalyzing α- and ß-tubulin tail processing and deglutamylation.

Tubulin posttranslational modifications represent an important mechanism involved in the regulation of microtubule functions. The most widespread among them are detyrosination, α∆2-tubulin, and polyglutamylation. Here, we describe a family of tubulin-modifying enzymes composed of two closely related proteins, KIAA0895L and KIAA0895, which have tubulin metallocarboxypeptidase activity and thus were termed TMCP1 and TMCP2, respectively. We show that TMCP1 (also known as MATCAP) acts as α-tubulin detyrosinase that also catalyzes α∆2-tubulin. In contrast, TMCP2 preferentially modifies ßI-tubulin by removing three amino acids from its C terminus, generating previously unknown ßI∆3 modification. We show that ßI∆3-tubulin is mostly found on centrioles and mitotic spindles and in cilia. Moreover, we demonstrate that TMCPs also remove posttranslational polyglutamylation and thus act as tubulin deglutamylases. Together, our study describes the identification and comprehensive biochemical analysis of a previously unknown type of tubulin-modifying enzymes involved in the processing of α- and ß-tubulin C-terminal tails and deglutamylation.

A release-and-capture mechanism generates an essential non-centrosomal microtubule array during tube budding.

Non-centrosomal microtubule arrays serve crucial functions in cells, yet the mechanisms of their generation are poorly understood. During budding of the epithelial tubes of the salivary glands in the Drosophila embryo, we previously demonstrated that the activity of pulsatile apical-medial actomyosin depends on a longitudinal non-centrosomal microtubule array. Here we uncover that the exit from the last embryonic division cycle of the epidermal cells of the salivary gland placode leads to one centrosome in the cells losing all microtubule-nucleation capacity. This restriction of nucleation activity to the second, Centrobin-enriched, centrosome is key for proper morphogenesis. Furthermore, the microtubule-severing protein Katanin and the minus-end-binding protein Patronin accumulate in an apical-medial position only in placodal cells. Loss of either in the placode prevents formation of the longitudinal microtubule array and leads to loss of apical-medial actomyosin and impaired apical constriction. We thus propose a mechanism whereby Katanin-severing at the single active centrosome releases microtubule minus-ends that are then anchored by apical-medial Patronin to promote formation of the longitudinal microtubule array crucial for apical constriction and tube formation.

Control of cell shape during epithelial morphogenesis: recent advances.

Morphogenesis is an essential process by which a given tissue, organ or organism acquires its final shape. A select number of mechanisms are used in order to drive epithelial morphogenesis, including cell shape changes as well as cell death or cell division. A cell's shape results from the combination of intrinsic properties of the actomyosin and microtubule (MTs) cytoskeletons, and extrinsic properties due to physical interactions with the neighbouring environment. While we now have a good understanding of the genetic pathways and some of the signalling pathways controlling cell shape changes, the mechanical properties of cells and their role in morphogenesis remain largely unexplored. Recent improvements in microscopy techniques and the development of modelling and quantitative methods have enabled a better understanding of the bio-mechanical events controlling cell shape during morphogenesis. This review aims to highlight recent findings elegantly unravelling and quantifying the contribution of mechanical forces during morphogenesis.

Force Transmission between Three Tissues Controls Bipolar Planar Polarity Establishment and Morphogenesis.

How tissues from different developmental origins interact to achieve coordinated morphogenesis at the level of a whole organism is a fundamental question in developmental biology. While biochemical signaling pathways controlling morphogenesis have been extensively studied [1-3], morphogenesis of epithelial tissues can also be directed by mechanotransduction pathways physically linking two tissues [4-8]. C. elegans embryonic elongation requires the coordination of three tissues: muscles, the dorsal and ventral epidermis, and the lateral epidermis. Elongation starts by cell-shape changes driven by actomyosin contractions in the lateral epidermis [9, 10]. At mid-elongation, muscles become connected to the apical surface of the dorsal and ventral epidermis by molecular tendons formed by muscle integrins, extracellular matrix, and C. elegans hemidesmosomes (CeHDs). The mechanical signal generated by the onset of muscle contractions in the antero-posterior axis from mid-elongation is translated into a biochemical pathway controlling the maturation of CeHDs in the dorsal and ventral epidermis [11]. Consistently, mutations affecting muscle contractions or molecular tendons lead to a mid-elongation arrest [12]. Here, we found that the mechanical force generated by muscle contractions and relayed by molecular tendons is transmitted by adherens junctions to lateral epidermal cells, where it establishes a newly identified bipolar planar polarity of the apical PAR module. The planar polarized PAR module is then required for actin planar organization, thus contributing to the determination of the orientation of cell-shape changes and the elongation axis of the whole embryo. This mechanotransduction pathway is therefore essential to coordinate the morphogenesis of three embryonic tissues.

Control of E-cadherin apical localisation and morphogenesis by a SOAP-1/AP-1/clathrin pathway in C. elegans epidermal cells.

E-cadherin (E-cad) is the main component of epithelial junctions in multicellular organisms, where it is essential for cell-cell adhesion. The localisation of E-cad is often strongly polarised in the apico-basal axis. However, the mechanisms required for its polarised distribution are still largely unknown. We performed a systematic RNAi screen in vivo to identify genes required for the strict E-cad apical localisation in C. elegans epithelial epidermal cells. We found that the loss of clathrin, its adaptor AP-1 and the AP-1 interactor SOAP-1 induced a basolateral localisation of E-cad without affecting the apico-basal diffusion barrier. We further found that SOAP-1 controls AP-1 localisation, and that AP-1 is required for clathrin recruitment. Finally, we also show that AP-1 controls E-cad apical delivery and actin organisation during embryonic elongation, the final morphogenetic step of embryogenesis. We therefore propose that a molecular pathway, containing SOAP-1, AP-1 and clathrin, controls the apical delivery of E-cad and morphogenesis.