Planar cell polarity defects and defective Vangl2 trafficking in mutants for the COPII gene Sec24b

Abstract

SUMMARYAmong the cellular properties that are essential for the organization of tissues during animal development, the importance of cell polarity in the plane of epithelial sheets has become increasingly clear in the past decades. Planar cell polarity (PCP) signaling in vertebrates has indispensable roles in many aspects of their development, in particular, controlling alignment of various types of epithelial cells. Disrupted PCP has been linked to developmental defects in animals and to human pathology. Neural tube closure defects (NTD) and disorganization of the mechanosensory cells of the organ of Corti are commonly known consequences of disturbed PCP signaling in mammals. We report here a typical PCP phenotype in a mouse mutant for the Sec24b gene, including the severe NTD craniorachischisis, abnormal arrangement of outflow tract vessels and disturbed development of the cochlea. In addition, we observed genetic interaction between Sec24b and the known PCP gene, scribble. Sec24b is a component of the COPII coat protein complex that is part of the endoplasmic reticulum (ER)-derived transport vesicles. Sec24 isoforms are thought to be directly involved in cargo selection, and we present evidence that Sec24b deficiency specifically affects transport of the PCP core protein Vangl2, based on experiments in embryos and in cultured primary cells.

Mechanisms of tissue fusion during development

“…Although NTDs are ultimately due to failure of NT closure, very few mouse models directly relate to fusion, the final step of NT closure. For example, mice mutant for genes in the planar cell polarity (PCP) pathway, such as Vangl2 and inturned (Intu), exhibit NTDs due to lack of convergent extension, which is needed to elongate the neural plate and bring the neural folds close together for fusion to occur (Ybot-Gonzalez et al, 2007;Wansleeben et al, 2010;Zeng et al, 2010). Moreover, many NTDs disrupt proliferation, hinge point formation, primary ciliogenesis or neural patterning, but these important processes occur independently of NT fusion (Murdoch and Copp, 2010).…”

The intracellular carboxyl terminal domain of Vangl proteins contains plasma membrane targeting signals

“…Both amino terminal deletions, including D1-13 (N1) which eliminates both tyrosine-based motifs YSGY (7)(8)(9)(10) and YSYY (10)(11)(12)(13)(14) and D1-95 (N2) which additionally removes the di-leucine motif LL (56) did not affect PM targeting. Indeed, both truncated constructs showed baso-lateral staining in MDCK cells, co-localization with Na,K-ATPase membrane marker, and showed staining with an HA antibody under non-permabilized conditions, suggesting that the amino terminus of Vangl proteins does not contain major determinants for PM membrane targeting.…”

“…This, combined with the observation that Sec24b mutant mice exhibit craniorachischisis, further emphasized the critical importance of Vangl proteins trafficking in regulating PCP and ultimately neural tube closure in mammals. 12,13 Here, we used deletion analysis to locate sequence determinants responsible for Vangl membrane targeting.…”

“…7-10, YSYY (pst. [10][11][12][13][14], and a di-leucine motifs (pst. 56) are found in the amino terminus, while YKDF (pst.…”

Les gènes et les protéines qui contrôlent la voie de sécrétion

“…Deux exemples frappants de la spécificité du tri des charges accompli par ces paralogues mammaliens de SEC24 ontété rapportés. Des mutations sur la chaîne terminale du gène SEC24B de souris provoquent un défaut majeur de fermeture du tube neural, désigné par le terme de crânio-rachiscisis (Merte et al, 2010 ;Wansleeben et al, 2010). La même anomalie aété vue dans les délétions des formes neurales de récepteurs de signalisation tels que Frizzled et Vangl, deux protéines de surface de l'épithélium neural, qui sont assemblées sur les membranes plasmiques distales et proximales de cellules neuralesépithéliales, respectivement (Wu & Mlodzik, 2009).…”