Planar cell polarity regulators in asymmetric organogenesis during development and disease

The phenomenon of planar cell polarity is critically required for a myriad of morphogenetic processes in metazoan and is accurately controlled by several conserved modules.Six“core”proteins,including Friz zled,Flamingo(Celsr),Van Gogh(Vangl),Dishevelled,Prickle,and Diego(Ankrd6),are major components of the Wnt/planar cell polarity pathway.The Fat/Dchs protocadherins and the Scrib polarity complex also function to instruct cellular polarization.In vertebrates,all these pathways are essential for tissue and organ morphogenesis,such as neural tube closure,left-right symmetry breaking,heart and gut morphogenesis,lung and kidney branching,stereociliary bundle orientation,and proximal-distal limb elongation.Mutations in planar polarity genes are closely linked to various congenital diseases.Striking advances have been made in deciphering their contribution to the establishment of spatially oriented pattern in developing or gans and the maintenance of tissue homeostasis.The challenge remains to clarify the complex interplay of different polarity pathways in organogenesis and the link of cell polarity to cell fate specification.Inter disciplinary approaches are also important to understand the roles of mechanical forces in coupling cellular polarization and differentiation.This review outlines current advances on planar polarity regulators in asymmetric organ formation,with the aim to identify questions that deserve further investigation.

Disruption of Planar Cell Polarity Pathway Attributable to Valproic Acid-Induced Congenital Heart Disease through Hdac3 Participation in Mice

Background： Valproic acid （VPA） exposure during pregnancy has been proven to contribute to congenital heart disease （CHD）. Our previous findings implied that disruption of planar cell polarity （PCP） signaling pathway in cardiomyocytes might be a factor for the cardiac teratogenesis of VPA. In addition, the teratogenic ability of VPA is positively correlated to its histone deacetylase （HDAC） inhibition activity. This study aimed to investigate the effect of the VPA on cardiac morphogenesis, HDAC1/2/3, and PCP key genes （Vangl2/Scrib/Rac 1）, subsequently screening out the specific HDACs regulating PCP pathway. Methods： VPA was administered to pregnant C57BL mice at 700 mg/kg intraperitoneally on embryonic day ! 0.5. Dams were sacrificed on E15.5, and death/absorption rates of embryos were evaluated. Embryonic hearts were observed by hematoxylin-eosin staining to identify cardiac abnormalities. H9C2 cells （undifferentiated rat cardiomyoblasts） were transfected with Hdac1/2/3 specific small interfering RNA （siRNA）. Based on the results of siRNA transfection, cells were transfected with Hdac3 expression plasmid and subsequently mock-treated or treated with 8.0 mmol/L VPA. Hdac1/2/3 as well as Vangl2/Scrib/Racl mRNA and protein levels were determined by real-time quantitative polymerase chain reaction and Western blotting, respectively. Total HDAC activity was detected by colorimetric assay.Results： VPA could induce CHD （P 〈 0.001） and inhibit mRNA or protein expression of Hdac1/2/3 as well as Vangl2/Scrib in fetal hearts, in association with total Hdac activity repression （all P 〈 0.05）. In vitro, Hdac3 inhibition could significantly decrease Vangl2/Scrib expression （P 〈 0.01 ）, while knockdown of Hdac 1/2 had no influence （P 〉 0.05）, VPA exposure dramatically decreased the expression of Vanlg2/Scrib together with Hdac activity （P 〈 0.01 ）, while overexpression of Hdac3 could rescue the VPA-induced inhibition （P 〉 0.05）. Conclusion： VPA could inhibit Hdac1/2/3, Vang12/Scrib, or total Hdac activity both in vitro and in vivo and Hdac3 might participate in the process of VPA-induced cardiac developmental anomalies.

Planar cell polarity genes, Celsr1-3, in neural development

flamingo is among the ＇core＇ planar cell-polarity genes, protein of which belongs to a unique cadherin subfamily. In contrast to the classic cadherins, composed of several extracellular cadherin repeats, one transmembrane domain and one cytoplasmic segment linked to catenin binding, Drosophila Flamingo has seven transmembrane segments and a cytoplasmic tail with no catenin-binding sequence. In Drosophila, Flamingo has pleotropic roles in controlling epithelial polarity and neuronal morphogenesis. Three mammalian orthologs of flamingo, Celsrl-3, are widely expressed in the nervous system. Recent work has shown that Celsrl-3 play important roles in neural development, such as in axon guidance, neuronal migration, and cilium polarity. CeIsrl-3 single-gene knockout mice exhibit different phenotypes, but there are cooperative interactions among these genes.

Loss of liver kinase B1 causes planar polarity defects in cochlear hair cells in mice

The tumor suppressor gene liver kinase B1 （LKB1）, also called STKll, encodes a serine/threonine kinase. LKB1 plays crucial roles in cell differentiation, proliferation, and polarity. In this study, LKB1 conditional knockout mice （LKB1pax2 CKO mice） were generated using Pax2-Cre mice to investigate the function of LKB1 in inner ear hair cells during early embryonic period. LKB1Pax2 CKO mice died perinatally. Immunofluorescence and scanning electron microscopy revealed that stereociliary bundles in LKB1Pax2 CKO mice were clustered and misoriented, respectively. Moreover, ectopic distribution of kinocilium bundles resulting from abnormal migration of kinocilium was observed in the mutant mice. The orientation of stereociliary bundles and the migration of kinocilia are critical indicators of planar cell polarity （PCP） of hair cells. LKB1 deficiency in LKB1Pax2 CKO mice thus disrupted hair cell planar polarity during embryonic development. Our results suggest that LKB1 is required in PCP formation in cochlear hair cells in mice.