Gating Molecular Mechanism Of The Ciliary Transition Zone Protein TCTN1 In Chlamydomonas

As a highly conserved subcellular structure,cilia exist widely in eukaryotic cells.Cilia has the functions of cell movement,perception and signal transduction.The abnormal structure and function of cilia lead to a variety of cilia related diseases,including renal cyst,nervous system degeneration and other syndromes.Studies have shown that ciliary diseases are mostly caused by ciliary transition zone gene mutation.The transition zone of cilia is a kind of gating device located at the base of cilia,which acts as the entrance and exit channel of ciliary components.Although the molecular structure of transition zone proteins is much konwn,the molecular mechanism of their gating is not well understood.Using a variety of model organisms to study the mechanism of cilia can more comprehensively grasp the dynamic changes of the organelle and the control mechanism of components in cilia,and provide a theoretical basis for ciliary diseases.In this study,we intend to study the molecular mechanism of the transition zone protein Tectonic 1(TCTN1)gating in Chlamydomonas.Previous studies showed that TCTN1 gene defect showed that the cells formed cysts and could not swim.After the cysts were broken,the cells could grow cilia again,but it was slightly lower than the wild type,and could return to swimming.Subsequent analysis showed that the mutant had bulge phenomenon when it was short cilia,and the Y structure of transition zone was abnormal.The results of western blotting,fluorescence and proteomic analysis showed that the absence of TCTN1 resulted in abnormal components in the cilia,including the localization of many cytoplasmic proteins in cilia and abnormal accumulation of IFT proteins.In order to further explore the network mode and molecular mechanism of TCTN1,we systematically compared the characteristic,protein co-localization and attachment relationship,and ciliary proteome after deletion of TCTN1,CEP290 and NPHP4 in Chlamydomonas.Characteristic and cilia proteome analysis showed that tctn1 mutation degree was lighter than cep290 and heavier than nphp4.Immunofluorescence analysis shows that the three proteins are located in the transition zone independent of each other,and TCTN1 is located between CEP290 and NPHP4.The study of the unknown domain DUF1619 of TCTN1 shows that DUF1619 and other protein parts are indispensable for the normal function of TCTN1.In conclusion,the joint action of TCTN1 and other proteins in ciliary transition zone gating regulates the protein components in cilia,which is the key to the function of cilia.