Dynamics of cell contacts during cell intercalation in epithelial tissue elongation of Drosophila embryos

by Deqing Kong
Doctoral thesis
Date of Examination:2017-09-20
Date of issue:2017-11-22
Advisor:Prof. Dr. Jörg Großhans
Referee:Prof. Dr. Jörg Großhans
Referee:Prof. Dr. Reinhard Schuh
Referee:Prof. Dr. Jr Christian Dahmann
Persistent Address: http://dx.doi.org/10.53846/goediss-6594

 

 

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Abstract

English

Cell rearrangement is one of the fundamental mechanisms underlying tissue morphogenesis. In epithelial tissues, cells rearrange without losing their tight neighbor interactions by junction remodeling according to a topological T1 transition, i. e. collapse of a junction followed by extension of a new junction in perpendicular orientation. The minimal functional units are cell quadruplets with two old and two new neighbors. The driving force for junction remodeling is provided by acto-myosin contractility in old neighbors. By now it has been unclear whether non-autonomous mechanism is involved, which coordinate the activities of old and new neighbors. In my doctoral research I employed xit mutant Drosophila embryos to study potential non-autonomous mechanism of coordination with cell quadruplets undergoing cell rearrangement. I characterized the phenotypes of xit mutants in detail, confirmed the assumed function of Xit as a glucosyl-transferase in the ER and identified E-Cadherin to be hypo-N-glycosylated in xit mutants. Hypo-N-glycosylated E-Cadherin is more mobile and shows altered clustering. Germ-band extension and cell intercalation are affected in xit embryos, similar to the phenotypes in E-Cadherin RNAi embryos. The T1 process, especially the new junction extension phase is delayed in xit mutant embryos. Large-scale data analysis of several hundred cell quadruplets passing through T1 processes revealed a T1 specific and xit and E-Cadherin dependent anti-correlation of area fluctuations between old and new neighbors, indicating a function of xit and E-Cadherin in coordination behavior of old and new neighbors (Collaboration with Dr. Lars Reichl and Prof. Fred Wolf). To test whether the observed correlations are functionally relevant I developed an optochemical method by Ca2+ uncaging to induce rapid and transient cell contraction at single cell resolution. Inducing cell contraction in T1 cell quadruplets, I found that synchronous contractions of cardinal cells are sufficient for junction extension in wild type but not in xit mutant embryos. Furthermore, induced cell contractions in new neighbors interfered with junction extension. I propose a model that the hypo-N-glycosylation of E-Cadherin affects E-Cad-based mechanotransduction and cell-cell communications in Drosophila embryos. E-Cadherin cis-interaction could be affected by hypo-N-glycosylation, and E-Cadherin relative bigger cluster can be formed initially, but the increased myosin activity spits, instead of stabilize the cluster as in wild type, and furthermore affects E-Cadherin/F-actin interaction. The E-Cad-based mechanotransduction is affected consequently in xit embryos.
Keywords: Drosophila; Germ-band extension; epithelial tissue elongation; cell intercalation; T1 transition; E-Cadherin; xiantuan (xit); N-glycosylation; mechanotransduction
 
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