M.Sc Thesis

M.Sc StudentBen-El Rina
SubjectMorphogenesis of the Chordotonal Organ Depends on the
Proper Composition of the ECM
DepartmentDepartment of Medicine
Supervisor PROF. Adi Salzberg
Full Thesis textFull thesis text - English Version


In the fruit fly, Drosophila melanogaster, sensory feedback from within the body is relayed to the brain by stretch-receptive type I sensory organs called chordotonal organs (ChO). The sensory unit of the organ is anchored to the cuticle on both sides in order to sense relative displacement of body parts. Proper attachment of the ChO is required for its ability to withstand mechanical forces and function as a stretch receptor.

It has been shown that the unique architecture and characteristics of tissues and organs are affected by the extra cellular matrix (ECM) composition. As the cells that compose the ChO react differently to mechanical strain, we predict that this may be in part due to differences in the ECM composition. The goal of this research was to identify and characterize ECM-related genes required for the normal morphogenesis of the ChOs.

Two separate approaches were taken in parallel. First, a small, RNAi-based genetic screen for novel ECM-related genes required for ChO development and function has been performed. One gene that was identified in the RNAi-based screen, is Thrombospondin (Tsp), a Disintegrin and Metalloprotease with Thrombospondin repeats (ADAMTS)-like protein. We show that the Tsp protein starts to accumulate in the extracellular matrix surrounding the ChO attachment cells towards the end of embryogenesis. It then becomes highly concentrated at the attachment junctions during larval stages. Phenotypic analysis of tsp mutants indicated that this ECM protein is necessary for the correct migration of the cells of the LCh5. Tsp mutants display un-stretched cap cells that may indicate that organ integrity is not maintained. Most interestingly, in larval stages the Tsp protein was found to decorate the ChO cap cells along their entire length, suggesting that the elongated cap cells are supported by the extracellular matrix (ECM) to which they attach via integrin-based, Tsp- dependent, adhesion plaques.

In addition, the expression profile of Pericardin (Prc), a collagen IV-like protein, was characterized. The analysis showed that it is found in the ECM of only a subset of ChO cells in 3rd instar larvae. The over-stretching of the cap cells that was exhibited in prc mutants suggests that Prc in the ECM is responsible for aiding in the resistance of mechanical strain. Loh mutants exhibited an abnormal distribution of Prc in the cap cells, suggesting that Loh is, at least in part, required for the proper dispersal of Prc throughout the length of the cap cell. Lastly, examination of larvae in which βPS expression was reduced, revealed an interesting redistribution of Prc in the cells of the ChO. Altogether, these findings identified proteins that incorporate into the ECM of the ChO in a cell-specific manner and aid in conferring these cells with their unique mechanical characteristics.