טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentSarnatzki Yael
SubjectThe Drosophila Brain Tumor Suppressor brat Can Block Cell
Proliferation and Differentiation during
Development
DepartmentDepartment of Biology
Supervisor Assistant Professor Ze'ev Lev


Abstract

Inactivation of both alleles of the fruit fly D. melanogaster brain tumor (brat) gene results in the production of a tumor-like neoplasm in the larval brain, and lethality in the larval third instar and pupal stages. The brat gene was cloned in our laboratory. brat encodes for an 1037 amino acid protein with an N-terminal B-box1 zinc finger followed by a B-box2 zinc finger,and a coiled-coil domain (BBCC), and a C-terminal β-propeller domain with six blades. All these motifs are known to mediate protein-protein interactions. The brat gene is expressed in the embryonic central and peripheral nervous systems including the embryonic brain.

Staining of larval tissues against Brat reveled that Brat is located in the cytoplasm and expressed in the optic neuroblasts of the brain, in the peripodial membrane of the imaginal discs, in parts of the digestive system (gastric caecaes), in the garland cells, in the ring gland and in the salivary gland and its imaginal rings. These tissues can be classified as secreting tissues or as transporting tissues. In addition, according to the localization of Brat in several tissues it is possible to assume that Brat has a role in the transformation from larva to adult.

            To understand the contribution of Brat domains to its activity as tumor suppressor, ectopic expression of the b-propeller and the BBCC (the N-terminus doamin) domains was conducted and compared to the ectopic expression of the full-length protein. The results of these experiments and the fact that all brat mutants tested were mutated in the b-propeller domain suggest that the b-propeller domain is essential and sufficient for the tumor suppressor activity of Brat.

To understand the function of Brat as tumor suppressor, we overexpressed it in Schneider cells and in Drosophila tissues. Our results indicate that Brat can block cell proliferation, yet without involving excessive apoptosis. In addition, Brat can also affect the differentiation of cells in developing imaginal discs.

Thus, brat may play a double role: blocking proliferation and differentiation as well. This double role of Brat during neuroblasts development in the embryo may be the reason for its function as a tumor suppressor gene.