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Hillary K Andrews1, Shuya Wu2,
Hamed Jafar-Nejad3, Flo Quiocho2, Hugo J
Bellen1,3,4. 1) Program in Developmental Biology,
Baylor College of Medicine, Houston, TX; 2) Verna and Marrs McLean
Department of Biochemistry and Molecular Biology, Baylor College of
Medicine, Houston, TX; 3) Molecular and Human Genetics, Baylor
College of Medicine, Houston, TX; 4) HHMI, Baylor College of
Medicine, Houston, TX.
Asymmetric division of sensory organ precursors (SOPs) in Drosophila
generates the different cell types of the mature sensory organ. In a
genetic screen designed to identify novel players in this process,
we isolated a mutation in Drosophila sec15, which encodes a
component of the exocyst, an evolutionarily conserved complex
implicated in intracellular vesicle transport. Loss of sec15
function results in the generation of extra neurons at the expense
of support cells, a phenotype compatible with loss of Notch
signaling. Although sec15 mutant cells are able to establish
apical-basal
polarity, a vesicular compartment containing Notch, Sanpodo and
endocytosed Delta accumulates in the basal areas of mutant SOPs.
Sec15 shows a dynamic trafficking pattern and colocalizes with the
recycling endosomal marker Rab11 in wild-type
SOPs. Based on the aberrant distribution of Rab11 in sec15 clones,
we propose that a defect in Delta recycling causes cell fate
transformation in sec15- sensory lineages. Based on the crystal
structure of Sec15 and Rab11, we have identified specific amino
acids required for binding to Rab11 in vitro. To test our model for
Sec15-Rab11 function in Notch signaling, we
have created transgenic flies which contain point mutations in the
Rab11 binding domain of Sec15. Our data indicate that Sec15 and
Rab11 mediate a specific vesicle trafficking event which ensures
proper neuronal fate specification in Drosophila. |
