Control of spindle orientation in Drosophila by the Par-3-related PDZ-domain protein Bazooka.
BACKGROUND
The orientation of the mitotic spindle influences the asymmetric distribution of cytoplasmic determinants and the positioning of the sibling cell, and therefore has important influences on cell-fate determination and patterning of the embryo. Both the establishment of an axis of polarity and the adjustment of this axis with respect to the coordinates of the embryo have to be controlled. None of the genes identified so far that are involved in these processes seems to have been conserved between flies and nematodes.


RESULTS
Here, we show that the bazooka gene encodes a protein with three putative protein-interaction motifs known as PDZ domains and is the first Drosophila representative of the par gene family of Caenorhabditis elegans, members of which are required for establishment of anterior-posterior polarity of the nematode embryo. The bazooka RNA and protein were found to be restricted to the apical cortical cytoplasm of epithelial cells and neuroblasts. Embryos that were mutant for bazooka frequently failed to coordinate the axis of cell polarity with that of the embryo. This was manifested as defective spindle orientation and mispositioning of the daughter cell after division.


CONCLUSIONS
The Drosophila gene bazooka is likely to be part of a regulatory mechanism required to coordinate the axis of polarity of a cell with that of the embryo. The PDZ domains of Bazooka provide several protein-protein interfaces, which possibly participate in the assembly of a multiprotein complex at the apical pole.
Kuchinke
U
U
Institut für Genetik, Heinrich-Heine Universität Düsseldorf, Universitätsstrasse 1, 40225 Düsseldorf, Germany.
Grawe
F
F
Knust
E
E
D000595:Amino Acid Sequence; D000818:Animals; D019521:Body Patterning / Q000235:genetics; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D016764:Cell Polarity / Q000235:genetics; D003001:Cloning, Molecular; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D029721:Drosophila Proteins; D047108:Embryonic Development; D015801:Helminth Proteins / Q000235:genetics*; D019476:Insect Proteins / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D009420:Nervous System / Q000196:embryology; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000032:analysis; D017386:Sequence Homology, Amino Acid; D008941:Spindle Apparatus / Q000378:metabolism*; D014960:X Chromosome
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D029721:Drosophila Proteins; D015801:Helminth Proteins; D019476:Insect Proteins; D047908:Intracellular Signaling Peptides and Proteins; D012333:RNA, Messenger; C400774:baz protein, Drosophila; C097238:PAR-3 protein, C elegans; D017346:Protein Serine-Threonine Kinases