The mago nashi gene is required for the polarisation of the oocyte and the formation of perpendicular axes in Drosophila.
BACKGROUND
Drosophila axis formation requires a series of inductive interactions between the oocyte and the somatic follicle cells. Early in oogenesis, Gurken protein, a member of the transforming growth factor alpha family, is produced by the oocyte to induce the adiacent follicle cells to adopt a posterior cell fate. These cells subsequently send an unidentified signal back to the oocyte to induce the formation of a polarised microtubule array that defines the anterior-posterior axis. The polarised microtubules also direct the movement of the nucleus and gurken mRNA from the posterior to the anterior of the oocyte, where Gurken signals a second time to induce the dorsal follicle cells, thereby polarising the dorsal-ventral axis.


RESULTS
In addition to its previously described role in the localisation of oskar mRNA, the mago nashi gene is required in the germ line for the transduction of the polarising signal from the posterior follicle cells. Using a new in vivo marker for microtubules, we show that mago nashi mutant oocytes develop a symmetric microtubule cytoskeleton that leads to the transient localisation of bicoid mRNA to both poles. Furthermore, the oocyte nucleus often fails to migrate to the anterior, causing the second Gurken signal to be sent in the same direction as the first. This results in a novel phenotype in which the anterior of the egg is ventralised and the posterior dorsalised, demonstrating that the migration of the oocyte nucleus determines the relative orientation of the two principal axes of Drosophila. The mago nashi gene is highly conserved from plants to animals, and encodes a protein that is predominantly localised to nuclei.


CONCLUSIONS
The mago nashi gene plays two essential roles in Drosophila axis formation: it is required downstream of the signal from the posterior follicle cells for the polarisation of the oocyte microtubule cytoskeleton, and has a second, independent role in the localisation of oskar mRNA to the posterior of the oocyte.
Micklem
D R
DR
Wellcome/CRC Institute, Department of Genetics, University of Cambridge, Cambridge, UK.
Dasgupta
R
R
Elliott
H
H
Gergely
F
F
Davidson
C
C
Brand
A
A
González-Reyes
A
A
St Johnston
D
D
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019521:Body Patterning / Q000235:genetics*; D002467:Cell Nucleus; D016764:Cell Polarity; D004247:DNA; D004330:Drosophila / Q000196:embryology* / Q000235:genetics; D029721:Drosophila Proteins; D005260:Female; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D019476:Insect Proteins / Q000235:genetics; D008870:Microtubules; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics* / Q000502:physiology; D009865:Oocytes / Q000166:cytology*; D016601:RNA-Binding Proteins; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000235:genetics; D016211:Transforming Growth Factor alpha; D015291:Transforming Growth Factors / Q000235:genetics
D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D019476:Insect Proteins; C491494:MAGOH protein, human; C107372:Mago protein, Drosophila; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D015534:Trans-Activators; D016211:Transforming Growth Factor alpha; C056478:bcd protein, Drosophila; C083730:grk protein, Drosophila; C091675:osk protein, Drosophila; D015291:Transforming Growth Factors; D004247:DNA