Role of spectraplakin in Drosophila photoreceptor morphogenesis.
BACKGROUND
Crumbs (Crb), a cell polarity gene, has been shown to provide a positional cue for the apical membrane domain and adherens junction during Drosophila photoreceptor morphogenesis. It has recently been found that stable microtubules in developing Drosophila photoreceptors were linked to Crb localization. Coordinated interactions between microtubule and actin cytoskeletons are involved in many polarized cellular processes. Since Spectraplakin is able to bind both microtubule and actin cytoskeletons, the role of Spectraplakin was analyzed in the regulations of apical Crb domain in developing Drosophila photoreceptors.


RESULTS
The localization pattern of Spectraplakin in developing pupal photoreceptors showed a unique intracellular distribution. Spectraplakin localized at rhabdomere terminal web which is at the basal side of the apical Crb or rhabdomere, and in between the adherens junctions. The spectraplakin mutant photoreceptors showed dramatic mislocalizations of Crb, adherens junctions, and the stable microtubules. This role of Spectraplakin in Crb and adherens junction regulation was further supported by spectraplakin's gain-of-function phenotype. Spectraplakin overexpression in photoreceptors caused a cell polarity defect including dramatic mislocalization of Crb, adherens junctions and the stable microtubules in the developing photoreceptors. Furthermore, a strong genetic interaction between spectraplakin and crb was found using a genetic modifier test.


CONCLUSIONS
In summary, we found a unique localization of Spectraplakin in photoreceptors, and identified the role of spectraplakin in the regulation of the apical Crb domain and adherens junctions through genetic mutational analysis. Our data suggest that Spectraplakin, an actin-microtubule cross-linker, is essential in the apical and adherens junction controls during the photoreceptors morphogenesis.
Department of Biology, Baylor University, Waco, Texas, United States of America.
Uyen Ngoc
UN
Mui
Christina M
CM
Lubczyk
Sang-Chul
SC
Nam
D022005:Adherens Junctions / Q000378:metabolism; D000818:Animals; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000254:growth & development*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D009024:Morphogenesis; D017956:Photoreceptor Cells, Invertebrate / Q000166:cytology / Q000378:metabolism*; D021381:Protein Transport; D011679:Pupa / Q000166:cytology / Q000254:growth & development / Q000378:metabolism
D029721:Drosophila Proteins; D008565:Membrane Proteins; D008840:Microfilament Proteins; C064360:crb protein, Drosophila; C450828:shot protein, Drosophila