Bifocal and PP1 interaction regulates targeting of the R-cell growth cone in Drosophila.
Bifocal is a putative cytoskeletal regulator and a Protein phosphatase-1 (PP1) interacting protein that mediates normal photoreceptor morphology in Drosophila. We show here that Bif and PP1-87B as well as their ability to interact with each other are required for photoreceptor growth cone targeting in the larval visual system. Single mutants for bif or PP1-87B show defects in axonal projections in which the axons of the outer photoreceptors bypass the lamina, where they normally terminate. The data show that the functions of bif and PP1-87B in either stabilizing R-cell morphology (for Bif) or regulating the cell cycle (for PP1-87B) can be uncoupled from their function in visual axon targeting. Interestingly, the axon targeting phenotypes are observed in both PP1-87B mutants and PP1-87B overexpression studies, suggesting that an optimal PP1 activity may be required for normal axon targeting. bif mutants also display strong genetic interactions with receptor tyrosine phosphatases, dptp10d and dptp69d, and biochemical studies demonstrate that Bif interacts directly with F-actin in vitro. We propose that, as a downstream component of axon signaling pathways, Bif regulates PP1 activity, and both proteins influence cytoskeleton dynamics in the growth cone of R cells to allow proper axon targeting.
Babu
Kavita
K
Temasek Life Science Laboratory and Department of Biological Sciences, 1 Research Link, National University of Singapore, 117604, Singapore. kavita@molbio.mgh.harvard.edu
Bahri
Sami
S
Alphey
Luke
L
Chia
William
W
D000199:Actins / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000502:physiology*; D001665:Binding Sites; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D004789:Enzyme Activation; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D020439:Growth Cones / Q000502:physiology*; D007814:Larva; D009154:Mutation; D009899:Optic Lobe, Nonmammalian / Q000254:growth & development / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism; D011485:Protein Binding; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism; D054557:Receptor-Like Protein Tyrosine Phosphatases; D015398:Signal Transduction
D000199:Actins; D003598:Cytoskeletal Proteins; D029721:Drosophila Proteins; D005136:Eye Proteins; C107943:bif protein, Drosophila; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; C482451:PTP69D protein, Drosophila; D017027:Protein Tyrosine Phosphatases; D054557:Receptor-Like Protein Tyrosine Phosphatases