Frequenin/NCS-1 and the Ca2+-channel alpha1-subunit co-regulate synaptic transmission and nerve-terminal growth.
Drosophila Frequenin (Frq) and its mammalian and worm homologue, NCS-1, are Ca(2+)-binding proteins involved in neurotransmission. Using site-specific recombination in Drosophila, we created two deletions that removed the entire frq1 gene and part of the frq2 gene, resulting in no detectable Frq protein. Frq-null mutants were viable, but had defects in larval locomotion, deficient synaptic transmission, impaired Ca(2+) entry and enhanced nerve-terminal growth. The impaired Ca(2+) entry was sufficient to account for reduced neurotransmitter release. We hypothesized that Frq either modulates Ca(2+) channels, or that it regulates the PI4Kbeta pathway as described in other organisms. To determine whether Frq interacts with PI4Kbeta with consequent effects on Ca(2+) channels, we first characterized a PI4Kbeta-null mutant and found that PI4Kbeta was dispensable for synaptic transmission and nerve-terminal growth. Frq gain-of-function phenotypes remained present in a PI4Kbeta-null background. We conclude that the effects of Frq are not due to an interaction with PI4Kbeta. Using flies that were trans-heterozygous for a null frq allele and a null cacophony (encoding the alpha(1)-subunit of voltage-gated Ca(2+) channels) allele, we show a synergistic effect between these proteins in neurotransmitter release. Gain-of-function Frq phenotypes were rescued by a hypomorphic cacophony mutation. Overall, Frq modulates Ca(2+) entry through a functional interaction with the alpha(1) voltage-gated Ca(2+)-channel subunit; this interaction regulates neurotransmission and nerve-terminal growth.
Dason
Jeffrey S
JS
Department of Physiology, University of Toronto, Toronto, Ontario, M5S 1A8, Canada. jeff.dason@utoronto.ca
Romero-Pozuelo
Jesús
J
Marin
Leo
L
Iyengar
Balaji G
BG
Klose
Markus K
MK
Ferrús
Alberto
A
Atwood
Harold L
HL
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004594:Electrophysiology; D055786:Gene Knockout Techniques; D007814:Larva / Q000166:cytology / Q000502:physiology; D008124:Locomotion; D015778:Minor Histocompatibility Antigens; D009411:Nerve Endings / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D029721:Drosophila Proteins; C082454:Frq protein, Drosophila; D015778:Minor Histocompatibility Antigens; D009419:Nerve Tissue Proteins; D021122:Protein Subunits; D017853:Phosphotransferases (Alcohol Group Acceptor); C402182:phosphatidylinositol phosphate 4-kinase; D002118:Calcium