Different functions of two putative Drosophila α₂δ subunits in the same identified motoneurons

Voltage gated calcium channels (VGCCs) regulate neuronal excitability and translate activity into calcium dependent signaling. The α₁ subunit of high voltage activated (HVA) VGCCs associates with α₂δ accessory subunits, which may affect calcium channel biophysical properties, cell surface expression, localization and transport and are thus important players in calcium-dependent signaling. In vertebrates, the functions of the different combinations of the four α₂δ and the seven HVA α₁ subunits are incompletely understood, in particular with respect to partially redundant or separate functions in neurons. This study capitalizes on the relatively simpler situation in the Drosophila genetic model containing two neuronal putative α₂δ subunits, straightjacket and CG4587, and one Ca_v1 and Ca_v2 homolog each, both with well-described functions in different compartments of identified motoneurons. Straightjacket is required for normal Ca_v1 and Ca_v2 current amplitudes and correct Ca_v2 channel function in all neuronal compartments. By contrast, CG4587 does not affect Ca_v1 or Ca_v2 current amplitudes or presynaptic function, but is required for correct Ca_v2 channel allocation to the axonal versus the dendritic domain. We suggest that the two different putative α₂δ subunits are required in the same neurons to regulate different functions of VGCCs.