Different functions of two putative Drosophila α(2)δ subunits in the same identified motoneurons

Voltage gated calcium channels (VGCCs) regulate neuronal excitability and translate activity into calcium dependent signaling. The α(1) subunit of high voltage activated (HVA) VGCCs associates with α(2)δ 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 α(2)δ and the seven HVA α(1) 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 α(2)δ subunits, straightjacket and CG4587, and one Ca(v)1 and Ca(v)2 homolog each, both with well-described functions in different compartments of identified motoneurons. Straightjacket is required for normal Ca(v)1 and Ca(v)2 current amplitudes and correct Ca(v)2 channel function in all neuronal compartments. By contrast, CG4587 does not affect Ca(v)1 or Ca(v)2 current amplitudes or presynaptic function, but is required for correct Ca(v)2 channel allocation to the axonal versus the dendritic domain. We suggest that the two different putative α(2)δ subunits are required in the same neurons to regulate different functions of VGCCs.