Hofstee C A, Henderson S, Hardie R C, Stavenga D G
Department of Biophysics, University of Groningen, The Netherlands.
Vis Neurosci. 1996 Sep-Oct;13(5):897-906. doi: 10.1017/s0952523800009147.
The Drosophila ninaC locus encodes two retinal specific proteins (p132 and p174) both consisting of a protein kinase joined to a myosin head domain and a C terminal with a calmodulin-binding domain. The role of p132 and p174 was studied via whole-cell recording and through measurements of the pupil mechanism, i.e. the pigment migration in the photoreceptor cells, in the ninaC mutants, P[ninaC delta 132] (p132 absent), P[ninaC delta 174] (p174 absent), and ninaCP235 (null mutant). Voltage-clamped flash responses in P[ninaC delta 174] and ninaCP235 showed delayed response termination. In response to steady light, plateau responses in both P[ninaC delta 174] and ninaCP235 were also large. In both cases the defect was significantly more severe in ninaCP235. Responses in P[ninaC delta 132] were apparently normal. P[ninaC delta 174] and ninaCP235 were also characterized by spontaneous quantum bump-like activity in the dark and by larger and longer light-induced quantum bumps. The turn-off of the pupil mechanism in P[ninaC delta 174] and ninaCP235 was also defective, although in this case the rate of return to baseline in both mutants was more or less the same. In all ninaC mutants, the amplitudes of the pupillary pigment migration were distinctly smaller than that in the wild type. The reduction of the amplitude was largest in P[ninaC delta 174]. The light sensitivity of the pupil mechanism of P[ninaC delta 174] compared to that of wild type was reduced by 1.3 log units. Remarkably, the light sensitivity of P[ninaC delta 132] and ninaCP235 was ca. 0.5 log units higher than that of the wild type. The results suggest that the p174 protein is required for normal termination of the transduction cascade. The diverse phenotypes observed may suggest multiple roles calmodulin distribution for controlling response termination and regulating pigment migration in Drosophila photoreceptors.
果蝇ninaC基因座编码两种视网膜特异性蛋白（p132和p174），二者均由一个与肌球蛋白头部结构域相连的蛋白激酶以及一个带有钙调蛋白结合结构域的C末端组成。通过全细胞记录以及对瞳孔机制（即光感受器细胞中的色素迁移）的测量，研究了p132和p174在ninaC突变体P[ninaC delta 132]（缺失p132）、P[ninaC delta 174]（缺失p174）和ninaCP235（无效突变体）中的作用。P[ninaC delta 174]和ninaCP235中的电压钳制闪光反应显示反应终止延迟。在持续光照下，P[ninaC delta 174]和ninaCP235中的平台反应也很大。在这两种情况下，ninaCP235中的缺陷明显更严重。P[ninaC delta 132]中的反应明显正常。P[ninaC delta 174]和ninaCP235的特征还在于在黑暗中具有自发的量子撞击样活动，以及更大、更长的光诱导量子撞击。P[ninaC delta 174]和ninaCP235中瞳孔机制的关闭也存在缺陷，不过在这种情况下，两种突变体回到基线的速率大致相同。在所有ninaC突变体中，瞳孔色素迁移的幅度明显小于野生型。在P[ninaC delta 174]中幅度的降低最大。与野生型相比，P[ninaC delta 174]瞳孔机制的光敏感性降低了1.3个对数单位。值得注意的是，P[ninaC delta 132]和ninaCP235的光敏感性比野生型高约0.5个对数单位。结果表明，p174蛋白是转导级联正常终止所必需的。观察到的多种表型可能表明钙调蛋白分布在控制果蝇光感受器中的反应终止和调节色素迁移方面具有多种作用。
