Division of Neurobiology, Institute for Biology, Freie Universität Berlin, 14195 Berlin, Germany.
Institute of Developmental Biology and Neurobiology (iDN), Hanns-Dieter-Hüsch-Weg 15, 55128 Mainz, Germany.
Cell Rep. 2021 Dec 21;37(12):110145. doi: 10.1016/j.celrep.2021.110145.
Variability of synapse numbers and partners despite identical genes reveals the limits of genetic determinism. Here, we use developmental temperature as a non-genetic perturbation to study variability of brain wiring and behavior in Drosophila. Unexpectedly, slower development at lower temperatures increases axo-dendritic branching, synapse numbers, and non-canonical synaptic partnerships of various neurons, while maintaining robust ratios of canonical synapses. Using R7 photoreceptors as a model, we show that changing the relative availability of synaptic partners using a DIPγ mutant that ablates R7's preferred partner leads to temperature-dependent recruitment of non-canonical partners to reach normal synapse numbers. Hence, R7 synaptic specificity is not absolute but based on the relative availability of postsynaptic partners and presynaptic control of synapse numbers. Behaviorally, movement precision is temperature robust, while movement activity is optimized for the developmentally encountered temperature. These findings suggest genetically encoded relative and scalable synapse formation to develop functional, but not identical, brains and behaviors.
尽管基因相同，但突触数量和伙伴的可变性揭示了遗传决定论的局限性。在这里，我们使用发育温度作为非遗传扰动来研究果蝇大脑连接和行为的可变性。出乎意料的是，较低温度下较慢的发育会增加轴突-树突分支、突触数量和各种神经元的非经典突触伙伴关系，同时保持经典突触的比例稳健。使用 R7 光感受器作为模型，我们表明，通过使用 DIPγ 突变体改变突触伙伴的相对可用性，该突变体消除了 R7 的首选伙伴，从而导致温度依赖性招募非经典伙伴以达到正常的突触数量。因此，R7 的突触特异性不是绝对的，而是基于突触后伙伴的相对可用性和突触数量的前突触控制。行为上，运动精度对温度具有鲁棒性，而运动活性则针对发育过程中遇到的温度进行了优化。这些发现表明，基因编码的相对和可扩展的突触形成可以发展出功能但不相同的大脑和行为。
