Abstract

A cGMP-dependent protein kinase (PKG) encoded by the Drosophila foraging (for) gene regulates both synaptic structure (nerve terminal growth) and function (neurotransmission) through independent mechanisms at the Drosophila larval neuromuscular junction (nmj). Glial for is known to restrict nerve terminal growth, whereas presynaptic for inhibits synaptic vesicle (SV) exocytosis during low frequency stimulation. Presynaptic for also facilitates SV endocytosis during high frequency stimulation. for’s effects on neurotransmission can occur independent of any changes in nerve terminal growth. However, it remains unclear if for’s effects on neurotransmission affect nerve terminal growth. Furthermore, it’s possible that for’s effects on synaptic structure contribute to changes in neurotransmission. In the present study, we examined these questions using RNA interference to selectively knockdown for in presynaptic neurons or glia at the Drosophila larval nmj. Consistent with our previous findings, presynaptic knockdown of for impaired SV endocytosis, whereas knockdown of glial for had no effect on SV endocytosis. Surprisingly, we found that knockdown of either presynaptic or glial for increased neurotransmitter release in response to low frequency stimulation. Knockdown of presynaptic for did not affect nerve terminal growth, demonstrating that for’s effects on neurotransmission does not alter nerve terminal growth. In contrast, knockdown of glial for enhanced nerve terminal growth. This enhanced nerve terminal growth was likely the cause of the enhanced neurotransmitter release seen following knockdown of glial for. Overall, we show that for can affect neurotransmitter release by regulating both synaptic structure and function.

摘要

由果蝇觅食( for ) 基因编码的 cGMP 依赖性蛋白激酶 (PKG)通过果蝇幼虫神经肌肉接头 (nmj)的独立机制调节突触结构（神经末梢生长）和功能（神经传递）。众所周知，胶质细胞会限制神经末梢的生长，而突触前细胞会在低频刺激期间抑制突触小泡 (SV) 胞吐作用。突触前还促进高频刺激期间的 SV 内吞作用。for对神经传递的影响可以独立于神经末梢生长的任何变化而发生。但是，目前尚不清楚是否为对神经传递的影响会影响神经末梢的生长。此外，for对突触结构的影响可能会导致神经传递的变化。在本研究中，我们使用 RNA 干扰来检查这些问题，以选择性地敲除果蝇幼虫 nmj的突触前神经元或神经胶质细胞。与我们之前的研究结果一致，SV 内吞作用受损的突触前敲低，而胶质细胞的敲低对 SV 内吞作用没有影响。令人惊讶的是，我们发现敲除突触前或神经胶质细胞可增加神经递质释放以响应低频刺激。突触前敲除不影响神经末梢生长，证明for对神经传递的影响不会改变神经末梢生长。相比之下，神经胶质细胞的敲除以增强神经末梢的生长。这种增强的神经末梢生长很可能是神经递质释放增强的原因，因为在神经胶质细胞被击倒后，神经递质释放增加。总体而言，我们表明它可以通过调节突触结构和功能来影响神经递质的释放。