Institute of Molecular and Cellular Biology, National Taiwan University, Taipei 10617, Taiwan.
Genome and Systems Biology Degree Program, National Taiwan University and Academia Sinica, Taipei 10617, Taiwan.
Proc Natl Acad Sci U S A. 2019 Feb 19;116(8):3262-3267. doi: 10.1073/pnas.1812169116. Epub 2019 Feb 6.
Patterned spontaneous activity periodically displays in developing retinas termed retinal waves, essential for visual circuit refinement. In neonatal rodents, retinal waves initiate in starburst amacrine cells (SACs), propagating across retinal ganglion cells (RGCs), further through visual centers. Although these waves are shown temporally synchronized with transiently high PKA activity, the downstream PKA target important for regulating the transmission from SACs remains unidentified. A t-SNARE, synaptosome-associated protein of 25 kDa (SNAP-25/SN25), serves as a PKA substrate, implying a potential role of SN25 in regulating retinal development. Here, we examined whether SN25 in SACs could regulate wave properties and retinogeniculate projection during development. In developing SACs, overexpression of wild-type SN25b, but not the PKA-phosphodeficient mutant (SN25b-T138A), decreased the frequency and spatial correlation of wave-associated calcium transients. Overexpressing SN25b, but not SN25b-T138A, in SACs dampened spontaneous, wave-associated, postsynaptic currents in RGCs and decreased the SAC release upon augmenting the cAMP-PKA signaling. These results suggest that SN25b overexpression may inhibit the strength of transmission from SACs via PKA-mediated phosphorylation at T138. Moreover, knockdown of endogenous SN25b increased the frequency of wave-associated calcium transients, supporting the role of SN25 in restraining wave periodicity. Finally, the eye-specific segregation of retinogeniculate projection was impaired by in vivo overexpression of SN25b, but not SN25b-T138A, in SACs. These results suggest that SN25 in developing SACs dampens the spatiotemporal properties of retinal waves and limits visual circuit refinement by phosphorylation at T138. Therefore, SN25 in SACs plays a profound role in regulating visual circuit refinement.
发育中的视网膜会周期性地显示出有规律的自发活动，称为视网膜波，这对视觉回路的精炼至关重要。在新生啮齿动物中，视网膜波始于星爆型无长突细胞（SAC），在视网膜神经节细胞（RGC）中传播，进一步传播到视觉中枢。尽管这些波在时间上与瞬时高 PKA 活性同步，但对于调节 SAC 之间的传递至关重要的下游 PKA 靶标仍未确定。一种 t-SNARE，突触体相关蛋白 25kDa（SNAP-25/SN25），作为 PKA 的底物，暗示 SN25 在调节视网膜发育中可能发挥作用。在这里，我们研究了 SAC 中的 SN25 是否可以调节波特性和视网膜神经节突起的发育。在发育中的 SAC 中，过表达野生型 SN25b，但不是 PKA 磷酸缺陷型突变体（SN25b-T138A），会降低波相关钙瞬变的频率和空间相关性。在 SAC 中过表达 SN25b，但不是 SN25b-T138A，会抑制 RGC 中的自发、波相关的突触后电流，并在增强 cAMP-PKA 信号时减少 SAC 的释放。这些结果表明，SN25b 的过表达可能通过 T138 的 PKA 介导磷酸化抑制 SAC 之间的传递强度。此外，内源性 SN25b 的敲低增加了波相关钙瞬变的频率，支持 SN25 在限制波周期性中的作用。最后，在 SAC 中体内过表达 SN25b 会损害视网膜神经节突起的眼特异性分离，但过表达 SN25b-T138A 不会。这些结果表明，发育中的 SAC 中的 SN25 通过 T138 的磷酸化来抑制视网膜波的时空特性，并限制视觉回路的精炼。因此，SAC 中的 SN25 在调节视觉回路精炼中起着重要作用。
