Gray Noah W, Weimer Robby M, Bureau Ingrid, Svoboda Karel
Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, USA.
PLoS Biol. 2006 Nov;4(11):e370. doi: 10.1371/journal.pbio.0040370.
Most excitatory synapses terminate on dendritic spines. Spines vary in size, and their volumes are proportional to the area of the postsynaptic density (PSD) and synaptic strength. PSD-95 is an abundant multi-domain postsynaptic scaffolding protein that clusters glutamate receptors and organizes the associated signaling complexes. PSD-95 is thought to determine the size and strength of synapses. Although spines and their synapses can persist for months in vivo, PSD-95 and other PSD proteins have shorter half-lives in vitro, on the order of hours. To probe the mechanisms underlying synapse stability, we measured the dynamics of synaptic PSD-95 clusters in vivo. Using two-photon microscopy, we imaged PSD-95 tagged with GFP in layer 2/3 dendrites in the developing (postnatal day 10-21) barrel cortex. A subset of PSD-95 clusters was stable for days. Using two-photon photoactivation of PSD-95 tagged with photoactivatable GFP (paGFP), we measured the time over which PSD-95 molecules were retained in individual spines. Synaptic PSD-95 turned over rapidly (median retention times tau(r) is approximately 22-63 min from P10-P21) and exchanged with PSD-95 in neighboring spines by diffusion. PSDs therefore share a dynamic pool of PSD-95. Large PSDs in large spines captured more diffusing PSD-95 and also retained PSD-95 longer than small PSDs. Changes in the sizes of individual PSDs over days were associated with concomitant changes in PSD-95 retention times. Furthermore, retention times increased with developmental age (tau(r) is approximately 100 min at postnatal day 70) and decreased dramatically following sensory deprivation. Our data suggest that individual PSDs compete for PSD-95 and that the kinetic interactions between PSD molecules and PSDs are tuned to regulate PSD size.
大多数兴奋性突触终止于树突棘。树突棘大小各异，其体积与突触后致密区（PSD）的面积及突触强度成正比。PSD - 95是一种丰富的多结构域突触后支架蛋白，它能聚集谷氨酸受体并组织相关的信号复合物。PSD - 95被认为决定了突触的大小和强度。尽管树突棘及其突触在体内可维持数月，但PSD - 95和其他PSD蛋白在体外的半衰期较短，约为数小时。为探究突触稳定性的潜在机制，我们在体内测量了突触PSD - 95簇的动态变化。利用双光子显微镜，我们对发育中（出生后第10 - 21天）桶状皮层第2/3层树突中标记有绿色荧光蛋白（GFP）的PSD - 95进行成像。一部分PSD - 95簇能稳定存在数天。通过对标记有光激活绿色荧光蛋白（paGFP）的PSD - 95进行双光子光激活，我们测量了PSD - 95分子在单个树突棘中保留的时间。突触PSD - 95周转迅速（从出生后第10天到第21天，中位保留时间τ(r)约为22 - 63分钟），并通过扩散与相邻树突棘中的PSD - 95进行交换。因此，PSD共享一个动态的PSD - 95库。大的树突棘中的大PSD捕获更多扩散的PSD - 95，并且比小PSD保留PSD - 95的时间更长。数天内单个PSD大小的变化与PSD - 95保留时间的相应变化相关。此外，保留时间随着发育年龄增加（出生后第70天约为100分钟），而在感觉剥夺后显著减少。我们的数据表明，单个PSD竞争PSD - 95，并且PSD分子与PSD之间的动力学相互作用被调节以控制PSD大小。
