探討PAR複合體和細胞骨架在神經元極化過程中的作用

Abstract

神經元是一種極化細胞，具有兩種功能不同的細胞結構：軸突和樹突。在培養的皮質神經元中，神經元極性建立的起初事件是軸突特異化(axon specification)，這個過程是需要重塑細胞骨架(cytoskeletons)，像是肌動蛋白絲(actin filamens)和微管(microtubules)。在未來軸突的特異化過程中，微管會變得更穩定，而肌動蛋白絲在生長錐(growth cone)中更具活性。由PAR-3，PAR-6 和非典型蛋白激酶C（atypical protein kinase C, aPKC）組成的PAR 蛋白複合物被認為會積累在最長的神經突(neurites)的尖端，以促進軸突特異化。儘管已經在體外研究中對神經元極性的過程了解透徹，但是在體內極化過程的調控仍然不清楚。在我的研究中，我利用秀麗隱桿線蟲(Caenorhabditis elegans)中的PVD 神經元來研究神經元極性和神經發育的機制。為了了解PAR 複合物如何在體內調節神經元極化，我對par-3 和pkc-3 基因進行了遺傳分析。我發現par-3 和pkc-3 不僅參與在軸突特異化中，而且其對於樹突形成也是十分重要的。它們同時也調控了PVD中的粒線體的運輸。我還發現了PAR3-PAR6-aPKC 複合的輔助因子osm-3、unc-76 和unc-69 是維持軸突正常生長所必需的，它們同時也參與了神經元中的粒線體數量的調控。此外，我對於肌動蛋白異型體(actin isoforms)和肌動蛋白結合蛋白(actin-binding proteins)的候選基因進行了檢查(candidate screening)。我發現了通過act-1,2,3 基因簇所調控的恆定肌動蛋白動力學對於神經元極化至關重要，這個過程同時涉及到肌動蛋白的聚合因子wve-1、fhod-1 和解聚因子unc-60 的調節。我也發現在PVD 神經元中的粒線體分佈是受到act-1, 2, 3、wsp-1、wve-1、fhod-1、pfn-1 和unc-60 所調控。我的研究將提供有關於信息調控因子和細胞骨架動力學在神經元極化的過程中所扮演的角色。

Neuron is a polarized cell with two kinds of functional distinct cellular processes, axons and dendrites. In cultured cortical neurons, the initial event of neuronal polarity establishment is axon specification that requires the remodeling of cytoskeletons such as actin filament and microtubules. In the specification of the future axon, microtubules are more stabilized, while actin filaments are more dynamic in the growth cone. PAR protein complex, which is composed of PAR-3, PAR-6 and atypical protein kinase C (aPKC), accumulates at the tip of the longest neurites to promote axon specification. Although the processes of neuronal polarity have been studied in vitro, the regulation of polarization in vivo is still unclear. In my study, I utilized the PVD neurons in Caenorhabditis elegans to study the mechanism of neuronal polarity and neurite development. To identify how the PAR complex regulates neuronal polarization in vivo, I have a genetic analysis on par-3 and pkc-3 genes. I found that par-3 and pkc-3 not only require for axon specification, but also for dendrites formation. They also modulate the mitochondrial distribution in PVDs. I also found that osm-3, unc-76 and unc-69, the PAR3-PAR6-aPKC complex cofactors, are required for axon maintenance and regulate mitochondria amount in PVDs. In addition, I performed a candidate screening in actin isoforms and actin-binding proteins. I demonstrated that the constant actin dynamics modulate by act-1, 2, 3 cluster is critical for neuronal polarization, which is modulated by actin polymerization factor wve-1 and fhod-1, as well as depolymerizing factor unc-60. I also found that the mitochondrial distribution in PVDs is regulated by act-1, 2, 3, wsp-1, wve-1, fhod-1, pfn-1 and unc-60. My study will provide insights of how neuronal polarization is established by the signaling regulators and cytoskeletal dynamics.