Kleitman N, Johnson M I
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri.
Cell Motil Cytoskeleton. 1989;13(4):288-300. doi: 10.1002/cm.970130407.
To determine the relationship between growth cone structure and motility, we compared the neurite extension rate, the form of individual growth cones, and the organization of f-actin in embryonic (E21) and postnatal (P30) sympathetic neurons in culture. Neurites extended faster on laminin than on collagen, but the P30 nerites were less than half as long as E21 neurites on both substrata. Growth cone shape was classified into one of five categories, ranging from fully lamellipodial to blunt endings. The leading margins of lamellipodia advanced smoothly across the substratum ahead of any filopodial activity and contained meshworks of actin filaments with no linear f-actin bundles, indicating that filopodia need not underlie lamellipodia. Rapid translocation (averaging 0.9-1.4 microns/min) was correlated with the presence of lamellipodia; translocation associated with filopodia averaged only 0.3-0.5 microns/min. This relationship extended to growth cones on a branched neurite where the translocation of each growth cone was dependent on its shape. Growth cones with both filopodial and lamellipodial components moved at intermediate rates. The prevalence of lamellipodial growth cones depended on age of the neurites; early in culture, 70% of E21 growth cones were primarily lamellipodial compared to 38% of P30 growth cones. A high percentage of E21 lamellipodial growth cones were associated with rapid neurite elongation (1.2 mm/day), whereas a week later, only 16% were lamellipodial, and neurites extended at 0.5 mm/day. Age-related differences in neurite extension thus reflected the proportion of lamellipodial growth cones present rather than disparities in basic structure or in the rates at which growth cones of a given type moved at different ages. Filopodia and lamellipodia are each sufficient to advance the neurite margin; however, rapid extension of superior cervical ganglion neurites was supported by lamellipodia independent of filopodial activity.
为了确定生长锥结构与运动性之间的关系，我们比较了培养的胚胎期（E21）和出生后（P30）交感神经元的神经突延伸速率、单个生长锥的形态以及丝状肌动蛋白（f-actin）的组织情况。神经突在层粘连蛋白上的延伸速度比在胶原蛋白上快，但在两种基质上，P30神经突的长度都不到E21神经突的一半。生长锥形状分为五类之一，从完全片状伪足到钝端。片状伪足的前缘在任何丝状伪足活动之前平滑地越过基质，并且包含没有线性f-肌动蛋白束的肌动蛋白丝网络，这表明丝状伪足不一定是片状伪足的基础。快速移位（平均0.9 - 1.4微米/分钟）与片状伪足的存在相关；与丝状伪足相关的移位平均仅为0.3 - 0.5微米/分钟。这种关系扩展到分支神经突上的生长锥，其中每个生长锥的移位取决于其形状。同时具有丝状伪足和片状伪足成分的生长锥以中等速度移动。片状伪足生长锥的比例取决于神经突的年龄；在培养早期，70%的E21生长锥主要是片状伪足，而P30生长锥的这一比例为38%。E21的高比例片状伪足生长锥与快速的神经突伸长（1.2毫米/天）相关，而一周后，只有16%是片状伪足，神经突以0.5毫米/天的速度延伸。因此，神经突延伸的年龄相关差异反映的是存在的片状伪足生长锥的比例，而不是基本结构的差异或给定类型的生长锥在不同年龄移动的速率差异。丝状伪足和片状伪足各自都足以推进神经突边缘；然而，颈上神经节神经突的快速延伸由独立于丝状伪足活动的片状伪足支持。
