Meeker M L, Farel P B
Department of Physiology, School of Medicine, University of North Carolina, Chapel Hill 27599.
J Comp Neurol. 1993 Mar 8;329(2):257-68. doi: 10.1002/cne.903290207.
The Schwann cell-derived basal lamina forms a tube around single peripheral axons or small groups of axons that is continuous from the spinal cord to the target. In bullfrog tadpoles (Rana catesbeiana), motor axons transected at early developmental stages regenerate to the appropriate hindlimb region. In the present paper, we found that at these stages Schwann tubes are absent by morphological criteria, and individual axons are separated only by occasional extensions of support cells. At stages when axons no longer regenerate to the correct hindlimb region, every axon is encased in a basal lamina tube. Schwann tubes persist in the distal stump after nerve transection, and regenerating axons grow within these tubes. These findings are consistent with previous results showing that the errors regenerating axons make in older animals are not random, but depend upon the course of the denervated Schwann tubes to which they have access. In order to determine whether formation of the Schwann tube itself or interaction of its molecular constituents with growing axons was associated with loss of regenerative specificity, the expression during development of two major constituents of the basal lamina, laminin and heparan sulfate proteoglycan, was investigated. Immunoreactivity to both constituents was present both before and after the transition from specific to nonspecific regeneration, indicating that their expression per se was not sufficient to limit regenerative specificity. These data support the hypothesis that the physical constraint imposed by the Schwann cell-derived basal lamina prevents regenerative specificity.
雪旺细胞衍生的基膜围绕单个外周轴突或小群轴突形成一个管,该管从脊髓到靶组织是连续的。在牛蛙蝌蚪(牛蛙)中,在早期发育阶段横断的运动轴突可再生至适当的后肢区域。在本文中,我们发现,在这些阶段,从形态学标准来看雪旺管并不存在,单个轴突仅偶尔被支持细胞的延伸部分分隔开。在轴突不再能再生至正确的后肢区域的阶段,每个轴突都被包裹在一个基膜管中。神经横断后雪旺管在远端残端持续存在,再生轴突在这些管内生长。这些发现与先前的结果一致,表明成年动物中再生轴突所犯的错误并非随机的,而是取决于它们能够接触到的失神经支配的雪旺管的走向。为了确定雪旺管本身的形成或其分子成分与生长轴突的相互作用是否与再生特异性的丧失有关,我们研究了基膜的两种主要成分层粘连蛋白和硫酸乙酰肝素蛋白聚糖在发育过程中的表达。在从特异性再生转变为非特异性再生之前和之后,对这两种成分均存在免疫反应性,这表明它们本身的表达不足以限制再生特异性。这些数据支持这样一种假说,即雪旺细胞衍生的基膜所施加的物理限制会阻止再生特异性。