Shiga T, Gaur V P, Yamaguchi K, Oppenheim R W
Department of Neurobiology and Anatomy, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157-1010, USA.
J Comp Neurol. 1995 Sep 25;360(3):463-74. doi: 10.1002/cne.903600308.
To investigate the role of retinoic acid (RA) in the development of interneurons in the spinal cord, we examined the expression of cellular retinoic acid binding protein type I (CRABP I). The earliest developing interneurons in the chick spinal cord can be divided into two major groups: circumferential (C) neurons and primitive longitudinal (PL) neurons. In brachial segments, both types of interneurons began to express CRABP I at stage (st.) 13+ of the V. Hamburger and H.L. Hamilton (1951, J. Morphol. 88:49-92) stage series, which is before the onset of axonogenesis. Subsequently, with the onset of axonal outgrowth, C neurons and PL neurons expressed CRABP I in their cell bodies, axons, and growth cones. The expression of CRABP I was developmentally regulated. CRABP I immunoreactivity gradually decreased after st. 36 (embryonic day [E] 10) such that no interneurons expressed this protein by E21. The transient expression of CRABP I during a period of intensive axonal growth suggested that RA may be involved in the development of interneurons. To test this idea, we implanted an all-trans RA-containing ion exchange bead into either rostral segments of the spinal cord at st. 12-13 or into caudal segments at st. 15-16, all stages that are well before the appearance of CRABP-I-positive neurons in these segments. In the RA-treated spinal cord, increased numbers of pyknotic cells were found predominantly in dorsal regions, presumably reflecting the death of neuroepithelial cells, C neurons and premigratory neural crest cells. Surviving C neurons in the RA-treated spinal cord extended their axons ventrally toward the floor plate as in control embryos. PL neurons also projected their axons rostrally or caudally in the RA-treated spinal cord, similarly to control embryos. However, the proportion of caudally projecting PL neurons was significantly increased in segments rostral to the RA-containing bead. These results suggest that RA may regulate the survival and axonal orientation (directionality) of subpopulations of spinal interneurons.
为研究视黄酸（RA）在脊髓中间神经元发育中的作用，我们检测了I型细胞视黄酸结合蛋白（CRABP I）的表达。鸡脊髓中最早发育的中间神经元可分为两大主要类型：环周（C）神经元和原始纵行（PL）神经元。在臂段，这两种类型的中间神经元在V. 汉堡和H.L. 汉密尔顿（1951年，《形态学杂志》88:49 - 92）分期系列的13 +期开始表达CRABP I，此阶段早于轴突发生。随后，随着轴突生长的开始，C神经元和PL神经元在其细胞体、轴突和生长锥中表达CRABP I。CRABP I的表达受发育调控。在36期（胚胎第[E]10天）后，CRABP I免疫反应性逐渐降低，以至于到E21时没有中间神经元表达这种蛋白。在轴突大量生长期间CRABP I的短暂表达表明RA可能参与中间神经元的发育。为验证这一想法，我们在12 - 13期将含全反式RA的离子交换珠植入脊髓的吻段，或在15 - 16期植入尾段，这些阶段均远早于这些节段中出现CRABP - I阳性神经元的时间。在经RA处理的脊髓中，主要在背侧区域发现固缩细胞数量增加，推测这反映了神经上皮细胞、C神经元和迁移前神经嵴细胞的死亡。经RA处理的脊髓中存活的C神经元如在对照胚胎中一样，其轴突向腹侧伸向底板。PL神经元在经RA处理的脊髓中也向吻侧或尾侧投射其轴突，与对照胚胎相似。然而，在含RA珠前方的节段中，向尾侧投射的PL神经元比例显著增加。这些结果表明RA可能调节脊髓中间神经元亚群的存活和轴突定向（方向性）。
