Gonzalez M de L, Malemud C J, Silver J
Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4975.
Exp Neurol. 1993 Sep;123(1):91-105. doi: 10.1006/exnr.1993.1143.
We describe the development of the olfactory bulb (OB) glomeruli, focusing on the role of purported astroglial-associated boundary molecules, as potential guidance factors in glomeruli formation. Glomeruli are unusual structures within the OB formed by extremely tight bundles of afferent fibers that fail to grow deeply into the brain. Using olfactory marker protein antibodies, we found that olfactory axons of stage E17-E18 rat embryos were organized into long strands at the outer-most edge of the bulb. By E20-E21 the axons clustered and formed small spheres and by PD1 they gathered into distinct glomeruli. Prior to and during the transformation of olfactory afferents into glomeruli, there was an enhanced expression of cytotactin/tenascin (CT) and chondroitin sulfate-containing proteoglycan (CS-PG) associated with VIM/GFAP-positive astroglial cell processes at the base of the glomeruli. During later stages of development (PD3-PD9), the GFAP-positive astroglial processes beneath and within the base of the glomeruli showed intensified GFAP staining while maintaining expression of CT and CS-PG. Some astroglial processes had extended and others went even further peripherally into the olfactory nerve layer (ONL) to encapsulate and fully infiltrate the glomeruli. By PD9, CS-PG and CT levels increased inside and outside the glomeruli. However, by PD15 both molecules had decreased inside the glomeruli but remained highly concentrated around the glomeruli to form rings. Thus, at later stages, axon/glia interactions which result in astroglial rearrangement and matrix alterations in relation to the glomeruli occur. Western blots of stage E20 bulb proteins revealed the presence of three proteoglycan core proteins each containing chondroitin-6-sulfate moieties. In addition, a type of keratan sulfate (KS) glycosaminoglycan was present in a core protein not associated with chondroitin-6-sulfate. Our data suggest that astroglial-associated ECM molecules CT and CS-PG, and perhaps KS-PG, present in the core of the early developing OB, could form a molecular "wall" that helps confine ingrowing olfactory axons within the ONL at the outer edge of the astroglial territory. We suggest that the astroglia do not precisely regulate the specific shape of the glomeruli, but rather play a fundamental role in directing the gross position at which formation of the synaptic glomeruli will occur.
我们描述了嗅球（OB）肾小球的发育过程，重点关注所谓的星形胶质细胞相关边界分子在肾小球形成中作为潜在引导因子的作用。肾小球是OB内的特殊结构，由紧密排列的传入纤维束形成，这些纤维束不会深入大脑生长。使用嗅觉标记蛋白抗体，我们发现E17 - E18期大鼠胚胎的嗅觉轴突在嗅球最外缘被组织成细长束。到E20 - E21期，轴突聚集形成小球体，到出生后第1天（PD1），它们聚集形成明显的肾小球。在嗅觉传入纤维转变为肾小球之前及过程中，在肾小球基部与波形蛋白/胶质纤维酸性蛋白（VIM/GFAP）阳性星形胶质细胞过程相关的细胞粘着蛋白/腱生蛋白（CT）和含硫酸软骨素的蛋白聚糖（CS - PG）表达增强。在发育后期（PD3 - PD9），肾小球基部下方和内部的GFAP阳性星形胶质细胞过程显示GFAP染色增强，同时保持CT和CS - PG的表达。一些星形胶质细胞过程延伸，其他一些甚至进一步向周围延伸到嗅神经层（ONL）以包裹并完全浸润肾小球。到PD9时，CS - PG和CT水平在肾小球内外均升高。然而，到PD15时，这两种分子在肾小球内减少，但仍高度集中在肾小球周围形成环。因此，在后期，会发生轴突/胶质细胞相互作用，导致与肾小球相关的星形胶质细胞重排和基质改变。对E20期嗅球蛋白的蛋白质印迹分析显示存在三种蛋白聚糖核心蛋白，每种都含有硫酸软骨素 - 6 -硫酸酯部分。此外，一种硫酸角质素（KS）糖胺聚糖存在于一种与硫酸软骨素 - 6 -硫酸酯不相关的核心蛋白中。我们的数据表明，在早期发育的嗅球核心中存在的星形胶质细胞相关细胞外基质分子CT和CS - PG，可能还有KS - PG，可能形成一个分子“壁”，有助于将向内生长的嗅觉轴突限制在星形胶质细胞区域外缘的嗅神经层内。我们认为星形胶质细胞并不精确调节肾小球的特定形状，而是在指导突触肾小球形成的大致位置方面发挥着基本作用。
