Biochemical comparison of brain glycosaminoglycans between normal and reeler mutant mice

The Role of Chondroitin Sulfate Proteoglycans in Nervous System Development

The orderly development of the nervous system is characterized by phases of cell proliferation and differentiation, neural migration, axonal outgrowth and synapse formation, and stabilization. Each of these processes is a result of the modulation of genetic programs by extracellular cues. In particular, chondroitin sulfate proteoglycans (CSPGs) have been found to be involved in almost every aspect of this well-orchestrated yet delicate process. The evidence of their involvement is complex, often contradictory, and lacking in mechanistic clarity; however, it remains obvious that CSPGs are key cogs in building a functional brain. This review focuses on current knowledge of the role of CSPGs in each of the major stages of neural development with emphasis on areas requiring further investigation.

A 3D model of Reelin subrepeat regions predicts Reelin binding to carbohydrates

Reelin is a large molecule of the extracellular matrix (ECM) which regulates neuronal positioning during the early stages of cortical development in vertebrate species. The Reelin molecule can be subdivided into a smaller N-terminal domain, showing homology with F-spondin, and a larger C-terminal region containing 8 EGF-like repeats. The localization of Reelin in the ECM, its large dimensions and the modular organization of its primary structure led us to suppose a structure of its modules similar to domains commonly found in ECM proteins such as Agrin, laminins and thrombospondins. We therefore performed a sequence alignment and molecular modeling analysis to study the three-dimensional fold of the Reelin subrepeat regions. Our analysis produces a tentative model of the core region of the Reelin subrepeat sequences and suggests the presence in this 3D model of structural features common to polysaccharide-binding modules which are often found on proteoglycans of the ECM. These findings provide a conceptual framework for further experiments aimed at testing the functions of the EGF-like repeat regions of Reelin.

Chondroitin sulfate proteoglycans in the developing cerebral cortex: the distribution of neurocan distinguishes forming afferent and efferent axonal pathways

The first thalamocortical axons to arrive in the developing cerebral cortex traverse a pathway that is separate from the adjacent intracortical pathway for early efferents, suggesting that different molecular signals guide their growth. We previously demonstrated that the intracortical pathway for thalamic axons is centered on the subplate (Bicknese et al. [1994] J. Neurosci. 14:3500-3510), which is rich in chondroitin sulfate proteoglycans (CSPGs; Sheppard et al. [1991] J. Neurosci. 11:3928-3942), whereas efferent axons cross the subplate to exit in a zone containing much less CSPG. To define the molecular composition of the subplate further, we used antibodies against CSPG core proteins and chondroitin sulfate disaccharides in an immunohistochemical analysis of their distribution in the developing neocortex of the rat. Immunolabeling for neurocan, a central nervous system-specific CSPG (Rauch et al. [1992] J. Biol. Chem. 267:19537-19547), and for chondroitin 6-sulfate and unsulfated chondroitin becomes prominent in the subplate before the arrival of thalamic afferents. Immunolabeling is initially sparse in the cortical plate but appears later in maturing cortical layers. A postnatal decline in immunolabeling occurs uniformly for most proteoglycans, but, in the somatosensory cortex, labeling for neurocan, phosphacan, and chondroitin 4- and 6-sulfate declines in the centers of the whisker barrels before the walls. In contrast to neurocan, immunolabeling for other proteoglycans is either uniformly distributed (syndecan-1, N-syndecan, 5F3, phosphacan, chondroitin 4-sulfate), restricted to axons (PGM1), distributed exclusively on nonneuronal elements (2D6, NG2, and CD44), or undetectable (9.2.27, aggrecan, decorin). Thus, neurocan is a candidate molecule for delineating the intracortical pathway of thalamocortical axons and distinguishing it from that of cortical efferents.