Differential regulation of expression of hyaluronan-binding proteoglycans in developing brain: aggrecan, versican, neurocan, and brevican.

We have used a slot-blot radioimmunoassay to quantitate the levels of hyaluronan-binding chondroitin sulfate proteoglycans in developing rat brain from embryonic day 14 (E 14) to eight months postnatal. Recombinant nonhomologous regions of the core proteins were used for immunization to obtain polyclonal antibodies specific for aggrecan, the alpha and beta domains of versican mRNA splice variants, and N- and C-terminal portions of neurocan, while brevican was quantitated using a specific monoclonal antibody. The concentration of aggrecan increased steadily during brain development up to 5 months of age, when it reached a level that was 18-fold higher than at E14. Alternatively spliced versican isoforms containing the alpha domain of the glycosaminoglycan attachment region were present at a relatively low level during the late embryonic and early postnatal period, decreased by approximately 50% between 1 and 2 weeks postnatal, and then increased steadily in concentration to reach a maximum at 100 days that was 7-fold that present at 10 days postnatal. In contrast to these results, versican isoforms containing the beta domain more than doubled in concentration between E14 and birth, after which they decreased by greater than 90% to reach a low "mature" level that remained unchanged between 2 and 8 months. The N- and C-terminal portions of neurocan (produced by a developmentally-regulated proteolytic cleavage in the middle of its chondroitin sulfate attachment region) both increased in embryonic brain during development, reached a peak in the early postnatal period, and then declined thereafter. As in the case of aggrecan, only traces of brevican were detected in embryonic brain and its concentration increased steadily after birth to reach an adult level that was approximately 14-fold higher than that present in neonatal brain. These striking and distinctive changes in the concentrations of the different members of this family of structurally related proteoglycans in developing brain, including changes in opposite directions for versican mRNA splice variants, indicate that the individual proteoglycans and their isoforms probably serve unique functions during nervous tissue histogenesis.