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. Recombi nant nonhomologous regions of the core proteins were used for immuniza tion to obtain polyclonal antibodies specific for aggrecan, the alpha and beta domains of versican mRNA splice variants, and N- and C-termin al portions of neurocan, while brevican was quantitated using a specif ic monoclonal antibody. The concentration of aggrecan increased steadi ly during brain development up to 5 months of age, when it reached a l evel that was 18-fold higher than at E14. Alternatively spliced versic an isoforms containing the alpha domain of the glycosaminoglycan attac hment region were present at a relatively low level during the late em bryonic and early postnatal period, decreased by similar to 50% betwee n 1 and 2 weeks postnatal, and then increased steadily in concentratio n to reach a maximum at 100 days that was 7-fold that present at 10 da ys postnatal. In contrast to these results, versican isoforms containi ng 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-re gulated proteolytic cleavage in the middle of its chondroitin sulfate attachment region) both increased in embryonic brain during developmen t, reached a peak in the early postnatal period, and then declined the reafter, As in the case of aggrecan, only traces of brevican were dete cted in embryonic brain and its concentration increased steadily after birth to reach an adult level that was approximately 14-fold higher t han that present in neonatal brain. These striking and distinctive cha nges in the concentrations of the different members of this family of structurally related proteoglycans in developing brain, including chan ges in opposite directions for versican mRNA splice variants, indicate that the individual proteoglycans and their isoforms probably serve u nique functions during nervous tissue histogenesis. (C) 1998 Academic Press.