DEVELOPMENTAL CHARACTERIZATION OF THYMOSIN BETA(4) AND BETA(10) EXPRESSION IN ENRICHED NEURONAL CULTURES FROM RAT CEREBELLA

The beta(4) and beta(10) thymosins are G-actin binding proteins that e xhibit complex patterns of expression during rat cerebellar developmen t. Their expression in vivo is initially high in immature granule cell s and diminishes as they migrate and differentiate, ceasing altogether by postnatal day 21. Thymosin beta(4) is present in a subset of glia throughout postnatal development, and its synthesis is also induced in maturing Bergmann glia. In contrast, thymosin beta(10) is only presen t at very low levels in a very small subpopulation of glia in the adul t cerebellum. To study the factors differentially regulating expressio n of the beta-thymosins, we characterized their patterns of expression in primary cultures of rat cerebellum. Both beta-thymosins were initi ally expressed in granule cells, although expression, especially of th ymosin beta(4), was truncated compared with the in vivo time course. A s in vivo, thymosin beta(4) was synthesized at much higher levels in a strocytes and microglia in cultures from postnatal cerebellum than was thymosin beta(10). Unlike in vivo, the latter was expressed in glia c ultured from fetal cerebellum. The similarities between the in vivo an d in vitro expression of the beta-thymosins show that modulation of ti ssue culture conditions could be used to identify factors regulating b eta-thymosin expression in vivo. The differences would identify regula tory mechanisms that are not evident from the in vivo studies alone.