Developmental Characterization of Thymosin β 4 and β 10 Expression in Enriched Neuronal Cultures from Rat Cerebella

The β 4 and β 10 thymosins are G‐actin binding proteins that exhibit complex patterns of expression during rat cerebellar development. Their expression in vivo is initially high in immature granule cells and diminishes as they migrate and differentiate, ceasing altogether by postnatal day 21. Thymosin β 4 is present in a subset of glia throughout postnatal development, and its synthesis is also induced in maturing Bergmann glia. In contrast, thymosin β 10 is only present at very low levels in a very small subpopulation of glia in the adult cerebellum. To study the factors differentially regulating expression of the β‐thymosins, we characterized their patterns of expression in primary cultures of rat cerebellum. Both β‐thymosins were initially expressed in granule cells, although expression, especially of thymosin β 4 , was truncated compared with the in vivo time course. As in vivo, thymosin β 4 was synthesized at much higher levels in astrocytes and microglia in cultures from postnatal cerebellum than was thymosin β 10 . Unlike in vivo, the latter was expressed in glia cultured from fetal cerebellum. The similarities between the in vivo and in vitro expression of the β‐thymosins show that modulation of tissue culture conditions could be used to identify factors regulating β‐thymosin expression in vivo. The differences would identify regulatory mechanisms that are not evident from the in vivo studies alone.