Tetraspanin-5 (Tm4sf9) mRNA expression parallels neuronal maturation in the cerebellum of normal and L7En-2 transgenic mice.

Tetraspanin-5 (Tspan-5) mRNA was recently shown to be strongly expressed within the central nervous system. In order to address Tspan-5 function during nervous system development, we performed a detailed expression analysis in the postnatal FVB/N mouse cerebellum using in situ hybridizations. Tspan-5 mRNA was expressed within cerebellar Purkinje cells (PCs) throughout postnatal development. The expression level, however, changed significantly with ongoing development. At the day of birth (P0), Tspan-5 mRNA was expressed at very low levels in PCs. At this time, PCs of the FVB/N strain are postmitotic and bear axons, but no dendrites. At P7, Tspan-5 mRNA expression was visible in all PCs, but was more prominent in those of the posterior lobules as compared to those of the anterior lobules. After P7, high levels of Tspan-5 mRNA were seen in all PCs, which is when PCs elaborate and maintain their typical dendritic tree. This demonstrates that the level of Tspan-5 mRNA is related to the developmental status of PCs. Consistently, expression of Tspan-5 mRNA was specifically reduced in PCs of L7En-2 animals, which display a delay in PC maturation during postnatal cerebellar development. In addition, whereas no Tspan-5 mRNA signal could be detected in the proliferating granule cell layer, low levels could be found in postmitotic, premigratory granule cells and high levels in settled and differentiated granule cells. Thus, the level of Tspan-5 mRNA expression correlates very well with the differentiation status of particular neurons. The level of Tspan-5 expression might therefore be important for distinct phases of neuronal maturation.