Expression of the tissue specific splicing protein SmN in neuronal cell lines and in regions of the brain with different splicing capacities.

The SmN protein is closely related to the ubiquitously expressed SmB and B' RNA splicing proteins but is expressed in only a limited range of tissues and cell types. The expression of SmN in a range of neuronal and non-neuronal cell lines correlates with their ability to splice the calcitonin/CGRP transcript to produce the mRNA encoding CGRP rather than that encoding calcitonin. Moreover, the SmN mRNA shows a widespread distribution within the brain and spinal ganglia being present in neuronal cells in all regions which naturally produce CGRP as well as in those areas which do not naturally express the calcitonin/CGRP gene but which can correctly splice the CGRP mRNA in transgenic mice expressing the calcitonin/CGRP gene in all cell types. Interestingly however the mRNA encoding SmN is also found in a few areas of the brain which can only carry out calcitonin-specific splicing in transgenic mice, such as the Purkinje layer of the cerebellum and the inferior colliculus. The possible role of SmN in the regulation of splicing in neuronal cells is discussed in the light of these results.