EDITORThe APC tumour suppressor gene contains at least 21 exons, including four exons upstream of exon 1.^1 2 Alternative splicing involves at least seven exons, including the first five exons, and creates distinct splice forms of APC RNA.^1-4 Exon 1 contains an in frame stop codon upstream of its initiating methionine; hence only splice forms of APC that lack exon 1 allow exons 5' of exon 1 to be translated. Interestingly, splice forms lacking exon 1 are enriched in terminally differentiated tissues including brain,⁵ intimating that protein isoforms containing domains encoded by the exons 5' to exon 1 may be important in cellular differentiation. This study evaluates neurones and glia of the rodent nervous system and asks which cell types express APC isoforms lacking exon 1.

Medulloblastomas and glioblastomas are neuroepithelial tumours derived from neuronal progenitor cells and glial cells, respectively.^6 7 Both tumour types occur at increased frequency in a subset of adenomatous polyposis coli . . . [Full text of this article]