NEURONATIN MESSENGER-RNA - ALTERNATIVELY SPLICED FORMS OF A NOVEL BRAIN-SPECIFIC MAMMALIAN DEVELOPMENTAL GENE

Neurogenesis begins with the closure of the neural tube around mid ges tation and continues in the rat for about two weeks postnatally. There fore, we investigated the role of neuronatin, a novel cDNA that we clo ned from neonatal rat brain (Joseph et al., Biochem. Biophys. Res. Com mun., 201 (1994) 1227-1234), in brain development. Further studies des cribed in the present manuscript, lead to the identification of two al ternatively spliced forms of neuronatin mRNA, alpha and beta, with the same open reading frame. Neuronatin-alpha encoded a novel protein of 81 aa, and the beta-form encoded 54 aa. Both forms were identical, exc ept that the alpha-form had an additional 81 bp sequence inserted into the middle of the coding region. On Northern analyses, neuronatin mRN A was relatively selective for the brain. It first appeared at E11-14, a time when the neural tube has closed and neuroepithelial proliferat ion initiated, became pronounced at E16-19 with a surge in neurogenesi s, and declined postnatally to adult levels with the completion of neu rogenesis. In order to determine whether there were other forms of neu ronatin mRNA, and to study the expression of the alpha and beta forms separately during development, reverse transcriptase-polymerase chain reaction was carried out using primers flanking the coding region of t he alpha and beta forms. The RT-PCR results clearly indicated that the re were only two forms of neuronatin. The beta-form first appeared at E11-14, whereas the alpha-form was present even earlier at E7-10. Toge ther, these findings indicate that the two forms of neuronatin mRNA ar e regulated differently during brain development. The appearance of th e beta-form at mid-gestation, coinciding with the onset of neurogenesi s, may suggest that alternative splicing of neuronatin mRNA has releva nce in brain development.