Journal of Neuroscience, Vol 12, 895-905, Copyright © 1992 by Society for Neuroscience
Alternative splicing of micro-exons creates multiple forms of the insect cell adhesion molecule fasciclin I
L McAllister, EJ Rehm, GS Goodman and K Zinn
Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Fasciclin I is a homophilic cell adhesion molecule in insects that is
dynamically expressed on a subset of axon pathways in the embryonic nervous
system, and on a variety of other cells and tissues during development. The
fasciclin I protein consists of four homologous 150 amino acid domains. In
this article, we describe the complete sequence of the Drosophila fasciclin
I (fasI) gene. The gene consists of 15 exons and is distributed over 14
kilobases of DNA. We examine the structure and temporal expression pattern
of multiple fasciclin I mRNAs that differ in the lengths of their 3'
untranslated regions. We also show that a highly conserved sequence at the
end of the second domain can be altered by the addition of three or six
amino acids that are encoded by two alternatively spliced 9 base pair (bp)
micro-exons. In grasshopper fasciclin I mRNAs, there are 9 bp and 6 bp
insertions at the same position. The first of these insertions is identical
in sequence to the first fly micro-exon. The grasshopper insertions are not
found together in the same mRNA, so grasshopper fasciclin I species differ
by the addition of three or two extra amino acids to the second domain. The
alternatively spliced mRNAs are differentially expressed during
embryogenesis, and all three of them are present in nerve cord
preparations. We suggest that the amino acids inserted by alternative
micro-exon splicing may alter the binding specificity of fasciclin I.