CHARACTERIZATION OF NEUROFILAMENT PROTEIN NF70 MESSENGER-RNA FROM THEGASTROPOD HELIX-ASPERSA REVEALS THAT NEURONAL AND NONNEURONAL INTERMEDIATE FILAMENT PROTEINS OF CEREBRAL GANGLIA ARISE FROM SEPARATE LAMIN-RELATED GENES

The neuronal cytoplasmic intermediate filament (IF) protein HeNF70 of the gastropod Helix aspersa is identified by sequence analysis of the corresponding 4,600 bp cDNA isolated from a cerebral ganglion cDNA lib rary. HeNF70 shares 60% sequence identity with the neuronal LoNF70 pro tein of the cephalopod Loligo pealei and only 36% identity with the He lix non-neuronal IF-A protein. All three molluscan IF proteins display the lamin-type extended coil 1b subdomain harbouring six additional h eptads and all have long C-terminal sequences with substantial homolog y to the tail domains of nuclear lamins, The lamin-like tail domains o f the two neurofilament proteins share a unique motif comprising 13 re sidues, which is absent from Helix IF-A and all other known nonneurona l IF proteins, HeNF70 is encoded by a 9.5 kb RNA transcript. The very long 7.2 kb 3'-untranslated sequence contains a unique 26 nucleotide r epeat extending over 0.5 kb in its 5'-region. The HeNF70 mRNA is expre ssed at low abundancy in cerebral ganglia but not in any of the 13 non -neuronal tissues tested. In contrast, all tissues express at fairly h igh levels the same 4.6 and 4.2 kb mRNAs encoding the Helix non-neuron al IF-A/B proteins. Blot hybridisation studies on genomic DNA and gang lion mRNA with subprobes from the cloned HeNF70 cDNA, as well as seque nce analysis of an RT-PCR generated partial cDNA encoding a putative H eNF60 protein, indicate at least two different neuronal IF genes in He lix.