Blackwell Publishing Journal Backfiles 1879-2005
Abstract: The sequence of a high molecular weight (HMW) τ cDNA cloned from a neuroblastoma N115 library contains, in addition to the C-and N-terminal and middle regions present in the low molecular weight mouse brain τ proteins, a 711-bp nonhomologous domain (exon 4a) and a region of 198 bp corresponding to exon 6 of the τ gene. Protein immunoblot analysis, performed with antibodies specific either for a sequence present in the N-terminal region of all the τ variants or for exon 4a revealed several bands suggesting that more than one τ form is expressed in this cell line. Northern blot experiments performed with a number of cDNA probes spanning domains common and uncommon to low molecular weight and HMW τ allowed the identification of four τ transcripts differing in the size of their coding and noncoding regions. All these transcripts contain the sequence encoded by exon 6, but two of them lack exon 4a. As shown by RNase protection assays, the N-terminal region of these transcripts is also variable and contains either exon 1, or exons 1 and 2, or exons 1–3. Yet all these HMW τ forms contain four homologous repeats in their C-terminal domain both in the differentiated and nondifferentiated cells, i.e., have adult characteristics. In conclusion, the data reported in this article demonstrate that several HMW τ variants are expressed in neuroblastoma N115 cells and that the transition between immature to mature τ forms occurring during brain development is not required for neurite outgrowth during morphological differentiation of this cell line.
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