Expression of a novel gene containing ankyrin-repeat in SAMP8 mouse hippocampus

The SAMP8 mouse is a suitable animal model to examine the decline in learning ability with senescence. We tried to identify genes related to brain senescence by using fluorescent differential display analysis. Total RNAs were extracted from hippocampus and cerebrum of groups of five male SAMP8 and SAMR1 (control) mice, 8 months of age. A cDNA fragment of 165 bp encoding a part of EST was cloned. An mRNA sequence of 2487 bp that consists of five exons and contains ORF (684 bp for 228 amino acids) could be linked to chromosome 15 by using EST clusters in the National Center for Biotechnology Information (NCBI) database. Expression of 2.5-kb cDNA was confirmed in hippocampus and cerebrum by RT-PCR, and sequenced. This was a novel gene, named as ankyrin small (ank-s), the protein of which contained 4 ankyrin-repeats in N-terminal side and membrane-binding site in C-terminus side. Northern blot showed that expression of ank-s was the highest in brain, especially in hippocampus where its expression doubled after birth and in 8-month-old SAMP8 was twice that in SAMR1 mice. These results suggest that ank-s is related to neuronal degeneration in SAMP8 hippocampus.