Production of a transgenic mouse model of familial amyloidotic polyneuropathy.

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Familial amyloidotic polyneuropathy is an autosomal dominant disorder which is characterized by extracellular deposition of amyloid fibrils and by prominent peripheral and autonomic nerve involvement. This amyloid prothein is mainyl composed of transthyretin (TTR) with a substitution of methionine for valine at position 30 in the FAP type. I. This amino acid substitution is thought to lead to amyloid deposition.In order ot analyze the pathological process of amyloid deposition and the factor(s) other than mutant TTR gene, we have produced transgenic mice by microinjecting the cloned human mutant TTR gene into fertilized eggs of C57BL/6 mice. In order to produce large quantities of variant TTR in transgenic mice, we prepared two constructs. One is the 7.6-kilobase (kb) fragment (0.6-hTTR30) containing about 600-base pair (bp) upstream region and entire human mutant TTR gene. The other is the 7.8 kb fragment in which the promotor region was replaced with that of the mouse metallotheionein-I gene (MT-hTTR30). We produced 9 and 5 transgenic mice, respectively. There was no significant difference in serum concentrations of human mutant TTR between two lines and they ranged from 0.2 tof 5.0/mg/dl. However, the actual amount of homo-tetramers composed of human TTR (hTTR4) was 300 times higher in MT-hTTR30 than in 0.6-hTTR30 as judged from the fissue specificityf of each gene. Amyloid deposition was observed in the submucosa of alimentary tract and renal glomeruli of MT-hTTR30 line but not of 0.6-hTTR30 line. These results suggest that the presence of hTTR4 is important for amyloid deposition. But the possibility that the Xpression of hTTR gene in the choroid plexus is important for amyloid deposition cannot be ruled out from these results. We are now atempting ot produce transgenic mice by microinjecting the human mutant TTR gene containg about 6.0 kb upstream region.