CLONING OF THE CDNA AND GENE ENCODING MOUSE LYSOSOMAL SIALIDASE AND CORRECTION OF SIALIDASE DEFICIENCY IN HUMAN SIALIDOSIS AND MOUSE SM J FIBROBLASTS/

Lysosomal sialidase occurs in a multienzyme complex that also contains beta-galactosidase and cathepsin A. We previously cloned the human ly sosomal sialidase cDNA and characterized mutations in human sialidosis patients, Here, we report the cloning and expression of the mouse lys osomal sialidase cDNA and gene, The 1.77 kb cDNA encodes an open readi ng frame of 408 amino acids which shows high homology to the human lys osomal sialidase (80%), the rat cytosolic sialidase (65%) and viral an d bacterial sialidases (50-55%). The sialidase gene is similar to 4 kb long and contains six exons, The five introns range in size from 96 t o 1200 bp, Northern blot analysis revealed high expression of multiple sialidase transcripts in kidney and epididymis, moderate levels in br ain and spinal cord, and low levels in adrenal, heart, liver, lung and spleen, Transient expression of the cDNA clone in sialidase-deficient SM/J mouse fibroblasts and human sialidosis fibroblasts restored norm al levels of sialidase activities in both cell types, Immunocytochemic ally expressed sialidase co-localized with a lysosomal marker, LAMP2, confirming its lysosomal nature, Since sialidase activity requires its association with P-galactosidase and cathepsin A, the expression of m ouse sialidase within human sialidosis cells underlines the structural similarity between mouse and human enzymes and suggests that the mech anism for complex formation and function is highly conserved.