The mouse ortholog of the neuronal ceroid lipofuscinosis CLN5 gene encodes a soluble lysosomal glycoprotein expressed in the developing brain Ville Holmberg, a Anu Jalanko, a Juha Isosomppi, a Anna-Liisa Fabritius, b Leena Peltonen, a,c, * and Outi Kopra a a Department of Molecular Medicine, National Public Health Institute, FIN-00251 Helsinki, Finland b Department of Applied Biology, University of Helsinki, Finland c Department of Medical Genetics, University of Helsinki, Finland Received 12 March 2003; revised 16 December 2003; accepted 18 December 2003 Available online 19 March 2004 Neuronal ceroid lipofuscinoses (NCLs) are recessively inherited neurodegenerative lysosomal storage disorders characterized by progressive motor and mental retardation, visual failure, and epileptic seizures. Finnish variant late infantile NCL (vLINCL Fin ) is caused by mutations in the CLN5 gene. We have isolated the mouse Cln5 gene and analyzed its spatiotemporal expression in the central nervous system (CNS) by in situ hybridization and immunohistochemistry. Cln5 was expressed throughout the embryonic brain already at E15 and the expression steadily increased during development. Prominent expres- sion was observed in cerebellar Purkinje cells, cerebral neurons, hippocampal pyramidal cells, and hippocampal interneurons. The expression pattern correlated with those CNS regions that get degenerated in CLN5 patients. In vitro expression of Cln5 in COS-1, HeLa, and neuronal cells further implied that mouse Cln5 is a soluble lysosomal glycoprotein, closely resembling human CLN5. D 2004 Elsevier Inc. All rights reserved. Keywords: Neuronal ceroid lipofuscinosis; CLN5; Lysosomal storage disease; Neurodegeneration; Mouse Introduction Neuronal ceroid lipofuscinoses (NCLs) are the most common progressive neurodegenerative diseases of childhood. They are lysosomal storage disorders with a recessive autosomal inheritance characterized by the accumulation of autofluorescent material resembling ceroid and lipofuscin in neurons and other cells. Clinical features include progressive mental and visual decline, motor disturbances, epilepsy, and premature death. The incidence of NCL diseases is highest in Northern Europe and North America, being approximately 1:10,000 (Santavuori, 1988). Six genes and more than 100 mutations underlying different subtypes of NCL have been identified (Mole, 1999; Mole et al., 2001). Based on the clinical course of the disease, the childhood forms have tradition- ally been divided into three main types: infantile NCL (INCL; locus definition CLN1; MIM256730), classical late infantile NCL (LINCL; CLN2; MIM204500), and juvenile NCL (JNCL; CLN3; MIM256731). One of the subtypes is the Finnish variant late infantile neuronal ceroid lipofuscinosis (vLINCL Fin ; CLN5; MIM256731). Its clini- cal onset occurs at 2– 7 years of age resulting in death at the age of 14 – 36 years. The first symptom is motor clumsiness, followed by mental retardation, progressive visual failure, and later myoclonus, ataxia, and epileptic seizures (Holmberg et al., 2000; Santavuori et al., 1982, 1991). Histopathological and biochemical studies indi- cate that the major storage component in CLN5 patients is subunit C of the mitochondrial ATP synthase complex (Tyynela ¨ et al., 1997). The ultrastructure of the lysosomal storage material, seen in electron microscopy, consists of curvilinear (CLP) and fingerprint (FPP) profiles (Santavuori, 1988). Early cerebellar atrophy was the most striking abnormality both in brain imaging studies and in autopsy specimens (Autti et al., 1992). The CLN5 locus was initially mapped to 13q22, and a novel gene, CLN5, was subsequently identified using positional cloning strategies (Klockars et al., 1996; Savukoski et al., 1994, 1998). The predicted amino acid sequence showed no homology to previously reported proteins. Four mutations underlying the disease have been reported (http://www.ucl.ac.uk/ncl/CLN5.html/): the major muta- tion among Finnish patients is a two base pair deletion, c.1175delAT, resulting in Y392X. The carrier frequency of the major mutation is 1:24 –1:44 in the high-risk area in Western Finland, where clustering of the ancestors’ birthplaces has been demonstrated (Pastinen et al., 2001; Varilo et al., 1996). Another mutation found among Finnish patients is c.225G>A, leading to a severely truncated polypeptide (W75X). The mutation c.669insC (frameshift after H223) was found in one Swedish and one Finnish patient, both being a compound heterozygote for the mutation. The fourth mutation, c.835G>A (D279N), was identified in a Dutch family. 0969-9961/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.nbd.2003.12.019 * Corresponding author. Department of Molecular Medicine, National Public Health Institute, Biomedicum, PO Box 104, FIN-00251 Helsinki, Finland. Fax: +358-9-4744-8480. E-mail address: leena.peltonen@ktl.fi (L. Peltonen). Available online on ScienceDirect (www.sciencedirect.com.) www.elsevier.com/locate/ynbdi Neurobiology of Disease 16 (2004) 29 – 40