Disease relevance of ALS2

• Amyotrophic lateral sclerosis 2 (ALS2) is an autosomal recessive form of juvenile ALS and has been mapped to human chromosome 2q33 [1].
• We analyzed ALS2, recently found mutated in consanguineous Arabic families presenting either an ALS2 phenotype or juvenile-onset primary lateral sclerosis (JPLS), as a candidate gene [2].
• Mutations in the ALS2 gene have been known to account for a juvenile recessive form of amyotrophic lateral sclerosis (ALS2), a rare juvenile recessive form of primary lateral sclerosis, and a form of hereditary spastic paraplegia (HSP), indicating that the ALS2 protein is essential for the maintenance of motor neurons [3].
• Here we describe a ninth ALS2 mutation, in two siblings affected by infantile-onset ascending spastic paraplegia with bulbar involvement [4].
• Behavioral studies demonstrated slowed movement without muscle weakness in ALS2(-/-) mice, consistent with upper motor neuron defects that lead to spasticity in humans [5].

High impact information on ALS2

• Here we report the identification of two independent deletion mutations linked to ALS2 in the coding exons of the new gene ALS2 [1].
• We have identified a familial juvenile PLS (JPLS) locus overlapping the previously identified ALS2 locus on chromosome 2q33 [6].
• Two papers in this issue of Nature Genetics describe homozygous mutations in a new gene on chromosome 2q33 in 4 families of Arabian origin with a rare form of juvenile onset ALS (ALS2) [7].
• The predicted sequence of the protein (alsin) may indicate a mechanism for motor-neuron degeneration, as it may include several cell-signaling motifs with known functions, including three associated with guanine-nucleotide exchange factors for GTPases (GEFs) [6].
• The gene encoding alsin, a protein with three guanine-nucleotide exchange factor domains, is mutated in a form of recessive amyotrophic lateral sclerosis [6].

Biological context of ALS2

• Single-nucleotide polymorphisms in uncoding regions of ALS2 gene of Japanese patients with autosomal-recessive amyotrophic lateral sclerosis [8].
• Here, we describe the first homozygous missense mutation in ALS2, p.G540E [9].
• In the six remaining families, absence of cDNA ALS2 mutations suggests either mutations in regulatory ALS2 regions or genetic heterogeneity, as already reported in JPLS [2].
• We have established a yeast artificial chromosome (YAC) contig spanning an approximately 8-Mb region of the ALS2 candidate region and mapped 52 transcribed DNA sequences including 13 known genes and 39 expressed sequenced tags within this YAC contig [10].
• Alsin mutations were found in only 4 of the 10 families, whereas haplotype analysis excluded the ALS2 locus in one family [11].

Anatomical context of ALS2

• Thus, a perturbation of endosomal dynamics caused by loss of ALS2 rab5GEF activity might underlie neuronal dysfunction and degeneration in a number of motor neuron diseases [12].
• Further, the DH/PH domain in the middle portion of ALS2 protein enhances the VPS9 domain-mediated endosome fusions [12].
• Endogenous ALS2 is shown here to be enriched in nervous tissue and to be peripherally bound to the cytoplasmic face of endosomal membranes, an association that requires the amino-terminal "RCC1 (regulator of chromatin condensation)-like" GEF domain [13].
• Disease-causing mutants and a naturally truncated isoform of ALS2 are shown to be rapidly degraded when expressed in cultured human cells, including lymphocytes derived from patients with ALS2 mutations [13].
• Finally, we demonstrate that ALS2 promotes neurite outgrowth [14].

Associations of ALS2 with chemical compounds

• ALS2, a novel guanine nucleotide exchange factor for the small GTPase Rab5, is implicated in endosomal dynamics [12].
• This homozygous G669A mutation in exon 4 is predicted to result in a tyrosine substitution at cysteine 156 of the RCC1 (regulator of chromatin condensation)-like domain, encoding a putative guanine exchange factor for Ran guanosine triphosphatase, leading to a loss of ALS2 function due to instability of mutant protein [15].
• Real-time RT-PCR analysis demonstrated that in maltose-containing medium, strain 2342 overexpressed ALS2 compared to wild-type cells; however no overexpression phenotype was apparent [16].
• Real-time RT-PCR analysis of strain 2342 grown in glucose-containing medium (non-inducing conditions) showed that although ALS2 transcript levels were greatly reduced compared to wild-type cells, some ALS2 transcript remained [16].
• Mutant alsin induced neuronal death itself and also significantly enhanced the apoptogenic effect of NMDA and staurosporine [9].

Regulatory relationships of ALS2

• The remaining ALS2 allele was placed under control of the C. albicans MAL2 promoter to create an als2Delta/PMAL2-ALS2 strain (named 2342) [16].

Other interactions of ALS2

• Among the up-regulated genes were ALS2 and ALS5 both of which encode proteins that provide an adherence function for C. albicans [17].
• However, familial forms of ALS have been described--autosomal dominant forms (ALS1, ALS3), clinically indistinguishable from the sporadic form, and autosomal recessive forms with early onset and slower progression of symptoms (ALS2) [18].
• METHODS: DNA from 95 unrelated familial, 95 unrelated sporadic, and 11 early-onset ALS patients was screened for mutations in ALS2 by denaturing high-performance liquid chromatography and direct sequencing of polymerase chain reaction-amplified fragments [19].
• Computational genomic analysis identified ALS2CL, which is a novel protein highly homologous to the C-terminal region of ALS2 [20].
• Procedures are presented in this chapter for the expression, purification, and biochemical characterization of the individual GEF domains of Alsin [21].

Analytical, diagnostic and therapeutic context of ALS2

• By RT-PCR, ALS2 and 5, similar to the microarray data, were significantly increased in infected cells at 3 h [17].
• METHODS: ALS2-deficient mice were generated by gene targeting [5].

References