Biomedical subjects

Subramaniam Ganesh

Publications and source records attributed to Subramaniam Ganesh.

5 recordsLinked to original sources

PubMed2003

The Lafora disease gene product laforin interacts with HIRIP5, a phylogenetically conserved protein containing a NifU-like domain.

Lafora disease is an autosomal recessive type of progressive myoclonus epilepsy caused by mutations in the EPM2A gene. The EPM2A gene-encoded protein laforin is a dual-specificity phosphatase that associates with polyribosomes. Because the cellular functions of laforin are largely unknown, we used the yeast-two hybrid system to screen for protein(s) that interact with laforin. We found that laforin interacts with a phylogenetically conserved protein HIRIP5 that harbors a NifU-like domain. Both in vitro and in vivo assay have shown that the interaction is specific and that laforin probably uses its N-terminal CBD-4 domain to interact with the C-terminal NifU-like domain of the HIRIP5 protein. HIRIP5 encodes a cytosolic protein and is expressed ubiquitously, perhaps reflecting a house-keeping function. The presence of a NifU-like domain in the HIRIP5 protein raises an interesting possibility that it may be involved in iron homeostasis. Although the significance of the interaction between HIRIP5 and laforin proteins is not yet fully known, because laforin dephosphorylated HIRIP5 in vitro, HIRIP5 promises to be an interesting laforin-binding partner and would contribute to the understanding of the molecular pathology of Lafora disease.

Amino Acid Sequence↗

PubMed2002

Targeted disruption of the Epm2a gene causes formation of Lafora inclusion bodies, neurodegeneration, ataxia, myoclonus epilepsy and impaired behavioral response in mice.

Mutations in the EPM2A gene encoding a dual-specificity phosphatase (laforin) cause Lafora disease (LD), a progressive and invariably fatal epilepsy with periodic acid-Schiff-positive (PAS+) cytoplasmic inclusions (Lafora bodies) in the central nervous system. To study the pathology of LD and the functions of laforin, we disrupted the Epm2a gene in mice. At two months of age, homozygous null mutants developed widespread degeneration of neurons, most of which occurred in the absence of Lafora bodies. Dying neurons characteristically exhibit swelling in the endoplasmic reticulum, Golgi networks and mitochondria in the absence of apoptotic bodies or fragmentation of DNA. As Lafora bodies become more prominent at 4-12 months, organelles and nuclei are disrupted. The Lafora bodies, present both in neuronal and non-neural tissues, are positive for ubiquitin and advanced glycation end-products only in neurons, suggesting different pathological consequence for Lafora inclusions in neuronal tissues. Neuronal degeneration and Lafora inclusion bodies predate the onset of impaired behavioral responses, ataxia, spontaneous myoclonic seizures and EEG epileptiform activity. Our results suggest that LD is a primary neurodegenerative disorder that may utilize a non-apoptotic mechanism of cell death.

Animals↗

PubMed2002

Genotype-phenotype correlations for EPM2A mutations in Lafora's progressive myoclonus epilepsy: exon 1 mutations associate with an early-onset cognitive deficit subphenotype.

Mutations in the EPM2A gene encoding a dual-specificity phosphatase (laforin) cause an autosomal recessive fatal disorder called Lafora's disease (LD) classically described as an adolescent-onset stimulus-sensitive myoclonus, epilepsy and neurologic deterioration. Here we related mutations in EPM2A with phenotypes of 22 patients (14 families) and identified two subsyndromes: (i) classical LD with adolescent-onset stimulus-sensitive grand mal, absence and myoclonic seizures followed by dementia and neurologic deterioration, and associated mainly with mutations in exon 4 (P = 0.0007); (ii) atypical LD with childhood-onset dyslexia and learning disorder followed by epilepsy and neurologic deterioration, and associated mainly with mutations in exon 1 (P = 0.0015). To understand the two subsyndromes better, we investigated the effect of five missense mutations in the carbohydrate-binding domain (CBD-4; coded by exon 1) and three missense mutations in the dual phosphatase domain (DSPD; coded by exons 3 and 4) on laforin's intracellular localization in HeLa cells. Expression of three mutant proteins (T194I, G279S and Y294N) in DSPD formed ubiquitin-positive cytoplasmic aggregates, suggesting that they were folding mutants set for degradation. In contrast, none of the three CBD-4 mutants showed cytoplasmic clumping. However, CBD-4 mutants W32G and R108C targeted both cytoplasm and nucleus, suggesting that laforin had diminished its usual affinity for polysomes. Our data, thus, represent the first report of a novel childhood syndrome for LD. Our results also provide clues for distinct roles for the CBD-4 and DSP domains of laforin in the etiology of two subsyndromes of LD.

Adolescent↗

PubMed2002

Alternative splicing modulates subcellular localization of laforin.

Laforin is a dual-specificity phosphatase coded by the EPM2A gene defective in Lafora's progressive myoclonus epilepsy. We reported earlier that laforin is a cytoplasmic protein associated primarily with polyribosome. In the present study we characterized the expression of an EPM2A splice variant, named C-terISO, originating from the usage of a novel exon located in the 3'-untranslated region of exon 4 and encoding a laforin isoform containing unique sequences at its carboxyl terminus. Transfection studies demonstrate that, in addition to cytoplasm, the protein coded by C-terISO was targeted to the nucleus, a distinctive feature that was not observed for laforin coded by the major transcript of the EPM2A gene. The unique C-terminal sequence did not affect laforin's affinity for polysome, but sequestered nearly an equal amount of the protein into the nucleus. Our results are significant in light of the finding that laforin is an active phosphatase; therefore, isoforms targeted to different cellular compartments might dephosphorylate and regulate distinct cellular substrates.

Alternative Splicing↗

PubMed2002

Evolutionarily conserved, DMRT1, encodes alternatively spliced transcripts and shows dimorphic expression during gonadal differentiation in the lizard, Calotes versicolor.

An orthologue of Dmrt1 has been cloned and characterized in the lizard, Calotes versicolor (CvDmrt1). CvDmrt1 encodes alternatively spliced transcripts in genital ridge during gonadal differentiation and in adult testis. Its expression in genital ridge initiates from day 3 and is restricted to mesenchymal cells, which differentiate into the Sertoli cells. Lack of expression in the coelomic epithelium of GR shows that CvDmrt1 expression occurs only in the testicular pathway, and that the Sertoli and granulosa cells in GR may originate from different primordia. From day 25 onwards, the expression shifts majorly towards the germ cells both in testis and ovary. Thus its role in sexual differentiation of C. versicolor, which lacks CSD and TSD, is well documented.

Alternative Splicing↗