ABSTRACT
Expansion of the FRAXE CCG repeat to a full mutation is associated with methylation and transcriptional silencing of the FMR2 gene, and as a consequence, mild-to-borderline mental retardation. FMR2 is a member of a family of four proteins, AF4, LAF4, FMR2, and AF5q31. The proteins associated with this family localize to the cell nucleus. Various regions of FMR2, and each of the other members of the protein family, were cloned and analyzed for transcription activation in yeast and mammalian cells. In both yeast and mammalian cells, FMR2 showed strong transcription activation. AF4 activation potential was several-fold lower. Interestingly, isoforms of both FMR2 and LAF4 lacking exon 3 activated transcription better than the larger isoforms containing exon 3. Compared with the other members of the family, activation by FMR2 was the strongest. Our results show that FMR2 is a potent transcription activator and that its function is conserved. Elucidation of the function of the FMR2 protein as a transcription activator may place FMR2 within the molecular signalling pathways involved in nonspecific X-linked mental retardation (MRX).
Subject(s)
Fragile X Syndrome/genetics , Nuclear Proteins/physiology , Trans-Activators/physiology , Transcriptional Activation/drug effects , Alternative Splicing , Amino Acid Sequence , DNA-Binding Proteins/genetics , DNA-Binding Proteins/pharmacology , DNA-Binding Proteins/physiology , Gene Transfer, Horizontal , HeLa Cells , Humans , Molecular Sequence Data , Nuclear Proteins/genetics , Nuclear Proteins/pharmacology , Saccharomyces cerevisiae , Trans-Activators/genetics , Trans-Activators/pharmacology , Transcriptional Elongation FactorsABSTRACT
Spondyloepiphyseal dysplasia tarda (SEDL) is an X-linked recessive disorder of endochondral bone formation caused by mutations in the SEDL gene. Here we present the structural analysis and subcellular localization of human SEDL. The SEDL gene is composed of six exons and spans a genomic region of approximately 20 kb in Xp22. It contains four Alu sequences in its 3' UTR and an alternatively spliced MER20 sequence in its 5' UTR (exon 2). Complex alternative splicing was detected for exon 4. Altogether seven SEDL pseudogenes were detected in the human genome: SEDLP1, a transcribed retropseudogene (or retro-xaptonuon) on chromosome 19q13.4 with potential to encode a protein identical to that of the SEDL gene; SEDLP2, another retropseudogene (not transcribed) on chromosome 8; and five truncated pseudogenes, SEDLP3-SEDLP7, on chromosome Yq11.23. Based on the knowledge of the yeast SEDL ortholog we speculated that the SEDL protein may participate along the ER-to-Golgi transport compartments. To test this hypothesis we performed transient transfection studies with tagged recombinant mammalian SEDL proteins in Cos-7 cells. The tagged SEDL proteins localized to perinuclear structures that partly overlapped with the intermediate ER-Golgi compartment (ERGIC; or vesicular tubular complex, VTC). Two human SEDL mutations (157-158delAT and C271T(STOP)) introduced into SEDL FLAG and GFP constructs led to the misplacement of the SEDL protein primarily to the cell nucleus and partially to the cytoplasm. Based on these experiments we suggest that the COOH end of the SEDL protein might be responsible for proper targeting of SEDL along the ER-Golgi membrane compartments (including Golgi and ERGIC/VTC).
Subject(s)
Carrier Proteins/genetics , Carrier Proteins/metabolism , Membrane Transport Proteins , Osteochondrodysplasias/genetics , Alternative Splicing , Expressed Sequence Tags , Frameshift Mutation , Genome, Human , Humans , Pseudogenes , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Sequence Homology, Nucleic Acid , Subcellular Fractions , Transcription FactorsABSTRACT
Peripheral neuropathy is a significant complication of human diabetes and a source of morbidity. Appropriate experimental models may aid in understanding its pathogenesis and in developing therapeutic strategies. We sought to determine whether spontaneously diabetic obese adult monkeys developed peripheral neuropathy and whether it occurred early or late in relation to the onset of hyperglycemia. We studied nerve conduction in both motor (peroneal, median, and ulnar) and sensory (median and ulnar) nerves in 13 adult male rhesus monkeys, 4 overtly diabetic and 9 nondiabetic (mean age 21 +/- 2 and 16 +/- 2 yr, respectively, NS; mean fasting plasma glucose 14.5 +/- 3.4 and 4.4 +/- 0.6 mM, P = .001). The diabetic animals had significantly reduced motor conduction velocities and prolonged F-wave latencies. Motor-evoked amplitudes did not differ. In the diabetic monkeys, nerve conduction times were increased in motor fibers, which could be identified as early as 2 yr after the onset of hyperglycemia. These abnormalities are similar to those seen in humans and suggest further study of these animals as a primate model of human diabetic neuropathy.
