Cloning of the peroxiredoxin gene family in rats and characterization of the fourth member.
Peroxiredoxin (PRx) exhibits thioredoxin-dependent peroxidase activity and constitutes a family of proteins. Four members of genes from rat tissues were isolated by PCR using degenerated primers based on the sequences which encode a pair of highly conserved Cys-containing domains, and were then cloned to full-length cDNAs. These included two genes which have previously been isolated in rats, PRx I and PRx II, and two rat homologues of PRx III and PRx IV. We showed, for the first time, the simultaneous expression of all four genes in various rat tissues by Northern blotting. Since a discrepancy exists regarding cellular distribution, we further characterized PRx IV by expressing it in COS-1 cells. This clearly demonstrates that PRx IV is a secretory form and functions within the extracellular space. (+info)
PrKX is a novel catalytic subunit of the cAMP-dependent protein kinase regulated by the regulatory subunit type I.
The human X chromosome-encoded protein kinase X (PrKX) belongs to the family of cAMP-dependent protein kinases. The catalytically active recombinant enzyme expressed in COS cells phosphorylates the heptapeptide Kemptide (LRRASLG) with a specific activity of 1.5 micromol/(min.mg). Using surface plasmon resonance, high affinity interactions were demonstrated with the regulatory subunit type I (RIalpha) of cAMP-dependent protein kinase (KD = 10 nM) and the heat-stable protein kinase inhibitor (KD = 15 nM), but not with the type II regulatory subunit (RIIalpha, KD = 2.3 microM) under physiological conditions. Kemptide and autophosphorylation activities of PrKX are strongly inhibited by the RIalpha subunit and by protein kinase inhibitor in vitro, but only weakly by the RIIalpha subunit. The inhibition by the RIalpha subunit is reversed by addition of nanomolar concentrations of cAMP (Ka = 40 nM), thus demonstrating that PrKX is a novel, type I cAMP-dependent protein kinase that is activated at lower cAMP concentrations than the holoenzyme with the Calpha subunit of cAMP-dependent protein kinase. Microinjection data clearly indicate that the type I R subunit but not type II binds to PrKX in vivo, preventing the translocation of PrKX to the nucleus in the absence of cAMP. The RIIalpha subunit is an excellent substrate for PrKX and is phosphorylated in vitro in a cAMP-independent manner. We discuss how PrKX can modulate the cAMP-mediated signal transduction pathway by preferential binding to the RIalpha subunit and by phosphorylating the RIIalpha subunit in the absence of cAMP. (+info)
Four new mutations in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene causing X-linked sideroblastic anemia: increased pyridoxine responsiveness after removal of iron overload by phlebotomy and coinheritance of hereditary hemochromatosis.
X-linked sideroblastic anemia (XLSA) in four unrelated male probands was caused by missense mutations in the erythroid-specific 5-aminolevulinate synthase gene (ALAS2). All were new mutations: T647C, C1283T, G1395A, and C1406T predicting amino acid substitutions Y199H, R411C, R448Q, and R452C. All probands were clinically pyridoxine-responsive. The mutation Y199H was shown to be the first de novo XLSA mutation and occurred in a gamete of the proband's maternal grandfather. There was a significantly higher frequency of coinheritance of the hereditary hemochromatosis (HH) HFE mutant allele C282Y in 18 unrelated XLSA hemizygotes than found in the normal population, indicating a role for coinheritance of HFE alleles in the expression of this disorder. One proband (Y199H) with severe and early iron loading coinherited HH as a C282Y homozygote. The clinical and hematologic histories of two XLSA probands suggest that iron overload suppresses pyridoxine responsiveness. Notably, reversal of the iron overload in the Y199H proband by phlebotomy resulted in higher hemoglobin concentrations during pyridoxine supplementation. The proband with the R452C mutation was symptom-free on occasional phlebotomy and daily pyridoxine. These studies indicate the value of combined phlebotomy and pyridoxine supplementation in the management of XLSA probands in order to prevent a downward spiral of iron toxicity and refractory anemia. (+info)
Mitotic recombination in the heterochromatin of the sex chromosomes of Drosophila melanogaster.
The frequency of spontaneous and X-ray-induced mitotic recombination involving the Y chromosome has been studied in individuals with a marked Y chromosome arm and different XY compound chromosomes. The genotypes used include X chromosomes with different amounts of X heterochromatin and either or both arms of the Y chromosome attached to either side of the centromere. Individuals with two Y chromosomes have also been studied. The results show that the bulk of mitotic recombination takes place between homologous regions. (+info)
Germ cell development in the XXY mouse: evidence that X chromosome reactivation is independent of sexual differentiation.
Prior to entry into meiosis, XX germ cells in the fetal ovary undergo X chromosome reactivation. The signal for reactivation is thought to emanate from the genital ridge, but it is unclear whether it is specific to the developing ovary. To determine whether the signals are present in the developing testis as well as the ovary, we examined the expression of X-linked genes in germ cells from XXY male mice. To facilitate this analysis, we generated XXY and XX fetuses carrying X chromosomes that were differentially marked and subject to nonrandom inactivation. This pattern of nonrandom inactivation was maintained in somatic cells but, in XX as well as XXY fetuses, both parental alleles were expressed in germ cell-enriched cell populations. Because testis differentiation is temporally and morphologically normal in the XXY testis and because all germ cells embark upon a male pathway of development, these results provide compelling evidence that X chromosome reactivation in fetal germ cells is independent of the somatic events of sexual differentiation. Proper X chromosome dosage is essential for the normal fertility of male mammals, and abnormalities in germ cell development are apparent in the XXY testis within several days of X reactivation. Studies of exceptional germ cells that survive in the postnatal XXY testis demonstrated that surviving germ cells are exclusively XY and result from rare nondisjunctional events that give rise to clones of XY cells. (+info)
A new X linked neurodegenerative syndrome with mental retardation, blindness, convulsions, spasticity, mild hypomyelination, and early death maps to the pericentromeric region.
We report on a family with an X linked neurodegenerative disorder consisting of mental retardation, blindness, convulsions, spasticity, and early death. Neuropathological examination showed mild hypomyelination. By linkage analysis, the underlying genetic defect could be assigned to the pericentromeric region of the X chromosome with a maximum lod score of 3.30 at theta=0.0 for the DXS1204 locus with DXS337 and PGK1P1 as flanking markers. (+info)
Evidence that mutations in the X-linked DDP gene cause incompletely penetrant and variable skewed X inactivation.
X chromosome inactivation results in the random transcriptional silencing of one of the two X chromosomes early in female development. After random inactivation, certain deleterious X-linked mutations can create a selective disadvantage for cells in which the mutation is on the active X chromosome, leading to X inactivation patterns with the mutation on the inactive X chromosome in nearly 100% of the individual's cells. In contrast to the homogeneous patterns of complete skewed inactivation noted for many X-linked disorders, here we describe a family segregating a mutation in the dystonia-deafness peptide (DDP) gene, in which female carriers show incompletely penetrant and variable X inactivation patterns in peripheral blood leukocytes, ranging between 50:50 and >95:5. To address the genetic basis for the unusual pattern of skewing in this family, we first mapped the locus responsible for the variable skewing to the proximal long arm (Xq12-q22) of the X chromosome (Z=5. 7, P=.002, LOD score 3.57), a region that includes both the DDP and the XIST genes. Examination of multiple cell types from women carrying a DDP mutation and of peripheral blood leukocytes from women from two unrelated families who carry different mutations in the DDP gene suggests that the skewed X inactivation is the result of selection against cells containing the mutant DDP gene on the active X chromosome, although skewing is apparently not as severe as that seen for many other deleterious X-linked mutations. Thus, DDP is an example of an X-linked gene for which mutations cause partial cell selection and thus incompletely skewed X inactivation in peripheral blood leukocytes. (+info)
Immunodeficiency due to a unique protracted developmental delay in the B-cell lineage.
A unique immune deficiency in a 24-month-old male characterized by a transient but protracted developmental delay in the B-cell lineage is reported. Significant deficiencies in the number of B cells in the blood, the concentrations of immunoglobulins in the serum, and the titers of antibodies to T-dependent and T-independent antigens resolved spontaneously by the age of 39 months in a sequence that duplicated the normal development of the B-cell lineage: blood B cells followed by immunoglobulin M (IgM), IgG, IgA, and specific IgG antibodies to T-independent antigens (pneumococcal polysaccharides). Because of the sequence of recovery, the disorder could have been confused with other defects in humoral immunity, depending on when in the course of disease immunologic studies were conducted. Investigations of X-chromosome polymorphisms suggested that the disorder was not X linked in that the mother appeared to have identical X chromosomes. An autosomal recessive disorder involving a gene that controls B-cell development and maturation seems more likely. In summary, this case appears to be a novel protracted delay in the development of the B-cell lineage, possibly due to an autosomal recessive genetic defect. (+info)