Golgi alpha-mannosidase II deficiency in vertebrate systems: implications for asparagine-linked oligosaccharide processing in mammals

The maturation of N-glycans to complex type structures on cellular and secreted proteins is essential for the roles that these structures play in cell adhesion and recognition events in metazoan organisms. Critical steps in the biosynthetic pathway leading from high mannose to complex structures include the trimming of mannose residues by processing mannosidases in the endoplasmic reticulum (ER) and Golgi complex. These exo-mannosidases comprise two separate families of enzymes that are distinguished by enzymatic characteristics and sequence similarity. Members of the Class 2 mannosidase family (glycosylhydrolase family 38) include enzymes involved in trimming reactions in N-glycan maturation in the Golgi complex (Golgi mannosidase II) as well as catabolic enzymes in lysosomes and cytosol. Studies on the biological roles of complex type N-glycans have employed a variety of strategies including the treatment of cells with glycosidase inhibitors, characterization of human patients with enzymatic defects in processing enzymes, and generation of mouse models for the enzyme deficiency by selective gene disruption approaches. Corresponding studies on Golgi mannosidase II have employed swainsonine, an alkaloid natural plant product that causes "locoism", a phenocopy of the lysosomal storage disease, alpha-mannosidosis, as a result of the additional targeting of the broad-specificity lysosomal mannosidase by this compound. The human deficiency in Golgi mannosidase II is characterized by congenital dyserythropoietic anemia with splenomegaly and various additional abnormalities and complications. Mouse models for Golgi mannosidase II deficiency recapitulate many of the pathological features of the human disease and confirm that the unexpectedly mild effects of the enzyme deficiency result from a tissue-specific and glycoprotein substrate-specific alternate pathway for synthesis of complex N-glycans. In addition, the mutant mice develop symptoms of a systemic autoimmune disorder as a consequence of the altered glycosylation. This review will discuss the biochemical features of Golgi mannosidase II and the consequences of its deficiency in mammalian systems as a model for the effects of alterations in vertebrate N-glycan maturation during development.     

Generation of a phagemid mouse recombinant antibody fragment library by multisite-directed mutagenesis

A nonimmune phagemid recombinant antibody fragment (rFab) library was generated with a nominal diversity of 1.16 x 10(7) using the QuikChange Multi Site-Directed Mutagenesis kit. Two degenerate primers spanning the third complementarity-determining region (CDR) loops of the antibody fragment light and heavy chain were mutated such that eight or nine amino acids were randomly changed per CDR loop. Seven proteins were used to evaluate the library quality. Protein-specific rFab antibodies were selected after three panning cycles. From 12% to 64% of the randomly selected colonies produced positive ELISA signals to the phagemid rFabs. Multisite-directed mutagenesis allowed a diverse rFab library to be rapidly constructed while retaining the structural framework of a Fab that had been optimized for production in Escherichia coli.     

IL-11 and IL-11Rα immunolocalisation at primate implantation sites supports a role for IL-11 in placentation and fetal development

Embryo implantation, endometrial stromal cell decidualization and formation of a functional placenta are critical processes in the establishment and maintenance of pregnancy. Interleukin (IL)-11 signalling is essential for adequate decidualization in the mouse uterus and IL-11 promotes decidualization in the human. IL-11 action is mediated via binding to the specific IL-11 receptor α (IL-11Rα). The present study examined immunoreactive IL-11 and IL-11Rα in cycling rhesus monkey endometrium, at implantation sites in cynomolgus and rhesus monkeys and in human first trimester decidua and defined distinct spatial and temporal patterns. In cycling rhesus monkey endometrium, IL-11 and IL-11Rα increased in both basalis and functionalis regions during the secretory compared with the proliferative phase, with changing cellular locations in luminal and glandular epithelium and stroma. The patterns were similar overall to those previously described in human endometrium. Differences were seen in immunostaining during implantation in cynomologus and rhesus monkey. In the cynomolgus, very little staining for IL-11 or IL-11Rα was seen in syncytio- and cyto-trophoblast cells in the villi between days 12 and 150 of pregnancy although there was moderate staining in cytotrophoblast in the shell between days 12 and 17 and in subpopulations of cytotrophoblast cells invading the arteries at day 17. By contrast in the rhesus monkey between days 24 and 35 of pregnancy and in human first trimester placenta, cyto- and syncytio-trophoblast in the villi but not cytotrophoblast in the shell were positively stained. The most intense staining for both IL-11 and IL-11Rα was present within the decidua in the maternal component of implantation sites in all three primates but moderate staining was also present in maternal vascular smooth muscle and glands perivascular cells and epithelial plaques. These results are consistent with a role for IL-11 both during decidualization and placentation in primates.     

Thermally induced disintegration of the oligomeric structure of αB-crystallin mutant F28S is associated with diminished chapterone activity

B-crystallin, a member of the small heat-shock protein (hsp) family of proteins, is able to function as a molecular chaperone by protecting other proteins from stress-induced aggregation by recognizing and binding to partially unfolded species of damaged proteins. The present work has investigated the role of phenylalanine-28 (F28) of the ²²RLFDQFF²⁸ region of B-crystallin in maintaining chaperone function and oligomeric structure under physiological condition and under thermal stress. Bovine B-crystallin was cloned for the first time and the cDNA sequence revealed greater than 90% homology to that of human, rat and mouse B-crystallins. F28 was mutated to a serine followed by expression of the mutant F28S and the wild-type B (B-wt) in E. coli and subsequent purification of the protein by size-exclusion chromatography. Secondary and tertiary structure analyses showed some structural changes in the mutant. Chaperone activity and oligomeric size of the mutant was unchanged at 37°C whereas at 58°C the chaperone activity was significantly decreased and the oligomeric size ranged from low molecular weight to high molecular weight showing disintegration of the oligomeric structure. The data support the idea that the participation of large oligomeric structure rather than smaller units is required to have optimal chaperone activity and the hydrophobic F28 residue is needed for maintaining the native oligomeric structure under thermal stress.     

Novel application of a fibrin cell block method to evaluate melanocytic cell populations

Confirming melanocytic lineage and purity is important for experiments using cultured human melanocytes. The objective of this study was to develop a simple, reliable method to evaluate and archive cultured melanocytic cells. Melanocytes were isolated from adult skin biopsies or from neonatal foreskins using standard culturing methods. Fibrin cell blocks (FCBs) were prepared from cultured cells at passages two and six. Fibrin blocks were paraffin-embedded and sectioned for immunohistochemical (CD68, Melan-A, and HMB-45) and H & E staining. Flow cytometry was performed (Melan-A) at passage six. A mixing experiment with cultured melanocytes and fibroblasts was performed and cell population purity was determined by manual counts of positively staining cells in the FCBs and by flow cytometry. The FCB method of evaluating population purity was validated experimentally and by correlation with flow cytometry results. Preparation of a FCB followed by immunohistochemical staining is an easy and inexpensive way to confirm melanocytic lineage, estimate population purity, and provide a permanent archive of cultured cells.     

Neuropeptide-Y in the paraventricular nucleus increases ethanol self-administration

The paraventricular nucleus (PVN) of the hypothalamus is known to modulate feeding, obesity, and ethanol intake. Neuropeptide-Y (NPY), which is released endogenously by neurons projecting from the arcuate nucleus to the PVN, is one of the most potent stimulants of feeding behavior known. The role of NPY in the PVN on ethanol self-administration is unknown. To address this issue, rats were trained to self-administer ethanol via a sucrose fading procedure and injector guide cannulae aimed at the PVN were surgically implanted. Microinjections of NPY and NPY antagonists in the PVN were conducted prior to ethanol self-administration sessions. All doses of NPY significantly increased ethanol self-administration and preference, and decreased water intake. The NPY antagonist D-NPY partially reduced ethanol self-administration and completely blocked the effects of an intermediate dose of NPY (10 fmol) on ethanol intake, preference, and water intake. The competitive non-peptide Y1 receptor antagonist BIBP 3226 did not significantly alter ethanol self-administration or water intake when administered alone in the PVN but it completely blocked the effect of NPY (10 fmol) on ethanol intake. NPY infused in the PVN had no effect on ethanol self-administration when tested in rats that did not have a long history of ethanol self-administration. The doses of NPY tested produced no effect on food intake or body weight measured during the 24-h period after infusion in either ethanol-experienced or ethanol-inexperienced rats. These results indicate that elevation of NPY levels in the PVN potently increases ethanol self-administration and that this effect is mediated through NPY Y1 receptors.     

The M34T allele variant of connexin 26

GJB2 encodes the protein Connexin 26, one of the building blocks of gap junctions. Each Connexin 26 molecule can oligomerize with five other connexins to form a connexon; two connexons, in turn, can form a gap junction. Because mutations in GJB2 are the most common cause of congenital severe-to-profound autosomal recessive nonsyndromic hearing loss, the effect of the Connexin 26 allele variants on this dynamic 'construction' process and the function of any gap junctions that do form is particularly germane. One of the more controversial allele variants, M34T, has been hypothesized to cause autosomal dominant nonsyndromic hearing loss. In this paper, we present clinical and genotypic data that refutes this hypothesis and suggests that the effect of the M34T allele variant may be dependent on the mutations segregating in the opposing allele.     

Novel mutations in the connexin 26 gene (GJB2) that cause autosomal recessive (DFNB1) hearing loss.

Mutations in the connexin 26 (Cx26) gene (GJB2) are associated with the type of autosomal recessive nonsyndromic neurosensory deafness known as "DFNB1." Studies indicate that DFNB1 (13q11-12) causes 20% of all childhood deafness and may have a carrier rate as high as 2. 8%. This study describes the analysis of 58 multiplex families each having at least two affected children diagnosed with autosomal recessive nonsyndromic deafness. Twenty of the 58 families were observed to have mutations in both alleles of Cx26. Thirty-three of 116 chromosomes contained a 30delG allele, for a frequency of .284. This mutation was observed in 2 of 192 control chromosomes, for an estimated gene frequency of .01+/-.007. The homozygous frequency of the 30delG allele is then estimated at .0001, or 1/10,000. Given that the frequency of all childhood hearing impairment is 1/1,000 and that half of that is genetic, the specific mutation 30delG is responsible for 10% of all childhood hearing loss and for 20% of all childhood hereditary hearing loss. Six novel mutations were also observed in the affected population. The deletions detected cause frameshifts that would severely disrupt the protein structure. Three novel missense mutations, Val84Met, Val95Met, and Ser113Pro, were observed. The missense mutation 101T-->C has been reported to be a dominant allele of DFNA3, a dominant nonsyndromic hearing loss. Data further supporting the finding that this mutation does not cause dominant hearing loss are presented. This allele was found in a recessive family segregating independently from the hearing-loss phenotype and in 3 of 192 control chromosomes. These results indicate that 101T-->C is not sufficient to cause hearing loss.