Hereditary inclusion body myopathy (HIBM; OMIM 600737) is a unique group of neuromuscular disorders characterized by adult onset, slowly progressive distal and proximal weakness and a typical muscle pathology including rimmed vacuoles and filamentous inclusions. The autosomal recessive form described in Jews of Persian descent is the HIBM prototype. This myopathy affects mainly leg muscles, but with an unusual distribution that spares the quadriceps. This particular pattern of weakness distribution, termed quadriceps-sparing myopathy (QSM), was later found in Jews originating from other Middle Eastern countries as well as in non-Jews. We previously localized the gene causing HIBM in Middle Eastern Jews on chromosome 9p12-13 (ref. 5) within a genomic interval of about 700 kb (ref. 6). Haplotype analysis around the HIBM gene region of 104 affected people from 47 Middle Eastern families indicates one unique ancestral founder chromosome in this community. By contrast, single non-Jewish families from India, Georgia (USA) and the Bahamas, with QSM and linkage to the same 9p12-13 region, show three distinct haplotypes. After excluding other potential candidate genes, we eventually identified mutations in the UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE) gene in the HIBM families: all patients from Middle Eastern descent shared a single homozygous missense mutation, whereas distinct compound heterozygotes were identified in affected individuals of families of other ethnic origins. Our findings indicate that GNE is the gene responsible for recessive HIBM.

The signals that control the developmental switch from primary to secondary wall synthesis in higher plants are not known. This transition is characterized by a cessation of synthesis of polymers unique to the primary cell wall accompanied by enhanced rates of cellulose deposition and induction of synthesis of specific secondary wall matrix polysaccharides and lignin. The developing fibers of cotton (Gossypium hirsutum) and tracheary elements differentiated from isolated mesophyll cells of zinnia have emerged as two good model systems for studying this transition. In the zinnia system the mesophyll cells are cultured in noninductive medium and differentiation is induced by changes in hormonal balance. Specialized, localized regions of secondary wall formation unique to these tracheary elements have been shown to contain large amounts of cellulose, xylan, and lignin (for reviews, see Fukuda, 1991Fukuda, , 1996. The developing cotton fiber is unique in that the secondary wall consists of nearly pure cellulose and is devoid of hemicellulose and lignin (for reviews of cotton fiber development, see Basra and Malik, 1984;Ryser, 1985). Furthermore, development occurs synchronously for nearly all fibers within a boll, with the transition to secondary wall formation beginning abruptly in varieties of cotton at about 14 to 16 DPA, which is a few days prior to the cessation of fiber elongation (Meinert and Delmer, 1977).Rates of secondary wall cellulose synthesis peak at about 24 DPA; the fibers mature and die sometime after 40 DPA, presumably by a process of programmed cell death. During the transition the rate of cellulose synthesis increases abruptly to about 100-fold (Meinert and Delmer, 1977), and recent evidence indicates that genes that most likely encode the catalytic subunit of cellulose synthase are also strongly induced at this time (Pear et al., 1996). During xylogenesis there is also evidence that expression of genes involved in synthesis of hemicellulose (Bolwell and Northcote, 1981) and lignin (Fukuda, 1991) also undergo induction. The transition in both cotton fibers and tracheary elements is also characterized by a reorganization of the cytoskeleton that directs the specific patterns of cellulose deposition (Seagull, 1990; Fukuda, 1991 Fukuda, , 1996.Our interest in the events regulating this transition was stimulated by our recent characterization of genes that encode two small GTPases of the Rho subfamily in cotton, named Rac13 and Rac9. Rac13 in particular shows highly induced expression at the transition from primary to secondary wall synthesis (Delmer et al., 1995). In animals Rac proteins function in several possibly related signal transduction pathways. Rac has been shown to be involved in regulation of reorganization of the actin cytoskeleton (Symons, 1996) and it plays another role in leukocytes as a specific activator of the plasma membrane NADPH oxidase (Freeman et al., 1996). Activation of the NADPH oxidase leads to generation of the oxidative burst, which serves as a defense against pathoge...

SummaryA homozygous recessive mutant of Arabidopsis thaliana has been selected which displays altered patterns of cellulose deposition. The mutant was selected because leaf and stem trichomes lacked the strong birofringence under polarized light which is characteristic of plant cells which contain highly ordered cellulose in their secondary cell walls. Compared with wild-typa A. thafiana, this mutant (designated tbr for trichome birofringence) also displays reduced birefringence in the xylem of the leaf. Direct chemical analyses of root, stem, and leaf tissues, including isolated leaf trichomes, support the conclusion that tbr is impaired in its ability to deposit secondary wall cellulose in specific cell types, most notably in trichomes where the secondary wall appears to be totally absent. Altered patterns of wound-induced cellose deposition in trichomes and surrounding cells is another trait which also cosegregates with the tbr mutation.

Hyperinsulinism of infancy is a genetically heterogeneous disease characterized by dysregulation of insulin secretion resulting in severe hypoglycemia. To date, mutations in five different genes, the sulfonylurea receptor (SUR1, ABCC8), the inward rectifying potassium channel (K(IR)6.2, KCNJ11), glucokinase (GCK), glutamate dehydrogenase (GLUD1), and short-chain 3-hydroxyacyl-coenzyme A dehydrogenase (SCHAD), have been implicated. Previous reports suggest that, in 40% of patients, no mutation can be identified in any of these genes, suggesting additional locus heterogeneity. However, previous studies did not screen all five genes using direct sequencing, the most sensitive technique available for mutation detection. We selected 15 hyperinsulinism of infancy patients and systematically sequenced the promoter and all coding exons and intron/exon boundaries of ABCC8 and KCNJ11. If no mutation was identified, the coding sequence and intron/exon boundaries of GCK, GLUD1, and SCHAD were sequenced. Seven novel mutations were found in the ABCC8 coding region, one mutation was found in the KCNJ11 coding region, and one novel mutation was found in each of the two promoter regions screened. Functional studies on beta-cells from six patients showed abnormal ATP-sensitive K+ channel function in five of the patients; the sixth had normal channel activity, and no mutations were found. Photolabeling studies using a reconstituted system showed that all missense mutations altered intracellular trafficking. Each of the promoter mutations decreased expression of a reporter gene by about 60% in a heterologous expression system. In four patients (27%), no mutations were identified. Thus, further genetic heterogeneity is suggested in this disorder. These patients represent a cohort that can be used for searching for mutations in other candidate genes.

The first evidence that higher plants contain annexins was presented in 1989. Since that time, annexins have been purfied and characterized from a variety of plant sources. Analyses of the deduced proteins encoded by annexin cDNAs indicate that the majority of these plant annexins possess the characteristic four repeats of 70 to 75 amino acids and possess motifs proposed to be involved in Ca2+ binding. Like animal annexins, plant annexins bind Ca2+ and phospholipids and are abundant proteins, but there are indications that the number of distinct plant annexin genes may be considerably fewer than that found in animals. Regarding function, a number of studies show that various members of the annexin family of plants may play roles in secretion and/or fruit ripening, show interaction with the enzyme callose (1.3-beta-glucan) synthase, possess intrinsic nucleotide phosphodiesterase activity, bind to F-actin, and/or have peroxidase activity.