Improvement in nitrogen fixation capacity could be part of the domestication process in soybean.

Biological nitrogen fixation (BNF) in soybeans is a complex process involving the interplay between the plant host and the symbiotic rhizobia. As nitrogen supply has a crucial role in growth and development, higher nitrogen fixation capacity would be important to achieve bigger plants and larger seeds, which were important selection criteria during plant domestication by humans. To test this hypothesis, we monitored the nitrogen fixation-related performance in 31 cultivated and 17 wild soybeans after inoculation with the slow-growing Bradyrhizobium diazoefficiens sp. nov. USDA110 and the fast-growing Sinorhizobium (Ensifer) fredii CCBAU45436. Our results showed that, in general, cultivated soybeans gave better performance in BNF. Electron microscopic studies indicated that there was an exceptionally high accumulation of poly-ß-hydroxybutyrate bodies in bacteroids in the nodules of all wild soybeans tested, suggesting that the C/N balance in wild soybeans may not be optimized for nitrogen fixation. Furthermore, we identified new quantitative trait loci (QTLs) for total ureides and total nodule fresh weight by employing a recombinant inbred population composed of descendants from a cross between a cultivated and a wild parent. Using nucleotide diversity (θπ), divergence index (Fst) and distribution of fixed single-nucleotide polymorphisms as parameters, we found that some regions in the total ureides QTL on chromosome 17 and the total nodule fresh weight QTL on chromosome 12 exhibited very low diversity among cultivated soybeans, suggesting that these were traits specially selected during the domestication and breeding process.

The fear-avoidance model of chronic pain: assessing the role of neuroticism and negative affect in pain catastrophizing using structural equation modeling.

BACKGROUND: Previous research on the fear-avoidance model (FAM) of chronic pain suggests that the personality traits of neuroticism and negative affect (NA) influence pain catastrophizing. However, the mechanisms of their influence on pain catastrophizing remain unclear. PURPOSE: This study examined four possible models of relationships between neuroticism, NA, and pain catastrophizing within the FAM framework using structural equation modeling. METHOD: A total of 401 patients with chronic musculoskeletal pain completed measures of neuroticism, NA, three core FAM components (pain catastrophizing, pain-related fear, and pain anxiety), and adjustment outcomes (pain-related disability and depression). RESULTS: Regression analyses refuted the possibility that neuroticism and NA moderated each other's effect on pain catastrophic thoughts (p > 0.05). Results of structural equation modeling (SEM) evidenced superior data-model fit for the collapsed models in which neuroticism and NA were two secondary traits underlying a latent construct, negative emotion (disability: comparative fit index (CFI) = 0.93; depression: CFI = 0.91). CONCLUSION: The results offer preliminary evidence that patients presenting with more neurotic symptom and heightened NA probably elicit more catastrophic thoughts about pain.

The effects of anxiety sensitivity, pain hypervigilance, and pain catastrophizing on quality of life outcomes of patients with chronic pain: a preliminary, cross-sectional analysis.

PURPOSE: In the fear-avoidance model (FAM) of chronic pain, pain-related fear is one of the most prominent predictors of negative adjustment outcomes. While existing data point to the effects of anxiety sensitivity, pain hypervigilance, and pain catastrophizing on pain-related fear, the nature of their multivariate relationships remains unclear. This study explored the possible mediating role of pain hypervigilance in the relationship of anxiety sensitivity and pain catastrophizing with pain-related fear, and their effects on quality of life (QoL) outcomes within the FAM framework. METHODS: A sample of 401 Chinese patients with chronic musculoskeletal pain completed the standardized measures assessing the FAM components and QoL. Structural equation modeling (SEM) was used to evaluate six hypothesized models. RESULTS: Results of SEM showed adequate data-model fit [comparative fit indexes (CFIs) ranging from 0.92 to 0.94] on models which specified pain hypervigilance as mediator of anxiety sensitivity and pain catastrophizing with pain-related fear on two QoL outcomes (QoL-Physical and QoL-Mental). Results consistent with net suppression effects of pain catastrophizing on anxiety sensitivity were found in SEM when both anxiety sensitivity and pain catastrophizing were included in the same full model to predict QoL-Physical (CFI = 0.95; Sobel z = 8.06, p < 0.001) and QoL-Mental (CFI = 0.93; Sobel z = 8.31, p < 0.001). CONCLUSIONS: These cross-sectional analyses gave results consistent with pain hypervigilance, mediating the relationship of pain catastrophic cognition and anxiety sensitivity with pain-related fear. The net suppression effects of pain catastrophizing point to anxiety sensitivity, enhancing the effect of pain catastrophic cognition on pain hypervigilance. These findings elucidate how the interdependence of dispositional factors might influence pain adjustment and functioning.

Breast Implant-associated Anaplastic Large Cell Lymphoma - a Systematic Review with Pooled Analysis.

The association of breast implants and anaplastic large cell lymphoma (BIA-ALCL) was first described in 1997. Such an association has aroused public health concerns on breast implant safety. A systematic review was carried out with a pooled analysis of data. In total, 674 non-duplicate articles were retrieved; 77 articles were included for data extraction; 395 patients were identified for analysis. The median age at the time of diagnosis was 52 years. Implant texture was described in 201 (50.9%) patients; all 201 patients had a textured implant. The median time from the last implant insertion to diagnosis was 7.5 years. Most patients presented with seroma (67.1%, n = 265), 20.5% of patients presented with breast mass (n = 81). Patients with a breast mass at presentation, lymphadenopathy and those without seroma had more disseminated disease (P < 0.001). 73.2% of patients (n = 289) opted for primary surgery, among which 68.6% (n = 271) received removal of the implant, 61% (n = 241) received capsulectomy and 2% (n = 8) received mastectomy. Of note, 5.3% (n = 21) had reinsertion of an implant after primary surgery. Non-surgical modalities included chemotherapy, radiotherapy and haematopoietic stem cell transplant. The median follow-up interval was 2 years (range 0-14.5 years). Seventeen patients (4.3%) had recurrence of BIA-ALCL and 195 patients (49.4%) did not. The median duration to first recurrence was 1 year (range 1-3 years). Long-term clinical outcome was not reported in 183 patients. BIA-ALCL is an indolent disease that presents with seroma after implant insertion. A high index of suspicion is needed for early diagnosis and treatment.

Correlation between AS1 gene expression and seed protein contents in different soybean (Glycine max [L.] Merr.) cultivars.

In higher plants, asparagine synthetase (AS) plays an important role in regulating the nitrogen sink-source relationship. We studied the expression of AS genes in five Chinese soybean cultivars exhibiting contrasting seed protein contents. We found that only the AS2 but not the AS1 gene was induced by dark treatment. On the other hand, the expression of AS1 in leaves (especially in trifoliate leaves of young seedlings) showed a positive correlation with seed protein contents in the soybean cultivars tested. Therefore, in spite of the fact that the principle transporting compounds in soybean plants for nitrogen acquired via symbiotic fixation are ureides, AS may still play an important role in the process of nitrogen assimilation.

Metabolite and light regulation of metabolism in plants: lessons from the study of a single biochemical pathway.

We are using molecular, biochemical, and genetic approaches to study the structural and regulatory genes controlling the assimilation of inorganic nitrogen into the amino acids glutamine, glutamate, aspartate and asparagine. These amino acids serve as the principal nitrogen-transport amino acids in most crop and higher plants including Arabidopsis thaliana. We have begun to investigate the regulatory mechanisms controlling nitrogen assimilation into these amino acids in plants using molecular and genetic approaches in Arabidopsis. The synthesis of the amide amino acids glutamine and asparagine is subject to tight regulation in response to environmental factors such as light and to metabolic factors such as sucrose and amino acids. For instance, light induces the expression of glutamine synthetase (GLN2) and represses expression of asparagine synthetase (ASN1) genes. This reciprocal regulation of GLN2 and ASN1 genes by light is reflected at the level of transcription and at the level of glutamine and asparagine biosynthesis. Moreover, we have shown that the regulation of these genes is also reciprocally controlled by both organic nitrogen and carbon metabolites. We have recently used a reverse genetic approach to study putative components of such metabolic sensing mechanisms in plants that may be conserved in evolution. These components include an Arabidopsis homolog for a glutamate receptor gene originally found in animal systems and a plant PII gene, which is a homolog of a component of the bacterial Ntr system. Based on our observations on the biology of both structural and regulatory genes of the nitrogen assimilatory pathway, we have developed a model for metabolic control of the genes involved in the nitrogen assimilatory pathway in plants.

[From an urge for life to a wish to die. A sociocultural analysis]. / Van levenswens naar stervenswens. Een cultuursociologische beschouwing.

In euthanasia and assisted suicide the wish to die has become greater than the wish to continue life. The reasons of this turn to death are subject of analysis. Examples, two from the Netherlands and one from the Eskimos demonstrate that the beginning of this process is an experience of irreversible loss. Cultural norms determine the meaning of this experience. Likewise, prevailing norms determine the possible unacceptability of the resulting deviancy. Coping with unacceptable deviancy is a restaurative strategy which fits in the prevailing cultural model. Eskimo assisted suicide is aimed at sectional interest: the request for life-ending help is posed on behalf of group survival. In the Netherlands euthanasia and assisted suicide are part of an individualistic culture with an earthly system of meaning. The emphasis is on good health, youth and representative appearance. The individual request for help is posed on behalf of the individual himself, to prevent social isolation, and to die in a clean way in self-selected company.

The GCN2 homologue in Arabidopsis thaliana interacts with uncharged tRNA and uses Arabidopsis eIF2α molecules as direct substrates.

Phosphorylation of eIF2α is an important strategy for living organisms to adapt to metabolic and physiological changes that are often associated with external stimuli. GCN2 is one of the well-studied eIF2α kinases in yeast and mammals, which is responsible for the survival of the organism under amino acid starvation. Despite the downstream reactions being quite divergent, AtGCN2 exhibits a high primary sequence similarity to its yeast and animal counterparts. In this study, we provide experimental evidence to show that AtGCN2 shares similar biochemical properties to the yeast and animal homologues. Our in vitro assays demonstrate the binding of the C-terminus of AtGCN2 to uncharged tRNA molecules and the enzymatic activities of AtGCN2 on both eIF2α homologues in A. thaliana, thus providing essential information for further understanding the functions of plant general control non-repressible (GCN) homologues.

Activation of GPR30 inhibits the growth of prostate cancer cells through sustained activation of Erk1/2, c-jun/c-fos-dependent upregulation of p21, and induction of G(2) cell-cycle arrest.

G-protein-coupled receptor-30 (GPR30) shows estrogen-binding affinity and mediates non-genomic signaling of estrogen to regulate cell growth. We here showed for the first time, in contrast to the reported promoting action of GPR30 on the growth of breast and ovarian cancer cells, that activation of GPR30 by the receptor-specific, non-estrogenic ligand G-1 inhibited the growth of androgen-dependent and androgen-independent prostate cancer (PCa) cells in vitro and PC-3 xenografts in vivo. However, G-1 elicited no growth or histological changes in the prostates of intact mice and did not inhibit growth in quiescent BPH-1, an immortalized benign prostatic epithelial cell line. Treatment of PC-3 cells with G-1 induced cell-cycle arrest at the G(2) phase and reduced the expression of G(2)-checkpoint regulators (cyclin-A2, cyclin-B1, cdc25c, and cdc2) and phosphorylation of their common transcriptional regulator NF-YA in PC-3 cells. With extensive use of siRNA-knockdown experiments and the MEK inhibitor PD98059 in this study, we dissected the mechanism underlying G-1-induced inhibition of PC-3 cell growth, which was mediated through GPR30, followed by sustained activation of Erk1/2 and a c-jun/c-fos-dependent upregulation of p21, resulting in the arrest of PC-3 growth at the G(2) phase. The discovery of this signaling pathway lays the foundation for future development of GPR30-based therapies for PCa.

Characterization of the complex pdxH-tyrS operon of Escherichia coli K-12 and pleiotropic phenotypes caused by pdxH insertion mutations.

We report the first molecular genetic analysis of a pyridoxine 5'-phosphate oxidase, the PdxH gene product of Escherichia coli K-12. Chromosomal insertions in and around pdxH were generated with various transposons, and the resulting phenotypes were characterized. The DNA sequence of pdxH was determined, and the promoters of pdxH and the downstream gene tyrS, which encodes tyrosyl-tRNA synthetase, were mapped by RNase T2 protection assays of chromosomal transcripts. These combined approaches led to the following conclusions: (i) pdxH is transcribed from a sigma 70-type promoter and shares its transcript with tyrS; (ii) tyrS is additionally transcribed from a relatively strong, nonconventional internal promoter that may contain an upstream activating sequence but whose expression is unaffected by a fis mutation; (iii) PdxH oxidase is basic, has a molecular mass of 25,545 Da, and shares striking homology (greater than 40% identity) with the developmentally regulated FprA protein of Myxococcus xanthus; (iv) mild pyridoxal 5'-phosphate limitation of pdxH mutants inhibits cell division and leads to formation of unsegregated nucleoids; (v) E. coli PdxH oxidase is required aerobically and anaerobically, but second-site suppressors that replace pdxH function entirely can be isolated; and (vi) pdxH mutants excrete significant amounts of L-glutamate and a compound, probably alpha-ketoisovalerate, that triggers L-valine inhibition of E. coli K-12 strains. These findings extend earlier observations that pyridoxal 5'-phosphate biosynthetic and aminoacyl-tRNA synthetase genes are often members of complex, multifunctional operons. Our results also show that loss of pdxH function seriously disrupts cellular metabolism in unanticipated ways.

Metabolic relationships between pyridoxine (vitamin B6) and serine biosynthesis in Escherichia coli K-12.

We propose a pathway leading from erythrose-4-phosphate and glutamate to nitrogen 1 and carbons 5,5', and 6 of the pyridoxine ring. This pathway, which parallels the phosphorylated pathway of serine biosynthesis, is predicted on the homology between PdxB and SerA, the structural similarity between serine and 4-hydroxythreonine, and the possible involvement of SerC in pyridoxine biosynthesis. Several predictions of this hypothetical scheme were tested. Consistent with the proposed pathway, supplement inhibition patterns strongly suggest that SerA enzyme acts in a an alternate pathway of pyridoxine biosynthesis in pdxB mutants. Direct enzyme assays detected erythrose-4-phosphate dehydrogenase activity in crude extracts, which again supports the proposed pathway. Chromosomal insertions in serC caused a requirement for pyridoxine, serine, and aromatic compounds, which directly verified that SerC functions in the pyridoxine biosynthetic pathway. Complementation analysis showed that pdxF and pdxC mutations reported previously are most likely alleles of serC. Growth of serC chromosomal insertion mutants on glycoalaldehyde was found to occur without acquisition of second-site mutations and confirmed that pdxB and serC, but not pdxA, function in the same branch of the pyridoxine pathway. In addition, serC::mini-Mu d insertions revealed that the complex serC-aroA operon lacks internal promoters, that the amino terminus of SerC is not strictly essential for activity, and that antisense transcription occurs in the serC-aroA operon. Growth responses of pdxA, pdxB, and serC mutants to beta-hydroxypyruvate, D-alanine, and glycolate could also be reconciled with the proposed pathway. Finally, the proposed scheme is consistent with previous isotope labeling data and accounts for several other observations about pyridoxine biosynthesis. Together, these physiological and biochemical analyses support the proposed pathway and an evolutionary scenario in which this branch of the pyridoxine pathway evolved from the serine pathway by gene recruitment.

Metabolic regulation of the gene encoding glutamine-dependent asparagine synthetase in Arabidopsis thaliana.

Here, we characterize a cDNA encoding a glutamine-dependent asparagine synthetase (ASN1) from Arabidopsis thaliana and assess the effects of metabolic regulation on ASN1 mRNA levels. Sequence analysis shows that the predicted ASN1 peptide contains a purF-type glutamine-binding domain. Southern blot experiments and cDNA clone analysis suggest that ASN1 is the only gene encoding glutamine-dependent asparagine synthetase in A. thaliana. The ASN1 gene is expressed predominantly in shoot tissues, where light has a negative effect on its mRNA accumulation. This negative effect of light on ASN1 mRNA levels was shown to be mediated, at least in part, via the photoreceptor phytochrome. We also investigated whether light-induced changes in nitrogen to carbon ratios might exert a metabolic regulation of the ASN1 mRNA accumulation. These experiments demonstrated that the accumulation of ASN1 mRNA in dark-grown plants is strongly repressed by the presence of exogenous sucrose. Moreover, this sucrose repression of ASN1 expression can be partially rescued by supplementation with exogenous amino acids such as asparagine, glutamine, and glutamate. These findings suggest that the expression of the ASN1 gene is under the metabolic control of the nitrogen to carbon ratio in cells. This is consistent with the fact that asparagine, synthesized by the ASN1 gene product, is a favored compound for nitrogen storage and nitrogen transport in dark-grown plants. We have put forth a working model suggesting that when nitrogen to carbon ratios are high, the gene product of ASN1 functions to re-direct the flow of nitrogen into asparagine, which acts as a shunt for storage and/or long-distance transport of nitrogen.

Reciprocal regulation of distinct asparagine synthetase genes by light and metabolites in Arabidopsis thaliana.

In plants, the amino acid asparagine serves as an important nitrogen transport compound whose levels are dramatically regulated by light in many plant species, including Arabidopsis thaliana. To elucidate the mechanisms regulating the flux of assimilated nitrogen into asparagine, we examined the regulation of the gene family for asparagine synthetase in Arabidopsis. In addition to the previously identified ASN1 gene, we identified a novel class of asparagine synthetase genes in Arabidopsis (ASN2 and ASN3) by functional complementation of a yeast asparagine auxotroph. The proteins encoded by the ASN2/3 cDNAs contain a Pur-F type glutamine-binding triad suggesting that they, like ASN1, encode glutamine-dependent asparagine synthetase isoenzymes. However, the ASN2/3 isoenzymes form a novel dendritic group with monocot AS genes which is distinct from all other dicot AS genes including Arabidopsis ASN1. In addition to these distinctions in sequence, the ASN1 and ASN2 genes are reciprocally regulated by light and metabolites. Time-course experiments reveal that light induces levels of ASN2 mRNA while it represses levels of ASN1 mRNA in a kinetically reciprocal fashion. Moreover, the levels of ASN2 and ASN1 mRNA are also reciprocally regulated by carbon and nitrogen metabolites. The distinct regulation of ASN1 and ASN2 genes combined with their distinct encoded isoenzymes suggest that they may play different roles in nitrogen metabolism, as discussed in this paper.

Suppression of insertions in the complex pdxJ operon of Escherichia coli K-12 by lon and other mutations.

Complementation analyses using minimal recombinant clones showed that all known pdx point mutations, which cause pyridoxine (vitamin B6) or pyridoxal auxotrophy, are located in the pdxA, pdxB, serC, pdxJ, and pdxH genes. Antibiotic enrichments for chromosomal transposon mutants that require pyridoxine (vitamin B6) or pyridoxal led to the isolation of insertions in pdxA, pdxB, and pdxH but not in pdxJ. This observation suggested that pdxJ, like pdxA, pdxB, and serC, might be in a complex operon. To test this hypothesis, we constructed stable insertion mutations in and around pdxJ in plasmids and forced them into the bacterial chromosome. Physiological properties of the resulting insertion mutants were characterized, and the DNA sequence of pdxJ and adjacent regions was determined. These combined approaches led to the following conclusions: (i) pdxJ is the first gene in a two-gene operon that contains a gene, temporarily designated dpj, essential for Escherichia coli growth; (ii) expression of the rnc-era-recO and pdxJ-dpj operons can occur independently, although the pdxJ-dpj promoter may lie within recO; (iii) pdxJ encodes a 26,384-Da polypeptide whose coding region is preceded by a PDX box, and dpj probably encodes a basic, 14,052-Da polypeptide; (iv) mini-Mud insertions in dpj and pdxJ, which are polar on dpj, severely limit E. coli growth; and (v) three classes of suppressors, including mutations in lon and suppressors of lon, that allow faster growth of pdxJ::mini-Mud mutants can be isolated. A model to account for the action of dpj suppressors is presented, and aspects of this genetic analysis are related to the pyridoxal 5'-phosphate biosynthetic pathway.

Molecular evolution of glutamate receptors: a primitive signaling mechanism that existed before plants and animals diverged.

We performed a genealogical analysis of the ionotropic glutamate receptor (iGluR) gene family, which includes the animal iGluRs and the newly isolated glutamate receptor-like genes (GLR) of plants discovered in Arabidopsis. Distance measures firmly placed the plant GLR genes within the iGluR clade as opposed to other ion channel clades and indicated that iGluRs may be a primitive signaling mechanism that predated the divergence of animals and plants. Moreover, phylogenetic analyses using both parsimony and neighbor joining indicated that the divergence of animal iGluRs and plant GLR genes predated the divergence of iGluR subtypes (NMDA vs. AMPA/KA) in animals. By estimating the congruence of the various glutamate receptor gene regions, we showed that the different functional domains, including the two ligand-binding domains and the transmembrane regions, have coevolved, suggesting that they assembled together before plants and animals diverged. Based on residue conservation and divergence as well as positions of residues with respect to functional domains of iGluR proteins, we attempted to examine structure-function relationships. This analysis defined M3 as the most highly conserved transmembrane domain and identified potential functionally important conserved residues whose function can be examined in future studies.

A PII-like protein in Arabidopsis: putative role in nitrogen sensing.

PII is a protein allosteric effector in Escherichia coli and other bacteria that indirectly regulates glutamine synthetase at the transcriptional and post-translational levels in response to nitrogen availability. Data supporting the notion that plants have a nitrogen regulatory system(s) includes previous studies showing that the levels of mRNA for plant nitrogen assimilatory genes such as glutamine synthetase (GLN) and asparagine synthetase (ASN) are modulated by carbon and organic nitrogen metabolites. Here, we have characterized a PII homolog (GLB1) in two higher plants, Arabidopsis thaliana and Ricinus communis (Castor bean). Each plant PII-like protein has high overall identity to E. coli PII (50%). Western blot analyses reveal that the plant PII-like protein is a nuclear-encoded chloroplast protein. The PII-like protein of plants appears to be regulated at the transcriptional level in that levels of GLB1 mRNA are affected by light and metabolites. To initiate studies of the in vivo function of the Arabidopsis PII-like protein, we have constructed transgenic lines in which PII expression is uncoupled from its native regulation. Analyses of these transgenic plants support the notion that the plant PII-like protein may serve as part of a complex signal transduction network involved in perceiving the status of carbon and organic nitrogen. Thus, the PII protein found in archaea, bacteria, and now in higher eukaryotes (plants) is one of the most widespread regulatory proteins known, providing evidence for an ancestral metabolic regulatory mechanism that may have existed before the divergence of these three domains of life.

THE MOLECULAR-GENETICS OF NITROGEN ASSIMILATION INTO AMINO ACIDS IN HIGHER PLANTS.

Nitrogen assimilation is a vital process controlling plant growth and development. Inorganic nitrogen is assimilated into the amino acids glutamine, glutamate, asparagine, and aspartate, which serve as important nitrogen carriers in plants. The enzymes glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), aspartate aminotransferase (AspAT), and asparagine synthetase (AS) are responsible for the biosynthesis of these nitrogen-carrying amino acids. Biochemical studies have revealed the existence of multiple isoenzymes for each of these enzymes. Recent molecular analyses demonstrate that each enzyme is encoded by a gene family wherein individual members encode distinct isoenzymes that are differentially regulated by environmental stimuli, metabolic control, developmental control, and tissue/cell-type specificity. We review the recent progress in using molecular-genetic approaches to delineate the regulatory mechanisms controlling nitrogen assimilation into amino acids and to define the physiological role of each isoenzyme involved in this metabolic pathway.

Identification of mutations in the transglutaminase 1 gene in lamellar ichthyosis.

Lamellar ichthyosis (LI) is an autosomal recessive disorder of cornification. Mutations in the transglutaminase 1 gene (TGM1) have been identified in several families with this disorder. We analyzed two unrelated families with offspring affected with LI. Family 1 included affected monozygotic twins, in which a homozygous G-to-T transversion was identified in exon 6 at amino acid residue R315L. This mutation was also identified in the unaffected mother. In family 2, which consisted of one affected infant, a T-to-G transversion in exon 8 resulted in a change of phenylalanine to valine, F400V, and a C-to-T transition in exon 4 resulted in a change of proline to leucine, P248L. In this family, the mutation F400V was found in the unaffected father, and the mutation P248L was identified in the unaffected mother. These findings extend the growing body of literature documenting mutations in the TGM1 gene as the molecular basis of certain cases of lamellar ichthyosis.

A recurrent mutation in the loricrin gene underlies the ichthyotic variant of Vohwinkel syndrome.

Vohwinkel syndrome (VS) is a family of genodermatoses which exhibits extensive clinical and genetic heterogeneity. Here, we studied a pedigree originating from the UK with typical features of the ichthyotic variant of VS and identified a recurrent insertion mutation in the loricrin gene resulting in a mutant polypeptide with an unusual C terminus. Functional studies in transgenic mice have shown that the accumulation of mutant loricrin in the nucleus appears to interfere with the later stages of epidermal differentiation, thereby explaining the clinical manifestations of ichthyosis, keratoderma and pseudoainhum. Our findings extend the body of evidence implicating mutations in the loricrin gene as the underlying cause of VS.

C73R is a hotspot mutation in the uroporphyrinogen III synthase gene in congenital erythropoietic porphyria.

Congenital erythropoietic porphyria (CEP) results from profoundly deficient activity of the fourth enzyme of the haeme biosynthetic pathway, uroporphyrinogen III synthase (UROIIIS). CEP is a rare, recessively inherited disorder, and mutations in the UROIIIS gene detected in CEP patients are heterogeneous. The notable exception to this rule is a single missense mutation, designated C73R, which represents over 40% of all mutant UROIIIS alleles. In this study, we investigated three separate families with CEP from different ethnic backgrounds. We performed haplotype analysis using two microsatellite markers that closely flank the UROIIIS gene on chromosome 10q24, spanning a region of 4 cM on the GB4 linkage panel. Haplotype analysis revealed the occurrence of C73R on different haplotypes in four out of four disease chromosomes studied. The results are consistent with the hypothesis that C73R is a hotspot mutation for CEP, and does not represent wide dispersion of a single ancestral mutant C73R allele.