Analysis of mammalian pigmentation at the molecular level

There has been great interest lately in the cloning of pigment-related genes; several laboratories have succeeded in isolating melanocyte-specific genes which have many of the characteristics expected for tyrosinase. In this paper, we review the selection criteria, the physical properties, and the functional characteristics of several of these gene products. Two of the clones map to the brown (b) and albino (c) loci, genes that are involved in the regulation of the quantity and quality of melanin production. The functional characteristics of these gene products are not easily reconciled with existing schemes of melanogenesis, and a reevaluation of our concepts of melanogenic regulation may be necessary. The altered expression of these gene products in normal and in transformed melanocytes, and the alternative mRNA processing that occurs in those cells, makes this system an appropriate and interesting one for studies of normal metabolic regulation of gene expression, as well as altered gene expression by neoplastic cells.     

Ferritin H gene polymorphism in idiopathic hemochromatosis

Summary We have analysed karyotypes and DNA from three patients with aniridia (congenital absence of irises) and Wilms' tumour. All three had constitutional deletions from the short arm of chromosome 11. The minimum region of overlap of the deletion involves a small region of band 11p13 presumed to contain the genetic loci responsible for both phenotypic abnormalities. Using cells from these patients, somatic cell hybrids with transformed mouse cells have been prepared. Individual subclones retaining either the deletion-11 chromosome or the normal chromosome 11, in addition to a variety of other human chromosomes, have been identified. The relative position of these breakpoints have been determined and the panel of hybrids has been used to map randomly-isolated 11p13 DNA sequences. The characterisation of these deletions has provided a useful panel of hybrids for random mapping strategies designed to identify the Wilms' and aniridia genes.     

Immunogold localization of chymotrypsin inhibitor-2, a lysine-rich protein,in developing barley endosperm

Chymotrypsin inhibitor-2, a lysine-rich protein in the barley endosperm, has been localized at the ultrastructural level by immunocytochemistry in developing barley endosperm cells 14 days post anthesis. The protein is deposited in the protein bodies. Two morphologically distinct types of protein bodies, small spherical and large irregularly shaped, are present. Golgi-apparatus-derived vesicles whose content is labelled by chymotrypsin inhibitor-2 antibody-gold particles are observed at the Golgi complex and around the vacuoles. These observations indicate that the transport of the protein to the site of deposition is mediated by the Golgi apparatus.Abbreviations CI chymotrypsin inhibitor - DPA days post anthesis - ER endoplasmic reticulum The authors wish to thank Dr. V.R. Franceschi (Department of Botany, Washington State University, Pullman, USA) for many helpful discussions and advice during the work, and the staff at the Electron Microscope Center at Washington State University for technical assistance.     

Quantitative phenotypical expression of three mutant genes in barley and the basis for defining an ideotype for Mediterranean environments

Summary Three mutants induced in the two-rowed barley variety Beka and their three binary recombinants have been used in an attempt to define an ideotype suitable for Mediterranean agroclimatic conditions. Physiological methods (classical plant growth analysis) together with the study of genotype x environment interaction for grain yield were used to characterize the genotypes. That characterization brought out the huge phenotypical variation produced by only three mutant genes, suggesting that single Mendelian genes may alone explain the quantitative variation, including grain yield, without the necessity of using the polygenic concept. The genotype best adapted to the environments studied is later in heading and has shorter straw and denser spikes than Beka; it also has higher inverse of leaf area rate and grain: leaf area ratio, a lower rate of leaf senescence, and a shorter grain filling period than the original variety.     

The role of secreted acid hydrolases in the utilization of complex nutrients byTetrahymena

In an attempt to extend our knowledge of the biology of feeding of the ciliateTetrahymena thermophila, this organism was grown axenically on complex organic material. The nutrient substrate was based on autoclaved wheat grains and adjusted to either pH 5.5 or 7.5. In wild type cultures the cells grew and multiplied only under acidic conditions. In cultures of a mutant cell line blocked in the secretion of acid hydrolases the cells did not grow at either pH value. Thus released acid hydrolases may play a key role in the utilization of complex nutrients in combination with uptake of small organic molecules. Mechanisms in the feeding biology ofTetrahymena thermophila andParamecium tetraurelia are compared.     

Metabolism of i.v. administered 45 kDa epidermal growth factor in the rat

The 45 kDa epidermal growth factor (EGF-(45 kDa)) has been purified from rat urine. We have investigated the distribution and the processing of i.v. injected 125I-labeled EGF-(45 kDa) in the rat. 2.5 min after the i.v. injection only 12% of the label remained in the blood. Most of the label was found in the liver (54%), in the kidneys (7%) and in the skin (4%). The submandibular glands, stomach, small intestine, colon, spleen and lungs contained 1% or less of the radioactivity. Some of the 125I-EGF-(45 kDa) was processed to 125I-EGF-(6 kDa) immunoreactivity in the liver and in the kidneys. The kidneys excreted 125I-EGF-(45 kDa) in the urine, but we were not able to demonstrate 125I-EGF-(6 kDa) in urine. In conclusion, this study shows that homologous EGF-(45 kDa) is cleared from the circulation of rats within a few minutes, mainly by the liver and the kidneys. In vivo both the liver and the kidneys are able to process some of the EGF-(45 kDa) to EGF-(6 kDa) immunoreactivity.     

Dsb-insensitive expression of CcrA, a metallo-beta-lactamase from Bacteroides fragilis, in Escherichia coli after amino acid substitution at two cysteine residues within CcrA.

It has previously been shown that functional expression of CcrA, a metallo-beta-lactamase from Bacteroides fragilis, in Escherichia coli requires a mutation in either dsbA or dsbB, components of a periplasmic disulfide bond-catalyzing system. Site-directed mutagenesis resulting in the substitution of various amino acids for two of the three cysteine residues within CcrA allowed the expression of CcrA in a dsb+ background. This finding supports the hypothesis that DsbA creates aberrant disulfide bonds involving the Cys residues of CcrA.     

Changes in extracellular levels of dopamine metabolites in somatosensory cortex after peripheral denervation

This study examined the effects of a nerve transection on monoamine release from primary somatosensory cortex. The technique of microdialysis was employed to sample extracellular levels of norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) in the barrel field of freely moving rats following the surgical transection of the contralateral infraorbital nerve. Microdialysates obtained 3, 4, and 5 days after deafferentation were analyzed using high-performance liquid chromatography with electrochemical detection. We found a significant increase in the release of the dopamine metabolites, DOPAC and HVA from the deafferented cortex. Three days after deafferentation the release of DOPAC was three-fold higher in the deafferented than in the control animals, and remained about 100% higher in the next two days in this group of animals. The release of HVA showed a gradual increase following the deafferentation procedure, since a 92% larger value on day 3 increased to a 338% difference on day 5. On the other hand, the release rate of NE and the levels of the serotonin metabolite 5-HIAA were not significantly affected by the deafferentation procedure. These results are discussed in the context of the possible participation of dopamine in the reorganization of the deafferented somatosensory cortex.     

Ecophysiology and distribution of the endemic leafless spurgeEuphorbia aphylla and the introducedE. tirucalli (Euphorbiaceae,Euphorbia sect.Tirucalli) in the Canary Islands

The leafless spurgeEuphorbia aphylla (Euphorbiaceae), an endemic species restricted to several of the Canary Islands where it inhabits coastal and arid localities, expresses Crassulacean Acid Metabolism (CAM) when it is subjected to summer drought. A flexible CAM is consistent with the general ecology of the species. It is the only member of sect.Tirucalli native to the Canary Islands and is at the north-western edge of the section's biogeographical range. The other members of the section have a paleotropic distribution and are found throughout Africa. Many of them are regarded as obligate CAM plants, includingE. tirucalli which was used as a comparison in ecophysiological experiments examining the response ofE. aphylla to drought and temperature.