Comparative expression of homologous proteins. A novel mode of transcriptional regulation by the coding sequence folding compatibility of chimeras

Marmosets have a greater diversity of c-Fos response after hyperstimulation in distinct cortical regions as compared to rats

Previous evidence indicated a potential mechanism that might support the fact that primates exhibit greater neural integration capacity as a result of the activation of different structures of the central nervous system, as compared to rodents. The current study aimed to provide further evidence to confirm previous findings by analyzing the patterns of c-Fos expression in more neocortical structures of rats and marmosets using a more robust quantitative technique and evaluating a larger number of brain areas. Nineteen Wistar rats and 21 marmosets (Callithrix jacchus) were distributed among control groups (animals without injections) and animals injected with pentylenetetrazol (PTZ) and euthanized at different time points after stimulus. Immunohistochemical detection of c-Fos was quantified using unbiased and efficient stereological cell counting in eight neocortical regions. Marmosets had a c-Fos expression that was notably more widely expressed (5× more cells) and longer lasting (up to 3 hr) than rats. c-Fos expression in rats presented similar patterns of expression according to the function of the brain cortical structures (associative, sensorial, and motor functions), which was not observed for marmosets (in which no clear pattern could be drawn, and a more diverse profile emerged). Our results provide evidence that the marmoset brain has a greater neuronal activation after intense stimulation by means of PTZ and a more complex pattern of brain activation. We speculate that these functional differences may contribute for the understanding of the different neuronal processing capacities of the neocortex in these mammals' orders.

Functional expression of human α9* nicotinic acetylcholine receptors in X. laevis oocytes is dependent on the α9 subunit 5' UTR

Nicotinic acetylcholine receptors (nAChRs) containing the α9 subunit are expressed in a wide variety of non-neuronal tissues ranging from immune cells to breast carcinomas. The α9 subunit is able to assemble into a functional homomeric nAChR and also co-assemble with the α10 subunit into functional heteromeric nAChRs. Despite the increasing awareness of the important roles of this subunit in vertebrates, the study of human α9-containing nAChRs has been severely limited by difficulties in its expression in heterologous systems. In Xenopus laevis oocytes, functional expression of human α9α10 nAChRs is very low compared to that of rat α9α10 nAChRs. When oocytes were co-injected with cRNA of α9 and α10 subunits of human versus those of rat, oocytes with the rat α9 human α10 combination had an ∼-fold higher level of acetylcholine-gated currents (I_ACh) than those with the human α9 rat α10 combination, suggesting difficulties with human α9 expression. When the ratio of injected human α9 cRNA to human α10 cRNA was increased from 1∶1 to 5∶1, I_ACh increased 36-fold (from 142±23 nA to 5171±748 nA). Functional expression of human α9-containing receptors in oocytes was markedly improved by appending the 5′-untranslated region of alfalfa mosaic virus RNA4 to the 5′-leader sequence of the α9 subunit cRNA. This increased the functional expression of homomeric human α9 receptors by 70-fold (from 7±1 nA to 475±158 nA) and of human α9α10 heteromeric receptors by 80-fold (from 113±62 nA to 9192±1137 nA). These findings indicate the importance of the composition of the 5′ untranslated leader sequence for expression of α9-containing nAChRs.

Complex transcriptional and translational regulation of iPLAgamma resulting in multiple gene products containing dual competing sites for mitochondrial or peroxisomal localization

Membrane-associated calcium-independent phospholipase A2gamma (iPLA2gamma) contains four potential in-frame methionine start sites (Mancuso, D.J. Jenkins, C.M. & Gross, R.W. (2000) J. Biol. Chem.275, 9937-9945), but the mechanisms regulating the types, amount and subcellular localization of iPLA2gamma in cells are incompletely understood. We now: (a) demonstrate the dramatic transcriptional repression of mRNA synthesis encoding iPLA2gamma by a nucleotide sequence nested in the coding sequence itself; (b) localize the site of transcriptional repression to the most 5' sequence encoding the iPLA2gamma holoprotein; (c) identify the presence of nuclear protein constituents which bind to the repressor region by gel shift analysis; (d) demonstrate the translational regulation of distinct iPLA2gamma isoforms; (e) identify multiple novel exons, promoters, and alternative splice variants of human iPLA2gamma; (f) document the presence of dual-competing subcellular localization signals in discrete isoforms of iPLA2gamma; and (g) demonstrate the functional integrity of an N-terminal mitochondrial localization signal by fluorescence imaging and the presence of iPLA2gamma in the mitochondrial compartment of rat myocardium. The intricacy of the regulatory mechanisms of iPLA2gamma biosynthesis in rat myocardium is underscored by the identification of seven distinct protein products that utilize multiple mechanisms (transcription, translation and proteolysis) to produce discrete iPLA2gamma polypeptides containing either single or dual subcellular localization signals. This unanticipated complex interplay between peroxisomes and mitochondria mediated by competition for uptake of the nascent iPLA2gamma polypeptide identifies a new level of phospholipase-mediated metabolic regulation. Because uncoupling protein function is regulated by free fatty acids in mitochondria, these results suggest that iPLA2gamma processing contributes to integrating respiration and thermogenesis in mitochondria.

Multiple ace genes encoding acetylcholinesterases of Caenorhabditis elegans have distinct tissue expression

ace-1 and ace-2 genes encoding acetylcholinesterase in the nematode Caenorhabditis elegans present 35% identity in coding sequences but no homology in noncoding regions (introns, 5'- and 3'-untranslated regions). A 5'-region of ace-2 was defined by rescue of ace-1;ace-2 mutants. When green fluorescent protein (GFP) expression was driven by this regulatory region, the resulting pattern was distinct from that of ace-1. This latter gene is expressed in all body-wall and vulval muscle cells (Culetto et al., 1999), whereas ace-2 is expressed almost exclusively in neurons. ace-3 and ace-4 genes are located in close proximity on chromosome II (Combes et al., 2000). These two genes were first transcribed in vivo as a bicistronic messenger and thus constitute an ace-3;ace-4 operon. However, there was a very low level of monocistronic mRNA of ace-4 (the upstream gene) in vivo, and no ACE-4 enzymatic activity was ever detected. GFP expression driven by a 5' upstream region of the ace-3;ace-4 operon was detected in several muscle cells of the pharynx (pm3, pm4, pm5 and pm7) and in the two canal associated neurons (CAN cells). A dorsal row of body-wall muscle cells was intensively labelled in larval stages but no longer detected in adults. The distinct tissue-specific expression of ace-1, ace-2 and ace-3 (coexpressed only in pm5 cells) indicates that ace genes are not redundant.

Design of acetylcholinesterases for biosensor applications

In recent years, the use of acetylcholinesterases (AChEs) in biosensor technology has gained enormous attention, in particular with respect to insecticide detection. The principle of biosensors using AChE as a biological recognition element is based on the inhibition of the enzyme's natural catalytic activity by the agent that is to be detected. The advanced understanding of the structure-function-relationship of AChEs serves as the basis for developing enzyme variants, which, compared to the wild type, show an increased inhibition efficiency at low insecticide concentrations and thus a higher sensitivity. This review describes different expression systems that have been used for the production of recombinant AChE. In addition, approaches to purify recombinant AChEs to a degree that is suitable for analytical applications will be elucidated as well as the various attempts that have been undertaken to increase the sensitivity of AChE to specified organophosphates and carbamates using side-directed mutagenesis and employing the enzyme in different assay formats.

Transcriptional regulation of gene expression by the coding sequence: An attempt to enhance expression of human AChE

In a previous report, Morel and Massoulié showed that Bungarus AChE (bBAChE) is produced more efficiently than rat AChE in various expression systems, mainly because the Bungarus coding sequence exerts a stimulatory effect on transcription (Morel and Massoulié, 2000). They reported that a 5' Bungarus fragment could partially transfer this property to a CAT expression vector. This appeared to offer the possibility of increasing the production of recombinant proteins. In the present paper, we show that insertion of this fragment in the transcribed region, before the polyadenylation site, may have either stimulatory or inhibitory effects, depending on the vector and on the reporter gene. Since the stimulatory effect of Bungarus coding region could not be attached to a small number of discrete motifs, we reasoned that it might result from a general feature of the sequence. Therefore it might be possible to partially transfer this property to the very homologous human AChE (hHAChE) coding sequence by modifications based on synonymous codons, which increased nucleotide identity between the 5' fragment (721 nucleotides) of bBAChE and hHAChE from 71% to 85%. The production of human AChE in transfected COS cells was increased nearly 2-fold with this modified construct, but still remained about 4-fold smaller than that of Bungarus AChE. There was no change in expression level in transformed Pichia pastoris. We thus confirm that coding sequences can strongly influence gene expression, but in a manner that depends on the context and cannot yet be predicted.