Can we use local climate zones for predicting malaria prevalence across sub-Saharan African cities?

Malaria burden is increasing in sub-Saharan cities because of rapid and uncontrolled urbanization. Yet very few studies have studied the interactions between urban environments and malaria. Additionally, no standardized urban land-use/land-cover has been defined for urban malaria studies. Here, we demonstrate the potential of local climate zones (LCZs) for modeling malaria prevalence rate (Pf PR_2-10) and studying malaria prevalence in urban settings across nine sub-Saharan African cities. Using a random forest classification algorithm over a set of 365 malaria surveys we: (i) identify a suitable set of covariates derived from open-source earth observations; and (ii) depict the best buffer size at which to aggregate them for modeling Pf PR_2-10. Our results demonstrate that geographical models can learn from LCZ over a set of cities and be transferred over a city of choice that has few or no malaria surveys. In particular, we find that urban areas systematically have lower Pf PR_2-10 (5%-30%) than rural areas (15%-40%). The Pf PR_2-10 urban-to-rural gradient is dependent on the climatic environment in which the city is located. Further, LCZs show that more open urban environments located close to wetlands have higher Pf PR_2-10. Informal settlements-represented by the LCZ 7 (lightweight lowrise)-have higher malaria prevalence than other densely built-up residential areas with a mean prevalence of 11.11%. Overall, we suggest the applicability of LCZs for more exploratory modeling in urban malaria studies.

[Pericardial foreign body: an unusual cause of chest pain in children]

Penetrating thoracic trauma by a needle or pin is rarely described in children. Localization of the needle may sometimes be difficult. The needle can migrate from the entrance site into many organs with time and cause little initial morbidity. We describe the case of a 14-year-old male patient with a sewing needle accidentally inserted through the chest wall. The foreign body had migrated spontaneously to the pericardium. A computed tomography scan of the chest is needed to determine the location of the needle and show any complications. Pericardium foreign bodies are dangerous and need electrocardiography and cardiac ultrasound before treatment. Removal of the needle by thoracotomy or thoracoscopy is indicated.

Successful unilateral thoracoscopy for bilateral ectopic mediastinal parathyroidectomy

Ectopic parathyroid glands are frequently located in the thymus and may become hyperplasic in patients with secondary hyperparathyroidism. When medical management fails, surgical removal is required, using either a traditional open sternotomy approach or video-assisted thoracic surgery (VATS). We were able to excise large, bilateral, mediastinal parathyroid glands using only left VATS. To the authors' knowledge, this is the first reported case of the use of unilateral thoracoscopic subtotal thymectomy for the excision of bilateral ectopic mediastinal parathyroid glands.

Population, environmental, and community effects on local bank vole (Myodes glareolus) Puumala virus infection in an area with low human incidence

In this study, the distribution of Puumala hantavirus (PUUV) infection in local bank vole Myodes glareolus populations in an area with low human PUUV infection (nephropathia epidemica [NE]) incidence in northern Belgium was monitored for 2 consecutive years. Bank voles were trapped in preferred habitat and tested for anti-PUUV IgG. Infection data were related to individual bank vole features, population demography, and environmental variables. Rare occurrence of PUUV infection was found and PUUV prevalence was low compared with data from the high NE incidence area in southern Belgium. Small-scale climatic differences seemed to play a role in PUUV occurrence, vegetation index and deciduous forest patch size both influenced PUUV prevalence and number of infected voles in a positive way. The data suggested a density threshold in vole populations below which PUUV infection does not occur. This threshold may vary between years, but the abundance of bank voles does not seem to affect the degree of PUUV seroprevalence further. We found indications for a dilution effect on PUUV prevalence, dependent on the relative proportion of nonhost wood mice Apodemus sylvaticus in a study site. In conclusion, we regard the combination of a dilution effect, a possible threshold density that depends on local conditions, and a higher fragmentation of suitable bank vole habitat in our study area as plausible explanations for the sparse occurrence of PUUV infection and low prevalence detected. Thus, beside human activity patterns, local environmental conditions and rodent community structure are also likely to play a role in determining PUUV infection risk for humans.

Short-term effects of depleted uranium on immune status in rat intestine

In the event of ingestion, the digestive tract is the first biological system exposed to depleted uranium (DU) intake via the intestinal lumen. However, little research has addressed the biological consequences of a contamination with depleted uranium on intestinal properties such as the barrier function and/or the immune status of this tissue. The aim of this study was to determine if the ingestion of depleted uranium led to changes in the gut immune system of the intestine. The experiments were performed at 1 and 3 d following a per os administration of DU to rats at sublethal dose (204 mg/kg). Several parameters referring to the immune status, such as gene and protein expressions of cytokines and chemokines, and localization and density of immune cell populations, were assessed in the intestine. In addition, the overall toxicity of DU on the small intestine was estimated in this study, with histological appearance, proliferation rate, differentiation pattern, and apoptosis process. Firstly, the results of this study indicated that DU was not toxic for the intestine, as measured by the proliferation, differentiation, and apoptosis processes. Concerning the immune properties of the intestine, the ingestion of depleted uranium induced some changes in the production of chemokines and in the expression of cytokines. A diminished production of monocyte chemoattractant protein-1 (MCP-1) was noted at 1 day post exposure. At 3 d, the increased gene expression of interferon gamma (IFNgamma) was associated with an enhanced mRNA level of Fas ligand, suggesting an activation of the apoptosis pathway. However, no increased apoptotic cells were observed at 3 d in the contaminated animals. There were no changes in the localization and density of neutrophils, helper T lymphocytes, and cytotoxic T lymphocytes after DU administration. In conclusion, these results suggest that depleted uranium is not toxic for the intestine after acute exposure. Nevertheless, DU seems to modulate the expression and/or production of cytokines (IFNgamma) and chemokines (MCP-1) in the intestine. Further experiments need to be performed to determine if a chronic contamination at low dose leads in the long term to modifications of cytokines/chemokines patterns, and to subsequent changes in immune response of the intestine.

In vivo effects of chronic contamination with depleted uranium on CYP3A and associated nuclear receptors PXR and CAR in the rat

In addition to its natural presence at high concentrations in some areas, uranium has several civilian and military applications that could cause contamination of human populations, mainly through chronic ingestion. Reports describe the accumulation of this radionuclide in some organs (including the bone, kidney, and liver) after acute or chronic contamination and show that it produces chemical or radiological toxicity or both. The literature is essentially devoid of information about uranium-related cellular and molecular effects on metabolic functions such as xenobiotic detoxification. The present study thus evaluated rats chronically exposed to depleted uranium in their drinking water (1mg/(ratday)) for 9 months. Our specific aim was to evaluate the hepatic and extrahepatic mRNA expression of CYP3A1/A2, CYP2B1, and CYP1A1 as well as of the nuclear receptors PXR, CAR, and RXR in these rats. CYP3A1 mRNA expression was significantly higher in the brain (200%), liver (300%), and kidneys (900%) of exposed rats compared with control rats, while CYP3A2 mRNA levels were higher in the lungs (300%) and liver (200%), and CYP2B1 mRNA expression in the kidneys (300%). Expression of CYP1A1 mRNA did not change significantly during this study. PXR mRNA levels increased in the brain (200%), liver (150%), and kidneys (200%). Uranium caused CAR mRNA expression in the lungs to double. Expression of RXR mRNA did not change significantly in the course of this study, nor did the hepatic activity of CYP2C, CYP3A, CYP2A, or CYP2B. Uranium probably affects the expression of drug-metabolizing CYP enzymes through the PXR and CAR nuclear receptors. These results suggest that the stimulating effect of uranium on these enzymes might lead to hepatic or extrahepatic toxicity (or both) during drug treatment and then affect the entire organism.

IL-1beta, TNFalpha and IL-6 induction in the rat brain after partial-body irradiation: role of vagal afferents

PURPOSE

To evaluate the central nervous system neuroimmune and inflammatory responses during the prodromal phase of the acute irradiation syndrome in rat brains after partial-body exposure (head-protected) and to investigate the potential neural signalling pathways from the irradiated periphery to the non-irradiated brain.

MATERIAL AND METHODS

The study included four groups of rats: one irradiated group and one sham irradiated group, each containing non-vagotomized and vagotomized rats. In vagotomized rat groups, the subdiaphragmatic vagal section surgery was carried out 45 days before the irradiation exposure. The rats were partial-body irradiated with the head shielded with (60)Co gamma-rays to a dose of 15 Gy. They were sacrificed 6 h after the end of exposure. The hypothalamus, hippocampus, thalamus and cortex were then collected, and the concentrations of IL-1beta, TNFalpha and IL-6 in each were measured by ELISA assays.

RESULTS

Six hours after irradiation, IL-1beta levels had increased in the hypothalamus, thalamus and hippocampus, and TNFalpha and IL-6 levels had increased significantly in the hypothalamus. Vagotomy before irradiation prevented these responses.

CONCLUSIONS

It was concluded that the hypothalamus, hippocampus, thalamus and cortex react rapidly to peripheral irradiation by releasing pro-inflammatory mediators. The results also show that the vagus nerve is one of the major ascending pathways for rapid signalling to the brain with respect to partial body irradiation.

Abdominal irradiation increases inflammatory cytokine expression and activates NF-kappaB in rat ileal muscularis layer

The small bowel is an important dose-limiting organ in abdominal radiotherapy because irradiation can cause acute enteritis that, in turn, leads to progressively reduced motility and finally, in a later phase, to fibrosis. Because these clinical symptoms may be caused by the early stage of an inflammatory process, we characterized the radiation-induced intestinal inflammation in rats. Abdominal gamma-irradiation (10-Gy) induced a cascade of inflammatory events characterized by an early (6 h after exposure) increase in IL-1beta, TNF-alpha, and IL-6 mRNA levels in the rat ileal muscularis layer. IL-8 [a cytokine-induced neutrophil chemoattractant (CINC)] mRNA appeared later (at 3 days). The expression of TGF-beta (a profibrotic cytokine) was higher in irradiated than control tissue at day 1, whereas IL-10 (an anti-inflammatory cytokine) expression vanished completely. Despite strong IL-1ra expression, the IL-1ra/IL-1beta ratio, which is an indicator of inflammatory balance, was -41% at day 1 in irradiated compared with control tissue. The nuclear transcription factors NF-kappaB and activator protein-1 (AP-1) govern transcription of these genes, directly or indirectly. Although expression of the subunits of NF-kappaB (p65, p50) and AP-1 (c-fos, c-jun) did not increase, irradiation caused a rapid and persistent translocation of p65 and p50. An imbalance between proinflammatory and anti-inflammatory mediators may contribute to perpetuating intestinal inflammation, thus making it chronic.

Absence of protective role of afferent nerves in early intestinal mucosal alterations induced by abdominal irradiation in rats

PURPOSE

To assess the early effects of primary afferent nerve suppression by systemic treatment with the neurotoxin capsaicin in an acute model of abdominal irradiation in rats (10Gy, gamma).

MATERIALS AND METHODS

Changes in myeloperoxidase (MPO) activity, calcitonin gene-related peptide (CGRP) tissue content, number of mast cells and apoptotic cells were determined in jejunum and ileum in four groups of rat male Wistar (vehicle sham-irradiated, vehicle irradiated, capsaicin sham-irradiated and capsaicin irradiated) at 1 and 3 days post-irradiation.

RESULTS

In vehicle irradiated rats, CGRP was significantly increased from the first day after irradiation in jejunal mucosa; MPO activity increased in both segments at day 3 but not at day 1 after irradiation; the number of detectable mucosal mast cells dropped to nearly zero on days 1 and 3, while the apoptotic cells in the intestinal mucosa were significantly increased at day 1. Similar results were obtained for mast cells and apoptosis in capsaicin irradiated rats as compared to capsaicin sham-irradiated rats, while MPO activity was significantly increased and CGRP concentration in jejunal mucosa significantly decreased from the first day in these rats in comparison with capsaicin sham-irradiated rats.

CONCLUSIONS

Intestinal sensory innervation seems not to have a major protective role against a radiation-induced intestinal inflammatory reaction.

Inflammatory response following acute magnesium deficiency in the rat

The importance of inflammatory processes in the pathology of Mg deficiency has been recently reconsidered but the sequence of events leading to the inflammatory response remains unclear. Thus, the purpose of the present study was to characterize more precisely the acute phase response following Mg deficiency in the rat. Weaning male Wistar rats were pair-fed either a Mg-deficient or a control diet for either 4 or 8 days. The characteristic allergy-like crisis of Mg-deficient rats was accompanied by a blood leukocyte response and changes in leukocytes subpopulations. A significant increase in interleukin-6 (IL-6) plasma level was observed in Mg-deficient rats compared to rats fed a control diet. The inflammatory process was accompanied by an increase in plasma levels of acute phase proteins. The concentrations of alpha2-macroglobulin and alpha1-acid glycoprotein in the plasma of Mg-deficient rats were higher than in control rats. This was accompanied in the liver by an increase in the level of mRNA coding for these proteins. Moreover, Mg-deficient rats showed a significant increase in plasma fibrinogen and a significant decrease in albumin concentrations. Macrophages found in greater number in the peritoneal cavity of Mg-deficient rats were activated endogenously and appeared to be primed for superoxide production following phorbol myristate acetate stimulation. A high plasma level of IL-6 could be detected as early as day 4 for the Mg-deficient diet. Substance P does not appear to be the initiator of inflammation since IL-6 increase was observed without plasma elevation of this neuropeptide. The fact that the inflammatory response was an early consequence of Mg deficiency suggests that reduced extracellular Mg might be responsible for the activated state of immune cells.

Long-term effects of X-irradiation on gastrointestinal function and regulatory peptides in monkeys

PURPOSE

To investigate the long-term effects of X-irradiation on different aspects of gastrointestinal function in the non-human primate (Macaca mulatta).

MATERIALS AND METHODS

Animals were exposed to X-radiation (5 or 6 Gy) or not (sham) and gastrointestinal function was investigated 4-6 years after exposure. Basal and agonist-stimulated short circuit current (Isc) responses were measured in isolated jejunum. Intestinal tissue was taken for histological analysis as well as for determination of mucosal marker enzyme activities and gastrointestinal regulatory peptide levels. Vasoactive intestinal peptide receptor characteristics were determined as well as VIP-stimulated Isc responses. GI peptides were also measured in plasma.

RESULTS

Few differences were seen in basal electrical parameters or tissue morphology but there was a tendency for reduced basolateral membrane enzyme activity. VIP-stimulated Isc responses were reduced in irradiated animals as were VIP-stimulated adenylate cyclase responses. Plasma and tissue (ileal and colonic muscle layers) gastrin releasing peptide levels were increased in irradiated animals. In contrast circulating gastrin levels were lower.

CONCLUSIONS

Late effects of total-body irradiation on GI function in monkeys showed altered circulating and tissue levels of some GI peptides. In addition the biological effects of vasoactive intestinal peptide were modified.

A substance P receptor antagonist (FK 888) modifies gut alterations induced by ionizing radiation

PURPOSE

We previously reported disturbances of ileal substance P (SP) levels and of characteristics of specific receptors after ionizing radiation associated with disorders of intestinal motility. The aim of this study was to investigate the effect of a SP receptor blockade by FK 888 on gut SP levels and contractile properties after rat irradiation.

MATERIALS AND METHODS

Rats were exposed to 6 Gy whole-body gamma-irradiation and injected 1 h post-irradiation with FK 888 for 3 days (0.1 mg/kg/day). Plasma and ileal SP concentrations, ileal muscle SP receptor binding and SP-induced contractions in isolated ileum were investigated 3 and 14 days post-irradiation and FK 888 treatment.

RESULTS

Irradiation induced an increase of total SP binding site number at day 3 (1.3-fold) and day 14 (1.6-fold). FK 888 had no effect on SP receptor characteristics in irradiated animals. In contrast, FK 888 treatment caused a reduction of endogenous ileal SP level in mucosal (-29%) and muscularis (-40%) layers at day 3 and these decreases were greater at day 14, -88% in mucosal and -61% in muscularis layers. FK 888 treatment decreased efficacy of ileal contraction in both the control and irradiated rat but surprisingly it increased potency at day 3 and decreased it at day 14 in the irradiated rat.

CONCLUSIONS

The findings demonstrate that a SP receptor antagonist could be effective on intestine contractility alteration induced several days after ionizing radiation exposure but not at 3 days after irradiation.

Exposure to ionizing radiation modifies circulating gastrin levels and gastrointestinal endocrine cell densities in the rat

PURPOSE

Gastrointestinal functions, controlled partly by gut peptides, are disturbed by ionizing radiation exposure. The effect of whole-body irradiation on circulating gastrin levels, densities of gastrointestinal endocrine cells and gastric acid secretion was investigated.

MATERIALS AND METHODS

Rats were exposed to 2 or 6 Gy gamma-radiation. They were killed 3 or 7 days later and compared with shams. Plasma gastrin and basal acid output were measured. Endocrine cells were identified by argyrophilia or immunohistochemistry and their densities estimated.

RESULTS

Radiation exposure significantly increased gastrinaemia and gastric acid output at the times studied (p<0.05-p<0.001). Endocrine cells displayed different sensitivities to irradiation. In the gastric mucosa, a 6 Gy dose induced a decrease in fundic argyrophil cell, antral gastrin and somatostatin cell densities, always accentuated 7 days after irradiation, while in the intestinal mucosa it induced an increase, with highest values often at 7 days post-irradiation (p<0.01-p<0.001). This was true for neurotensin cells in the jejunum and ileum, substance P cells in ileum and enteroglucagon cells in the descending colon.

CONCLUSIONS

Whole-body irradiation in rats significantly alters plasma gastrin levels, and several gut endocrine cell densities. This has repercussions on hormonal function, such as that exerted on acid secretion, and may explain gastrointestinal dysfunction observed following radiation exposure.

Changes in gut neurotensin and modified colonic motility following whole-body irradiation in rat

Exposure to ionizing radiation induces gastrointestinal dysfunction often associated with disorders of intestinal motility. Neurotensin is one of the mediators involved in the control of intestinal muscle activity. The aim of this study was to relate neurotensin tissue content and specific receptor binding with contractile effect of neurotensin in rat colon after irradiation. Rats were exposed to whole-body gamma-irradiation (60Co; 6 Gy). Intestinal (caecum, colon) neurotensin-like immunoreactivity, colonic muscle neurotensin receptor binding and neurotensin-induced contractions in isolated colon were investigated 3 and 7 days after irradiation. Irradiation produced a marked increase in the intestinal muscle content of neurotensin-like immunoreactivity (2.5-fold in caecum, 5-fold in colon) 3 days post-irradiation. At 7 days, the intestinal neurotensin content was close to that of the control values. Three days after irradiation, neurotensin receptors in colonic muscle were characterized by the appearance of a transient second class of sites of low affinity-high capacity. A three-fold increase in the total number of sites was observed. In addition, effects of neurotensin on isolated colon preparations showed an increase (37%) of potency but a decrease (7-fold) of efficacy. Seven days after irradiation, the efficacy was close to the control. Modifications of intestinal neurotensin content and specific receptor characteristics induced by irradiation can influence the colonic contractile activity.

Modulation of gut substance P after whole-body irradiation. A new pathological feature

Exposure to ionizing radiation induces gastrointestinal dysfunction and inflammatory reactions. The present study carried out in the rat, focuses on substance P, an inflammatory mediator implicated in the control of intestinal motility. We have investigated the effects of gamma irradiation on plasma and tissue substance P levels, ileal smooth muscle activity, and properties of specific receptors. Plasma and ileal (mucosa and muscle) substance P concentrations were measured by radioimmunoassay. At doses ranging from 1 to 8 Gy, plasma substance P levels increased in a dose-dependent manner up to four days after irradiation. Ileal mucosal concentration decreased rapidly 1 hr after a 6-Gy irradiation as compared to controls. A second class of binding sites appeared three days after 6 Gy irradiation. In addition, substance P contractile effects measured on isolated ileum showed a fourfold decrease of EC50, three days after 6 Gy irradiation. These results indicated that gamma irradiation induced an increase of plasma levels concomitant with a modification of gastro-intestinal substance P specific binding sites and contractile activity.

Bombesin activation of phospholipase C beta 1 in rat acinar pancreatic cells involves the pertussis toxin-sensitive G alpha i3 protein

Bombesin stimulation of inositol 1,4,5-trisphosphate (Ins P3) formation in rat sonicated pancreatic acinar cells was inhibited by an antibody directed against the pertussis toxin (PTX)-sensitive GTP-binding G alpha i3 protein but not by an anti-G alpha q-11 antibody. After solubilization and gel filtration, [125I-Tyr4]bombesin binding sites were recovered in a peak of protein of 67 approximately 90 kDa with a maximal enrichment corresponding to a molecular mass of 83-kDa. Results obtained from the non-hydrolysable GTP analog guanosine-5'-[gamma-thio]triphosphate (GTP gamma S) binding, PTX-stimulated ADP-ribosylation and immunoblotting showed that the 83-kDa fraction contained the G alpha i3 protein but not the G alpha q-11 protein. Furthermore, GTP gamma S increased the bombesin binding dissociation constant (KD) from 0.32 to 0.60 nM, while the anti-G alpha i3 antibody decreased the maximal binding capacity (Bmax) from 50 to 25 fmol/mg protein without affecting the KD. Mixing solubilized bombesin binding sites with a phospholipase C (PLC) preparation from rat pancreas reconstituted a bombesin-stimulated PLC activity which was markedly inhibited by the anti-G alpha i3 antibody but unaffected by the anti-G alpha q-11 antibody. In addition, this stimulation was inhibited by an anti-PLC beta 1 antibody. This result supports the involvement of the PLC beta 1 isoform in bombesin receptor activation.

Somatostatin inhibition of phosphoinositides turnover in isolated rat acinar pancreatic cells: interaction with bombesin

The effects of somatostatin-14 and bombesin on [3H]inositol phosphate accumulation were studied in 24 h myo-[3H]inositol-prelabeled cultured rat acinar cells. Bombesin, 10 nM, stimulated basal formation of phosphatidyl monophosphate (InsP1), phosphatidyl 4,5-biphosphate (InsP2) and inositol 1,4,5-triphosphate (InsP3) by 128 +/- 5.2%, 147 +/- 10% and 155 +/- 5%, respectively. At 5 s, the ED50 value for InsP3 stimulation was 0.70 +/- 0.2 nM. This stimulation was partly blocked (64 +/- 0.04% inhibition) by 10 ng/ml Bordetella pertussis toxin. In contrast to bombesin, somatostatin, 10 nM, inhibited basal InsP1, InsP2 and InsP3 formation. At 5 s, the inhibition degree for InsP3 was 18 +/- 2.5% and the IC50s values 1 +/- 0.09 nM, 1 +/- 0.12 nM and 0.07 +/- 0.005 nM for InsP1, InsP2 and InsP3, respectively. Bombesin-stimulated InsP3 formation was also inhibited by somatostatin. At 5 s, the inhibition degree was 85 +/- 3.5% at 10 nM and the IC50 value, 0.10 +/- 0.05 nM. Furthermore, somatostatin inhibition of bombesin stimulation was partly blocked (66 +/- 4% inhibition) by Bordetella pertussis toxin. These data therefore suggest that the acinar pancreatic cells contain a somatostatin receptor exerting a negative control on basal and bombesin receptor-stimulated phosphatidyl inositol turnover.

Solubilization and immunopurification of a somatostatin receptor from the human gastric tumoral cell line HGT-1

The human gastric tumoral cell line HGT-1 was previously shown to contain a membrane somatostatin receptor negatively coupled to adenylate cyclase through a pertussis toxin-sensitive inhibitory GTP-binding regulatory protein (Gi) (Reyl-Desmars, F., Laboisse, C., and Lewin, M. J. M. (1986) Regul. Pept. 16, 207-215). In this study, we have solubilized this receptor in a free unoccupied form using Triton X-100 as detergent and [125I-Tyr11]somatostatin-14 to monitor specific binding. Furthermore, we have prepared a monoclonal antibody against a chromatographically enriched soluble receptor fraction and used this antibody (30F3) to immunopurify the receptor in conjunction with Sepharose-somatostatin-14 immunopurification and steric exclusion high pressure liquid chromatography (HPLC). The purified fraction showed 18,600-fold enrichment in terms of specific binding (i.e. from 0.6 +/- 0.05 to 11,300 +/- 830 pmol/mg of protein) and a single dissociation constant (kappa D) of 76 +/- 8 nM. On HPLC, it migrated as a single and symmetric 90-kDa peak. Moreover, after 125I-protein labeling, it gave a single 90-kDa band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis autoradiography. On the other hand, the 30F3 monoclonal antibody immunoblotted with a single 90-kDa band contained in the HGT-1 cell membrane. We therefore suggest that this antibody is specific to the HGT-1 membrane somatostatin receptor, that this receptor has a molecular mass of 90 kDa, and that we have obtained a homogeneous preparation of nondenatured receptor suitable for further cloning studies.

Higher order structures of the 5'-proximal region decrease the efficiency of translation of the porcine pro-opiomelanocortin mRNA

The SP6 polymerase/promoter system was used to synthesize porcine pro-opiomelanocortin mRNAs with nucleotide sequence deletions in the 5'- as well as 3'-untranslated and coding regions. The translational efficiency of the mutant mRNAs was evaluated by cell-free translation or by monitoring the rate and extent of ribosome binding in the presence of sparsomycin. The results of these experiments indicate that specific nucleotide sequences in the 5'-untranslated and coding regions of the pro-opiomelanocortin mRNA decrease its rate of translation. Structure mapping of the mRNA with double-strand and single-strand specific nucleases suggests that these sequences can form stable secondary structures.