Clinical characterization of a family with a mutation in the uromodulin (Tamm-Horsfall glycoprotein) gene.

BACKGROUND: We have recently identified a mutation in the uromodulin gene in a large family affected with hyperuricemia, gout, and renal failure. The purpose of this investigation is to provide a comprehensive characterization of the clinical findings of this syndrome in family members who had a mutation in the uromodulin gene. METHODS: An extended family suffering from hyperuricemia and gout was identified by a local practitioner. After consent was obtained, patients provided a directed clinical history and blood and urine specimens for chemical and genetic testing. All family members were tested for the presence of uromodulin gene mutations by direct DNA sequence analysis. The clinical and biochemical characteristics of family members carrying the affected mutation were then investigated. RESULTS: Thirty-nine family members were found to have an exon 5 uromodulin gene mutation (g.1966 1922 del), and 29 unaffected family members were identified. The cardinal clinical features in individuals with the uromodulin mutation included hyperuricemia, decreased fractional excretion of uric acid, and chronic interstitial renal disease leading to end-stage renal disease (ESRD) in the fifth through seventh decade. Women did not always develop hyperuricemia or gout, but still developed progressive chronic renal failure. CONCLUSION: Mutation of the uromodulin gene resulted in hyperuricemia, reduced fractional excretion of uric acid, and renal failure. Genetic testing will be required to definitively identify individuals suffering from this condition. We are interested in studying other families that may suffer from this condition and would appreciate any such referrals.

Molecular and cellular regulation of neuropeptide expression: the bag cell model system.

The bag cell neuroendocrine system of Aplysia californica has been under intensive investigation for nearly two decades. The favorable morphology and hardiness in organ culture of this preparation have permitted a wide range of electrophysiological, cellular, and molecular studies. In this review we have focused our attention on the biochemical and physiological processes that serve the principle function of the bag cells: the synthesis and secretion of the neuropeptide egg-laying hormone. Although these cells were at first considered a model system for the most elementary neuroendocrine mechanisms, increasing knowledge has disclosed a surprising degree of complexity in both neuropeptide biosynthesis and the electrophysiological processes responsible for secretion. Not only may various components of the prohormone be sorted into different classes of neurosecretory granules, which may in turn have different probabilities of secretion, but biosynthesis itself appears to be regulated by the same intracellular messengers that mediate the electrophysiological discharge cycle. Hence, the bag cells, and presumably other peptidergic neurons, appear to possess an array of regulatory processes that can modulate the amount and character of their secretory output. The interactions of these processes may confer a degree of plasticity to the functional expression of peptidergic neurons unanticipated in studies of other neuron types.

Inverse diffusion methods for data peak separation.

Previous methods for separation of overlapping data peaks include geometrical assessment and Fourier deconvolution. On the basis of inverse diffusion theory, we present new separation methods suitable for convenient programming and rapid calculation of Gaussian area contributions. Both continuum and discrete inverse diffusion models are described. Example computations are given for biological data: density gradient centrifugation, isoelectric focusing electrophoresis, and high-pressure liquid chromatography.

Dissimilar associations of two secretory peptides with a neurosecretory granule-enriched fraction from the bag cells.

The bag cell neurons of Aplysia californica synthesize and secrete several neuropeptides. To gain more detailed information about their posttranslational routing and transport, we have undertaken isolation of the neurosecretory granules (NSG). Extracts of radiolabeled cells were subjected to discontinuous, isosmotic density-gradient centrifugation. Radiolabeled peptides likely to be contained in NSG were found to relocate from the starting zone and to be associated with particulate structures. Assay of enzyme markers for lysosomes and endoplasmic reticulum disclosed gradient distributions that differed from that shown by the peptides. Hence, it is probable that the position of peak concentrations of particulate peptides represents the location of NSG. Of particular interest is the further observation that the known secretory peptides ELH and AP do not evidence strict covariance across the gradient. This deviation from covariance is consistent with hypotheses that the peptides are in different associations with the NSG cores or that more than one type of neurosecretory granule is produced in the bag cells.

Neuropeptide routing in the bag cells: kinetic differences in the appearance of newly labeled peptides in transport and secretion.

The bag cell neurons of Aplysia synthesize and secrete several peptides. Some of these, in addition to the egg-laying hormone (ELH), are strongly implicated in the various alterations of central neuronal activity that accompany an electrical discharge of the bag cells. Thus, the secreted peptides appear to play a variety of roles in the animal's physiology. We have been interested in the intracellular mechanisms that precede peptide secretion from the bag cells because of the evidence that most, if not all, of these peptides are derived from a common precursor. Our objective has been to determine if presumed products of this precursor are processed coordinately following their synthesis. We have concentrated on two peptides (ELH and the acidic peptide, AP) because they are most easily identified in our analytical systems. On pulse-chase radiolabeling of the cells in vitro, we found that labeled AP appears before labeled ELH in axonal transport. This observation is not easily accounted for by the assumption, taken from studies of other peptide-secreting cells, that a precursor to both peptides is loaded into secretory granules before further processing ensues. Since the initial disproportion in the representation of the peptides in transport is no longer detectable at long chase times (18 and 24 hr), we examined the possibilities that ELH production is delayed relative to that of AP or that AP is degraded more rapidly than ELH. No evidence was found for either process. The disproportion between the newly labeled peptides in transport was evident on analysis of the medium bathing bag cells depolarized after 24 hr of chase.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructure of secretion in the atrial gland of a mollusc (Aplysia).

Extracts of the atrial gland of the sea hare Aplysia californica (Mollusca) induce egg laying when injected into mature individuals. Since egg laying is controlled endogenously by a peptide secreted by neuroendocrine cells in the central nervous system, the relationship between the atrial gland and these central neurons has become an issue of interest. With the particular objective of examining secretory structures we undertook an ultrastructural study of the atrial gland and adjacent tissues. This study revealed that the atrial gland epithelium in composed of two major cell types: 'goblet-like' exocrine cells containing large electron-dense granules, and ciliated 'capping cells'. A non-secretory, and possibly post-secretory, cell containing electron-lucent granules was noted. A region of the large hermaphroditic duct contiguous ot the atrial gland, known as the red hemiduct, also displayed capping cells and secretory cells with large granules. The content of these granules is organized into crista-like condensations. The cell also contains iron-rich pigment inclusions.

Activation of neurosecretory cells enhances their synthesis of secretory protein.

We have asked whether neurosecretory cells respond to activation by selectively augmenting their synthesis of secretory protein, using the bag cells of Aplysia, which produce and secrete a peptide egg-laying hormone, ELH. Exposure of bag cell organs to 100 mM K+ for 4 h increased their incorporation of tritiated leucine into ELH precursors by about 25%, an effect which persisted for at least 8 h after the stimulus. Since the high potassium treatment had no effect on the rate of loss of label from previously-synthesized ELH proteins, we conclude that the enhanced labeling represents enhanced synthesis. Elevated external potassium did not enhance ELH synthesis in clusters of bag cell somata which had been surgically isolated from their neurites, suggesting that the augmentation of synthesis is not mediated by direct effects of the high potassium solution. Mediation by a secretion-linked process is indicated by the fact that low Ca2+/high Mg2+ media blocked the effect of high K+. Whether the regulatory signal involves receipt of presynaptic transmitter or hormone secretion remains to be determined.

Evidence for mediation of a neuronal interaction by a behaviorally active peptide.

Egg laying hormone, a peptide neurohormone with an approximate molecular weight of 6000, was isolated from the region of the abdominal ganglion of Aplysia that contains the neuroendocrine bag cells and purified by gel filtration chromatography, isoelectric focusing, and dialysis. A 1-min local application of egg laying hormone to the identified neuron R15 produced prolonged (greater than 1 hr) augmentation of impulse activity in this neuron. The distinctive quality and prolonged duration of the response are apparently identical to the previously described response to electrically elicited bag cell activity. The results provide evidence that egg laying hormone is the mediator of this prolonged neuronal interaction.

A cytochemical study of the bag cell organs of Aplysia californica.

Egg-laying hormone in Aplysia californica is synthesized and secreted by cells that seem to be homogeneous ultrastructurally and electrophysiologically. Several conventional methods have been used to demonstrate histochemical homogeneity and special staining techniques based on the known properties of the hormone show the neuroendocrine organ to be uniform in appearance. Furthermore, since stain specificity for egg-laying hormone is demonstrable using release and biochemical studies, the authors concluded that the organ consists of a population of biochemically homogeneous neurons.

Biochemical isolation and physiological identification of the egg-laying hormone in Aplysia californica.

It has been determined that the bag cells of Aplysia californica produce two polypeptide species that comigrate on electrophoretic gels containing sodium dodecyl sulfate. By this separation procedure both species can be assigned a molecular weight of approximately 6,000. One of these molecules has an Rf of 0.65 on alkaline discontinuous electrophoresis gels, an isoelectric point at pH 4.8, a gel filtration molecular weight of approximately 12,000, and has no known biological function. The other does not enter alkaline disk gels, has an isoelectric point at approximately pH 9.3, shows a gel filtration molecular weight consistent with that determined by SDS gel electrophoresis, and is the egg-laying hormone.

Precursor and product processing in the bag cell neurons of Aplysia californica.

Posttranslational processing in the biosynthesis of the egg-laying hormone (ELH) by the bag cell neurons of Aplysia californica was studied. The precursor (pro-ELH) to ELH was found to be resistant to solubilization in denaturant-free media throughout its lifetime. Its principle products show a similar insolubility for 3 h, but two of these, ca. 6,000 daltons, subsequently become readily recoverable in the low-speed supernatant of a homogenate of the cells. The remaining product shows no change in solubility characteristics. From studies employing ultracentrifugation and examination of axoplasmic transport, the solubility shift for the lower molecular weight products is interpreted to represent the liberation of secretory vesicles into the cytoplasm from larger membranous associations. This event is accompanied by, but does appear to be dependent upon, a 15% reduction in the molecular weight of one of the products. These findings are considered in the light of the extensively studied posttranslational processing regimen for the production of insulin in the pancreatic beta cell.

Polypeptide secretion from the eye of Aplysia californica.

The possibility of neurosecretory activity by the eye of Aplysia californica has been suggested by morphological findings. An investigation was conducted to determine if evidence for the release of macromolecular material labeled with radioactive amino acids could be obtained. Depolarization of the eye by superfusion with medium containing an elevated potassium concentration resulted in a significant increase of labeled macromolecular material in the superfusate. This potassium-induced release could be blocked by reduction of the calcium concentration in the superfusing medium. The locus of release appears to be the eye proper and not to involve the optic nerve.

Biosynthesis of the egg-laying hormone (ELH) in the bag cell neurons of Aplysia californica.

Biosynthesis of the egg-laying hormone in the bag cell neurons of Aplysia californica was studied. Bag cells were incubated with leucine-(3)H in vitro for 30 min and rinsed for variable periods of time in a chase medium. The distribution of incorporated label among proteins within the cells was assayed by electrophoresis of an homogenate on sodium dodecyl sulfate polyacrylamide gels. Results from rinse times shorter than 30 min revealed that the predominant synthetic product is a 25,000 dalton protein. With longer rinse times, this species was reduced and two species of lower molecular weight became prominent. This redistribution of radioactivity was quantitative and was not prevented by inhibition of protein synthesis during the rinse. A 10 degrees C reduction in temperature (from 15 degrees C) blocked the redistribution. These data are interpreted to indicate that the 25,000 dalton molecule is a precursor which is cleaved enzymatically to yield two lower molecular weight products. One product is a 12,000 dalton molecule which remains in the cell bodies. The other is a molecule of <10,000 daltons which is exported from the somata into the neurohemal regions of the connective tissue. Perfusion of these regions with high [K(+)] medium results in the release of this product into the medium. It is concluded that this product is the 6000 dalton egg-laying hormone (ELH).

Polypeptide secretion from the isolated parietovisceral ganglion of Aplysia californica.

In vitro studies of the secretory behavior of the parietovisceral ganglion in Aplysia californica were performed. The aim of these studies was to investigate the release of polypeptides in response to depolarizing stimuli, and, in particular, to determine if a specific polypeptide known to induce egg laying in the intact animal is secreted into the bathing medium. During continuous perfusion of a ganglion preincubated in leucine-(3)H the application of either high-potassium medium or a burst of electrical stimuli (via the pleurovisceral connective nerve) evoked a marked increase in the amount of trichloroacetic acid (TCA)-precipitable radioactivity recovered in the perfusate. Enhanced release could be detected within 80 sec of the initial exposure to high potassium; however, incubation of a ganglion in calcium-free media before the application of high-potassium medium abolished the increase of precipitable radioactivity. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of perfusate samples revealed a significant change in the polypeptide species washed from the ganglion during high-potassium depolarization. Bioassays confirmed that egg laying is induced when high-potassium medium used to bathe a ganglion is injected into a recipient animal. These and other results permit the conclusion that the bulk of the polypeptide material secreted from the ganglion in response to depolarization is a specific neurohormone produced by two identified cell clusters, the so-called bag cells.