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M W Miller

Publications and source records attributed to M W Miller.

At least 163 records · Page 9Linked to original sources
PubMed1994

Pleiotropic effects of the mouse lethal yellow (Ay) mutation explained by deletion of a maternally expressed gene and the simultaneous production of agouti fusion RNAs.

Heterozygosity for the mouse lethal yellow (Ay) mutation leads to obesity, increased tumor susceptibility and increased activity of the agouti coat color gene; homozygosity for Ay results in embryonic death around the time of implantation. Although these pleiotropic effects have not been separated by recombination, previous studies have suggested that the dominant and recessive effects result from distinct genetic lesions. Here we use a combination of genomic and cDNA cloning experiments to demonstrate that the Ay mutation is caused by a 120 kb deletion which lies centromere-proximal to the agouti coat color gene. The deletion removes coding but not 5' untranslated sequences for a ubiquitously expressed gene predicted to encode a protein similar in sequence to an RNA-binding protein, which we named Merc, for maternally expressed hnRNP C-related gene, but have renamed Raly, since the gene is nearly identical to one reported recently by Michaud et al. (Gene Dev. 7, 1203-1213, 1993). The Ay deletion results in the splicing of Merc/Raly 5' untranslated sequences to agouti protein-coding sequences, which suggests that ectopic expression of the normal agouti protein by the Ay fusion RNA is responsible for the pleiotropic effects associated with heterozygosity for Ay. We find that Merc/Raly RNA is present in the unfertilized egg and is also transcribed in preimplantation embryos. Using a PCR-based assay to determine the genotype of individual embryos from an Ay/a x Ay/a intercross, we show that, in the absence of zygotic Merc/Raly expression, Ay/Ay embryos develop to the blastocyst stage, but do not hatch from the zona pellucida or form trophoblastic outgrowths. Injection of a Merc/Raly antisense oligonucleotide into non-mutant embryos blocks development prior to the blastocyst stage, and can be rescued by coinjection of a Merc/Raly transgene. These results suggest that maternal expression of Merc/Raly plays an important role in preimplantation development and that its deletion of is sufficient to explain Ay-associated embryonic lethality.

Agouti Signaling Protein↗
PubMed1994

Effects of modified Cary and Blair medium on recovery of nonhemolytic Pasteurella haemolytica from Rocky Mountain bighorn sheep (Ovis canadensis canadensis) pharyngeal swabs.

Modified Cary and Blair transport medium (MCB) was evaluated for recovery of Pasteurella spp. from pharyngeal swabs of healthy Rocky Mountain bighorn sheep (Ovis canadensis canadensis). In experiment one, three pharyngeal swabs were collected from each of 25 bighorns. Pasteurella haemolytica was recovered from 21 of 25 swabs tested almost immediately and from 16 of 25 swabs held in MCB medium at about 22 C for 24 hr before testing (P > 0.10). Recovery of P. haemolytica decreased (P < 0.005) to 1 of 25 when swabs were held in MCB medium at about 22 C for 48 hr before testing. In experiment two, four pharyngeal swabs were collected from each of ten bighorns and held in MCB medium at about 5 C for < or = 5, 24, 48, or 72 hr prior to testing. Recovery was unaffected by storage at 5 C; P. haemolytica was isolated from all 40 of these samples. All Pasteurella spp. isolates were nonhemolytic P. haemolytica. In experiment one, most isolates were serotype 4; in experiment two, serotype 3 was most common. We propose that MCB medium is effective for transporting bighorn sheep pharyngeal swabs for P. haemolytica screening because it imposes minimal or no effect on recovery when held < or = 24 hr at 22 C or < or = 72 hr at 5 C.

Animals↗
PubMed1994

A population of SCP-containing neurons in the buccal ganglion of Aplysia are radula mechanoafferents and receive excitation of central origin.

The rostral cluster of SCP-immunoreactive cells, originally identified in each buccal hemiganglion of juvenile Aplysia, was examined in mature specimens. Immunohistochemical and dye-fill experiments showed that each rostral cluster consists of approximately 40 cells. Although these neurons exhibit heterogeneity of size and shape, all cells project an axon into the radula nerve. Tracing of dye-filled cells showed that they project to the layer of tissue that lines the inner surface of the food-grasping portion of the chitinous radula. This tissue contains SCP-immunoreactive nerve fibers and varicosities in regions corresponding to the projections of dye-filled neurons. Several observations indicate that rostral cluster neurons transduce tactile stimuli applied to the radula surface: (1) each cell responds to touch of a circumscribed receptive field with a rapidly adapting burst of action potentials, (2) the evoked spikes arise abruptly from the resting potential without prepotentials, and (3) the responses persist when central and peripheral synaptic transmission is blocked in high Mg2+, low Ca2+ artificial seawater solutions. These cells, designated radula mechanoafferent (RM) neurons, do not respond to chemical stimuli including NaCl, glutamate, and seaweed extract. The highest density of receptive fields is found on the posterodorsal edges of the radula halves, areas most directly involved in grasping food. The RM neurons are electrically coupled cells, with coupling coefficients ranging from 0.006 to 0.22. They fire phasically during buccal motor programs, even in the absence of peripheral feedback from the radula or other portions of the buccal mass. In radiolabeling studies the RM cells were found to synthesize authentic SCPA and SCPB. Sensorin-A, a peptide that is localized to other Aplysia mechanoafferent neurons, was not detected immunohistochemically in these cells.

Animals↗
PubMed1993

Prenatal exposure to ethanol alters the postnatal development and transformation of radial glia to astrocytes in the cortex.

Postmitotic neurons migrate from a zone(s) near the ventricles to the neocortex. During this migration, neurons associate with radial glia. After serving their role as guides for neuronal migration, the radial glia transform into astrocytes. Prenatal exposure to ethanol causes abnormal neuronal migration. We examined the effects of gestational exposure to ethanol on radial glia and astrocytes. Radial glia were stained immunohistochemically with the antibody RAT-401, and astrocytes were labeled with an antibody directed against glial fibrillary acidic protein (GFAP). The subjects were the offspring of rats fed an ethanol-containing liquid diet (Et), pair-fed a liquid control diet (Ct), or fed chow and water (Ch). During the first postnatal week, radial glial fibers (in Et-treated rats and controls) stretched from the ventricular surface through the developing cerebral wall to the pial surface. In the Et-treated rats, the radial processes were less dense and more poorly fasciculated than they were in the Ch- and Ct-treated rats. Moreover, by postnatal day (P) 5, there was a significant reduction in RAT-401 immunostaining in the Et-treated rats, particularly in the superficial cortex. A similar reduction in control rats did not begin until P10. In all three treatment groups, GFAP-immunoreactive astrocytes were in the cortex throughout the period from P1 to P45. In neonates, GFAP-positive cells were distributed in the marginal zone (layer I) and the intermediate zone (the white matter). The number of GFAP-positive cells in the cortical plate increased steadily with time so that, by P26, GFAP-immunoreactive astrocytes were distributed evenly through all cortical laminae. Interestingly, between P5 and P12, the number of astrocytes was significantly greater in Et-treated rats than in controls. Thus prenatal exposure to ethanol induces the premature loss of RAT-401-positive processes and the precocious increase in GFAP immunostaining. These ethanol-induced changes in glial development indicate that ethanol accelerates the transformation of radial glia into astrocytes. Moreover, the ethanol-induced premature degradation of the network of radial glial fibers may underlie the migration of late-generated neurons to ectopic sites.

Animals↗
PubMed1993

Effects of chronic ethanol administration on acetylcholinesterase activity in the somatosensory cortex and basal forebrain of the rat.

A chronic diet of ethanol has detrimental effects on the cholinergic system in adult humans and rats. This study examined the effects of chronic exposure to dietary ethanol on the anatomical organization of true acetylcholinesterase (AChE) active elements in rat cerebral cortex. We focused on the somatosensory cortex because of its highly organized chemical and cellular structure. Following 42 days of exposure to an ethanol diet (6.7% v/v), there were marked changes in the cortical plexus of AChE-positive fibers. The AChE-positive plexus in ethanol-treated rats was reduced in all cortical layers, in comparison to age-matched pair-fed control and chow-fed rats. The most marked reduction was evident in layers II/III, IV, and VIa. Moreover, the density of AChE-positive cell bodies was significantly reduced in the cortices of ethanol-fed rats, particularly in the deep laminae. These alterations in the chemoarchitecture of somatosensory cortex occurred in the absence of changes in the cytoarchitectonic organization of neocortex. There was no detectable ethanol-induced change in the density of Cresyl violet-stained neurons either in the horizontal limb of the diagonal band of Broca or in the nucleus basalis. The density of AChE-positive neurons in the nucleus basalis, however, was significantly lower in ethanol-fed rats than in controls. Thus, it appears that a mere 6 weeks of ethanol exposure is sufficient to alter the cholinergic innervation of the cerebral cortex. These cortical alterations occur despite the lack of an ethanol-induced death of neurons in the basal forebrain. Such changes may contribute to the memory loss associated with alcohol dementia.

Acetylcholinesterase↗
PubMed1993

Vibrissal stimulation affects glucose utilization in the trigeminal/somatosensory system of normal rats and rats prenatally exposed to ethanol.

The effect of gestational ethanol exposure on stimulus-induced sensory activity in the trigeminal/somatosensory system was determined. The mature offspring of mothers fed an ethanol-containing diet (Et) or pair-fed a nutritionally matched control diet (Ct) were examined. The C-row mystacial whiskers were stimulated. Glucose utilization in the principal sensory nucleus of the trigeminal nerve (PSN), ventrobasal thalamus, and somatosensory cortex was determined with [14C]2-deoxyglucose autoradiography. In Ct- and Et-treated rats, whisker stimulation increased glucose utilization in C-row barrel(oid)s in the left PSN, the right ventrobasal thalamus, and the right somatosensory cortex. The rate of glucose utilization in the C-row barrel(oid)s and in nonstimulated regions was lower in the Et-treated rats than in controls. In the cortices of Ct-treated rats, the activity in the C-row barrels on the right side was greater than in the right nonbarrel somatosensory cortex. Et-treated rats also exhibited an increase in glucose utilization, albeit smaller than that in the Ct-treated rats. In contrast, the glucose utilization in the left B- and C-row barrels of Ct-treated rats was decreased. No such decrease was evident in the left cortices of Et-treated rats. Thus, stroking whiskers stimulates the activity of sites in the trigeminal/somatosensory system. In cortex, the definition of these sites is emphasized by depressed activity, i.e., "surround" inhibition, in sites connected via callosal or corticocortical projections. Prenatal exposure to ethanol depresses the metabolic activity regardless of the physiological state; however, the "surround" inhibition of cortical activity is eliminated by prenatal exposure to ethanol through an exuberant projection.

Animals↗
PubMed1993

Left aortic arch and right ligamentum arteriosum causing esophageal obstruction in a dog.

A 10-week-old, mixed-breed dog was examined because of persistent regurgitation. Results of thoracic radiography and fluoroscopy of the esophagus, using a liquid suspension of barium sulfate, were suggestive of a vascular ring anomaly. During left lateral thoracotomy, a left aortic arch was identified, but the cause of the esophageal obstruction could not be determined. Results of endoscopic examination of the esophagus suggested a compressive lesion originating from the right side of the esophagus. An anomalous artery could not be identified on an aortogram. Post-mortem examination revealed a left aortic arch and right ligamentum arteriosum that were causing the esophageal obstruction.

Animals↗
PubMed1993

Orderly migration of neurons to the principal sensory nucleus of the trigeminal nerve of the rat.

As nuclei in the central nervous system develop, neurons actively migrate from their site of generation to their permanent residence. This study examines the spatiotemporal sequence of the migration of neurons to the principal sensory nucleus of the trigeminal nerve (PSN) of the rat. Tritiated thymidine autoradiography and bromodeoxyuridine immunohistochemistry were used to examine the spatiotemporal patterns of migration of PSN neurons born on gestational day (G) 12 (early-generated neurons) and of those born on G14 (late-generated neurons). The final residence of early- and late-generated neurons was determined by injecting a thymidine analog into a pregnant rat on G12 or G14 and sacrificing the pups on postnatal day (P) 30. Early- and late-generated neurons were distributed medially and laterally, respectively. The schedule of the migration of PSN neurons was also determined. A few pioneer neurons born on G12 reached the PSN by G14; however, the last of the neurons born on G12 arrived in the PSN by G18. The migration of neurons born on G14 was completed 2-6 days later than that of the early-generated neurons. The path followed by migrating neurons was delineated by radial glial fibers. These processes were identified in the developing metencephalon by RAT-401 immunohistochemistry. Radial glial fibers extended from the lateral part of the ventricular zone through the tegmentum and the PSN to the surface of the metencephalon external to the sensory tract of the trigeminal nerve. RAT-401-immunoreactive processes were detected during the period of neuronal migration, but disappeared by P5. Thus, the migration of PSN neurons follows an inside-to-outside sequence, which apparently is organized by radial glial fibers. The inside-to-outside sequence of neuronal migration directly opposes the outside-to-inside gradient of synaptogenesis.

Animals↗
PubMed1993

Development of the principal sensory nucleus of the trigeminal nerve of the rat and evidence for a transient synaptic field in the trigeminal sensory tract.

The early development of the principal sensory nucleus of the trigeminal nerve (PSN) was examined to determine whether spatiotemporal patterns of synaptogenesis coincide with patterns in neuronal generation, migration, and death. The morphogenesis of PSN neurons during the period from G16 to P14 was studied with a Golgi method. Prenatally, PSN neurons had dendrites that extended into the sensory tract of the trigeminal nerve (s5), and from as early as G18, these dendrites were studded with spines. The dendrites in the s5 degenerated or regressed in the early postnatal period so that the s5 was free of dendrites by P14. The development of anti-synapsin I immunoreactivity was traced from G14 to P10. Immunoreactive puncta (synaptic boutons) appeared in the medial third of the s5 transiently between G18 and P5. On the other hand, puncta in the PSN did not appear until G20, at which time they were confined to the lateral margin of the PSN. By P0, puncta were distributed throughout the PSN. Cytochrome oxidase activity in the PSN was low and unpatterned prenatally. Postnatally, cytochrome oxidase activity intensified and a segmented pattern of barreloids appeared in the ventral PSN on the day of birth. By P5, the complete pattern of barreloids, spanning the full width of the ventral PSN, was evident. The development of cytochrome oxidase activity in the PSN followed the lateral-to-medial gradient of synaptogenesis revealed by the development of synapsin 1 immunoreactivity. This gradient is opposite of that for neuronal generation, migration, and death. Moreover, the s5 serves as a transient synaptic field.

Afferent Pathways↗
PubMed1993

Numbers of neurons in the developing principal sensory nucleus of the trigeminal nerve: enhanced survival of early-generated neurons over late-generated neurons.

The overproduction and subsequent death of neurons is a common phenomenon in the developing vertebrate central nervous system (CNS). We tested the hypothesis that the survival of a neuronal subpopulation is related to its time of origin. Neuronal survival was examined in a well-defined CNS structure, the principal sensory nucleus of the trigeminal nerve (PSN) of the rat. The changes in the total number of PSN neurons and in the numbers of early- and late-generated neurons (i.e., neurons heavily labeled by a single injection of [3H] thymidine on G12 or G14, respectively), between gestational day (G) 16 and postnatal day (P) 10 were determined. The total number of neurons in the PSN rose prenatally to a maximum of 40,600 on G18.5. The increase in neuronal number correlates to the period of migration. More than half of the neurons that successfully migrated to the PSN were lost by P10. The patterns for the changes in the numbers of early- and late-generated neurons were similar; however, there were significant differences between the two subpopulations. The maximum number of early-generated neurons (4,250) was attained on G18.2 and subsequently 58.9% of these neurons were lost. In contrast, the maximum number of late-generated neurons (5,050) was attained on G20.0 and 66.6% of these neurons were lost by P10. Therefore, it appears that the survivability of early generated neurons is greater than for late-generated neurons. This enhanced survivability presumably results from a competitive advantage that early-generated neurons have for forming synapses or gaining access to trophic factor(s) that are in limited supply.

Animals↗
PubMed1993

On the mechanism of a 60-Hz electric field induced growth reduction of mammalian cells in vitro.

Data on 60-Hz electric field (EF) induced reduction in growth rate of plant roots have strongly supported the hypothesis that the effect is related to an EF-induced transmembrane potential (Vim). An investigation was undertaken to determine if this hypothesis is also applicable to 60-Hz EF-induced reductions in growth rate of mammalian cells in vitro. Human lymphoblastic (RPMI 1788) and human carcinoma (HeLa) cells were selected for study, the former having a relatively small diameter (11.2 microns), and the latter having a relatively large diameter (15.4 microns). The 60-Hz EFs ranged from 430-1200 V/m in the culture medium. The growth rate of RPMI 1788 cells after 4-days was depressed by about 42% at a 60-Hz EF of 1000-1200 V/m with a response threshold occurring at 950 V/m; the Vim at the response threshold was 8 mV. There was no 60-Hz EF-induced effect on HeLa cell growth rate of a Vim of 8 mV (60-Hz EF = 700 V/m); a statistically significant effect was achieved at Vim of 11 mV (950 V/m). The data support the hypothesis that above a threshold 60-Hz EF, Vim acts as the initial signal leading to growth rate reductions.

Cell Division↗
PubMed1993

Cell density dependence of the ultrasonic degassing of fixed erythrocyte suspensions.

Ultrasonic cell lysis in vitro shows a strong dependence on the cell density of the suspensions. The major determinant in this phenomenon appears to be the suspended particle density per se. Reported are the results of experiments designed to test the hypothesis that the majority of the cell density effect arises as a consequence of the cell density-dependent formation of cellular aggregates around oscillating bubbles in an ultrasound field (Nyborg and Miller 1982), which in turn diminishes the potential for the occurrence and sustenance of destructive cavitational events in the bulk suspension fluid. The hypothesis was tested indirectly using manometric methods to measure ultrasound-induced release of dissolved gas from saline solutions and fixed erythrocyte suspensions. Ultrasonic degassing of the fluids in excess of that attributable to thermal effects was observed, and was suppressed by the presence of fixed erythrocytes when the cell density was greater than 5 x 10(6) cells/mL. At higher cell densities, the inhibition of ultrasonic degassing by fixed cells increased monotonically with increasing cell density, attaining complete suppression at a cell density of 5 x 10(8) cells/mL. The data thus support the hypothesis.

Blood Cell Count↗
PubMed1993

Cloning of the mouse agouti gene predicts a secreted protein ubiquitously expressed in mice carrying the lethal yellow mutation.

The mouse agouti gene controls the deposition of yellow and black pigment in developing hairs. Several dominant alleles, including lethal yellow (Ay), result in the exclusive production of yellow pigment and have pleiotropic effects that include obesity and increased tumor susceptibility. In an interspecific backcross, we established genetic limits for the agouti gene and found that the Ay and the lethal non-agouti (ax) allele were not separated from a previously identified probe at the breakpoint of the Is1GsO chromosomal rearrangement. Using the Is1GsO probe, we isolated the agouti gene, and find that it has the potential to code for a secreted protein expressed in hair follicles and the epidermis, and that the level of expression correlates with the synthesis of yellow pigment. In the Ay mutation, there is a chromosomal rearrangement that results in the production of a chimeric RNA expressed in nearly every tissue of the body. The 5' portion of this chimeric RNA contains highly expressed novel 5' sequences, but the 3' portion retains the protein-coding potential of the nonmutant allele. We speculate that dominant pleiotropic effects of Ay are caused by ectopic activation of a signaling pathway similar to that used during normal hair growth.

Agouti Signaling Protein↗
PubMed1993

Migration of cortical neurons is altered by gestational exposure to ethanol.

Rats prenatally exposed to ethanol exhibit a variety of structural anomalies in the central nervous system. One of the key features of experimental fetal alcohol syndrome is microencephaly. Cerebral cortex is particularly susceptible to the effects of prenatal exposure to ethanol. Its total mass is reduced, it is thinner, and it contains fewer neurons and glia. Various studies in rats and humans suggest that chronic early exposure to ethanol leads to a massive reorganization of cortex characterized by heterotopic clusters of neurons. A pulse and chase study with [3H]thymidine autoradiography was used to determine if gestational exposure to ethanol leads to defects in neuronal migration. Rats were fed an ethanol-containing diet between gestational day (G) 6 and G21, pair-fed a liquid control diet, or fed chow. Ethanol delayed the migration of early-generated neurons (those born on G13) to deep cortex by 2 days. Moreover, the migration of late-generated neurons (those born on G21) was delayed 4 to 6 days by ethanol, and often these neurons terminated their migration in ectopic locations. Ethanol significantly decreased the rate of migration and the time postmitotic cells remained in the proliferative zones. On the other hand, ethanol did not have a significant effect on the rate of cortical expansion and the fraction of cells that left the proliferating population in order to migrate to cortex. Thus, the migration of young neurons was profoundly altered by prenatal exposure to ethanol. Such delays may lead to a desynchronization of cortical development that makes it impossible for cortical neurons to establish a normal circuitry.

Animals↗