Biomedical subjects

W G Tourtellotte

Publications and source records attributed to W G Tourtellotte.

15 recordsLinked to original sources

PubMed2001

The transcription factor Egr3 modulates sensory axon-myotube interactions during muscle spindle morphogenesis.

The Egr family of zinc-finger transcription factors, consisting of Egr1, Egr2, Egr3, and Egr4, are involved in cellular growth and differentiation. Adult Egr3-deficient mice are ataxic and lack muscle spindle proprioceptors that normally develop at the sites of Ia afferent-myotube contacts during embryogenesis. To resolve whether spindles form and then degenerate, or whether they never form in the absence of Egr3, we examined the spatiotemporal expression of Egr3 relative to spindle development. In wild type mice, Egr3 was expressed in developing myotubes shortly after they were innervated by Ia afferents and its expression was controlled by innervation because it dissipated following nerve transection. In Egr3-deficient mice, myotubes received Ia afferent innervation and assembled normally into spindles during embryogenesis. However, newborn Egr3-deficient spindles had few internal myonuclei in intrafusal fibers and thin capsules. Moreover, slow-developmental myosin heavy chain was not induced in embryonic Egr3-deficient spindles suggesting that impairments in differentiation were present before they could be detected morphologically. After birth, sensory and motor innervation withdrew from the Egr3-deficient spindles, and the spindles disassembled. In spite of the spindle disassembly and retraction of afferents from muscles, the cell bodies of proprioceptive neurons within dorsal root ganglia were retained. We conclude that Egr3 has an essential role in regulating genes required for the transformation of undifferentiated myotubes into intrafusal fibers, and hence for the phenotypic differentiation of spindles.

Afferent Pathways↗

PubMed2001

Primary myopathy and accumulation of PrPSc-like molecules in peripheral tissues of transgenic mice expressing a prion protein insertional mutation.

A nine-octapeptide insertional mutation in the prion protein (PrP) gene is associated with an inherited variant of Creutzfeldt-Jakob disease in humans. Transgenic mice that express the mouse PrP homologue of this mutation (designated PG14) under control of a PrP promoter display a progressive neurological disorder characterized by ataxia, apoptosis of cerebellar granule cells, and accumulation in the brain of mutant PrP molecules that display the biochemical hallmarks of PrP(Sc), the pathogenic isoform of PrP. In this report, we have investigated the expression of PG14 PrP in the peripheral tissues of these mice. We found highest levels of mutant PrP in the brain and spinal cord, intermediate levels in skeletal muscle, heart, and testis and low levels in kidney, lung, spleen, intestine, and stomach. Up to 70% of the PG14 PrP expressed in peripheral tissues was detergent-insoluble, and digestion with low concentrations of proteinase K yielded a PrP 27-30 fragment. These results suggest that the mutant protein was converted to a physical state reminiscent of PrP(Sc), although its infectivity remains to be determined. Histological analysis of skeletal muscle, one of the peripheral tissues with the highest level of PG14 PrP, revealed features indicative of a progressive, primary myopathy, including central nuclei, necrotic and regenerating fibers, and variable fiber size. These results indicate that the PG14 mutation structurally alters the protein in a way that promotes conversion to a PrP(Sc)-like state, regardless of the tissue context, and suggest that accumulation of PrP(Sc) can have deleterious effects on skeletal muscle cells as well as on neurons.

Aging↗

PubMed2000

Functional compensation by Egr4 in Egr1-dependent luteinizing hormone regulation and Leydig cell steroidogenesis.

The Egr family of zinc finger transcription factors, whose members are encoded by Egr1 (NGFI-A), Egr2 (Krox20), Egr3, and Egr4 (NGFI-C) regulate critical genetic programs involved in cellular growth, differentiation, and function. Egr1 regulates luteinizing hormone beta subunit (LHbeta) gene expression in the pituitary gland. Due to decreased levels of LHbeta, female Egr1-deficient mice are anovulatory, have low levels of progesterone, and are infertile. By contrast, male mutant mice show no identifiable defects in spermatogenesis, testosterone synthesis, or fertility. Here, we have shown that serum LH levels in male Egr1-deficient mice are adequate for maintenance of Leydig cell steroidogenesis and fertility because of partial functional redundancy with the closely related transcription factor Egr4. Egr4-Egr1 double mutant male mice had low steady-state levels of serum LH, physiologically low serum levels of testosterone, and atrophy of androgen-dependent organs that were not present in either Egr1- or Egr4-deficient males. In double mutant male mice, atrophic androgen-dependent organs and Leydig cell steroidogenesis were fully restored by administration of exogenous testosterone or human chorionic gonadotropin (an LH receptor agonist), respectively. Moreover, a normal distribution of gonadotropin-releasing hormone-containing neurons and normal innervation of the median eminence in the hypothalamus, as well as decreased levels of LH gene expression in Egr4-Egr1-relative to Egr1-deficient male mice, indicates a defect of LH regulation in pituitary gonadotropes. These results elucidate a novel level of redundancy between Egr4 and Egr1 in regulating LH production in male mice.

Animals↗

PubMed2000

The alpha4 isoform of the Na,K-ATPase is expressed in the germ cells of the testes.

In addition to the three isoforms of the catalytic subunit of the Na, K-ATPase originally identified (alpha1, alpha2, and alpha3), a fourth alpha polypeptide (alpha4) has recently been found in mammalian cells. This novel alpha-subunit of the Na,K-ATPase is selectively expressed in male gonadal tissues. In the testes, alpha4 is functionally active and comprises approximately half of the Na, K-ATPase activity of the organ. At present, the pattern of expression of the alpha4 polypeptide within the cells of the male gonad is unknown. By in situ hybridization, immunocytochemistry, and the ouabain inhibition profile of Na,K-ATPase activity, we show that the alpha4-subunit is expressed in the germ cells of rat testes. The highest amounts of the isoform are found in spermatozoa, where it constitutes two thirds of the Na,K-ATPase activity of the gametes. The other Na pump present in the cells is the ubiquitously expressed alpha1 polypeptide. The characteristic localization of alpha4 in the gonad is further supported by the drastic reduction of the polypeptide in mice that are infertile as a consequence of arrest in maturation of the germ cells. In addition, GC-1spg cells, a murine cell line derived from testis spermatogonia, also contain the Na, K-ATPase alpha4 polypeptide. However, the level of expression of the isoform in these cells is much lower than in the spermatozoa, a fact that may depend on the limited ability of the GC-1spg cells to differentiate in vitro. The particular expression of the Na,K-ATPase alpha4 isoform we encounter and the specific enzymatic properties of the polypeptide suggests its importance for ionic homeostasis of the germ cells of the testes.

Animals↗

PubMed1999

The EGR family of transcription-regulatory factors: progress at the interface of molecular and systems neuroscience.

The EGR family of transcription regulatory factors, which is implicated in orchestrating the changes in gene expression that underlie neuronal plasticity, has attracted the attention of both molecular and systems neuroscientists. In this article, the advances made in both these fields of research are reviewed. Recent systems-based studies underscore the remarkable sensitivity and specificity of the induction of the expression of genes encoding EGR-family members in naturally occurring plasticity paradigms. However, they also challenge conventional views of the role of this family in plasticity. Recent molecular studies have identified the gonadotropin subunit, luteinizing hormone beta, as an EGR1-regulated gene in vivo and uncovered an essential role for EGR3 in muscle-spindle development. In addition, the discovery of novel proteins that are capable of suppressing EGR-mediated transcription cast doubt over the prevalent assumption that changes in EGR mRNA or protein levels provide an accurate measure of EGR-driven transcriptional activity.

Animals↗

PubMed1999

Infertility associated with incomplete spermatogenic arrest and oligozoospermia in Egr4-deficient mice.

Male fertility is complex and depends upon endocrine/paracrine regulatory mechanisms and morphogenetic processes occurring during testicular development, spermatogenesis (mitosis and meiosis) and spermiogenesis (spermatid maturation). Egr4 (NGFI-C, pAT133), a member of the Egr family of zinc-finger transcription factors, is thought to be involved in cellular growth and differentiation, but its specific function has been previously unknown. We derived Egr4 null mice through targeted mutagenesis and found that they were phenotypically normal with the exception that males, but not females, were infertile. Egr4 is expressed at low levels within male germ cells during meiosis and is critical for germ cell maturation during the early-mid pachytene stage. While most Egr4 null male germ cells undergo apoptosis during early-mid pachytene, some are capable of maturing beyond an apparent Egr4-dependent developmental restriction point. Consequently, a limited degree of spermiogenesis occurs but this is accompanied by markedly abnormal spermatozoon morphology and severe oligozoospermia. Egr4 appears to regulate critical genes involved in early stages of meiosis and has a singularly important role in male murine fertility. These data raise the possibility that Egr4 may contribute to some forms of human idiopathic male infertility.

Animals↗

PubMed1998

Sensory ataxia and muscle spindle agenesis in mice lacking the transcription factor Egr3.

Muscle spindles are skeletal muscle sensory organs that provide axial and limb position information (proprioception) to the central nervous system. Spindles consist of encapsulated muscle fibers (intrafusal fibers) that are innervated by specialized motor and sensory axons. Although the molecular mechanisms involved in spindle ontogeny are poorly understood, the innervation of a subset of developing myotubes (type I) by peripheral sensory afferents (group Ia) is a critical event for inducing intrafusal fiber differentiation and subsequent spindle formation. The Egr family of zinc-finger transcription factors, whose members include Egr1 (NGFI-A), Egr2 (Krox-20), Egr3 and Egr4 (NGFI-C), are thought to regulate critical genetic programs involved in cellular growth and differentiation (refs 4-8, and W.G.T. et al., manuscript submitted). Mice deficient in Egr3 were generated by gene targeting and had gait ataxia, increased frequency of perinatal mortality, scoliosis, resting tremors and ptosis. Although extrafusal skeletal muscle fibers appeared normal, Egr3-deficient animals lacked muscle spindles, a finding that is consistent with their profound gait ataxia. Egr3 was highly expressed in developing muscle spindles, but not in Ia afferent neurons or their terminals during developmental periods that coincided with the induction of spindle morphogenesis by sensory afferent axons. These results indicate that type I myotubes are dependent upon Egr3-mediated transcription for proper spindle development.

Animals↗

PubMed1995

Bax-deficient mice with lymphoid hyperplasia and male germ cell death.

BAX, a heterodimeric partner of BCL2, counters BCL2 and promotes apoptosis in gain-of-function experiments. A Bax knockout mouse was generated that proved viable but displayed lineage-specific aberrations in cell death. Thymocytes and B cells in this mouse displayed hyperplasia, and Bax-deficient ovaries contained unusual atretic follicles with excess granulosa cells. In contrast, Bax-deficient males were infertile as a result of disordered seminiferous tubules with an accumulation of atypical premeiotic germ cells, but no mature haploid sperm. Multinucleated giant cells and dysplastic cells accompanied massive cell death. Thus, the loss of Bax results in hyperplasia or hypoplasia, depending on the cellular context.

Animals↗

PubMed1993

Anatomical distinctions between the two basal ganglia afferent territories in the primate motor thalamus.

In primates, the efferents of the two basal ganglia output structures, medial globus pallidus and substantia nigra pars reticularis, are completely segregated and target different thalamic regions. Despite similarities demonstrated earlier in non-primate species in the functional properties and ultrastructural features of the terminals of the two pathways, the present findings suggest significant differences between thalamic circuits associated with the two systems in primates. The data presented in this report further support the concept on functional and anatomical diversity of the subdivisions of the primate motor thalamus proposed in 1990 by Hinsky.

Afferent Pathways↗

PubMed1992

Computer-aided two-dimensional high-resolution axon tracing: an application using the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHAL).

A computer-aided method for mapping the spatial distribution of axons labeled with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHAL) has been devised. The method is based upon a histochemical charting system that controls a motorized microscope stage. The Computerized Charting System (CCS) does not require a camera lucida and can be installed on a common laboratory computer with minimal specialized hardware. The system provides features for storing, manipulating, and plotting the data, and recording the location of photographic images. The CCS has been used in our laboratory for: (1) the analysis of retrograde and anterograde neuroanatomical tract tracing using horseradish peroxidase, fluorescent dyes, PHAL, and 3H-labeled amino acids; (2) mapping the distribution of cells identified by immunohistochemistry; (3) mapping the distribution of silver grain-positive cells using in situ hybridization; (4) mapping the spatial distribution of neurofibrillary tangles and neuritic plaques in Alzheimer's disease; and (5) mapping the pattern of congophilic angiopathy in human brain. With the addition of high-resolution tracing features, the CCS provides a cost-effective and comprehensive alternative to the tedious and often inaccurate X-Y recording techniques used routinely in neuroanatomy and neuropathology.

Animals↗

PubMed1991

The axonal origin of a subpopulation of dystrophic neurites in Alzheimer's disease.

Dystrophic neurites are observed characteristically in Alzheimer's disease (AD). They are thought to arise from sprouting dendrites and contribute to dementia because of their abnormal growth and close association with neurofibrillary tangles and neuritic plaques. In the present study, dystrophic neurites are demonstrated in the thalamic reticular nucleus in AD in the context of a normal neural and glial architecture. They do not collocalize with somata and dendrites identified by simultaneous labeling with the microtubule-associated protein MAP2, suggesting that they are derived from axons. Throughout the brain, dystrophic neurites may well be comprised of a heterogeneous population of both dendrites and axon terminals and preterminals. While many recent studies have focused upon the dendritic origin of dystrophic neurites, these results emphasize that the interconnectivity of certain brain regions may be compromised by cytoskeletal changes occurring in neurons and their axons in AD.

Alzheimer Disease↗

PubMed1990

Alz-50 immunoreactivity in the thalamic reticular nucleus in Alzheimer's disease.

Examination of the thalamic reticular nucleus (Rt) with the monoclonal antibody Alz-50 in brains of Alzheimer's disease patients reveals dense extracellular and terminal-like immunoreactivity in the absence of neurofibrillary tangles or neuritic plaques. Similar terminal-like immunoreactivity is not present in other thalamic nuclei of AD brains or in the brains of controls. Based on (1) an immunocytochemical and histopathological analysis of areas known to project to the Rt, (2) that Alz-50 immunocytochemistry reveals immunoreactive neurons, neurofibrillary tangles and neuritic plaques, and (3) evidence that Alz-50 immunoreactivity can be demonstrated in the terminal fields of immunoreactive neurons, the terminal-like immunoreactivity in the Rt probably corresponds to altered preterminal axons and terminals from degenerating basal forebrain neurons. Given the presumed physiological role of the Rt, these selective lesions could alter thalamocortical processing and contribute to the cognitive impairment in Alzheimer's disease.

Alzheimer Disease↗

PubMed1990

A versatile dual axis programmable stepping motor controller for a personal computer: a specific application and tutorial for implementing a computer-controlled light microscope.

A simple programmable stepping motor circuit for controlling two independent stepping motors has been designed. The circuit is compatible with the IBM personal computer and needs only slight modification to work with virtually any other microcomputer. The motors can either be programmed by the host personal computer for remote operation, controlled directly by a joystick interface provided in the circuit, or a combination of the two procedures. Independent microprocessors control each stepping motor and can be easily programmed by the host computer via Input/Output ports designed into the circuit. A basic understanding of the circuit demonstrates some commonly used techniques for controlling microcomputer electronics through computer programming. The circuit will likely have many uses, although the implementation of a computerized microscope is explicitly described. The circuit is currently used in a neuroanatomical and neurochemical computer charting system at the University of Iowa.

Computer Peripherals↗

PubMed1989

A graphics-oriented personal computer-based microscope charting system for neuroanatomical and neurochemical studies.

This report describes a computerized microscope charting system based on the IBM personal computer or compatible. Stepping motors are used to control the movement of the microscope stage and to encode its position by hand manipulation of a joystick. Tissue section contours and the location of cells labeled with various compounds are stored by the computer, plotted at any magnification and manipulated into composites created from several charted sections. The system has many advantages: (1) it is based on an industry standardized computer that is affordable and familiar; (2) compact and commercially available stepping motor microprocessors control the stage movement. These controllers increase reliability, simplify implementation, and increase efficiency by relieving the computer of time consuming control tasks; (3) the system has an interactive graphics interface allowing the operator to view the image during data collection. Regions of the graphics display can be enlarged during the charting process to provide higher resolution and increased accuracy; (4) finally, the digitized data are stored at 0.5 micron resolution and can be routed directly to a multi-pen plotter or exported to a computer-aided design (CAD) program to generate a publication-quality montage composed of several computerized chartings. The system provides a useful tool for the acquisition and qualitative analysis of data representing stained cells or chemical markers in tissue. The modular design, together with data storage at high resolution, allows for potential analytical enhancements involving planimetric, stereologic and 3-D serial section reconstruction.

Computer Graphics↗

PubMed1983

Quantitation of human immunoglobulin G and albumin in electroimmunodiffusion gels containing ionic and nonionic detergents.

Quantitation of human immunoglobulin G (IgG) and albumin by agarose electroimmunodiffusion is influenced by the incorporation of ionic and nonionic detergents in the gel. The highest concentrations of each detergent at which human IgG and albumin determinations could be performed without perturbing the quantitations were 4% Triton X-100, 4% Tween 80, 1% NP-40, 0.5% sodium deoxycholate (SDOC), 0.5% Zwittergent, and 0.1% sodium dodecyl sulfate (SDS), and mixtures of Triton X-100, SDOC, and SDS. These detergent combinations all resulted in greater perturbations of albumin quantitation than of IgG. Immunoprecipitation of human IgG was quantitated in the absence and presence of Triton X-100, Zwittergent, and SDS. SDS was shown to cause nonspecific precipitation, whereas below 1% Triton X-100 or 0.5% Zwittergent no effects upon the immunoprecipitations were observed.

Albumins↗