The Myb leucine zipper is essential for leukemogenicity of the v-Myb protein

The AMV v-Myb oncoprotein causes oncogenic transformation of myelomonocytic cells in vivo and in vitro. Its transforming capacity is strictly dependent upon the N-terminal DNA binding domain, the central transactivation region, and on the C-terminal domain containing a putative leucine zipper motif. Here we show that the v-MybL3,4A mutant, in which Leu325 and Leu332 of the leucine zipper have been replaced by alanines, failed to induce leukemia in virus infected chicken. This demonstrates that the leucine zipper domain is indispensable for v-myb induced leukemogenesis in vivo. v-MybL3,4A was, however, still able to transform myelomonocytic cells from chicken bone marrow in vitro. Yet, while v-mybL3,4A transformed cells were impaired in growth at 37 degrees C, they failed to grow at 42 degrees C, the physiological body temperature of avian species. This might explain the loss of v-MybL3,4A leukemogenic potential in vivo. We also demonstrate that the v-Myb leucine zipper domain interacts in vitro with two host cell proteins, p26 and p28. This interaction is compromised in v-MybL3,4A indicating that binding of v-Myb to p26 and p28 might be important for the leukemogenic potential of v-Myb.     

Drosophila photoreceptors contain an autonomous circadian oscillator that can function without period mRNA cycling

Circadian oscillations in period (per) mRNA and per protein (PER) constitute, in part, a feedback loop that is required for circadian pacemaker function in Drosophila melanogaster. Oscillations in PER are required for oscillations in per mRNA, but the converse has not been rigorously tested because of a lack of measurable quantities of per mRNA and protein in the same cells. This circadian feedback loop operates synchronously in many neuronal and non-neuronal tissues, including a set of lateral brain neurons (LNs) that mediate rhythms in locomotor activity, but whether a hierarchy among these tissues maintains this synchrony is not known. To determine whether per mRNA cycling is necessary for PER cycling and whether cyclic per gene expression is tissue autonomous, we have generated per01 flies carrying a transgene that constitutively expresses per mRNA specifically in photoreceptors, a cell type that supports feedback loop function. These transformants were tested for different aspects of feedback loop function including per mRNA cycling, PER cycling, and PER nuclear localization. Under both light/dark (LD) cycling and constant dark (DD) conditions, PER abundance cycles in the absence of circadian cycling of per mRNA. These results show that per mRNA cycling is not required for PER cycling and indicate that Drosophila photoreceptors R1-R6 contain a tissue autonomous circadian oscillator.     

Drosophila engrailed can substitute for mouse Engrailed1 function in mid-hindbrain, but not limb development

The Engrailed-1 gene, En1, a murine homologue of the Drosophila homeobox gene engrailed (en), is required for midbrain and cerebellum development and dorsal/ventral patterning of the limbs. In Drosophila, en is involved in regulating a number of key patterning processes including segmentation of the epidermis. An important question is whether, during evolution, the biochemical properties of En proteins have been conserved, revealing a common underlying molecular mechanism to their diverse developmental activities. To address this question, we have replaced the coding sequences of En1 with Drosophila en. Mice expressing Drosophila en in place of En1 have a near complete rescue of the lethal En1 mutant brain defect and most skeletal abnormalities. In contrast, expression of Drosophila en in the embryonic limbs of En1 mutants does not lead to repression of Wnt7a in the embryonic ventral ectoderm or full rescue of the embryonic dorsal/ventral patterning defects. Furthermore, neither En2 nor en rescue the postnatal limb abnormalities that develop in rare En1 null mutants that survive. These studies demonstrate that the biochemical activity utilized in mouse to mediate brain development has been retained by Engrailed proteins across the phyla, and indicate that during evolution vertebrate En proteins have acquired two unique functions during embryonic and postnatal limb development and that only En1 can function postnatally.     

The mutation rates of di-, tri- and tetranucleotide repeats in Drosophila melanogaster

In a recent study, we reported that the combined average mutation rate of 10 di-, 6 tri-, and 8 tetranucleotide repeats in Drosophila melanogaster was 6.3 x 10(-6) mutations per locus per generation, a rate substantially below that of microsatellite repeat units in mammals studied to date (range = 10(-2)-10(-5) per locus per generation). To obtain a more precise estimate of mutation rate for dinucleotide repeat motifs alone, we assayed 39 new dinucleotide repeat microsatellite loci in the mutation accumulation lines from our earlier study. Our estimate of mutation rate for a total of 49 dinucleotide repeats is 9.3 x 10(-6) per locus per generation, only slightly higher than the estimate from our earlier study. We also estimated the relative difference in microsatellite mutation rate among di-, tri-, and tetranucleotide repeats in the genome of D. melanogaster using a method based on population variation, and we found that tri- and tetranucleotide repeats mutate at rates 6.4 and 8.4 times slower than that of dinucleotide repeats, respectively. The slower mutation rates of tri- and tetranucleotide repeats appear to be associated with a relatively short repeat unit length of these repeat motifs in the genome of D. melanogaster. A positive correlation between repeat unit length and allelic variation suggests that mutation rate increases as the repeat unit lengths of microsatellites increase.     

Enhancer point mutation results in a homeotic transformation in Drosophila

In Drosophila, the misexpression or altered activity of genes from the bithorax complex results in homeotic transformations. One of these genes, abd-A, normally specifies the identity of the second through fourth abdominal segments (A2 to A4). In the dominant Hyperabdominal mutations (Hab), portions of the third thoracic segment (T3) are transformed toward A2 as the result of ectopic abd-A expression. Sequence analysis and deoxyribonuclease I footprinting demonstrate that the misexpression of abd-A in two independent Hab mutations results from the same single base change in a binding site for the gap gene Krüppel protein. These results establish that the spatial limits of the homeotic genes are directly regulated by gap gene products.     

Wingless can bring about a mesoderm-to-ectoderm induction in Drosophila embryos

By means of nuclear transplantations, we make mosaics in which largely wingless- embryos contain patches of wingless+ cells. In these genetic mosaics, using a standard assay for wingless function (the maintenance of engrailed expression), we uncover an induction across germ layers: Wingless made in the mesoderm can sustain engrailed expression in the ectoderm. This result makes clear that Wingless is expressed in the mesoderm until at least one hour after gastrulation and may function in this germ layer in the wild type.     

Pro-epileptic changes in synaptic function can be accompanied by pro-epileptic changes in neuronal excitability

Repetitive sensory input, stroboscopic lights or repeated sounds can induce epileptic seizures in susceptible individuals. In order to understand the process we have to consider multiple factors. The output of a set of neurones is determined by the amount of excitatory synaptic input, the degree of positive feedback and their inherent electrical excitability, which can be modified by synaptic inhibition. Recent research has shown that it is possible to separate these phenomena, and that they do not always behave in unison.     

Evidence for sex transformation of germline cells in ovarian tumor mutants of Drosophila

Mutations at a few genetic loci in Drosophila cause ovarian tumors with hundreds of poorly differentiated germ cells. We examined several of these mutants to test the hypothesis that such ovarian tumors contain sex-transformed cells. By testing for expression of male germline traits, we determined that partial germline sex transformation occurs in otu, snf, Sxlfs, and bam ovarian tumors. Thus these genes are likely to be required for proper establishment of germline sexual identity.     

Specific short transmembrane sequences can inhibit transformation by the mutant neu growth factor receptor in vitro and in vivo

The neu oncogene is activated by a point mutation within its transmembrane domain that results in the substitution of glutamic acid for valine at position 664, and is associated with constitutive activation of the tyrosine kinase. It has been proposed that the mutation allows for stabilization of homodimers of the receptor that are necessary for transduction of the mitogenic signal. To investigate the role of the alpha-helical transmembrane sequence in the function of neu, we constructed an expression vector to produce a variety of short transmembrane neu proteins, lacking ligand binding or intracellular kinase domains. Such sequences should interact with full-length receptors and prevent receptor dimerization and thus act as specific inhibitors of function. These small proteins all included a pentapeptide from position 661-665, which has been proposed to be necessary for packing. We show that the short transmembrane molecules are expressed at the cell surface and can retard the growth of neu-transformed cells in monolayers, as colonies in soft agar and as tumours in animals. As predicted by molecular modelling, the magnitude of inhibition depended on the nature of the packing surface, suggesting that the neu transmembrane domain is directly involved in neu protein dimerization.     

Mechanism of transformation by v-ErbA: substitution for steroid hormone receptor function in self renewal induction

V-ErbA, a mutated thyroid hormone receptor (TR) alpha cooperates with tyrosine kinase oncoproteins to induce fatal erythroleukemia in chicks. In vitro, v-ErbA employs a similar cooperation to induce sustained proliferation and arrest differentiation of committed erythroid progenitors. V-ErbA has been proposed to function as a dominant-negative c-ErbA/TR alpha, since it lacks an AF-2 transactivation domain and cannot be activated by hormone but retains the capacity to bind corepressors. However, v-ErbA fails to heterodimerize with the coreceptor RXR, exhibits an altered DNA binding specificity and fails to suppress the action of coexpressed TR alpha/c-ErbA in erythroblasts. In this paper, we identify a novel mechanism by which v-ErbA contributes to leukemogenesis. Recently, the glucocorticoid receptor (GR) was identified as a key regulator of proliferation and differentiation in normal erythroid progenitors. For this, the GR required to cooperate with endogenous receptor tyrosine kinases (c-Kit) and with the estrogen receptor (ER). Here, we demonstrate that v-ErbA can substitute for the ligand-activated GR and ER, inducing proliferation and arresting differentiation in the presence of specific GR and ER antagonists. Like the GR, v-ErbA required to cooperate with c-Kit for both proliferation induction and differentiation arrest, being devoid of biological activity in the absence of an active c-Kit. In self-renewing erythroblasts, v-ErbA not only repressed known v-ErbA target genes but also maintained high expression of c-myb. These biological activities of v-ErbA depended on distinct mutations in the DNA-binding domain. Additionally, v-ErbA acted as a partial, weak repressor of c-ErbA/TR alpha function in normal erythroblasts. It could be converted into a truly dominant-negative receptor by restoring its ability to heterodimerize with RXR.     

Anxiety and perceptual structure: Individual differences in neuropsychological function.

Studied the cognitive performance of 24 high and 36 low trait anxious undergraduates under conditions of high and low situational stress, using tasks requiring greater contribution of the right or left hemisphere. In addition, a perceptual task was adapted from visual information processing research to assess Ss' global or analytic approaches to perception; if anxiety increased the left hemisphere's contribution to perception, anxious Ss might be expected to be more analytic and detail oriented. Results show no significant differences on left hemisphere tasks but a significant interaction of trait by state anxiety for right hemisphere tasks: Low trait Ss performed better and high trait Ss performed more poorly under situational stress. Trait anxiety showed a significant main effect on visual information processing strategy, low Ss tending to be more global and high Ss tending to process the stimulus analytically. Results support the utility of a neuropsychological model in describing the effects of emotion on perception. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)