Genetic mechanism regulating diversity in the placement of eyes on the head of animals

Despite the conservation of genetic machinery involved in eye development, there is a strong diversity in the placement of eyes on the head of animals. Morphogen gradients of signaling molecules are vital to patterning cues. During Drosophila eye development, Wingless (Wg), a ligand of Wnt/Wg signaling, is expressed anterolaterally to form a morphogen gradient to determine the eye- versus head-specific cell fate. The underlying mechanisms that regulate this process are yet to be fully understood. We characterized defective proventriculus (dve) (Drosophila ortholog of human SATB1), a K50 homeodomain transcription factor, as a dorsal eye gene, which regulates Wg signaling to determine eye versus head fate. Across Drosophila species, Dve is expressed in the dorsal head vertex region where it regulates wg transcription. Second, Dve suppresses eye fate by down-regulating retinal determination genes. Third, the dve-expressing dorsal head vertex region is important for Wg-mediated inhibition of retinal cell fate, as eliminating the Dve-expressing cells or preventing Wg transport from these dve-expressing cells leads to a dramatic expansion of the eye field. Together, these findings suggest that Dve regulates Wg expression in the dorsal head vertex, which is critical for determining eye versus head fate. Gain-of-function of SATB1 exhibits an eye fate suppression phenotype similar to Dve. Our data demonstrate a conserved role for Dve/SATB1 in the positioning of eyes on the head and the interocular distance by regulating Wg. This study provides evidence that dysregulation of the Wg morphogen gradient results in developmental defects such as hypertelorism in humans where disproportionate interocular distance and facial anomalies are reported.

Fecundity is optimized by levels of nutrient signal-dependent expression of Dve and EcR in Drosophila male accessory gland

Steroid hormones play various physiological roles including metabolism and reproduction. Steroid hormones in insects are ecdysteroids, and the major form in Drosophila melanogaster is ecdysone. In Drosophila males, the accessory gland is responsive to nutrient-dependent regulation of fertility/fecundity. The accessory gland is composed of two types of binucleated epithelial cells: a main cell and a secondary cell (SC). The transcription factors Defective proventriculus (Dve), Abdominal-B, and Ecdysone receptors (EcRs) are strongly expressed in adult SCs. We show that this EcR expression is regulated by parallel pathways of nutrient signaling and the Dve activity. Induction of Dve expression is also dependent on nutrient signaling, and it becomes nutrient signal-independent during a restricted period of development. Forced dve expression during the restricted period significantly increased the number of SCs. Here, we provide evidence that the level of nutrient signal-dependent Dve expression during the restricted period determines the number of SCs, and that ecdysone signaling is also crucial to optimize male fecundity through nutrient signal-dependent survival and maturation of SCs.

Functional opsin patterning for Drosophila color vision is established through signaling pathways in adjacent object-detection neurons

Vision is mainly based on two different tasks, object detection and color discrimination, carried out by photoreceptor (PR) cells. The Drosophila compound eye consists of ∼800 ommatidia. Every ommatidium contains eight PR cells, six outer cells (R1-R6) and two inner cells (R7 and R8), by which object detection and color vision are achieved, respectively. Expression of opsin genes in R7 and R8 is highly coordinated through the instructive signal from R7 to R8, and two major ommatidial subtypes are distributed stochastically; pale type expresses Rh3/Rh5 and yellow type expresses Rh4/Rh6 in R7/R8. The homeodomain protein Defective proventriculus (Dve) is expressed in yellow-type R7 and in six outer PRs, and it is involved in Rh3 repression to specify the yellow-type R7. dve mutant eyes exhibited atypical coupling, Rh3/Rh6 and Rh4/Rh5, indicating that Dve activity is required for proper opsin coupling. Surprisingly, Dve activity in R1 is required for the instructive signal, whereas activity in R6 and R7 blocks the signal. Our results indicate that functional coupling of two different neurons is established through signaling pathways from adjacent neurons that are functionally different.

Binucleation of Accessory Gland Lobe Contributes to Effective Ejection of Seminal Fluid in Drosophila melanogaster

The adult male accessory gland in insects is an internal reproductive organ analogous to the mammalian prostate, and secretes various components in the seminal fluid. Products of the accessory gland in the fruit fly Drosophila melanogaster are known to control reproductive behaviors in mated females, such as food uptake, oviposition rate, and rejection of re-mating with other males, all of which increase male reproductive capacity. Production of larger amounts of accessory gland products is thus thought to result in higher male reproductive success. The epithelium of the Drosophila accessory gland lobe is composed of a unique population of binucleate cells. We previously predicted, based on measurements of cell size in mono/binucleate mosaic accessory glands, that binucleation results in a higher plasticity in cell shape, enabling more effective ejection of seminal fluid. However, the actual effect of binucleation on ejection of seminal fluid or reproductive capacity remained unclear, as we were unable to generate an organ with uniformly mononucleate cells. In the present study, we generated organs in which most of the epithelial cells are mononucleate by manipulating aurora B or fizzy-related to block binucleation. Mononucleation resulted in a less elastic accessory gland lobe, which decreased ejection volume and the oviposition of mated females; these effects were particularly pronounced over the long term. These results suggest that binucleation in accessory gland epithelial cells contributes to higher plasticity in the volume of this organ, and enhances male reproductive success through enabling ejection of larger amounts of seminal fluid.

Spalt-mediated dve repression is a critical regulatory motif and coordinates with Iroquois complex in Drosophila vein formation

Veins are longitudinal cuticular structures that maintain shape of the wing. Drosophila melanogaster has six longitudinal veins (L1-L6) and two cross veins. The Zn-finger transcription factors of Spalt-complex (Sal) are required for positioning of the L2 and L5, and the homeodomain transcription factors of Iroquois complex (Iro-C) are required for formation of the L3 and L5 veins. The homeodomain transcriptional repressor Defective proventriculus (Dve) is uniformly expressed in the wing pouch of the larval imaginal disc. However, dve mutant wings showed loss of the L2 and L5, but not of the L3 and L4 veins. Temporal dve knockdown experiments indicate that the Dve activity is required for vein formation from late third larval instar to the prepupal stage. In the prepupal wing, Dve expression becomes nearly complementary to that of Sal through the Sal-mediated dve repression. Furthermore, coexpression of Dve and Iro-C relieved of Sal-mediated repression is required for the L5 formation in a dose-dependent manner. The relationship between Sal, Dve, and Iro-C in wing vein specification is quite similar to that in ommatidial cell-type specification. Our results provide information about the conserved function of dve regulatory motifs in cell differentiation.

Isoform-specific functions of Mud/NuMA mediate binucleation of Drosophila male accessory gland cells

Background

In standard cell division, the cells undergo karyokinesis and then cytokinesis. Some cells, however, such as cardiomyocytes and hepatocytes, can produce binucleate cells by going through mitosis without cytokinesis. This cytokinesis skipping is thought to be due to the inhibition of cytokinesis machinery such as the central spindle or the contractile ring, but the mechanisms regulating it are unclear. We investigated them by characterizing the binucleation event during development of the Drosophila male accessory gland, in which all cells are binucleate.

Results

The accessory gland cells arrested the cell cycle at 50 hours after puparium formation (APF) and in the middle of the pupal stage stopped proliferating for 5 hours. They then restarted the cell cycle and at 55 hours APF entered the M-phase synchronously. At this stage, accessory gland cells binucleated by mitosis without cytokinesis. Binucleating cells displayed the standard karyokinesis progression but also showed unusual features such as a non-round shape, spindle orientation along the apico-basal axis, and poor assembly of the central spindle. Mud, a Drosophila homolog of NuMA, regulated the processes responsible for these three features, the classical isoform Mud^PBD and the two newly characterized isoforms Mud^L and Mud^S regulated them differently: Mud^L repressed cell rounding, Mud^PBD and Mud^S oriented the spindle along the apico-basal axis, and Mud^S and Mud^L repressed central spindle assembly. Importantly, overexpression of Mud^S induced binucleation even in standard proliferating cells such as those in imaginal discs.

Conclusions

We characterized the binucleation in the Drosophila male accessory gland and examined mechanisms that regulated unusual morphologies of binucleating cells. We demonstrated that Mud, a microtubule binding protein regulating spindle orientation, was involved in this binucleation. We suggest that atypical functions exerted by three structurally different isoforms of Mud regulate cell rounding, spindle orientation and central spindle assembly in binucleation. We also propose that Mud^S is a key regulator triggering cytokinesis skipping in binucleation processes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-014-0046-5) contains supplementary material, which is available to authorized users.

A vertex specific dorsal selector Dve represses the ventral appendage identity in Drosophila head

Developmental fields are subdivided into lineage-restricted cell populations, known as compartments. In the eye imaginal disc of Drosophila, dorso-ventral (DV) lineage restriction is the primary event, whereas antero-posterior compartment boundary is the first lineage restriction in other imaginal discs. The Iroquois complex (Iro-C) genes function as dorsal selectors and repress the default, ventral, identity in the eye-head primordium. In Iro-C mutant clones, change of the dorsal identity to default ventral fate leads to generation of ectopic DV boundary, which results in dorsal eye enlargement, and duplication of ventral appendages like antenna and maxillary palp. Similar phenotypes were observed in heads with defective proventriculus (dve) mutant clones. Here, we show that the homeobox gene dve is a downstream effector of Iro-C in the dorsal head capsule (vertex) specification and represses the ventral (antennal) identity. Two homeodomain proteins Distal-less (Dll) and Homothorax (Hth) are known to be determinants of the antennal identity. Ectopic antenna formation in heads with dve mutant clones was associated with ectopic Dll expression and endogenous Hth expression in the vertex region. Interestingly, dve Dll double mutant clones could also induce ectopic antennae lacking the distal structures, suggesting that the Dve activity is crucial for repressing inappropriate antenna-forming potential in the vertex region. Our results clearly indicate that not only the activation of effector genes to execute developmental program but also the repression of inappropriate program is crucial for establishment of the organ identity.

The homeodomain protein defective proventriculus is essential for male accessory gland development to enhance fecundity in Drosophila

The Drosophila male accessory gland has functions similar to those of the mammalian prostate gland and the seminal vesicle, and secretes accessory gland proteins into the seminal fluid. Each of the two lobes of the accessory gland is composed of two types of binucleate cell: about 1,000 main cells and 40 secondary cells. A well-known accessory gland protein, sex peptide, is secreted from the main cells and induces female postmating response to increase progeny production, whereas little is known about physiological significance of the secondary cells. The homeodomain transcriptional repressor Defective proventriculus (Dve) is strongly expressed in adult secondary cells, and its mutation resulted in loss of secondary cells, mononucleation of main cells, and reduced size of the accessory gland. dve mutant males had low fecundity despite the presence of sex peptide, and failed to induce the female postmating responses of increased egg laying and reduced sexual receptivity. RNAi-mediated dve knockdown males also had low fecundity with normally binucleate main cells. We provide the first evidence that secondary cells are crucial for male fecundity, and also that Dve activity is required for survival of the secondary cells. These findings provide new insights into a mechanism of fertility/fecundity.

Blocking synaptic transmission with tetanus toxin light chain reveals modes of neurotransmission in the PDF-positive circadian clock neurons of Drosophila melanogaster

Circadian locomotor rhythms of Drosophila melanogaster are controlled by a neuronal circuit composed of approximately 150 clock neurons that are roughly classified into seven groups. In the circuit, a group of neurons expressing pigment-dispersing factor (PDF) play an important role in organizing the pacemaking system. Recent studies imply that unknown chemical neurotransmitter(s) (UNT) other than PDF is also expressed in the PDF-positive neurons. To explore its role in the circadian pacemaker, we examined the circadian locomotor rhythms of pdf-Gal4/UAS-TNT transgenic flies in which chemical synaptic transmission in PDF-positive neurons was blocked by expressed tetanus toxin light chain (TNT). In constant darkness (DD), the flies showed a free-running rhythm, which was similar to that of wild-type flies but significantly different from pdf null mutants. Under constant light conditions (LL), however, they often showed complex rhythms with a short period and a long period component. The UNT is thus likely involved in the synaptic transmission in the clock network and its release caused by LL leads to arrhythmicity. Immunocytochemistry revealed that LL induced phase separation in TIMELESS (TIM) cycling among some of the PDF-positive and PDF-negative clock neurons in the transgenic flies. These results suggest that both PDF and UNT play important roles in the Drosophila circadian clock, and activation of PDF pathway alone by LL leads to the complex locomotor rhythm through desynchronized oscillation among some of the clock neurons.

Interlocked feedforward loops control cell-type-specific Rhodopsin expression in the Drosophila eye

How complex networks of activators and repressors lead to exquisitely specific cell-type determination during development is poorly understood. In the Drosophila eye, expression patterns of Rhodopsins define at least eight functionally distinct though related subtypes of photoreceptors. Here, we describe a role for the transcription factor gene defective proventriculus (dve) as a critical node in the network regulating Rhodopsin expression. dve is a shared component of two opposing, interlocked feedforward loops (FFLs). Orthodenticle and Dve interact in an incoherent FFL to repress Rhodopsin expression throughout the eye. In R7 and R8 photoreceptors, a coherent FFL relieves repression by Dve while activating Rhodopsin expression. Therefore, this network uses repression to restrict and combinatorial activation to induce cell-type-specific expression. Furthermore, Dve levels are finely tuned to yield cell-type- and region-specific repression or activation outcomes. This interlocked FFL motif may be a general mechanism to control terminal cell-fate specification.

Notch-, Wingless-, and Dpp-mediated signaling pathways are required for functional specification of Drosophila midgut cells

The mechanisms for cell fate determination have been extensively studied whereas little is known about the mechanism through which functional specificity is established. In the Drosophila midgut, copper cells provide an excellent model system to examine this mechanism. Copper is an essential element for the activity of a number of physiologically important enzymes including Cu/Zn-superoxide dismutase, cytochrome c oxidase, and dopamine-beta-hydroxylase. Drosophila copper cells are involved in two distinct functions, i.e., copper absorption and acid secretion, which are visualized as a fluorescent signal and a color change of a pH indicator dye, respectively. Here we show that the absorptive function is established through two independent pathways, the Notch signaling pathway in adjacent interstitial cells and the Wingless signaling pathway in copper cells. Furthermore, the other function, acid secretion, is regulated through the Decapentaplegic and Wingless signaling pathways in interstitial cells. Our results clearly indicate that normal morphological development is insufficient for functional maturation, and that subsequent functional specification is achieved through several independent pathways. These results provide valuable insights into the molecular mechanism underlying functional specification.

Functional specification in the Drosophila endoderm

The discovery of homeobox gene clusters led us to realize that the mechanisms for body patterning and other developmental programs are evolutionally-conserved in vertebrates and invertebrates. The endoderm contributes to the lining of the gut and associated organs such as the liver and pancreas, which are critical for physiological functions. Our knowledge of endoderm development is limited; however, recent studies suggest that cooperation between the HNF3/Fork head and GATA transcription factors is crucial for endoderm specification. It is necessary to further understand the mechanism through which cells become functionally organized. Molecular genetic analyses of the Drosophila endoderm would provide insights into this issue. During proventriculus morphogenesis, a simple epithelial tube is folded into a functional multilayered structure, while two functions of midgut copper cells (i.e. copper absorption and acid secretion) can be easily visualized. The homeobox gene defective proventriculus (dve) plays key roles in these functional specifications.

Differential requirement of EGFR signaling for the expression of defective proventriculus gene in the Drosophila endoderm and ectoderm

A homeobox gene, defective proventriculus (dve), is expressed in various tissues including the ventral ectoderm and midgut. Here, we show the expression pattern of dve in the ventral ectoderm, in which dve expression is induced by Spitz, a ligand for Drosophila epidermal growth factor receptor (EGFR). In spitz mutants, dve expression is only lost in the ventral ectoderm and overexpression of Spitz induces ectopic dve activation in the ventral ectoderm. Dve expression in the middle midgut depends on Decapentaplegic (Dpp) signaling, while expression of a dominant-negative form of Drosophila EGFR (DER(DN)) also causes a marked decrease in dve expression in the middle midgut. Furthermore, heterozygous mutation of thick veins (tkv), a Dpp receptor, strongly enhances the effect of DER(DN). These results indicate that EGFR signaling is crucial for dve expression in the ventral ectoderm and is required in the middle midgut where it cooperates with Dpp signaling.

Characterization of the dCaMKII-GAL4 driver line whose expression is controlled by the Drosophila Ca2+/calmodulin-dependent protein kinase II promoter

Transgenic flies that can drive GAL4 expression under the control of the 7 kb 5'-region of the Drosophila Ca(2+)/calmodulin-dependent protein kinase II (dCaMKII) gene (dCaMKII-GAL4) were established. Characteristic features of this dCaMKII-GAL4 driven reporter expression were compatible with the endogenous dCaMKII expression pattern: The dCaMKII-GAL4 driven reporter gene was expressed preferentially in the central nervous system of the embryo and larvae. Reporter expression was also observed in the brain, thoracic ganglion, and gut of the adult. The whole-brain distribution and projections of dCaMKII-GAL4-expressing cells in the adults were visualized three-dimensionally by using UAS-linked reporter genes. Prominent signals of nuclear-localized beta-Gal reporter gene expression were found in extensive brain regions, especially in the Kenyon cells of the mushroom body (MB), cells in the pars intercerebralis, and subesophageal ganglion (SOG). tau reporter gene expression highlighting neurite projections was detected in the MB lobes, median bundle, antennal lobe glomeruli, and fibers of clusters in the SOG, ventrolateral protocerebrum and superior lateral protocerebrum. These observations agree with those of a previous study mapping the dCaMKII-dependent memory circuits in courtship conditioning. Interestingly, green fluorescent protein reporter gene expression in adult MB lobes was predominantly observed in the alpha and beta lobes with a core-deficient pattern, but not in the alpha' and beta' lobes, similar to Fasciclin II immunoreactivity.

Refinement of wingless expression by a wingless- and notch-responsive homeodomain protein, defective proventriculus

Pattern formation during animal development is often induced by extracellular signaling molecules, known as morphogens, which are secreted from localized sources. During wing development in Drosophila, Wingless (Wg) is activated by Notch signaling along the dorsal-ventral boundary of the wing imaginal disc and acts as a morphogen to organize gene expression and cell growth. Expression of wg is restricted to a narrow stripe by Wg itself, repressing its own expression in adjacent cells. This refinement of wg expression is essential for specification of the wing margin. Here, we show that a homeodomain protein, Defective proventriculus (Dve), mediates the refinement of wg expression in both the wing disc and embryonic proventriculus, where dve expression requires Wg signaling. Our results provide evidence for a feedback mechanism that establishes the wg-expressing domain through the action of a Wg-induced gene product.

A novel homeobox gene mediates the Dpp signal to establish functional specificity within target cells

Morphogen gradients of secreted molecules play critical roles in the establishment of the spatial pattern of gene expression. During midgut development in Drosophila, secreted molecules of Decapentaplegic (Dpp) and Wingless (Wg) establish unique transcriptional regulation within target cells to specify the resultant cell types. Here we report the identification of a novel homeobox gene, defective proventriculus (dve), which is required for the midgut specification under the control of Dpp and Wg. In dve mutants, two distinct parts of the midgut, the proventriculus and middle midgut, are abnormally organized. The Wg signal regulates dve expression during proventriculus development. On the other hand, dve is a downstream target of Dpp in the middle midgut and defines the functional specificity of copper cells along with another Dpp target gene, labial. Thus, the dve gene acts under the two distinct extracellular signals at distant parts of the midgut primordia.

Inactivation of a c-Myb/estrogen receptor fusion protein in transformed primary cells leads to granulocyte/macrophage differentiation and down regulation of c-kit but not c-myc or cdc2

Primary murine fetal hemopoietic cells were transformed with a fusion protein consisting of the ligand-binding domain of the estrogen receptor and a carboxyl-terminally truncated c-Myb protein (ERMYB). The ERMYB-transformed hemopoietic cells exhibit an immature myeloid phenotype when grown in the presence of beta-estradiol. Upon removal of beta-estradiol, the ERMYB cells display increased adherence, decreased clonogenicity and differentiate to cells exhibiting granulocyte or macrophage morphology. The expression of the c-myc, c-kit, cdc2 and bcl-2 genes, which are putatively regulated by Myb, was investigated in ERMYB cells grown in the presence or absence of beta-estradiol. Neither c-myc nor cdc2 expression was down-regulated after removal of beta-estradiol demonstrating that differentiation is not a consequence of decreased transactivation of these genes by ERMYB. While bcl-2 expression was reduced by 50% in ERMYB cells grown in the absence of beta-estradiol, there was no increase in DNA laddering, suggesting that Myb was not protecting ERMYB cells from apoptosis. In contrast, a substantial (200-fold) decrease in c-kit mRNA level was observed following differentiation of ERMYB cells, and c-kit mRNA could be partially re-induced by the re-addition of beta-estradiol. Furthermore, a reporter construct containing the c-kit promoter was activated when cotransfected with a Myb expression vector, providing further evidence of a role for Myb in the regulation of c-kit.

Still life, a protein in synaptic terminals of Drosophila homologous to GDP-GTP exchangers

The morphology of axon terminals changes with differentiation into mature synapses. A molecule that might regulate this process was identified by a screen of Drosophila mutants for abnormal motor activities. The still life (sif) gene encodes a protein homologous to guanine nucleotide exchange factors, which convert Rho-like guanosine triphosphatases (GTPases) from a guanosine diphosphate-bound inactive state to a guanosine triphosphate-bound active state. The SIF proteins are found adjacent to the plasma membrane of synaptic terminals. Expression of a truncated SIF protein resulted in defects in neuronal morphology and induced membrane ruffling with altered actin localization in human KB cells. Thus, SIF proteins may regulate synaptic differentiation through the organization of the actin cytoskeleton by activating Rho-like GTPases.

Asymmetric segregation of the homeodomain protein Prospero during Drosophila development

Asymmetric divisions that produce two distinct cells play fundamental roles in generating different cell types during development. In the Drosophila central nervous system, neural stem cells called neuroblasts divide unequally into another neuroblast and a ganglion mother cell which is subsequently cleaved into neurons. Correct gene expression of ganglion mother cells requires the transcription factor Prospero. Here we demonstrate the asymmetric segregation of Prospero on neuroblast division. Prospero synthesized in neuroblasts is retained in the cytoplasm and at mitosis is exclusively partitioned to ganglion mother cells, in which it is translocated to the nucleus. Differential segregation of Prospero was also found in the endoderm. We have identified a region in Prospero that is responsible for this event. The region shares a common motif with Numb, which also shows unequal segregation. We propose that asymmetric segregation of transcription factors is an intrinsic mechanism for establishing asymmetry in gene expression between sibling cells.

Human A-myb gene encodes a transcriptional activator containing the negative regulatory domains

The myb gene family has three members, c-myb, A-myb, and B-myb. A-myb mRNA is mainly expressed in testis and peripheral blood leukocytes. A-Myb can activate transcription from the promoter containing Myb-binding sites in all cells examined. In addition to the two domains (a DNA-binding domain and a transcriptional activation domain), two negative regulatory domains have been identified in A-Myb. These results indicate that A-Myb functions as a transcriptional activator mainly in testis and peripheral blood cells, and the regulatory mechanism of A-Myb activity is similar to that of c-Myb.

Functional domains of the human B-myb gene product

Three members of the human myb gene family (c-myb, A-myb, and B-myb) encode transcriptional regulators that can bind to specific DNA sequences. High levels of c-myb expression are usually found in immature hemopoietic cells, but the B-myb is more commonly expressed in many types of cells. To understand the regulation of the activity of B-myb gene product (B-Myb), its functional domains were analyzed. Like c-Myb, B-Myb also has a transcriptional activation domain containing a cluster of acidic amino acids in the region downstream of the DNA-binding domain, which consists of three tandem repeats of 51-52 amino acids. In contrast to c-Myb, B-Myb does not contain a negative regulatory domain. Furthermore, the multiple nuclear localization signals are in at least two regions in the COOH-terminal half of B-Myb, and one of them is adjacent to a potential cdc2 kinase site. These results indicate that B-Myb contains DNA-binding and transcriptional activation domains similar to those of c-Myb, but a regulatory mechanism of B-Myb activity is quite different from that for c-Myb.

Transcriptional control by myb oncogene product

Structure and function of two domains of c-Myb were analyzed. We show that a leucine zipper structure is a component of the negative regulatory domain, because its disruption markedly increases both the transactivating and transforming capacities of c-Myb. Our results suggest that an inhibitor which suppresses transactivation binds to c-Myb through the leucine zipper, and that c-Myb can be oncogenically activated by mis-sense mutation. We also proposed a model, the "tryptophan cluster", for the structure of the Myb DNA-binding domain, in which the three tryptophans form a cluster in the hydrophobic core in each repeat. The results of NMR analysis of repeat 3 revealed that the conserved tryptophans play a key role to make the hydrophobic core.

Overlap of the p53-responsive element and cAMP-responsive element in the enhancer of human T-cell leukemia virus type I

The wild-type p53 protein suppresses transformation, but certain missense mutants of p53 can transform cells. Although the wild-type p53 protein contains a transcriptional activation domain, no p53-responsive element has been identified. Here, we identified the p53-responsive element within the Tax-responsive element [21-base-pair (bp) enhancer] of human T-cell leukemia virus type I. Mutation analysis of the 21-bp enhancer indicated that the 16-bp sequence containing the cAMP-responsive element and its surrounding sequence was responsible for p53-induced transactivation. This 16-bp sequence was demonstrated to bind specifically to wild-type human p53 protein in vitro. Using a series of deletion mutants of p53, we showed that almost the entire region of p53 is needed for the transactivating capacity. Furthermore, the transforming mutants of p53 were unable to act as transcriptional activators. The p53-responsive element identified here should be useful to analyze the mechanism by which p53 regulates expression of a set of genes with a negative effect on cellular growth.

Transcriptional activation of the c-myc gene by the c-myb and B-myb gene products

To identify the target genes modulated by the myb gene product (Myb), a co-transfection assay with a Myb expression plasmid was performed. Both c-Myb and B-Myb, another member of the myb gene family, trans-activated the human c-myc promoter. DNAase I footprint analysis using the bacterially expressed c-Myb, identified multiple c-Myb binding sites in the c-myc promoter region. Deletion analysis of the c-myc promoter suggested that some number of Myb binding sites, not a specific Myb binding site, is important for the c-Myb-induced trans-activation of the c-myc promoter. Using the c-myc-chloramphenicol acetyltransferase (CAT) construct as a reporter in a co-transfection assay, the domains of c-Myb required for trans-activation were examined. The functional domains of c-Myb identified using the c-myc promoter were almost the same as those identified previously with the artificial target gene containing Myb binding sites, but unlike the case with the artificial target gene the N-terminal half of the previously identified negative regulatory domains and the C-terminal 136 amino acids were required for the maximal trans-activation of the c-myc promoter. These results indicate that there are some differences in the regulation of Myb-dependent trans-activation in different target genes.

Effects of prokaryotic termination signals on RNA polymerase II transcription in HeLa cells

Three prokaryotic termination signals, the Escherichia coli trp attenuator, lambda 4S RNA terminator, and lambda tR1 terminator, were examined as to their effects on transcription in vivo in HeLa cells. The trp attenuator inhibited the expression of downstream genes in an orientation-dependent manner, but both the lambda 4S RNA and lambda tR1 terminators did not. Furthermore, a point mutation of the attenuator that disrupted the secondary structure of mRNA abolished this inhibitory effect. These results suggest that an attenuator-like secondary structure is effective in inhibiting transcriptional elongation by RNA polymerase II.

The tryptophan cluster: a hypothetical structure of the DNA-binding domain of the myb protooncogene product

In the DNA-binding domain of the c-myb protooncogene product (c-Myb) which consists of three repeats of 51-52 amino acids, there are 3 perfectly conserved tryptophans in each repeat. Site-directed mutagenesis of these tryptophans showed that any single or multiple mutations of tryptophan to hydrophilic residues or alanine abolished or greatly reduced the sequence-specific DNA-binding activity, but mutations to hydrophobic amino acids retained considerable activity. Raman spectroscopic study showed that these tryptophans were buried in the protein core. These 3 tryptophans are proposed to form a cluster in the hydrophobic core in each repeat. This hypothetical structure is referred to as the "tryptophan cluster," and it may represent a characteristic property of a group of DNA-binding proteins including the myb- and ets-related proteins.

DNA binding activity and transcriptional activator function of the human B-myb protein compared with c-MYB

Three members of the myb gene family have been identified in human cDNA libraries c-myb, A-myb, and B-myb. We compared the DNA binding properties of the B-myb and c-myb proteins (B-MYB and c-MYB) using bacterially synthesized B-MYB and c-MYB in DNase I footprinting. B-MYB bound to most of the c-MYB binding sites examined, including the c-MYB binding site, MBS-I, in the simian virus (SV) 40 enhancer, in which the most frequent sequence was CCTAACTG. The MBS-I site was an enhancer element dependent on B-MYB and c-MYB in a co-transfection assay that used the B-myb or c-myb expression plasmid. Some sites in the SV40 genome, including the MBS-BI site, had high affinity with B-MYB but little or no affinity with c-MYB, in which the most frequent sequence was AGAAANPyrG. The MBS-BI site was an enhancer element dependent on B-MYB and a very weakly dependent on c-MYB. Our results showed that B-MYB is a transcriptional activator, like c-MYB, and that although B-MYB and c-MYB have similar sequence specificity for DNA binding some sequences were recognized by B-MYB preferentially.

Binding of the c-myb proto-oncogene product to the simian virus 40 enhancer stimulates transcription

The proto-oncogene c-myb encodes a nuclear protein which binds to DNA. Here we find that bacterially synthesized c-myb protein binds to one site of the simian virus 40 enhancer. The c-myb protein purified from the human T-cell line, Molt4, was also shown to recognize the same sequence. In co-transfection experiments with a c-myb expression plasmid, tandem repeats of a c-myb-binding sequence were shown to function as a c-myb-dependent enhancer. These results indicate the c-myb protein is a simian virus 40 enhancer-binding protein that can positively regulate transcription.

Transcriptional trans-repression by the c-myb proto-oncogene product

We report that the c-myb protein binds to another site, MBS-II, in the SV40 enhancer with low affinity. In co-transfection experiments with a c-myb expression plasmid, tandem repeats of the sequence containing the MBS-II site induced c-myb-dependent transcriptional repression. Results of mutational analyses of the sequence around the MBS-II site suggested that the c-myb protein represses transcription by competing with another trans-activator. These results indicate that c-myb protein can regulate transcription not only positively but also negatively.

Delineation of three functional domains of the transcriptional activator encoded by the c-myb protooncogene

The c-myb protooncogene encodes a sequence-specific DNA-binding protein (c-Myb) that induces transcriptional activation or repression. We have identified three functional domains of the mouse c-Myb protein that are responsible for DNA binding, transcriptional activation, and negative regulation, respectively. In addition to the DNA-binding domain, which is located near the N terminus, an adjacent region (the transcriptional activation domain) containing about 80 amino acids was found to be essential for transcriptional activation. Deletion of a region spanning about 175 amino acids of the C-proximal portion increased transcriptional activation markedly, revealing that this domain normally represses activation. Differences between the transcriptional activation and repression functions of c-Myb and v-Myb are discussed in the light of these functional domains. Our results suggest that transcriptional activation may be involved in transformation by myb gene products.

Trans-activation by the c-myb proto-oncogene

We present evidence that the mouse c-myb proto-oncogene encodes a transcriptional trans-activator. Trans-activation was assayed by cotransfection into CV1 monkey kidney cells of a c-myb cDNA expression plasmid together with a reporter plasmid carrying the chloramphenicol acetyltransferase (CAT) gene under the control of a test promoter and enhancer. Cotransfection with the c-myb cDNA plasmid caused a 20-fold stimulation of transcription from the promoter of the mouse alpha 2(I) collagen gene linked to tandem repeats of the simian virus 40 (SV40) enhancer element. Using different promoters in combination with varying numbers of repeats of the SV40 enhancer element, it was shown that tandem repeats of the SV40 enhancer mediated the c-myb-induced activation of transcription. These results show that the mouse c-myb gene product either is itself or induces, an activator of transcription that recognizes specific sequences in the SV40 enhancer.

Molecular cloning and expression of a gene for a factor which stabilizes formation of inhibitor-mitochondrial ATPase complex from Saccharomyces cerevisiae

Stabilizing factor, a 9 kDa protein, stabilizes and facilitates formation of the complex between mitochondrial ATP synthase and its intrinsic inhibitor protein. A clone containing the gene encoding the 9 kDa protein was selected from a yeast genomic library to determine the structure of its precursor protein. As deduced from the nucleotide sequence, the precursor of the yeast 9 kDa stabilizing factor contains 86 amino acid residues and has a molecular weight of 10,062. From the predicted sequence we infer that the stabilizing factor precursor contains a presequence of 23 amino acid residues at its amino terminus. We also used S1 mapping to determine the initiation site of transcription under glucose-repressed or derepressed conditions. These experiments suggest that transcription of this gene starts at three different sites and that only one of them is not affected by the presence of glucose.