Biomedical subjects

R A Schulz

Publications and source records attributed to R A Schulz.

At least 19 recordsLinked to original sources

PubMed2001

The Friend of GATA proteins U-shaped, FOG-1, and FOG-2 function as negative regulators of blood, heart, and eye development in Drosophila.

Friend of GATA (FOG) proteins regulate GATA factor-activated gene transcription. During vertebrate hematopoiesis, FOG and GATA proteins cooperate to promote erythrocyte and megakaryocyte differentiation. The Drosophila FOG homologue U-shaped (Ush) is expressed similarly in the blood cell anlage during embryogenesis. During hematopoiesis, the acute myeloid leukemia 1 homologue Lozenge and Glial cells missing are required for the production of crystal cells and plasmatocytes, respectively. However, additional factors have been predicted to control crystal cell proliferation. In this report, we show that Ush is expressed in hemocyte precursors and plasmatocytes throughout embryogenesis and larval development, and the GATA factor Serpent is essential for Ush embryonic expression. Furthermore, loss of ush function results in an overproduction of crystal cells, whereas forced expression of Ush reduces this cell population. Murine FOG-1 and FOG-2 also can repress crystal cell production, but a mutant version of FOG-2 lacking a conserved motif that binds the corepressor C-terminal binding protein fails to affect the cell lineage. The GATA factor Pannier (Pnr) is required for eye and heart development in Drosophila. When Ush, FOG-1, FOG-2, or mutant FOG-2 is coexpressed with Pnr during these developmental processes, severe eye and heart phenotypes result, consistent with a conserved negative regulation of Pnr function. These results indicate that the fly and mouse FOG proteins function similarly in three distinct cellular contexts in Drosophila, but may use different mechanisms to regulate genetic events in blood vs. cardial or eye cell lineages.

Animals↗

PubMed2001

Pannier is a transcriptional target and partner of Tinman during Drosophila cardiogenesis.

During Drosophila embryogenesis, the homeobox gene tinman is expressed in the dorsal mesoderm where it functions in the specification of precursor cells of the heart, visceral, and dorsal body wall muscles. The GATA factor gene pannier is similarly expressed in the dorsal-most part of the mesoderm where it is required for the formation of the cardial cell lineage. Despite these overlapping expression and functional properties, potential genetic and molecular interactions between the two genes remain largely unexplored. Here, we show that pannier is a direct transcriptional target of Tinman in the heart-forming region. The resulting coexpression of the two factors allows them to function combinatorially in the regulation of cardiac gene expression, and a physical interaction of the proteins has been demonstrated in cultured cells. We also define functional domains of Tinman and Pannier that are required for their synergistic activation of the D-mef2 differentiation gene in vivo. Together, these results provide important insights into the genetic mechanisms controlling heart formation in the Drosophila model system.

Animals↗

PubMed2001

Conserved cardiogenic functions of the multitype zinc-finger proteins: U-shaped and FOG-2.

Multitype zinc-finger proteins murine Friend of GATA-2 (FOG-2) and Drosophila U-shaped (Ush) are required for heart development. Both FOG proteins participate in signal transduction pathways that are essential for cardiogenesis. FOG-2 regulates signaling from the myocardium, which is required for the production of the coronary vasculature. Ush functions in a common pathway with the Heartless (Htl) fibroblast growth factor (FGF) receptor to control mesodermal cell migration, which is required for cardiogenic cell fate commitment. In vitro studies have demonstrated that both FOG proteins repress GATA factor transcriptional activation of cardiac promoters. These similarities provide further evidence for the conservation of gene functions during cardiogenesis in Drosophila and higher eukaryotes.

Animals↗

PubMed2001

Functional conservation of hematopoietic factors in Drosophila and vertebrates.

The GATA, Friend of GATA, and Runt homology domain protein families function during hematopoiesis to promote progenitor cell development and regulate lineage commitment and differentiation. The hematopoietic functions of these factors have been remarkably conserved across taxonomic groups, ranging from flies to humans. Furthermore, aspects of hematopoiesis and hemocyte function appear to be conserved. Thus, comparative studies using Drosophila and vertebrate models should enhance our understanding of blood cell development.

Animals↗

PubMed2000

Sequence and functional properties of Ets genes in the model organism Drosophila.

Detailed molecular and genetic studies, coupled with the recent sequencing of the fly genome, have identified eight Ets-related genes in the model organism Drosophila. All show homology to genes in vertebrate species. Functional analyses of some of the Drosophila ets genes have revealed their essential roles in developmental processes such as metamorphosis, oogenesis, neurogenesis, myogenesis, and eye development. Such studies have yielded important insights into our understanding of the genetic control of hormonally-regulated gene expression, programmed cell death, and signal transduction during cell fate determination and differentiation. The developmental roles of E74 (ELF1), pointed (Ets 1), yan (TEL), and D-elg (GABPalpha) will be reviewed in this article. The context of their participation in signal transduction and gene regulation will also be discussed. The information should be of significant value to the study of related processes in higher organisms due to the growing evidence for the cross species conservation of developmental mechanisms.

Amino Acid Sequence↗

PubMed2000

The multitype zinc-finger protein U-shaped functions in heart cell specification in the Drosophila embryo.

Multitype zinc-finger proteins of the Friend of GATA/U-shaped (Ush) class function as transcriptional regulators of gene expression through their modulation of GATA factor activity. To better understand intrinsic properties of these proteins, we investigated the expression and function of the ush gene during Drosophila embryogenesis. ush is dynamically expressed in the embryo, including several cell types present within the mesoderm. The gene is active in the cardiogenic mesoderm, and a loss of function results in an overproduction of both cardial and pericardial cells, indicating a requirement for the gene in the formation of these distinct cardiac cell types. Conversely, ectopic expression of ush results in a decrease in the number of cardioblasts in the heart and the inhibition of a cardial cell enhancer normally regulated by the synergistic activity of the Pannier and Tinman cardiogenic factors. These findings suggest that, similar to its known function in thoracic bristle patterning, Ush functions in the control of heart cell specification through its modulation of Pannier transcriptional activity. ush is also required for mesodermal cell migration early in embryogenesis, where it shows a genetic interaction with the Heartless fibroblast growth factor receptor gene. Taken together, these results demonstrate a critical role for the Ush transcriptional regulator in several diverse processes of mesoderm differentiation and heart formation.

Animals↗

PubMed2000

Genetically distinct cardial cells within the Drosophila heart.

Although often viewed as a simple pulsating tube, the Drosophila dorsal vessel is intricate in terms of its structure, cell types, and patterns of gene expression. Two nonidentical groups of cardial cells are observed in segments of the heart based on the differential expression of transcriptional regulators. These include sets of four cell pairs that express the homeodomain protein Tinman (Tin), alternating with groups of two cell pairs that express the orphan steroid hormone receptor Seven Up (Svp). Here we show that these myocardial cell populations are distinct in terms of their formation and gene expression profiles. The Svp-expressing cells are generated by asymmetric cell divisions of precursor cells based on decreases or increases in their numbers in numb or sanpodo mutant embryos. In contrast, the numbers of Tin-expressing cardial cells are unchanged in these genetic backgrounds, suggesting they arise from symmetric cell divisions. One function for Svp in the two pairs of cardial cells is to repress the expression of the tin gene and at least one of its targets, the beta3 tubulin gene. Further differences in the cells are substantiated by the identification of separable enhancers for D-mef2 gene transcription in the distinct cardioblast sets. Taken together, these results demonstrate a greater cellular and genetic complexity of the Drosophila heart than previously appreciated.

Animals↗

PubMed1999

Tinman regulates the transcription of the beta3 tubulin gene (betaTub60D) in the dorsal vessel of Drosophila.

During Drosophila embryogenesis, the beta3 tubulin gene is expressed in the visceral and somatic mesoderm as well as in the dorsal vessel. Transcription of the gene is limited to four pairs of cardioblasts per segment. Here we show that its expression in the dorsal vessel (dv) is mediated by a 333-bp enhancer located upstream of the gene. The homeodomain protein Tinman is also expressed in these cardioblasts, implying that Tinman might be a key regulator of the beta3 tubulin gene. Gel retardation and footprint assays indeed revealed two Tinman binding sites within the dv-specific enhancer. We analyzed the relevance of the Tinman binding sites in a transgenic fly assay and observed distinct functions for both sites. The BS(Tin-1460) site is absolutely required for expression in cardioblasts, while BS(Tin-1425) is needed for high-level expression. Thus, these two Tinman binding sites act in concert to drive beta3 tubulin gene expression during heart development. Tinman initially functions in the specification of visceral mesoderm and heart progenitors, but remains expressed in cardioblasts until dorsal closure. Overall, our data demonstrate a late function for Tinman in the regulation of beta3 tubulin gene expression in the forming heart of Drosophila.

Animals↗

PubMed1999

Ventral neuroblasts and the heartless FGF receptor are required for muscle founder cell specification in Drosophila.

Muscle founder cells are uniquely specified cells that fuse with neighboring myoblasts to generate the complex pattern of body wall muscles in the Drosophila embryo. We have investigated the positional specification of founder cells for ventral oblique muscles, marked by the restricted expression of tinman RNA and the activity of a D-mef2 enhancer. The formation of these ventral myoblasts requires the function of the Heartless FGF receptor in the mesoderm and the presence of ventral neuroblasts in the central nervous system. Overproduction of ventral neuroblasts due to the forced expression of the homeodomain protein Vnd leads to increased numbers of founder cells. These results suggest the use of a neuroectoderm-to-mesoderm signaling pathway in the specification of ventral muscle precursors.

Animals↗

PubMed1999

The homeodomain transcription factor NK-4 acts as either a transcriptional activator or repressor and interacts with the p300 coactivator and the Groucho corepressor.

NK-4 (tinman) encodes an NK-2 class homeodomain transcription factor that is required for development of the Drosophila dorsal mesoderm, including heart. Genetic evidence suggests its important role in mesoderm subdivision, yet the properties of NK-4 as a transcriptional regulator and the mechanism of gene transcription by NK-4 are not completely understood. Here, we describe its properties as a transcription factor and its interaction with the p300 coactivator and the Groucho corepressor. We demonstrate that NK-4 can activate or repress target genes in cultured cells, depending on functional domains that are conserved between Drosophila melanogaster and Drosophila virilis NK-4 genes. Using GAL4-NK-4 fusion constructs, we have mapped a transcriptional activation domain (amino acids 1-110) and repression domains (amino acids 111-188 and the homeodomain) and found an inhibitory function for the homeodomain in transactivation by NK-4. Furthermore, we demonstrate that NK-4-dependent transactivation is augmented by the p300 coactivator and show that NK-4 physically interacts with p300 via the activation domain. In addition, cotransfection experiments indicate that the repressor activity of NK-4 is strongly enhanced by the Groucho corepressor. Using immunoprecipitation and in vitro pull-down assays, we show that NK-4 directly interacts with the Groucho corepressor, for which the homeodomain is required. Together, our results indicate that NK-4 can act as either a transcriptional activator or repressor and provide the first evidence of NK-4 interactions with the p300 coactivator and the Groucho corepressor.

Amino Acid Sequence↗

PubMed1999

Oogenic function of the myogenic factor D-MEF2: negative regulation of the decapentaplegic receptor gene thick veins.

The myogenic factor D-MEF2 is required for the proper differentiation of muscle cells during Drosophila embryogenesis and the correct patterning of indirect flight muscles assembled during later metamorphosis. In addition to these essential myogenic functions, mutant D-mef2 adult females are weakly fertile and produce defective eggs. D-MEF2 is expressed in nurse and follicle cells of the wild-type egg chamber. We have analyzed the D-mef2 oogenic phenotype and show that the gene is required for the normal patterning and differentiation of the centripetally migrating follicle cells that are crucial for development of the anterior chorionic structures. D-mef2 alleles exhibit a genetic interaction with a dominant-negative allele of thick veins (tkv), which encodes a type I receptor of the Decapentaplegic-signaling pathway. tkv RNA is overexpressed in D-mef2 mutant egg chambers, and, conversely, forced expression of D-mef2 represses tkv expression. These results indicate a role for D-MEF2 in the regulation of tkv gene expression and Decapentaplegic signal transduction that are essential for proper determination and/or differentiation of the anterior follicle cells. Additionally, they demonstrate a vital function for the D-MEF2 transcription factor in multiple genetic pathways during Drosophila development.

Animals↗

PubMed1999

The zinc finger proteins Pannier and GATA4 function as cardiogenic factors in Drosophila.

The regulation of cardiac gene expression by GATA zinc finger transcription factors is well documented in vertebrates. However, genetic studies in mice have failed to demonstrate a function for these proteins in cardiomyocyte specification. In Drosophila, the existence of a cardiogenic GATA factor has been implicated through the analysis of a cardial cell enhancer of the muscle differentiation gene D-mef2. We show that the GATA gene pannier is expressed in the dorsal mesoderm and required for cardial cell formation while repressing a pericardial cell fate. Ectopic expression of Pannier results in cardial cell overproduction, while co-expression of Pannier and the homeodomain protein Tinman synergistically activate cardiac gene expression and induce cardial cells. The related GATA4 protein of mice likewise functions as a cardiogenic factor in Drosophila, demonstrating an evolutionarily conserved function between Pannier and GATA4 in heart development.

Animals↗

PubMed1999

An improved stereotactic technique for cyst cannulation.

Stereotactic techniques for cannulation of cystic structures, within the brain, are well known. Superimposed structures (vessels, ventricles, etc.) may make this problematic as does the need to approach the cystic structure perpendicular to its tangent plane (rather than "glancing") as with a craniopharyngioma cyst. To facilitate a three-dimensional visualization of the trajectory, we have employed digital holography. Transparent holographic images of cystic structures, ventricles, and sulci are rendered from T2-weighted MR data. Holographic images of vascular structures are rendered from CT or MR angiographic data. Vascular holograms are superimposed over the brain holograms, demonstrating the spatial relationships of these structures with regard to each other. Holographic images of the skull are rendered from CT slices. A Laitinen stereotactic frame (Sandstrom) is placed on the patient prior to obtaining the CT. The skull, pre-existing shunt catheters, and the stereotactic frame are all readily visible. The brain and vascular holograms are superimposed on these. The resulting image clearly demonstrates cystic structures, ventricles, vessels, pre-existing catheters, all within the skull and stereotactic frame. Using this holographic image as a "phantom", the actual Laitinen stereotactic frame is placed within its holographic image. The optical trajectory is then chosen, and the articulated arm of the stereotactic device is so adjusted. Subsequently, the frame is used to effect stereotactic placement of the cannula, in the usual manner. The major advantages of this technique are twofold. The first advantage lies with the fact that the surgeon can readily visualize the entire trajectory of the needle, and easily appreciate all structures which may be encountered by the needle on its passage from the skull to the target. Presumably, the surgeon's knowledge of anatomy would unable such knowledge to be apparent, but in complex cases the "safe" corridor may be rather small, and its limits may not be intuitively obvious. This is all the more the case, when obstacles along the pathway are pathologically distorted, or when they are not of tissue origin (shunt catheters, etc.). Employing this technique, we have successfully cannulated cystic structures in six patients, three of which presented with complex trajectory problems.

Brain Diseases↗

PubMed1998

The myogenic regulatory gene Mef2 is a direct target for transcriptional activation by Twist during Drosophila myogenesis.

MEF2 is a MADS-box transcription factor required for muscle development in Drosophila. Here, we show that the bHLH transcription factor Twist directly regulates Mef2 expression in adult somatic muscle precursor cells via a 175-bp enhancer located 2245 bp upstream of the transcriptional start site. Within this element, a single evolutionarily conserved E box is essential for enhancer activity. Twist protein can bind to this E box to activate Mef2 transcription, and ectopic expression of twist results in ectopic activation of the wild-type 175-bp enhancer. By use of a temperature-sensitive mutant of twist, we show that activation of Mef2 transcription via this enhancer by Twist is required for normal adult muscle development, and reduction in Twist function results in phenotypes similar to those observed previously in Mef2 mutant adults. The 175-bp enhancer is also active in the embryonic mesoderm, indicating that this enhancer functions at multiple times during development, and its function is dependent on the same conserved E box. In embryos, a reduction in Twist function also strongly reduced Mef2 expression. These findings define a novel transcriptional pathway required for skeletal muscle development and identify Twist as an essential and direct regulator of Mef2 expression in the somatic mesoderm.

Animals↗

PubMed1998

Combinatorial control of Drosophila mef2 gene expression in cardiac and somatic muscle cell lineages.

The Drosophila mef2 gene encodes a MADS domain transcription factor required for the differentiation of cardiac, somatic, and visceral muscles during embryogenesis and the patterning of adult indirect flight muscles assembled during metamorphosis. A prerequisite for D-MEF2 function in myogenesis is its precise expression in multiple cell types during development. Novel enhancers for D-mef2 transcription in cardiac and adult muscle precursor cells have been identified and their regulation by the Tinman and Twist myogenic factors have been demonstrated. However, these results suggested the existence of additional regulators and provided limited information on the specification of progenitor cells for different muscle lineages. We have further characterized the heart enhancer and show it is part of a complex regulatory region controlling the activation and repression of D-mef2 transcription in several cell types. The mutation of a GATA sequence in the enhancer changes its specificity from cardial to pericardial cells. Also, the addition of flanking sequences to the heart enhancer results in expression in a new cell type, that being the founder cells of a subset of body wall muscles. As tinman function is required for D-mef2 expression in both the cardial and founder cells, these results define a shared regulatory DNA that functions in distinct lineages due to the combinatorial activity of Tinman and other factors that work through adjacent sequences. The analysis of D-mef2-lacZ fusion genes in mutant embryos revealed that the specification of the muscle precursor cells involved the wingless gene and the activation of a receptor tyrosine kinase signaling pathway.

Animals↗

PubMed1997

Twist-mediated activation of the NK-4 homeobox gene in the visceral mesoderm of Drosophila requires two distinct clusters of E-box regulatory elements.

NK-4, also called msh2 and tinman, encodes a homeodomain transcription factor that is required for the development of the dorsal mesoderm and its derivatives in the Drosophila embryo. Genetic analyses indicate that NK-4 resides downstream of the mesodermal determinant twist, which encodes a basic helix-loop-helix-type transcription factor. However, the regulation of NK-4 by twist remains poorly understood. Using expression assays in cultured cells and transgenic flies, we show that two distinct clusters of E-box regulatory sequences, present upstream of the NK-4 gene, mediate NK-4 expression in the visceral mesoderm. These elements are conserved between the Drosophila melanogaster and Drosophila virilis NK-4 genes and serve as binding sites for Twist (E1 cluster) and NK-4 (E2 cluster) proteins. In cultured cells, Twist and NK-4 binding results in activation of NK-4 gene expression. In transgenic animals, the E1 and E2 clusters are functionally connected, and both elements are required for NK-4 activation in cells of the visceral mesoderm and also for NK-4 repression in cells of the somatic musculature. These results demonstrate that NK-4 is a direct transcriptional target for Twist and its own gene product in visceral mesodermal cells, supporting the idea that twist and NK-4 function in the subdivision of the mesoderm during Drosophila embryogenesis.

Animals↗

PubMed1997

D-mef2 is a target for Tinman activation during Drosophila heart development.

The NK-type homeobox gene tinman and the MADS box gene D-mef2 encode transcription factors required for the development and differentiation of the Drosophila heart, and closely related genes regulate cardiogenesis in vertebrates. Genetic analyses indicate that tinman and D-mef2 act at early and late steps, respectively, in the cardiogenic lineage. However, it is unknown whether regulatory interactions exist between these developmental control genes. We show that D-mef2 expression in the developing Drosophila heart requires a novel upstream enhancer containing two Tinman binding sites, both of which are essential for enhancer function in cardiac muscle cells. Transcriptional activity of this cardiac enhancer is dependent on tinman function, and ectopic Tinman expression activates the enhancer outside the cardiac lineage. These results define the only known in vivo target for transcriptional activation by Tinman and demonstrate that D-mef2 lies directly downstream of tinman in the genetic cascade controlling heart formation in Drosophila.

Animals↗

PubMed1996

Wingless signaling induces nautilus expression in the ventral mesoderm of the Drosophila embryo.

The segregation of founder cells from the somatic mesoderm is a prerequisite for the formation of body wall muscles in the Drosophila embryo. The myogenic basic helix-loop-helix protein, Nautilus (Nau), is expressed in a subset of these founder cells in medial and lateral positions in the somatic mesoderm. Mutations in the wingless (wg) gene, which encodes a secreted growth factor, lead to the complete loss of Nau-expressing medial muscle precursor cell clusters, but not lateral clusters. Using the GAL4/UAS system, we demonstrate that the wg-derived signal can originate from either ectoderm or mesoderm to influence nau expression. By using a temperature-sensitive wg allele, we also show that wg function is required during and after gastrulation for the formation of Nau-expressing medial muscle precursor cell clusters. Our results, combined with recent studies from chick, suggest a conserved role for Wg signaling pathways during muscle development.

Alleles↗