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R Bodmer

Publications and source records attributed to R Bodmer.

At least 19 recordsLinked to original sources
PubMed2001

The selector gene cut represses a neural cell fate that is specified independently of the Achaete-Scute-Complex and atonal.

The peripheral nervous system (PNS) of Drosophila offers a powerful system to precisely identify individual cells and dissect their genetic pathways of development. The mode of specification of a subset of larval PNS cells, the multiple dendritic (md) neurons (or type II neurons), is complex and still poorly understood. Within the dorsal thoracic and abdominal segments, two md neurons, dbd and dda1, apparently require the proneural gene amos but not atonal (ato) or Achaete-Scute-Complex (ASC) genes. ASC normally acts via the neural selector gene cut to specify appropriate sensory organ identities. Here, we show that dbd- and dda1-type differentiation is suppressed by cut in dorsal ASC-dependent md neurons. Thus, cut is not only required to promote an ASC-dependent mode of differentiation, but also represses an ASC- and ato-independent fate that leads to dbd and dda1 differentiation.

Alleles↗
PubMed2000

Cardiac enhancer activity of the homeobox gene tinman depends on CREB consensus binding sites in Drosophila.

The Drosophila homeobox gene tinman plays a critical role in subdividing the early mesoderm. In particular, tinman is absolutely required for formation of the heart and visceral mesoderm. tinman expression is initiated throughout the mesoderm of the trunk region under the control of the bHLH transcription factor encoded by the twist gene, a determinant of all mesoderm. Later, tinman expression is restricted to the dorsal portion of the mesoderm, a process that is directed by decapentaplegic (dpp) whose product (a TGF-beta-related protein) is secreted by the overlaying ectoderm. Further restriction of tinman expression to the cardiac progenitors, in which it will persist throughout development, involves the secreted segmentation gene product encoded by wingless (wg, a Drosophila Wnt gene). Here, we show that strong early expression depends on the synergistic action of an enhancer element at the 5' end of the gene in conjunction with an element in the first intron. Moreover, two distinct enhancer regions are responsible for tinman expression in the heart: one region confers expression in the heart-tube-associated pericardial cells, the other element drives expression in the contractile, myocardial cells. The latter element contains two CREB consensus binding sites that are essential for cardiac-specific expression. genesis 26:55-66, 2000.

Animals↗
PubMed1999

SIP1, a novel zinc finger/homeodomain repressor, interacts with Smad proteins and binds to 5'-CACCT sequences in candidate target genes.

Activation of transforming growth factor beta receptors causes the phosphorylation and nuclear translocation of Smad proteins, which then participate in the regulation of expression of target genes. We describe a novel Smad-interacting protein, SIP1, which was identified using the yeast two-hybrid system. Although SIP1 interacts with the MH2 domain of receptor-regulated Smads in yeast and in vitro, its interaction with full-length Smads in mammalian cells requires receptor-mediated Smad activation. SIP1 is a new member of the deltaEF1/Zfh-1 family of two-handed zinc finger/homeodomain proteins. Like deltaEF1, SIP1 binds to 5'-CACCT sequences in different promoters, including the Xenopus brachyury promoter. Overexpression of either full-length SIP1 or its C-terminal zinc finger cluster, which bind to the Xbra2 promoter in vitro, prevented expression of the endogenous Xbra gene in early Xenopus embryos. Therefore, SIP1, like deltaEF1, is likely to be a transcriptional repressor, which may be involved in the regulation of at least one immediate response gene for activin-dependent signal transduction pathways. The identification of this Smad-interacting protein opens new routes to investigate the mechanisms by which transforming growth factor beta members exert their effects on expression of target genes in responsive cells and in the vertebrate embryo.

Amino Acid Sequence↗
PubMed1999

Sequence and developmental expression of amphioxus AmphiNk2-1: insights into the evolutionary origin of the vertebrate thyroid gland and forebrain.

We characterized an amphioxus NK-2 homeobox gene (AmphiNk2-1), a homologue of vertebrate Nkx2-1, which is involved in the development of the central nervous system and thyroid gland. At the early neurula stage of amphioxus, AmphiNk2-1 expression is first detected medially in the neural plate. By the mid-neurula stage, expression is localized ventrally in the nerve cord and also begins in the endoderm. During the late neurula stage, the ventral neural expression becomes transiently segmented posteriorly and is then down-regulated except in the cerebral vesicle at the anterior end of the central nervous system. Within the cerebral vesicle AmphiNk2-1 is expressed in a broad ventral domain, probably comprising both the floor plate and basal plate regions; this pattern is comparable to Nkx2-1 expression in the mouse diencephalon. In the anterior part of the gut, expression becomes intense in the endostyle (the right wall of the pharynx), which is the presumed homologue of the vertebrate thyroid gland. More posteriorly, there is transitory expression in the midgut and hindgut. In sum, the present results help to support homologies (1) between the amphioxus endostyle and the vertebrate thyroid gland and (2) between the amphioxus cerebral vesicle and the vertebrate diencephalic forebrain.

Amino Acid Sequence↗
PubMed1999

The pioneer gene, apontic, is required for morphogenesis and function of the Drosophila heart.

In an effort to isolate genes required for heart development and to further our understanding of cardiac specification at the molecular level, we screened PlacZ enhancer trap lines for expression in the Drosophila heart. One of the lines generated in this screen, designated B2-2-15, was particularly interesting because of its early pattern of expression in cardiac precursor cells, which is dependent on the homeobox gene tinman, a key determinant of heart development in Drosophila. We isolated and characterized a gene in the vicinity of B2-2-15 that exhibits an identical expression pattern than the reporter gene of the enhancer trap. The product of his gene, apontic (apt; see also "Gellon et al., 1997"), does not appear to have any homology with known genes. apt mutant embryos show distinct abnormalities in heart morphology as early as mid-embryonic stages when the heart tube assembles, in that segments of heart cells (those of myocardial and pericardial identity) are often missing. Most strikingly, however, apt mutant embryos or larvae only develop a much reduced heart rate, perhaps because of defects in the assembly of an intact heart tube and/or because of defects in the function or physiological control of the myocardial cells, which normally mediate heart contractions. These cardiac defects may be the cause of death of these mutants during late embryonic or early larval stages.

Alleles↗
PubMed1999

A fluorescent quantitative PCR approach to map gene deletions in the Drosophila genome.

We report the application of TaqMan quantitative PCR (QPCR) to map Drosophila chromosome deficiencies by discrimination of twofold copy number differences. For a model system, we used this technology to confirm the X chromosomal mapping of Dspt6 given the autosomal mapping of Dspt4. We then used this technique on both preexisting deletion mutant flies and flies that we generated with deletions to demonstrate the presence or absence of Dspt6, Dspt4, and swa in various deletion mutant flies. In contrast with in situ hybridization studies, QPCR both vitiates the need to do these more intricate studies, and it is more accurate as the site of deletion can be known down to the 10(2)-bp level. We then successfully applied the technique to the analysis of transcription, demonstrating that the amount of Dspt6 or Dspt4 transcriptional product depended directly on the dosage of the Dspt6 or Dspt4 gene, respectively. The rapidity and precision of this method demonstrates its applicability in Drosophila genetics, the rapid and accurate mapping of Drosophila deletion mutants.

Animals↗
PubMed1999

The Drosophila homeobox genes zfh-1 and even-skipped are required for cardiac-specific differentiation of a numb-dependent lineage decision.

A series of inductive signals are necessary to subdivide the mesoderm in order to allow the formation of the progenitor cells of the heart. Mesoderm-endogenous transcription factors, such as those encoded by twist and tinman, seem to cooperate with these signals to confer correct context and competence for a cardiac cell fate. Additional factors are likely to be required for the appropriate specification of individual cell types within the forming heart. Similar to tinman, the zinc finger- and homeobox-containing gene, zfh-1, is expressed in the early mesoderm and later in the forming heart, suggesting a possible role in heart development. Here, we show that zfh-1 is specifically required for formation of the even-skipped (eve)-expressing subset of pericardial cells (EPCs), without affecting the formation of their siblings, the founders of a dorsal body wall muscle (DA1). In addition to zfh-1, mesodermal eve itself appears to be needed for correct EPC differentiation, possibly as a direct target of zfh-1. Epistasis experiments show that zfh-1 specifies EPC development independently of numb, the lineage gene that controls DA1 founder versus EPC cell fate. We discuss the combinatorial control mechanisms that specify the EPC cell fate in a spatially precise pattern within the embryo.

Animals↗
PubMed1998

Differential rescue of visceral and cardiac defects in Drosophila by vertebrate tinman-related genes.

tinman, a mesodermal NK2-type homeobox gene, is absolutely required for the subdivision of the early Drosophila mesoderm and for the formation of the heart as well as the visceral muscle primordia. Several vertebrate relatives of tinman, many of which are predominately expressed in the very early cardiac progenitors (and pharyngeal endoderm), also seem to promote heart development. Here, we show that most of these vertebrate tinman-related genes can readily substitute for Drosophila tinman function in promoting visceral mesoderm-specific marker gene expression, but much less in promoting cardiac-specific gene expression indicative of heart development. In addition, another mesodermal NK2-type gene from Drosophila, bagpipe, which is normally only needed for visceral mesoderm but not heart development, cannot substitute for tinman at all. These data indicate that the functional equivalence of the tinman-related subclass of NK2-type genes (in activating markers of visceral mesoderm development in Drosophila) is specific to this subclass and distinct from other homeobox genes. Despite the apparent overall conservation of heart development between vertebrates and invertebrates, the differential rescue of visceral mesoderm versus heart development suggests that some of the molecular mechanisms of organ formation may have diverged during evolution.

Animals↗
PubMed1998

Functional analysis of the Numb phosphotyrosine-binding domain using site-directed mutagenesis.

The Numb protein is involved in cell fate determination during Drosophila neural development. Numb has a protein domain homologous to the phosphotyrosine-binding domain (PTB) in the adaptor protein Shc. In Shc, this domain interacts with specific phosphotyrosine containing motifs on receptor tyrosine kinases and other signaling molecules. Residues N-terminal to the phosphotyrosine are also crucial for phosphopeptide binding to the Shc PTB domain. Several amino acid residues in Shc have been implicated by site-directed mutagenesis to be critical for Shc binding to receptor tyrosine kinases. We have generated homologous mutations in Numb to test whether, in vivo, these changes affect Numb function during Drosophila sensory organ development. Two independent amino acid changes that interfere with Shc binding to phosphotyrosine residues do not affect Numb activity in vivo. In contrast, a mutation shown to abrogate the ability of the Shc PTB domain to bind residues upstream of the phosphotyrosine virtually eliminates Numb function. Similar results were observed in vitro by examining the binding of the Numb PTB domain to proteins from Schneider S2 cells. Our data confirm the importance of the PTB domain for Numb function but strongly suggest that the Numb PTB domain is not involved in phosphotyrosine-dependent interactions.

Amino Acid Sequence↗
PubMed1998

Heart development in Drosophila and vertebrates: conservation of molecular mechanisms.

Vertebrate and insect (Drosophila) hearts look and function quite differently from each other. Nevertheless, during embryogenesis their mesodermal origin and initial assembly into a linear heart tube are comparable in many respects. In the past few years, numerous gene functions have been identified that are utilized by both vertebrates and Drosophila for the specification and differentiation of the heart progenitor cells. These studies have begun with the discovery of the homeobox gene tinman in Drosophila and its vertebrate counterparts. By now, there is also evidence that MEF2 transcription factors and TGF-beta signaling have cardiogenic functions in both these systems. Perhaps in a few years, the GATA and HAND transcription factors and Wnt signaling, which currently only have a demonstrated cardiogenic function in one of the systems, may also be part of this group. One of the pressing but still wide open questions is if the spectrum of targets for these transcription factors and signaling pathways is also conserved.

Animals↗
PubMed1998

Dual role for the zeste-white3/shaggy-encoded kinase in mesoderm and heart development of Drosophila.

A Drosophila homolog of the serine/threonine kinase GSK-3 beta, encoded by the zest-white3/shaggy gene (zw3), has been implicated as a maternally provided antagonist of zygotic signaling by the secreted segmentation gene wingless (wg). The wg signal apparently causes a spatially localized inhibition of the ubiquitous repressor function of zw3. This double negative mechanism of signal transduction has been shown to mediate the patterning function of Wg in a number of developmental processes. Although wg is absolutely required for specifying the heart progenitors within the mesoderm of Drosophila, the role of zw3 in this process has been unclear. Here, we present evidence that zw3 has a dual role in mesoderm development: (1) zw3 acts as an antagonist in cardiogenic wg signal transduction, and (2) zw3 also seems to be required to promote positively the formation of a larger mesodermal region, the tinman- and dpp-dependent "dorsal mesoderm," which is a prerequisite not only for cardiogenesis, but also for visceral mesoderm formation. We also demonstrate that a recently identified proximal component of the wg cascade, which is a transcription factor encoded by pangolin/dTCF (dTCF), also seems to mediate wg-dependent cardiogenesis. Further, we present evidence that Notch (N), which opposes wg signaling in other situations, is unlikely to be directly involved in the cardiogenic wg pathway, but seems to have multiple other myogenic functions, one of which is to inhibit mesoderm differentiation altogether, when overexpressed as a constitutively active form.

Animals↗
PubMed1998

Characterization and developmental expression of AmphiNk2-2, an NK2 class homeobox gene from Amphioxus. (Phylum Chordata; Subphylum Cephalochordata).

The genome of amphioxus includes AmphiNk2-2, the first gene of the NK2 homeobox class to be demonstrated in any invertebrate deuterostome. AmphiNk2-2 encodes a protein with a TN domain, homeodomain, and NK2-specific domain; on the basis of amino acid identities in these conserved regions, AmphiNk2-2 is a homolog of Drosophila vnd and vertebrate Nkx2-2. During amphioxus development, expression of Amph- iNk2-2 is first detected ventrally in the endoderm of late gastrulae. In neurulae, endodermal expression divides into three domains (the pharynx, midgut, and hindgut), and neural expression commences in two longitudinal bands of cells in the anterior neural tube. These neural tube cells occupy a ventrolateral position on either side of the cerebral vesicle (the probable homolog of the vertebrate diencephalic forebrain). The dynamic expression patterns of AmphiNkx2-2 suggest successive roles, first in regionalizing the endoderm and nervous system and later during differentiation of specific cell types in the gut (possibly peptide endocrine cells) and brain (possibly including axon outgrowth and guidance).

Amino Acid Sequence↗
PubMed1998

Mesodermal cell fate decisions in Drosophila are under the control of the lineage genes numb, Notch, and sanpodo.

In Drosophila, much has been learned about the specification of neuronal cell fates but little is known about the lineage of mesodermal cells with different developmental fates. Initially in development, individual mesodermal precursor cells are singled out to become the founder cells for specific muscles. The selection of muscle founder cells is thought to employ a Notch-mediated process of lateral inhibition, similar to what is observed for the specification of neural precursors. These muscle founder cells then seem to fuse with the surrounding, uncommitted myocytes inducing the formation of muscle fiber syncytia. In contrast, the differentiated progeny of neural precursor cells are usually the result of a fixed pattern of asymmetric cell divisions which are directed, in part, by interactions between numb, a localized intracellular-receptor protein, sanpodo (spdo), a potential tropomodulin homolog, and Notch, a transmembrane receptor protein. Here, we have investigated the role of these neural lineage genes in the cell fate specification of muscle and heart precursors. In particular, we have focused on a progenitor cell that is likely to produce a mixed lineage, generating both a pericardial heart cell and a somatic muscle founder cell. We show that the asymmetric segregation of Numb into one of these daughter cells antagonizes the function of Notch and spdo by preventing the presumptive muscle founder from assuming the same fate as its cardiac sibling. Our results suggest that asymmetric cell divisions, in addition to the previously-documented inductive mechanisms, play a major role in cardiac and somatic muscle patterning and that additionally the cytoskeleton may have a role in the asymmetrical localization of cell fate determinants.

Animals↗
PubMed1996

Primary structure, neural-specific expression, and chromosomal localization of Cux-2, a second murine homeobox gene related to Drosophila cut.

The cut locus of Drosophila encodes a diverged homeodomain-containing protein that is required for the development of external sensory (es) organs and other tissues. A homologous gene (Cux-1) that encodes a transcriptional repressor has been identified in the mouse and other mammals. We have identified a second murine homeobox-containing gene (designated Cux-2) that is structurally related to Drosophila cut. The murine Cux-2 homeobox was similar to Drosophila cut and encoded a homeodomain that contained a characteristic histidine residue at position 50. The predicted Cux-2 protein contained 1426 amino acids and included three internal 60-amino acid repeats (Cut repeats) that were previously found in Drosophila Cut and murine Cux-1. Unlike Cux-1, expression of Cux-2 was restricted to neural tissue. In the adult brain, Cux-2 was prominently expressed in neurons in the thalamus and limbic system. In embryos, Cux-2 was expressed in the developing central and peripheral nervous systems, including the telencephalon and peripheral ganglia of the trigeminal and glossopharyngeal nerves. A glutathione S-transferase fusion protein containing the carboxyl-terminal Cut repeat and homeodomain of Cux-2 exhibited sequence-specific binding to oligonucleotides derived from the promoter of the Ncam gene. Using an interspecific backcross panel, Cux-1 and Cux-2 were mapped to distinct loci that were genetically linked on distal chromosome 5. These results demonstrate that a family of homeobox genes related to Drosophila cut is located on chromosome 5 in the mouse. Cux-2 is expressed exclusively in the central and peripheral nervous systems, and the Cux-2 gene product binds to DNA in a sequence-specific manner. Cux-2 may encode a transcription factor that is involved in neural specification in mammals.

Amino Acid Sequence↗
PubMed1996

The wingless signaling pathway is directly involved in Drosophila heart development.

Heart development in both vertebrates and Drosophila is initiated by bilaterally symmetrical primordia that may be of equivalent embryological origin: the anterior lateral plate mesoderm in vertebrates and the dorsal-most mesoderm in arthropods. These mesodermal progenitors then merge into a heart tube at the ventral midline (vertebrates) or the dorsal midline (Drosophila). These observations suggest that there may be similarities between vertebrate and invertebrate heart development. The homeobox gene, tinman, is required for heart as well as visceral mesoderm formation in Drosophila, and at least one of several vertebrate genes with similarities in protein sequence and cardiac expression to tinman is crucial for heart development in vertebrates. Inductive signals are also required for Drosophila heart development: The secreted gene product of wingless (wg) is critical for heart development during a time period distinct from its function in segmentation and neurogenesis. Here, we show that wg is epistatic to hedgehog (hh), another secreted segmentation gene product, in its requirement for heart formation. We also provide evidence show that downstream of wg in the signal transduction cascade, dishevelled (dsh, a pioneer protein) and armadillo (arm, beta-catenin homolog) are mediating the cardiogenic Wg signal. In particular, overexpression of dsh can restore heart formation in the absence of wg function. We discuss the possibility that Wg signaling is part of a combinatorial mechanism to specify the cardiac mesoderm.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Cell lineage analysis of the Drosophila peripheral nervous system.

The peripheral nervous system (PNS) of Drosophila provides a very well-characterized model system for studying the genes involved in basic processes of neurogenesis. Because of its simplicity and stereotyped pattern, each cell of the PNS can be individually identified and the phenotypic consequences of mutations can be studied in detail. Thus, some of the genetic mechanisms leading to the formation of type I sensory organs, the external, bristle-type sensory organs (es), and the internal, stretch-receptive chordotonal organs (ch) have been elucidated. Each sensory organ seems to be generated by a stereotyped pattern of cell division of individual ectodermal precursor cells. Recent advances in cell lineage analysis of the PNS have provided a detailed picture of almost all the lineages in the PNS, including those giving rise to the type II sensory neurons, also known as multiple dendritic (md) neurons. This knowledge will be instrumental in the precise characterization of the phenotypes associated with mutations in known and new genes and their interactions which determine cell fate decisions during neurogenesis. Here, we describe and compare three recently developed methods by which cell lineages have been assessed: single cell transplantation, bromodeoxyuridine (BrdU) incorporation studies, and the flp/FRT recombinase system from yeast. In the light of a more complete knowledge of the PNS lineages, we will discuss the effects of known mutations that alter neuronal cell fates.

Animals↗