Biomedical subjects

Heinrich Reichert

Publications and source records attributed to Heinrich Reichert.

13 recordsLinked to original sources

PubMed2006

The brain tumor gene negatively regulates neural progenitor cell proliferation in the larval central brain of Drosophila.

Brain development in Drosophila is characterized by two neurogenic periods, one during embryogenesis and a second during larval life. Although much is known about embryonic neurogenesis, little is known about the genetic control of postembryonic brain development. Here we use mosaic analysis with a repressible cell marker (MARCM) to study the role of the brain tumor (brat) gene in neural proliferation control and tumour suppression in postembryonic brain development of Drosophila. Our findings indicate that overproliferation in brat mutants is due to loss of proliferation control in the larval central brain and not in the optic lobe. Clonal analysis indicates that the brat mutation affects cell proliferation in a cell-autonomous manner and cell cycle marker expression shows that cells of brat mutant clones show uncontrolled proliferation, which persists into adulthood. Analysis of the expression of molecular markers, which characterize cell types in wild-type neural lineages, indicates that brat mutant clones comprise an excessive number of cells, which have molecular features of undifferentiated progenitor cells that lack nuclear Prospero (Pros). pros mutant clones phenocopy brat mutant clones in the larval central brain, and targeted expression of wild-type pros in brat mutant clones promotes cell cycle exit and differentiation of brat mutant cells, thereby abrogating brain tumour formation. Taken together, our results provide evidence that the tumour suppressor brat negatively regulates cell proliferation during larval central brain development of Drosophila, and suggest that Prospero acts as a key downstream effector of brat in cell fate specification and proliferation control.

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PubMed2006

The columnar gene vnd is required for tritocerebral neuromere formation during embryonic brain development of Drosophila.

In Drosophila, evolutionarily conserved transcription factors are required for the specification of neural lineages along the anteroposterior and dorsoventral axes, such as Hox genes for anteroposterior and columnar genes for dorsoventral patterning. In this report, we analyse the role of the columnar patterning gene ventral nervous system defective (vnd) in embryonic brain development. Expression of vnd is observed in specific subsets of cells in all brain neuromeres. Loss-of-function analysis focussed on the tritocerebrum shows that inactivation of vnd results in regionalized axonal patterning defects, which are comparable with the brain phenotype caused by mutation of the Hox gene labial (lab). However, in contrast to lab activity in specifying tritocerebral neuronal identity, vnd is required for the formation and specification of tritocerebral neural lineages. Thus, in early vnd mutant embryos, the Tv1-Tv5 neuroblasts, which normally express lab, do not form. Later in embryogenesis, vnd mutants show an extensive loss of lab-expressing cells because of increased apoptotic activity, resulting in a gap-like brain phenotype that is characterized by an almost complete absence of the tritocerebral neuromere. Correspondingly, genetic block of apoptosis in vnd mutant embryos partially restores tritocerebral cells as well as axon tracts. Taken together, our results indicate that vnd is required for the genesis and proper identity specification of tritocerebral neural lineages during embryonic brain development of Drosophila.

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PubMed2005

ventral veins lacking is required for specification of the tritocerebrum in embryonic brain development of Drosophila.

The homeotic or Hox genes encode a network of conserved transcription factors which provide axial positional information and control segment morphology in development and evolution. During embryonic brain development of Drosophila, the Hox gene labial (lab) is essential for tritocerebral neuromere specification; lab loss of function results in tritocerebral cells that fail to adopt a neuronal identity, causing axonal pathfinding defects. Here we present evidence that the POU-homeodomain DNA-binding protein ventral veins lacking (vvl) acts genetically downstream of lab in the specification of the tritocerebral neuromere. In the embryonic brain, vvl expression is seen in all brain neuromeres, including the tritocerebral lab domain. Lab mutant analysis shows that vvl expression in the tritocerebrum is dependent on lab activity. Loss-of-function analysis focussed on the tritocerebrum reveals that inactivation of vvl results in patterning defects which are comparable to the brain phenotype caused by null mutation of lab. In the absence of vvl, mutant tritocerebral cells are generated and positioned correctly, but these cells fail to express neuronal markers indicating defects in neuronal differentiation. Moreover, longitudinal axon pathways in the tritocerebrum are severely reduced or absent and the tritocerebral commissure is missing in the vvl mutant brain. Genetic rescue experiments show that vvl is able to partially replace lab in the specification of the tritocerebral neuromere. Our results indicate that vvl acts downstream of the Hox gene lab and regulates specific aspects of neuronal differentiation within the tritocerebral neuromere during embryonic brain development of Drosophila.

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PubMed2005

The egghead gene is required for compartmentalization in Drosophila optic lobe development.

The correct targeting of photoreceptor neurons (R-cells) in the developing Drosophila visual system requires multiple guidance systems in the eye-brain complex as well as the precise organization of the target area. Here, we report that the egghead (egh) gene, encoding a glycosyltransferase, is required for a compartment boundary between lamina glia and lobula cortex, which is necessary for appropriate R1-R6 innervation of the lamina. In the absence of egh, R1-R6 axons form a disorganized lamina plexus and some R1-R6 axons project abnormally to the medulla instead of the lamina. Mosaic analysis demonstrates that this is not due to a loss of egh function in the eye or in the neurons and glia of the lamina. Rather, as indicated by clonal analysis and cell-specific genetic rescue experiments, egh is required in cells of the lobula complex primordium which transiently abuts the lamina and medulla in the developing larval brain. In the absence of egh, perturbation of sheath-like glial processes occurs at the boundary region delimiting lamina glia and lobula cortex, and inappropriate invasion of lobula cortex cells across this boundary region disrupts the pattern of lamina glia resulting in inappropriate R1-R6 innervation. This finding underscores the importance of the lamina/lobula compartment boundary in R1-R6 axon targeting.

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PubMed2005

A tripartite organization of the urbilaterian brain: developmental genetic evidence from Drosophila.

Developmental genetic studies suggest that the embryonic vertebrate brain has a tripartite ground plan consisting of a forebrain/midbrain, a hindbrain, and an intervening midbrain/hindbrain boundary region, which are characterized by the specific expression of the Otx, Hox and Pax-2/5/8 genes. Recent studies in Drosophila reveal similarities in the expression and function of these genes in patterning the embryonic brains of flies and vertebrates. Thus, in Drosophila, as is vertebrates, a Pax2/5/8 domain is located between an anterior otd/Otx2 region and a posterior Hox region of the embryonic brain. Moreover, in Drosophila, as in vertebrates, this Pax2/5/8 domain is located at the interface of the otd/Otx2 domain and a posterior unplugged/Gbx2 domain. Furthermore, in Drosophila, as in vertebrates, inactivation of otd/Otx2 or of unplugged/Gbx2 results in a comparable mispositioning or loss of orthologous gene expression domains in the embryonic brain. These developmental genetic similarities suggest that the tripartite ground plan, which characterizes the developing vertebrate brain, is also at the basis of the developing insect brain. This, in turn, implies that a tripartite organization of the embryonic brain may characterize all extant bilaterians, and thus may already have been established in the last common urbilaterian ancestor of all bilaterians.

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PubMed2004

Transcriptional signature of an adult brain tumor in Drosophila.

BACKGROUND: Mutations and gene expression alterations in brain tumors have been extensively investigated, however the causes of brain tumorigenesis are largely unknown. Animal models are necessary to correlate altered transcriptional activity and tumor phenotype and to better understand how these alterations cause malignant growth. In order to gain insights into the in vivo transcriptional activity associated with a brain tumor, we carried out genome-wide microarray expression analyses of an adult brain tumor in Drosophila caused by homozygous mutation in the tumor suppressor gene brain tumor (brat). RESULTS: Two independent genome-wide gene expression studies using two different oligonucleotide microarray platforms were used to compare the transcriptome of adult wildtype flies with mutants displaying the adult bratk06028 mutant brain tumor. Cross-validation and stringent statistical criteria identified a core transcriptional signature of brat(k06028) neoplastic tissue. We find significant expression level changes for 321 annotated genes associated with the adult neoplastic brat(k06028) tissue indicating elevated and aberrant metabolic and cell cycle activity, upregulation of the basal transcriptional machinery, as well as elevated and aberrant activity of ribosome synthesis and translation control. One fifth of these genes show homology to known mammalian genes involved in cancer formation. CONCLUSION: Our results identify for the first time the genome-wide transcriptional alterations associated with an adult brain tumor in Drosophila and reveal insights into the possible mechanisms of tumor formation caused by homozygous mutation of the translational repressor brat.

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PubMed2004

Hox gene cross-regulatory interactions in the embryonic brain of Drosophila.

During embryonic development of the Drosophila brain, the Hox gene labial is required for the regionalized specification of the tritocerebral neuromere. In order to gain further insight into the mechanisms of Hox gene action in the CNS, we have studied the molecular and genetic basis of cross-regulatory interactions between labial and other more posterior Hox genes using the GAL4/UAS system for targeted misexpression. Misexpression of posterior Hox genes in the embryonic neuroectoderm results in a labial loss-of function phenotype and a corresponding lack of Labial protein expression in the tritocerebrum. This is due to repression of labial gene transcription in the embryonic brain. Enhancer analysis suggests that this transcriptional repression operates on a 3.65 kb brain-specific labial-enhancer element. A functional analysis of Antennapedia and Ultrabithorax protein domains shows that the transcriptional repression of labial requires homeodomain-DNA interactions but is not dependent on a functional hexapeptide. The repressive activity of a Hox protein on labial expression in the tritocerebrum can, however, be abolished by concomitant misexpression of a Hox protein and the cofactors Homothorax and nuclear-targeted Extradenticle. Taken together, these results provide novel and detailed insight into the cross-regulatory interactions of Hox genes in embryonic brain development and suggest that specification of tritocerebral neuronal identity requires equilibrated levels of a Hox protein and Hth and n-Exd cofactors.

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PubMed2003

Identification of the Drosophila melanogaster homolog of the human spastin gene.

The human SPG4 locus encodes the spastin gene, which is responsible for the most prevalent form of autosomal dominant hereditary spastic paraplegia (AD-HSP), a neurodegenerative disorder. Here we identify the predicted gene product CG5977 as the Drosophila homolog of the human spastin gene, with much higher sequence similarities than any other related AAA domain protein in the fly. Furthermore we report a new potential transmembrane domain in the N-terminus of the two homologous proteins. During embryogenesis, the expression pattern of Drosophila spastin becomes restricted primarily to the central nervous system, in contrast to the ubiquitous expression of the vertebrate spastin genes. Given this nervous system-specific expression, it will be important to determine if Drosophila spastin loss-of-function mutations also lead to neurodegeneration.

Adenosine Triphosphatases↗

PubMed2003

Impressive expressions: developing a systematic database of gene-expression patterns in Drosophila embryogenesis.

The establishment of a database of gene-expression patterns derived from systematic high-throughput in situ hybridization studies on whole-mount Drosophila embryos, together with new information on the reannotated Drosophila genome and several recent microarray-based genomic analyses of Drosophila development, vastly increase the breadth and depth that can be reached by developmental genetics.

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PubMed2003

An urbilaterian origin of the tripartite brain: developmental genetic insights from Drosophila.

Studies on expression and function of key developmental control genes suggest that the embryonic vertebrate brain has a tripartite ground plan that consists of a forebrain/midbrain, a hindbrain and an intervening midbrain/hindbrain boundary region, which are characterized by the specific expression of the Otx, Hox and Pax2/5/8 genes, respectively. We show that the embryonic brain of the fruitfly Drosophila melanogaster expresses all three sets of homologous genes in a similar tripartite pattern. Thus, a Pax2/5/8 expression domain is located at the interface of brain-specific otd/Otx2 and unpg/Gbx2 expression domains anterior to Hox expression regions. We identify this territory as the deutocerebral/tritocerebral boundary region in the embryonic Drosophila brain. Mutational inactivation of otd/Otx2 and unpg/Gbx2 result in the loss or misplacement of the brain-specific expression domains of Pax2/5/8 and Hox genes. In addition, otd/Otx2 and unpg/Gbx2 appear to negatively regulate each other at the interface of their brain-specific expression domains. Our studies demonstrate that the deutocerebral/tritocerebral boundary region in the embryonic Drosophila brain displays developmental genetic features similar to those observed for the midbrain/hindbrain boundary region in vertebrate brain development. This suggests that a tripartite organization of the embryonic brain was already established in the last common urbilaterian ancestor of protostomes and deuterostomes.

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PubMed2002

Evolutionary conservation of otd/Otx2 transcription factor action: a genome-wide microarray analysis in Drosophila.

BACKGROUND: Homeobox genes of the orthodenticle (otd)/Otx family have conserved roles in the embryogenesis of head and brain. Gene replacement experiments show that the Drosophila otd gene and orthologous mammalian Otx genes are functionally equivalent, in that overexpression of either gene in null mutants of Drosophila or mouse can restore defects in cephalic and brain development. This suggests that otd and Otx genes control a comparable subset of downstream target genes in either organism. Here we use quantitative transcript imaging to analyze this equivalence of otd and Otx gene action at a genomic level. RESULTS: Oligonucleotide arrays representing 13,400 annotated Drosophila genes were used to study differential gene expression in flies in which either the Drosophila otd gene or the human Otx2 gene was overexpressed. Two hundred and eighty-seven identified transcripts showed highly significant changes in expression levels in response to otd overexpression, and 682 identified transcripts showed highly significant changes in expression levels in response to Otx2 overexpression. Among these, 93 showed differential expression changes following overexpression of either otd or Otx2, and for 90 of these, comparable changes were observed under both experimental conditions. We postulate that these transcripts are common downstream targets of the fly otd gene and the human Otx2 gene in Drosophila. CONCLUSION: Our experiments indicate that approximately one third of the otd-regulated transcripts also respond to overexpression of the human Otx2 gene in Drosophila. These common otd/Otx2 downstream genes are likely to represent the molecular basis of the functional equivalence of otd and Otx2 gene action in Drosophila.

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PubMed2002

Gliogenesis in Drosophila: genome-wide analysis of downstream genes of glial cells missing in the embryonic nervous system.

In Drosophila, the glial cells missing (gcm) gene encodes a transcription factor that controls the determination of glial versus neuronal fate. In gcm mutants, presumptive glial cells are transformed into neurons and, conversely, when gcm is ectopically misexpressed, presumptive neurons become glia. Although gcm is thought to initiate glial cell development through its action on downstream genes that execute the glial differentiation program, little is known about the identity of these genes. To identify gcm downstream genes in a comprehensive manner, we used genome-wide oligonucleotide arrays to analyze differential gene expression in wild-type embryos versus embryos in which gcm is misexpressed throughout the neuroectoderm. Transcripts were analyzed at two defined temporal windows during embryogenesis. During the first period of initial gcm action on determination of glial cell precursors, over 400 genes were differentially regulated. Among these are numerous genes that encode other transcription factors, which underscores the master regulatory role of gcm in gliogenesis. During a second later period, when glial cells had already differentiated, over 1200 genes were differentially regulated. Most of these genes, including many genes for chromatin remodeling factors and cell cycle regulators, were not differentially expressed at the early stage, indicating that the genetic control of glial fate determination is largely different from that involved in maintenance of differentiated cells. At both stages, glial-specific genes were upregulated and neuron-specific genes were downregulated, supporting a model whereby gcm promotes glial development by activating glial genes, while simultaneously repressing neuronal genes. In addition, at both stages, numerous genes that were not previously known to be involved in glial development were differentially regulated and, thus, identified as potential new downstream targets of gcm. For a subset of the differentially regulated genes, tissue-specific in vivo expression data were obtained that confirmed the transcript profiling results. This first genome-wide analysis of gene expression events downstream of a key developmental transcription factor presents a novel level of insight into the repertoire of genes that initiate and maintain cell fate choices in CNS development.

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PubMed2002

Conserved genetic mechanisms for embryonic brain patterning.

A wealth of comparative embryological studies on the expression and function of homeotic genes and cephalic gap genes indicates that both gene groups are important for establishing and specifying the anteroposterior body axis during embryogenesis in bilaterian animals. Recently, studies of this kind have been extended to embryonic brain development in two genetic model systems, Drosophila and mouse. These studies demonstrate striking similarities in the pattern of expression and mode of action of these developmental control genes during embryonic patterning of the brain in both species. Thus, in both insect and mammalian species, members of the homeotic gene complex are involved in patterning the posterior brain anlage, where they control regionalized neuronal identity, and members of the cephalic gap genes, notably the otd/Otx gene family, are involved in patterning the anterior brain anlage where they control regionalized neurogenesis and neuronal identity. Furthermore, striking cross-phylum rescue experiments show that insect and mammalian members of the orthodenticle gene family can functionally replace each other in embryonic brain and CNS patterning. Comparable cross-phylum rescue experiments have now also been carried out for the empty spiracles cephalic gap gene family. Taken together, these experiments suggest that the genetic mechanisms involved in embryonic brain development are conserved and indicative of a common evolutionary origin of the insect and vertebrate brain. For a more extensive and quantitative investigation of the molecular conservation of developmental mechanisms for brain patterning, functional genomic experiments are now underway in Drosophila. These experiments exploit the advent of sequenced genome information and the technology for large scale transcript imaging, with the goal of identifying the entire set of downstream genes which is under the control of these regulatory genes in embryonic brain development.

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