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Biomedical subjects

Martin Klingler

Publications and source records attributed to Martin Klingler.

9 recordsLinked to original sources
PubMed2006

Maintenance of segment and appendage primordia by the Tribolium gene knödel.

For homeotic and segment-polarity genes in Drosophila, a switch in gene regulation has been described that distinguishes patterning and maintenance phases. Maintenance of segment and organ primordia involves secondary patterning and differentiation steps, as well as survival factors regulating proliferation and organ size. In a screen for embryonic lethal mutations in the flour beetle Tribolium castaneum, we have recovered two alleles of the knödel gene, which result in short, bag-like embryos. These embryos have severely reduced appendages and differentiate a cuticle that lacks most overt signs of segmentation. In addition, they lack bristles and display defects in the nervous system. Early patterning in knödel mutant embryos is normal up to the extended germ band stage, as indicated by the formation of regular even-skipped (Tc'eve) and wingless (Tc'wg) stripes. Afterwards, however, these patterns degenerate. Similarly, proximo-distal growth and patterning of limbs are nearly normal initially, but limb primordia shrink, and proximo-distal patterns degenerate, during subsequent stages. knödel could be a segment polarity gene required for segment border maintenance in both trunk and appendages. Alternatively, it may have a more general role in tissue or organ maintenance.

Animals↗
PubMed2005

Breakdown of abdominal patterning in the Tribolium Kruppel mutant jaws.

During Drosophila segmentation, gap genes function as short-range gradients that determine the boundaries of pair-rule stripes. A classical example is Drosophila Krüppel (Dm'Kr) which is expressed in the middle of the syncytial blastoderm embryo. Patterning defects in Dm'Kr mutants are centred symmetrically around its bell-shaped expression profile. We have analysed the role of Krüppel in the short-germ beetle Tribolium castaneum where the pair-rule stripes corresponding to the 10 abdominal segments arise during growth stages subsequent to the blastoderm. We show that the previously described mutation jaws is an amorphic Tc'Kr allele. Pair-rule gene expression in the blastoderm is affected neither in the amorphic mutant nor in Tc'Kr RNAi embryos. Only during subsequent growth of the germ band does pair-rule patterning become disrupted. However, only segments arising posterior to the Tc'Kr expression domain are affected, i.e. the deletion profile is asymmetric relative to the expression domain. Moreover, stripe formation does not recover in posterior abdominal segments, i.e. the Tc'Kr(jaws) phenotype does not constitute a gap in segment formation but results from a breakdown of segmentation past the 5th eve stripe. Alteration of pair-rule gene expression in Tc'Kr(jaws) mutants does not suggest a direct role of Tc'Kr in defining specific stripe boundaries as in Drosophila. Together, these findings show that the segmentation function of Krüppel in this short-germ insect is fundamentally different from its role in the long-germ embryo of Drosophila. The role of Tc'Kr in Hox gene regulation, however, is in better accordance to the Drosophila paradigm.

Amino Acid Sequence↗
PubMed2005

Tribolium mae expression suggests roles in terminal and midline patterning and in the specification of mesoderm.

In Drosophila, the Mae protein ("modulator of the activity of Ets") regulates receptor tyrosine kinase (RTK)-dependent mitogen-activated protein kinase (MAPK) signaling. Mae has been shown to bind the Yan and Pointed-P2 transcription factors, thereby changing their ability to activate or repress target genes. In this work we show that the mae ortholog of the red flour beetle Tribolium castaneum (Tc'mae) is active at the posterior, but not the anterior pole of the blastoderm. Since MAPK signaling is known to be active at both poles, Tc'Mae could function to modulate terminal MAPK signaling to differentiate the developmental programs at the anterior and posterior poles of the Tribolium blastoderm embryo. Tc'mae is also expressed along the midline of the germband, similar as in Drosophila, where it is involved in the patterning of midline cells. Before gastrulation and in the growth zone, Tc'mae is active in mesoderm precursor cells. This suggests that in short germ embryos MAPK signaling may also be involved in the specification of mesoderm.

Amino Acid Sequence↗
PubMed2004

Tribolium.

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Animals↗
PubMed2004

Divergent segmentation mechanism in the short germ insect Tribolium revealed by giant expression and function.

Segmentation is well understood in Drosophila, where all segments are determined at the blastoderm stage. In the flour beetle Tribolium castaneum, as in most insects, the posterior segments are added at later stages from a posteriorly located growth zone, suggesting that formation of these segments may rely on a different mechanism. Nevertheless, the expression and function of many segmentation genes seem conserved between Tribolium and Drosophila. We have cloned the Tribolium ortholog of the abdominal gap gene giant. As in Drosophila, Tribolium giant is expressed in two primary domains, one each in the head and trunk. Although the position of the anterior domain is conserved, the posterior domain is located at least four segments anterior to that of Drosophila. Knockdown phenotypes generated with morpholino oligonucleotides, as well as embryonic and parental RNA interference, indicate that giant is required for segment formation and identity also in Tribolium. In giant-depleted embryos, the maxillary and labial segment primordia are normally formed but assume thoracic identity. The segmentation process is disrupted only in postgnathal metamers. Unlike Drosophila, segmentation defects are not restricted to a limited domain but extend to all thoracic and abdominal segments, many of which are specified long after giant expression has ceased. These data show that giant in Tribolium does not function as in Drosophila, and suggest that posterior gap genes underwent major regulatory and functional changes during the evolution from short to long germ embryogenesis.

Abdomen↗
PubMed2004

Efficient transformation of the beetle Tribolium castaneum using the Minos transposable element: quantitative and qualitative analysis of genomic integration events.

Genetic transformation in insects holds great promise as a tool for genetic manipulation in species of particular scientific, economic, or medical interest. A number of transposable elements have been tested recently as potential vectors for transformation in a range of insects. Minos is one of the most promising elements because it appears to be active in diverse species and has the capacity to carry large inserts. We report here the use of the Minos element as a transformation vector in the red flour beetle Tribolium castaneum (Coleoptera), an important species for comparative developmental and pest management studies. Transgenic G(1) beetles were recovered from 32.4% of fertile G(0)'s injected with a plasmid carrying a 3xP3-EGFP-marked transposon and in vitro synthesized mRNA encoding the Minos transposase. This transformation efficiency is 2.8-fold higher than that observed when using a plasmid helper. Molecular and genetic analyses show that several independent insertions can be recovered from a single injected parent, but that the majority of transformed individuals carry single Minos insertions. These results establish Minos as one of the most efficient vectors for genetic transformation in insects. In combination with piggyBac-based transgenesis, our work allows the introduction of sophisticated multicomponent genetic tools in Tribolium.

Animals↗
PubMed2003

Gene expression in spider appendages reveals reversal of exd/hth spatial specificity, altered leg gap gene dynamics, and suggests divergent distal morphogen signaling.

Leg development in Drosophila has been studied in much detail. However, Drosophila limbs form in the larva as imaginal discs and not during embryogenesis as in most other arthropods. Here, we analyze appendage genes in the spider Cupiennius salei and the beetle Tribolium castaneum. Differences in decapentaplegic (dpp) expression suggest a different mode of distal morphogen signaling suitable for the specific geometry of growing limb buds. Also, expression of the proximal genes homothorax (hth) and extradenticle (exd) is significantly altered: in the spider, exd is restricted to the proximal leg and hth expression extends distally, while in insects, exd is expressed in the entire leg and hth is restricted to proximal parts. This reversal of spatial specificity demonstrates an evolutionary shift, which is nevertheless compatible with a conserved role of this gene pair as instructor of proximal fate. Different expression dynamics of dachshund and Distal-less point to modifications in the regulation of the leg gap gene system. We comment on the significance of this finding for attempts to homologize leg segments in different arthropod classes. Comparison of the expression profiles of H15 and optomotor-blind to the Drosophila patterns suggests modifications also in the dorsal-ventral patterning system of the legs. Together, our results suggest alterations in many components of the leg developmental system, namely proximal-distal and dorsal-ventral patterning, and leg segmentation. Thus, the leg developmental system exhibits a propensity to evolutionary change, which probably forms the basis for the impressive diversity of arthropod leg morphologies.

Amino Acid Sequence↗
PubMedDate not supplied

Anterior localization of maternal mRNAs in a short germ insect lacking bicoid.

Anterior morphogens have long been postulated to function in early pattern formation in several insect taxa. Genetic studies in Drosophila revealed that the Bicoid protein performs as such in the fly. Maternally provided bicoid (bcd) mRNA is localized at the anterior pole of the oocyte and, upon fertilization, acts as the source of a morphogenetic gradient of Bicoid protein. Despite its central role in Drosophila, it is believed that bicoid arose rather recently during dipteran evolution through duplication of the Hox3 ortholog zen. Here we show that in the red flour beetle Tribolium castaneum, RNAs of the homologs of the Drosophila transcription factors eagle (Tc'eagle) and pangolin (Tc'pan) are maternally localized at the anterior pole of the egg. It is possible that underlying mechanisms for the anterior localization of maternal RNAs evolved independently in the two clades. However, considering the complexity of the process in Drosophila, it is more tempting to speculate that the molecular machinery evolved only once during insect evolution. Under this assumption, it was present before bicoid evolved as an anterior morphogen. To become concentrated at the anterior pole of the egg bicoid may only have had to acquire a signal sequence that was recognized by the preexisting localization machinery. Although we were not able to demonstrate a function in early embryogenesis for Tc'eagle or Tc'pan, our findings suggest that other factors likely function as anterior determinants in Tribolium, and other nondipteran insects.

Animals↗