Dataset Information

Knickkopf protein protects and organizes chitin in the newly synthesized insect exoskeleton.

ABSTRACT: During each molting cycle of insect development, synthesis of new cuticle occurs concurrently with the partial degradation of the overlying old exoskeleton. Protection of the newly synthesized cuticle from molting fluid enzymes has long been attributed to the presence of an impermeable envelope layer that was thought to serve as a physical barrier, preventing molting fluid enzymes from accessing the new cuticle and thereby ensuring selective degradation of only the old one. In this study, using the red flour beetle, Tribolium castaneum, as a model insect species, we show that an entirely different and unexpected mechanism accounts for the selective action of chitinases and possibly other molting enzymes. The molting fluid enzyme chitinase, which degrades the matrix polysaccharide chitin, is not excluded from the newly synthesized cuticle as previously assumed. Instead, the new cuticle is protected from chitinase action by the T. castaneum Knickkopf (TcKnk) protein. TcKnk colocalizes with chitin in the new cuticle and organizes it into laminae. Down-regulation of TcKnk results in chitinase-dependent loss of chitin, severe molting defects, and lethality at all developmental stages. The conservation of Knickkopf across insect, crustacean, and nematode taxa suggests that its critical roles in the laminar ordering and protection of exoskeletal chitin may be common to all chitinous invertebrates.

SUBMITTER: Chaudhari SS

PROVIDER: S-EPMC3193238 | biostudies-literature | 2011 Oct

REPOSITORIES: biostudies-literature

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Knickkopf protein protects and organizes chitin in the newly synthesized insect exoskeleton.

Chaudhari Sujata S SS Arakane Yasuyuki Y Specht Charles A CA Moussian Bernard B Boyle Daniel L DL Park Yoonseong Y Kramer Karl J KJ Beeman Richard W RW Muthukrishnan Subbaratnam S

Proceedings of the National Academy of Sciences of the United States of America 20110919 41

During each molting cycle of insect development, synthesis of new cuticle occurs concurrently with the partial degradation of the overlying old exoskeleton. Protection of the newly synthesized cuticle from molting fluid enzymes has long been attributed to the presence of an impermeable envelope layer that was thought to serve as a physical barrier, preventing molting fluid enzymes from accessing the new cuticle and thereby ensuring selective degradation of only the old one. In this study, using ...[more]

PMID: 21930896

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Project description:1. Primary cultures of chondrocytes from the Swarm rat chondrosarcoma were labelled with either [3H]glucosamine or [14C]glucosamine, and hyaluronate synthesized by the cells was isolated from the cell layer. Parallel cultures were labelled with either [3H]serine or [3H]lysine, and identical fractions were isolated from the cell layer. Some cultures were dual-labelled. 2. In cultures labelled with [3H]serine for between 30 min and 24 h and extracted with 4.0 M-guanidine, a procedure that solubilizes predominantly extracellular macromolecules, small amounts of [3H]serine-labelled molecules were found associated with the hyaluronate fraction purified from the extract by dissociative CsCl-density-gradient centrifugation and dissociative Sepharose CL-2B chromatography. About 75% of the [3H]serine-labelled molecules in the fraction were specifically associated with hyaluronate, since they could be removed by prior treatment with proteinase-free Streptomyces hyaluronidase. The association of the [3H]serine-labelled molecules with hyaluronate was non-covalent, since they could be separated from it by further centrifugation in CsCl density gradients containing 4 M-guanidinium chloride and a zwitterionic detergent. 3. In other experiments the cultures were extracted with a sequential zwitterionic-detergent/guanidinium chloride procedure that completely solubilized the cell layer and enabled fractions containing newly synthesized cell-associated hyaluronate to be isolated. Zwitterionic detergent was present throughout. No [3H]lysine was incorporated into these fractions, irrespective of whether the cultures were pulsed concurrently with [3H]lysine and [14C]glucosamine or sequentially with [3H]lysine to prelabel the protein pool (24 h) followed by [14C]-glucosamine to label hyaluronate (1 h). 4. The results show that newly synthesized hyaluronate is not associated with covalently bound protein, and suggest that chain synthesis is initiated by a mechanism other than on to a core protein. Small amounts of [3H]serine-labelled molecules are, however, non-covalently associated with extracellular hyaluronate. Their identity is at present unknown, but they are probably of low molecular weight.

Project description:The precise regulation of transcription requires the coordinated activity of numerous proteins and protein complexes. Although significant progress has been made in understanding the mechanisms that regulate transcription, many questions remain unresolved. Accurately defining the direct effects of transcriptional regulators is critical to addressing these questions. An effective approach for identifying the direct targets of transcriptional regulators is combining rapid protein depletion and quantification of newly synthesized RNA. The auxin-inducible degron (AID) system and thiol (SH)-linked alkylation for the metabolic sequencing of RNA (SLAM-seq) are powerful methods to rapidly degrade a target protein and directly quantify newly synthesized RNA, respectively. Both methods have been widely applied to study transcriptional regulation. To address unresolved questions in transcription, we assembled an end-to-end workflow to deplete proteins of interest using the AID system and measure newly synthesized RNA using SLAM-seq in the model eukaryote, Saccharomyces cerevisiae. We provide an open-source, step-by-step protocol to support rapid implementation of this workflow. We include methods for targeted protein degradation, 4-thiouracil (4tU) incorporation, rapid methanol fixation, RNA purification, RNA alkylation, mRNA-seq library construction, and data analysis. Additionally, we demonstrate that this workflow can help define the direct effects of transcriptional regulators using the bromodomain and extra-terminal domain (BET) proteins, Bdf1 and Bdf2, as an example. We provide evidence that data generated using this workflow is robust to normalization using whole-cell spike-in or total read counts, correlates well with 4tU-seq data, and identifies extensive differential expression due to the depletion of Bdf1 and Bdf2. Taken together, this workflow will help address outstanding questions underlying the molecular basis of transcriptional regulation and other processes in S. cerevisiae and other eukaryotes.

Dataset Information

Knickkopf protein protects and organizes chitin in the newly synthesized insect exoskeleton.

Publications

Knickkopf protein protects and organizes chitin in the newly synthesized insect exoskeleton.

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