Biology subjects

Merzendorfer, H.

Publications and source records attributed to Merzendorfer, H..

3 recordsLinked to original sources

bioRxiv2026

A fatty acid-binding protein links lipid handling to chitin synthase-dependent cuticle formation and nanoscale organization

Background: The insect cuticle is a chitin-containing extracellular matrix whose formation requires precise coordination of chitin biosynthesis, fibril organization, and post-synthetic maturation. Although lipids are essential components of the cuticle, the molecular mechanisms linking lipid transport to chitin deposition remain poorly understood. Here we identify TcFabp8, a fatty acid-binding protein in Tribolium castaneum, as a functionally important regulator of chitin synthase 1 (Chs1)-dependent cuticle formation. Results: RNAi-mediated depletion of TcFABP8 caused molting defects, reduced cuticle thickness, loss of apical TcChs1 immunoreactivity, and reduced chitin deposition and organization. The finding that TcCHS1 transcript levels were unaffected by RNAi targeting TcFABP8 suggests that a post-transcriptional step, potentially involving vesicular TcChs1 transport, is affected, thereby impairing chitin synthesis and deposition. Synchrotron X-ray diffraction analysis of adult elytra revealed that TcFabp8 depletion preserved characteristic -chitin-associated scattering features, but altered chitin fibril accumulation, crystalline coherence, and the spatially ordered alignment of fibrils within the cuticular matrix. The TcFabp8 gene locus encodes splice variants yielding different N-terminal architectures: TcFabp8X1 carries a Sec/SPI signal peptide which is absent in TcFabp8X2 and TcFabp8X3. Immunocytochemistry using TcFabp8-specific antibodies detected intracellular signals in subapical cytoplasmic puncta and extracellular signals within the cuticle layers, which partially colocalized with Nile red fluorescence indicating lipid-rich environments. Conclusions: Together, our data demonstrate that TcFabp8 is a critical facilitator of TcChs1-dependent chitin deposition and extends functional connection between lipid transport and chitin biosynthesis in insects.

physiology↗

bioRxiv2026

Chitinase-3-like protein 1 decodes chitosan acetylation patterns into toll-like receptor 2 signaling through heparan sulfate

Chitinase-3-like protein 1 (CHI3L1), which is associated with a wide range of inflammatory diseases, lacks chitinase activity but retains the ability to bind chitin and chitosan. Chitin is a major component of fungal cell walls, whereas chitosan is used in biomedicine. In addition to chitosan, CHI3L1 has been proposed to interact with heparan sulfate (HS), a highly sulfated glycosaminoglycan on mammalian cell surfaces. Here, we investigated how interactions with chitosan and HS regulate the pro-inflammatory activity of CHI3L1. Mapping of the chitin-binding cleft revealed preferential binding of CHI3L1 to chitosans with a regular acetylation pattern that, together with CHI3L1, promoted toll-like receptor 2 signaling. We further identified a dominant HS-binding site that recognizes a distinct HS sulfation code containing a coherent motif of N- and 6-O-sulfations. Mutation of this HS-binding site or impaired HS biosynthesis prevented CHI3L1 accumulation at the cell surface and abolished CHI3L1-mediated cell activation. Together, our findings establish HS as a critical co-receptor for CHI3L1 and reveal a pro-inflammatory cross-talk between HS, CHI3L1, and chitosan that may contribute to host defense against fungal pathogens and responses to chitosan-based biomaterials. These findings identify HS- and chitosan-dependent CHI3L1 signaling as a potential target for modulating inflammatory responses.

Molecular Biology↗

bioRxiv2026

Structural and chemical properties of insects' chitin-containing extracellular matrices

Insects body barriers rely on specialized extracellular matrices that protect against harmful environmental influences. The outer barrier is the cuticle, which is composed of chitin, cuticle proteins and lipids. The peritrophic matrix (PM) serves as an inner barrier lining the midgut epithelium. It is composed of chitin fibers that are organized by PM proteins. While cuticle and PM proteins have received considerable attention in the past, supramolecular organization and physicochemical properties of the chitin component - particularly of the PM - remain poorly understood. Here, we combine synchrotron-based X-ray diffraction data from the PMs of lepidopteran and coleopteran insects with RNA interference (RNAi), mass spectrometric and histochemical analyses of the PM from Tribolium castaneum to determine chitins allomorphic state and degree of acetylation. The chitin of the PM exhibits signatures characteristic of dihydrate {beta}-chitin along the entire midgut. In contrast, the cuticle is made of tightly packed -chitin nanofibrils. Mass spectrometry revealed that the PMs chitin is highly acetylated (>95%). RNAi silencing of gut-specific genes encoding chitin deacetylasesTcCDA6-9 further increases the degree of acetylation. Histochemical analyses staining chitin with different degrees of acetylation confirm the predominance of highly acetylated chitin in the PM. Notably, the larval cuticle has a layered organization with deacetylated chitin present in exo- and highly acetylated chitin in endocuticles. Depletion of both TcCDA1 or TcCDA2 impairs chitin deacetylation, which indicates that both proteins cooperate in their activity in the integument. These results establish fundamental principles of polysaccharide-based extracellular matrices, with broad implications for insect biology.

molecular biology↗