Proximate and ultimate reasons for cuticular fibre orientation in insects

• Applicants: Professor Dr. Jan-Henning Dirks; Professor Dr. Gerd Jürgens, since 5/2024; Professorin Yael Politi, Ph.D.
• Subject Area: Animal Physiology and Biochemistry ; Systematics and Morphology (Zoology)
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 281694208

The insect cuticle shows the presence of daily growth bands which consist of layers with parallel (deposited at day) and helicoidal (deposited at night) orientated chitin fibres. In our previous DFG-project, we used this local light sensitivity of locust cuticle to successfully identify several fundamental mechanisms of chitin fibre orientation. Specifically, we showed that while the formation of cuticle with unidirectional fiber architecture is tightly controlled by cells, the formation of helicoidal patterns involves co-assembly of chitin and proteins and occurs away from the cell surface. Also, we found that cuticle thickness does not scale linearly with the number of deposited layers, suggesting progressive compactization. Moreover, we identified the chitin modifying deacetylase LmCDA2 being crucial for chitin fibre orientation.The objective of this follow-up proposal by combining modern high-resolution histological methods with classical molecular-genetics is two-fold: (1) establish a deeper mechanistic understanding of the cell-regulated and co-assembly processes including the role of microvilli and newly discovered vesicular structures, the physico-chemistry of the co-assembly and the genetic control of the processes. And (2) to identify the “ultimate” reasons for this alternating fiber organization pattern, including a materials-level study of its effect on the cuticle physical properties.Our first WP will investigate fundamental proximal and ultimate principles of the dermal light sensor. We will grow insects under controlled conditions to investigate the wavelength and intensity response of the cuticular light sensor. We will perform a comprehensive mechanical analysis to investigate possible biomechanical advantages of the alternating cuticle layers. In addition, to better understand cuticle compactization, we will perform spatially resolved SAXS/XRD analysis of cuticles deployed from the animal at various times after ecdysis. We will use the knowledge to grow “customized” cuticle samples for the other WPs.In our second WP we will investigate genetic and molecular mechanisms leading to chitin orientation. We will perform quantitative mass-spectrometry analysis for unidirectional and helicoidal cuticles to identify proteins that maybe involved in the control of fibre orientation. Their function will be characterised in forward genetic experiments in combination with high-resolution histological and mechanical analyses from WP1 and 3 to dissect the underlying molecular mechanisms.Our third WP will focus on the role of cell-surface dynamics in controlling the chitin fibre orientation. In particular, we will investigate the apical cell membrane and vesicle turnover using high resolution confocal and STED microscopy. To better understand the cellular mechanisms governing the different microvilli organization between “day” and “night” states, we will perform a time dependent study of the transition period between day/night.

• DFG Programme: Research Grants
• Co-Investigator: Luca Bertinetti, Ph.D.
• Ehemaliger Antragsteller: Privatdozent Dr. Bernard Moussian, until 5/2024