The pupal cuticle of Drosophila: differential ultrastructural immunolocalization of cuticle proteins

Precise ultrastructural localization of Drosophila melanogaster pupal cuticle proteins (PCPs) was achieved by the immunogold labeling of frozen thin sections. PCPs were found in lamellate cuticle and intracellular vesicles but, curiously, were absent from the assembly zone of the cuticle. Antibodies that distinguish between the two classes of PCPs--low molecular weight (L-PCPs) and high molecular weight (H-PCPs)--revealed that the morphologically distinct outer lamellae contained L-PCPs and the inner lamellae contained H-PCPs. The sharp boundary between these two antigenic domains coincides with the transition from the outer to the inner lamellae, which in turn is correlated with the cessation of L-PCP synthesis and the initiation of H-PCP synthesis in response to 20-hydroxyecdysone (Doctor, J., D. Fristrom, and J.W. Fristrom, 1985, J. Cell Biol. 101:189-200). Hence, differences in protein composition are associated with differences in lamellar morphology.     

The ultrastructure of the cuticle of Nematoda

 The ultrastructure of the body cuticle in species of six of seven representative genera of Stilbonematinae (Eubostrichus, Catanema, Laxus, Robbea, Leptonemella, and Stilbonema) was investigated using SEM and TEM techniques. Additionally, one species of Spirinia (Spiriniinae) and one of Desmodora (Desmodorinae) were studied for outgroup comparison. The body cuticle of all investigated stilbonematids shows a consistent pattern composed of specific elements in a characteristic arrangement to each other. This pattern does not occur in Stilbonematinae alone, but also in Desmodorinae and Spiriniinae. Furthermore, a comparison within the Desmodorida reveals that this cuticular pattern apparently is present in the cuticle of representatives of Monoposthiidae, Epsilonematidae, and Draconematidae. The present results lead to the following conclusions: (1) the cuticle of Stilbonematinae contains no autapomorphic characters for this taxon, (2) there is a common cuticular pattern within the Desmodorida, and (3) this pattern is an autapomorphic character for the order Desmodorida. Accepted: 4 February 1996     

Analysis of the chitin recognition mechanism of cuticle proteins from the soft cuticle of the silkworm, Bombyx mori

Insect cuticle is composed mainly of chitin, a polymer of N-acetylglucosamine, and chitin-binding cuticle proteins. Four major cuticle proteins, BMCP30, 22, 18, and 17, have been previously identified and purified from the larval cuticle of silkworm, B. mori. We analyzed the chitin-binding activity of BMCP30 by use of chitin-affinity chromatography. The pH optimum for the binding of BMCP30 to chitin is 6.4, which corresponds to hemolymph pH. Competition experiments using chitooligosaccharides suggested that BMCP30 recognizes 4-6 mer of N-acetylglucosamine in chitin fiber as a unit for binding. The comparison of the binding properties of BMCP30 with those of BMCP18 showed that their binding activities to chitin are similar in a standard buffer but that BMCP30 binds to chitin more stably than BMCP18 in the presence of urea. BMCPs possess the RR-1 form of the R&R consensus, about 70 amino acids region conserved widely among cuticle proteins mainly from the soft cuticle of many insect and arthropod species. Analysis of the binding activity using deletion mutants of BMCPs revealed that this type of conserved region also functions as the chitin-binding domain, similarly to the RR-2 region previously shown to confer chitin binding. Thus, the extended R&R consensus is the general chitin-binding domain of cuticle proteins in Arthropoda.     

On the structure of the cuticle of Mecoptera

The chitin architecture of Mecoptera cuticle is of two kinds: helicoidal and helicoidal preferred with the preferred layers being cross-plied. Comparison of both systems of terminology currently in use to differentiate the subtypes of cuticle indicates that neither provides much information about the arrangement of chitin within cuticle and that both give information only about the extent of hardening in cuticle. All of the specimens of solid cuticle broken in tension exhibited a similar fracture behaviour in which the exocuticle failed in a brittle manner and the endocuticle failed plastically. The mode of endocuticular failure is dependent upon the arrangement of chitin microfibres within this region. The ultrastructural patterns of chitin microfibres determined by electron microscopy cannot be related to current notions about the phylogenetic interrelationships among Mecoptera and the usefulness of chitin fibre arrangement as a phylogenetic tool remains an open question.     

The cuticle of the Buxbaumia viridis sporophyte

The sporophytes of Buxbaumia viridis are covered with a cuticle-like skin, which is peeling off when the capsules are ripe. Scanning electron microscopy (SEM) analysis showed that the supposed peeling of the cuticle of ripe capsules is not restricted to the cuticle, but to the complete epidermis. Additionally the SEM investigations showed that the capsule epidermis is covered by epicuticular wax crystals in different morphologies. Wax crystal morphologies indicate the presence of massive wax layers with small embedded and superimposed platelets and granules on top. For bryophytes such wax crystals were so far reported only from the Polytrichales, but they are common wax types of various groups of several phanerogams. Based on these micro-morphological markers the phylogenetic relationship between the cuticles of moss sporophytes and tracheophytes is discussed here.     

The stabilization of locust cuticle

Cuticle from the metathoracic femur of adult locusts (Locusta migratoria) is characterized with respect to changes in water content and in protein extractability during maturation. The swelling behaviour and extractability of fully-sclerotized cuticle are compared to those of chemically-modified, unsclerotized cuticle.It is concluded that although dehydration may contribute to the stabilization of cuticle, it cannot account for the observed differences. The properties of mature cuticle can best be explained by the assumption that covalent cross-links are present between protein molecules.     

Studies on plant cuticle

The cuticles of plants of the Saxifragaceae, Rosaceae and Leguminosae are compared by chemical methods. Wide differences occur in the deposits of surface wax and cuticular membrane even within species of one genus. The relative proportions of four hydroxy-fatty acids in the cutin acids of plants of the families are assessed and the value of cutin analysis as a taxonomic criterion is discussed.     

The cuticle on the gametophyte calyptra matures before the sporophyte cuticle in the moss Funaria hygrometrica (Funariaceae)

? Premise of the study: In vascular plants, leaf primordia prevent desiccation of the shoot apical meristem. Lacking leaves, the undifferentiated moss sporophyte apex is covered by the calyptra, a cap of maternal gametophyte tissue that is hypothesized to function in desiccation protection. Herein, we compare cuticle development on the calyptra and sporophyte to assess the calyptra's potential to protect the sporophyte from desiccation. As the first comprehensive study of moss sporophyte cuticle development, this research broadens our perspectives on cuticle development and evolution across embryophytes. ? Methods: Calyptrae and sporophytes at nine developmental stages were collected from a laboratory-grown population of the moss Funaria hygrometrica. Tissues were embedded, sectioned, then examined using transmission electron microscopy. Epidermal cells were measured for thickness of the cuticle layers, cell wall thickness, and lumen size. ? Key results: The calyptra cuticle develops precociously and reaches maturity before the sporophyte cuticle. Calyptrae are covered by a four-layered cuticle at all stages, whereas sporophyte cuticle maturation is delayed until sporangium formation. The development and thickening of the sporophyte cuticle occurs in an acropetal wave. ? Conclusions: A multilayered calyptra cuticle at the earliest developmental stages is consistent with its ability to protect the immature sporophyte from desiccation. Young sporophytes lack a complex cuticle and thus may require protection, whereas in older sporophytes a mature cuticle develops. The moss calyptra is not a vestigial structure, but rather the calyptra's role in preventing desiccation offers a functional explanation for calyptra retention during the 450 Myr of moss evolution.