The localization of chitin synthase mediates the patterned deposition of chitin in developing Drosophila bristles

The insect exoskeleton is a complex structure that is a key for the life style of this very successful group of animals. It contains proteins, lipids and the N-acetyl glucosamine polymer chitin. Chitin is synthesized by the enzyme chitin synthase. In most body regions, chitin fibrils are found in a stack of parallel arrays that can be detected by transmission electron microscopy. Each array is rotated with respect to the layers above and below. In sensory bristles, chitin primarily accumulates in bands parallel to the proximal/distal axis of the bristle. These bands are visible by confocal microscopy providing experimental advantages. We have used this cell type and an edited chitin synthase gene to establish that the bands of chitin are closely associated with stripes of chitin synthase, arguing the localization of chitin synthase plays an important role in mediating the patterned deposition of chitin. This is reminiscent of what has been seen for chitin and chitin synthase in fungi and between cellulose and cellulose synthase in plants. Several genes are known to be essential for proper chitin deposition. We found one of these, Rab11 is required for the insertion of chitin synthase into the plasma membrane and a second, duskylike is required for plasma membrane chitin synthase to localize properly into stripes. We also established that the actin cytoskeleton is required for the proper localization of chitin synthase and chitin in developing sensory bristles.

Larval morphology of three species of Anteoninae (Hymenoptera, Dryinidae)

The last immature stage and the mature larva of Anteon flavicorne (Dalman) and Lonchodryinus ruficornis (Dalman) (Dryinidae, Anteoninae) are described. Figures and descriptions of some characters of the exuvia of the mature larva of Deinodryinus hispanicus (Olmi) are added. The immature larvae of the studied species are characterized by a layer (“mask”) covering the frontal region, the absence of cephalic vesicles, the body with its posterior region strongly bent ventrally, and the position on the host always on the thorax or between metathorax and abdomen. Main features of the mature larvae are the very long setae on the body and head, the labrum with few long sensory bristles and two sensory pits and with an apical row of sensory bristles, the epipharynx with two sensilla, the subtriangular labium with narrow subquadrate spinneret, and the bulb-shaped spiracles of approximately equal size in thorax and abdomen. The cocoon is built in the ground and covered by soil particles.

Drosophila bristles and the nature of quantitative genetic variation

Numbers of Drosophila sensory bristles present an ideal model system to elucidate the genetic basis of variation for quantitative traits. Here, we review recent evidence that the genetic architecture of variation for bristle numbers is surprisingly complex. A substantial fraction of the Drosophila genome affects bristle number, indicating pervasive pleiotropy of genes that affect quantitative traits. Further, a large number of loci, often with sex- and environment-specific effects that are also conditional on background genotype, affect natural variation in bristle number. Despite this complexity, an understanding of the molecular basis of natural variation in bristle number is emerging from linkage disequilibrium mapping studies of individual candidate genes that affect the development of sensory bristles. We show that there is naturally segregating genetic variance for environmental plasticity of abdominal and sternopleural bristle number. For abdominal bristle number this variance can be attributed in part to an abnormal abdomen -like phenotype that resembles the phenotype of mutants defective in catecholamine biosynthesis. Dopa decarboxylase ( Ddc ) encodes the enzyme that catalyses the final step in the synthesis of dopamine, a major Drosophila catecholamine and neurotransmitter. We found that molecular polymorphisms at Ddc are indeed associated with variation in environmental plasticity of abdominal bristle number.