Molecular and cytological analysis of a mariner transposon from Hessian fly.

Degenerate PCR primers for conserved regions of the mariner transposase have been shown to amplify DNA sequences from the Hessian fly (Mayetiola destructor). Using one of these sequences as a hybridization probe, a clone from an M. destructor genomic library in phage lambda was recovered and sequenced. A transposable element, Desmar 1, with perfect inverted terminal repeats and an open reading frame that encodes a mariner class transposase was found. When compared to mariner sequences in the gene database, the transposase proved to be similar to that of the active mariner Mos 1 from the fruit fly (Drosophila mauritiana). In situ hybridization of the transposon DNA sequence to salivary gland polytene chromosomes revealed the general cytological locations of mariner elements. The distribution of sequences with homology to the probe was predominantly, but not exclusively, n paracentromeric regions.

Mariner transposase-like sequences from the Hessian fly, Mayetiola destructor.

Transposable genetic elements are assumed to be a feature of all eukaryotic genomes. They can serve as vectors in gene transfer systems and as mutagenic agents for isolation of genes. Until recently their identification has been primarily limited to organisms subjected to extensive genetic or molecular study. The Hessian fly, Mayetiola destructor (Say), is an agriculturally important pest of wheat, Triticum aestivum L., in the United States and other parts of the world. We assessed the presence of mariner transposase-like sequences in M. destructor by polymerase chain reaction (PCR) assay designed to detect conserved regions of the mariner transposase gene. DNA sequence analysis of PCR products revealed sequences with similarities to putative mariner transposase gene subfamilies from Drosophila mauritiana and horn fly, Haematobia irritans. DNA gel blot analyses indicated sequences hybridizing to the mariner transposase-like PCR clones occur at a moderate to low copy number in M. destructor. Results suggest the presence of an endogenous mobile-element system in M. destructor, which might be developed into a gene transfer system or serve in mapping genes.

Lysozyme in the midgut of Manduca sexta during metamorphosis.

Low levels of lysozyme were found in the midgut epithelium of the tobacco hornworm, Manduca sexta, during the early part of the fifth larval stadium. This was observed in control insects as well as in bacterially challenged insects. No lysozyme was detected in the gut contents of either group of insects which were actively eating or in the early stages of metamorphosis. However, high levels of lysozyme activity were detected in homogenates of midgut tissue collected from insects later in the stadium. Immunocytochemical studies demonstrated that lysozyme accumulates in large apical vacuoles in regenerative cells of the midgut during the larval-pupal molt. These cells, initially scattered basally throughout the larval midgut epithelium, multiply and form a continuous cell layer underneath the larval midgut cells. At the larval/pupal ecdysis the larval midgut epithelium is sloughed off and the regenerative cells, now forming the single cell layer of the midgut, release the contents of their vacuoles into the midgut lumen. This release results in high lysozyme activity in the lumen of the pupal midgut and is thought to confer protection from bacterial infection. This is the first indication that the lysozyme gene may be developmentally regulated in a specific tissue in the absence of a bacterial infection.