Culture and analysis of insect salivary glands

Abstract

Insect salivary glands have proved to be important sources of information in the study of development and pathogen transmission. Studies involving the polytene chromosomes of dipteran larval glands have produced a wealth of information regarding gene expression and genomic mapping. For the most part, polytene chromosomes are prepared for analysis directly from extirpated salivary glands. However, for questions concerned with induction of gene expression in Drosophila, an in vitro culture system was devised (Ashburner, 1972). Culturing the glands enables the application of strictly controlled conditions for induction. Molecular genetic studies of metamorphosis and development in Drosophila have been greatly facilitated by studies of puffing patterns in polytene chromosomes in response to ecdysterone treatment of cultured larval salivary glands (Cherbas, 1993). In vector Diptera, adult salivary glands can serve as a major route of transmission of arthropod-borne pathogens. As such, they are compelling objects of study in the investigation of host/parasite interactions. The mechanisms involved in parasite invasion of the insect salivary glands, for the most part, are unknown, but constitute the focus of much research as transmission blocking strategies are evaluated for use in disease control (Touray et al., 1992). In addition, the evasion of host immune responses and haemostasis in blood-feeding (Ribeiro, 1987) raises a fascinating issue of the role of the salivary gland in parasite transmission.