Photoinduced bonding of endogenous ecdysterone to salivary gland chromosomes of Chironomus tentans.

Endogenous ecdysterone has been bonded to chromosomal loci by irradiation of Ch. tentans salivary glands. The hormone has been localized on the polytene chromosomes by indirect immunofluorescence microscopy. Hormone binding to chromosomes is stage-specific. Seven chromosomal loci could be identified which specifically bound hormone in larval salivary glands, and 21 chromosomal loci which specifically bound hormone in prepupal salivary glands. All puffs that have been described by Clever (1961) as being inducible by ecdysterone have been found to contain irreversibly bound ecdysterone in prepupal salivary gland chromosomes. A small number of puff sites in larval salivary gland chromosomes exhibited varying amounts of bound ecdysterone, (as judged by fluorescence intensity) most notably 117B and Balbiani rings 1 and 3 on chromosome IV. In addition to stage specific binding sites, there were many others showing equal binding of the hormone in both, larval and prepupal, stages of development.--Fluorescence intensities (reflecting the amount of bonded hormone) at puff sites along the tip section of the prepupal salivary gland chromosome arm IR have been computed indicating that differences between fluorescence intensities of different puffs can be expressed as multiples of a basic fluorescence intensity. Thus, the amount of fluorescence intensity (bonded hormone) in the various puffs may be quantized.--The data indicate that in Ch. tentans salivary glands ecdysterone acts, at the chromosomal level. The development of larvae into prepupae generates more puff sites and more hormone binding. This is discussed in the light of current models of hormone-receptor function.