Inhibition by ultraviolet light of pole cell formation in Smittia sp (Chironomidae, Diptera): action spectrum and photoreversibility.

The formation of pole cells (primordial germ cells) in Smittia sp can be inhibited by ultraviolet (uv) irradiation without causing significant mortality. Until 70 min after egg deposition, pole cells are suppressed by low uv doses applied to the posterior pole region. Microbeam irradiation of a target area including the oosome inhibits pole cell formation; this is not observed after irradiation of other target areas. The action spectrum for uv inhibition of pole cells shows a distinct peak at 260 nm; its shape suggests that a nucleic acid-protein complex acts as an effective target. Independent evidence for the involvement of a nucleic acid moiety is derived from the fact that uv inhibition of pole cell formation is photoreversible. The results are discussed in the context of pole cell determination by localized cytoplasmic components.