Permeability barriers and anionic sites of the ovarian basal laminae in the black blowfly Phormia regina (Meigen) (Diptera, Calliphoridae)

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Abstract
Ovaries from 24h liver-fed female flies of Phormia regina were exposed to various extracellular tracers either in vivo or in vitro to gain insight on how hemolymph proteins may enter terminal follicles. Ruthenium red and lanthanum nitrate administered to aldehyde-fixed ovaries permeated the intercellular spaces of the follicular epithelium to some extent, but thorium dioxide did not even enter the basal lamina. Ferritin injected into 24 h liver-fed female flies did not traverse the basal lamina, nor entered the oocyte. Cationized ferritin remained restricted to the basal lamina, allowing visualization of anionic sites in this structure. Peroxidase was the only tracer injected in vivo that stained Phormia ovaries from the basal lamina down to the follicle cell/oocyte interface with an efficiency that related linearly with time of exposure. These observations allow us to conclude that the basal lamina enclosing the ovarian follicles in Phormia regina acts as a coarse physical filter for hemolymph proteins heading towards the oolemma. However, the presence of anionic sites along the basal laminae of both the terminal follicles and the surrounding ovariolar sheaths may also serve to confer them an additional chemical selectivity.