Peripheral avian yolk assemblage and its persistence in the blastoderm, studied by trypan blue-induced fluorescence.

Shortly after subcutaneous or intraperitoneal injection of nontoxic quantities of trypan blue into laying Japanese quails, red fluorescent yolk granules appear in the peripheral ooplasm of their oocytes at the end of the lampbrush stage or subsequently. Later a red fluorescence can be observed in the apical cytoplasm of the granulosa cells. The results obtained by this method confirm our previous results (Callebaut 1979) obtained by autoradiography after 3H-leucine administration and furnish interesting additional data. The trypan blue-induced fluorescence method gives a good indication of the permeability of the oocytal cortex and its derivative the germinal disc. The avian yolk which is, or has been peripherally assembled (primordial, true white and yellow yolk) can be characteristically labelled by the administration of trypan blue. The injection of higher, still nontoxic quantities of trypan blue has a prolonged "retarding" effect and permits the marking of a broader part of the germinal disc or eventually of the blastoderm which develops from it.