Blood-eye barrier of the developing Drosophila melanogaster (Diptera: Drosophilidae)

For the past quarter century, it has been known that a blood-eye barrier exists in adult insects. However, the life stage at which the barrier arises and the anatomical correlate of the barrier were not known. Compound eye development in Drosophila melanogaster (Diptera: Drosophilidae) is essentially complete at approximately 140 h after pupariation; or about 20 h prior to eclosion. A search for a blood-eye barrier spanned late third-instar larvae, through late pupal life sampled at 40 and 140 h post-pupariation. No blood-eye barrier is present in the eye discs of last-instar larvae, based on tile presence of lanthanum tracer among ommatidial cells and their processes. Pleated-sheet septate junctions, which link larval ommatidial cells, are not yet capable of totally blocking tracer from paracellular passage. The blood-eye barrier is constructed in the early phase (0-60 h) of pupal development in the wake of apoptosis and new cellular reorganization, in the developing compound eye, mature photoreceptor neurons must then be protected from the ionic vagaries of hemolymph to become electrophysically competent. First vestiges of a barrier with occluding septate junctions tire seen in the 40-h old pupa, and by 140 h, the barrier is complete. The barrier prevails throughout adult life.