IN-VIVO FLUORESCENCE IMAGING OF THE FUNCTIONAL-ORGANIZATION OF TROPHOTAENIAL PLACENTAL CELLS OF GOODEID FISHES

Embryos of viviparous goodeid fishes undergo a 10 to 150 x increase in dry weight during gestation. Maternal nutrients are transferred acros s a trophotaenial placenta comprised of the ovarian lumenal epithelium and the trophotaeniae of the embryo. Trophotaeniae are externalized p rojections of the embryonic hindgut. Epithelial cells of the ribbon tr ophotaenia Ameca splendens) resemble intestinal absorptive cells of su ckling mammals and endocytose macromolecules. They possess an apical b rush border, endocytotic complex, endosomal-lysosomal system, and apic al and basal clusters of mitochondria. Cells of the rosette trophotaen ia (Goodea atripinnis) lack an endocytotic apparatus, have small lysos omes, two mitochondrial clusters, and transport small molecules. Organ elle-specific fluorescent probes were employed to characterize the fun ctional organization of the two types of trophotaenial cells. In A. sp lendens, Lucifer Yellow, a membrane-impermeable tracer of vesicular tr ansport, first appears in peripheral vesicles (15-45 sec), then passes into elongated tubular endosomes (1-3 min) and later appears in large central vacuoles (10-15 min). These vacuoles accumulate Acridine Oran ge, a classical probe for lysosomes, and have been shown to contain ly sosomal enzymes. Endosome-lysosome fusion was observed. In both A, spl endens and G. atripinnis, Rhodamine 123 fluorescence was localized in two clusters of fine spots that corresponded to mitochondria. 4',6-dia minido-2-phenyl-indole (DAPI) staining of nuclei established the posit ional relationships of cell organelles with respect to the nuclei. 3,3 '-dihexyloxacarbo-cyanine iodide (DiOC(6)) revealed the perinuclear di stribution of the endoplasmic reticulum. In order to compare in vivo f luorescence of Lucifer Yellow with previous ultrastructural observatio ns, we employed fluorescence photoconversion and electron microscopy. (C) 1994 Wiley-Liss, Inc.