Functional ultrastructure and cytochemistry of vitellogenesis stages of Rohdella amazonica (Aspidogastrea, Aspidogastridae, Rohdellinae), a parasite of the Amazoninan banded puffer fish Colomesus psittacus

Abstract

Vitellogenesis of Rohdella amazonica, parasites of the intestinal tract of a naturally infected banded puffer fish Colomesus psittacus, were studied by transmission electron microscopy (TEM) and TEM cytochemistry. Four vitellogenic stages were distinguished (I) stem cell stage of the gonial type (II) early differentiation stage, characterized by initiation of protein synthetic activity (III) an advanced differentiation and vitellocyte maturation stage, involving rapid accumulation of β-glycogen, large lipid droplets and smaller shell globules that fused progressively into large electron-dense shell globule clusters (IV) mature vitellocyte stage. The vitellogenesis process involves substantial increase in cell volume; extensive development of parallel cisternae of granular endoplasmic reticulum (GER) that become concentrically arranged in later stages and secrete shell globules; development of Golgi complexes engaged in the packaging of shell material; progressive accumulation, fusion and enlargement of unsaturated and saturated lipid droplets; formation of β-glycogen and α-glycogen and their accumulation into islands scattered among lipid droplets in maturing and mature vitellocytes; and finally during the advanced stage of maturation, rapid accumulation of large saturated lipid droplets α- and β-glycogen, and proteinaceous shell-globules and clusters in the peripheral cytoplasmic layer. Vitellogenesis in R. amazonica generally resembles that previously described for bothriocephalidean cestodes, but differs from that of other cestode orders. Positive cytochemical staining with periodic acid-thiocarbohydrazide-silver proteinate confirms β-glycogen and α-glycogen, around saturated lipid droplets of maturing and mature vitellocytes. These results from a basal trematode lead to a better understanding of the phylogenetic, functional, and developmental relationships among vitellogenesis patterns as they relate to egg formation, embryonic development, and life cycles among trematodes and cestodes.