Functional ultrastructure and cytochemistry of vitellogenesis and mature vitellocytes of the digenean Cainocreadium labracis (Dujardin, 1845), parasite of Dicentrarchus labrax (L., 1758)

Zdzisław Świderski,Jordi Miquel,John S Mackiewicz,Hichem Kacem

doi:10.1007/s00436-018-6180-4

Abstract

Vitellogenesis and vitellocytes of Cainocreadium labracis were studied by transmission electron microscopy (TEM) and TEM cytochemistry. Four developmental stages were distinguished during vitellogenesis: (I) stem cell of high nucleo-cytoplasmic ratio; (II) early differentiation with chief activity focused on the beginning of protein synthesis and shell globule formation; (III) advanced differentiation with rapid intensification of protein synthesis, progressive fusion of single shell globules into large globule clusters, and formation of unsaturated lipid droplets surrounded by β-glycogen particles; and (IV) mature vitellocyte. Early vitellogenesis with vitellocyte maturation consists of: (1) increase in cell volume; (2) increased development of large, parallel cisternae of GER with production of proteinaceous granules; (3) development of small Golgi complexes that package granules; and (4) within vacuoles, progressive enlargement of proteinaceous granules into shell globule clusters formed during vitellogenesis. Three types of inclusions accumulate in large amounts in mature vitelline cells: (1) shell globule clusters, important component in the formation of egg shell; (2) numerous unsaturated lipid droplets. Though fewer, there are also diphasic droplets consisting of saturated and unsaturated lipids in the same droplet, and (3) a relatively small amount of β-glycogen particles, usually surround a few groups of lipid droplets. The β-glycogen and lipid droplets are nutritive reserves for embryogenesis. General pattern and functional ultrastructure of vitellogenesis greatly resemble those observed in some lower cestodes, such as bothriocephalideans and diphyllobothrideans. Variations and differences in the amount of lipids and of glycogen during vitellogenesis in lower cestodes and other trematodes are compared and discussed.

Highlights

Vitellocytes of parasitic Platyhelminthes are a key element in the production of mature eggs containing invasive larvae
While much is known of the functional ultrastructure and cytochemistry of vitellogenesis and vitellocytes among parasitic Platyhelminthes, that include numerous cestode species from a wide range of hosts, similar transmission electron microscopy (TEM) studies on trematodes appear somewhat neglected
The aim of the present study is to describe the functional ultrastructure of vitellocytes and vitellogenesis in the trematode Cainocreadium labracis and compare it with data from

Summary

Introduction

Vitellocytes of parasitic Platyhelminthes are a key element in the production of mature eggs containing invasive larvae (for a review, see Świderski and Xylander 2000). An interruption in vitellocyte formation results in immediate blockage of the infective egg production and an interruption of the parasite’s life cycle. While much is known of the functional ultrastructure and cytochemistry of vitellogenesis and vitellocytes among parasitic Platyhelminthes, that include numerous cestode species from a wide range of hosts, similar TEM studies on trematodes appear somewhat neglected. Among the few studies on non-economically related trematode parasites include, e.g., papers on Maritrema linguilla (Microphallidae) by Hendow and James (1989), Gorgoderina vitelliloba (Gorgoderidae) by Irwin and Maguire (1979), and the aspidogastrean Aspidogaster limacoides by Levron et al (2010)

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