Ultrastructural studies on egg envelopes surrounding the miracidia of Mediogonimus jourdanei Mas-Coma et Rocamora, 1978 (Digenea, Microphalloidea, Prosthogonimidae)

Abstract

The intrauterine, mature and fully embryonated eggs of the prosthogonimid trematode Mediogonimus jourdanei Mas-Coma et Rocamora, 1978 were examined by means of transmission electron microscopy (TEM), using high pressure freezing, freeze substitution and infiltration with resin techniques. Each embryonated egg is composed of a miracidium surrounded by three envelopes: (1) the egg shell, (2) the outer and (3) inner envelopes. Egg envelopes play an important role in the protection, metabolism, storage of nutritive reserves and the general biology of the M. jourdanei egg. The inner envelope is characterised by large, flattened nuclei, and its syncytial cytoplasm contains a heavy accumulation of glycogen, lipid droplets, mitochondria and large vesicles. These traits indicate that this layer has the features of a metabolically-active syncytial layer with an energy storage capability. In the infective eggs observed before the hatching of the miracidium, areas of so-called "focal cytoplasmic degradation" were frequently observed, which may be involved in the autolytic process of all components of this envelopes.

Light and electron microscopy observations of embryogenesis and egg development in the human liver fluke, Opisthorchis viverrini (Platyhelminthes, Digenea)

“…Before this study, TEM descriptions of eggs have been provided for two digenean groups, the schistosomes and one prosthogonimid digenean (Jones et al 2008;Świderski et al 2010) and now O. viverrini. For schistosomes, the eggshell is shown to be richly porous (Neill et al 1988;Świderski 1994;Ashton et al 2001;Jones et al 2008).…”

“…In O. viverrini, vitelline cells degrade, indicating that these last cells do not contribute to the embryonic envelopes. The outer envelope of digenean eggs is an acellular and electron-opaque layer immediately beneath the shell (Neill et al 1988;Jones et al 2008;Świderski et al 2010) and is thought to be derived from the developing embryo (el-Shoura et al 1995;Ashton et al 2001). While this envelope encompasses the inner envelope and embryo in schistosomes, it is much reduced in O. viverrini and Mediogonimus (Świderski et al 2010).…”

“…With this method, it was possible to observe the formation of the eggshell in the ootype and the structure of eggs from the proximal and middle regions of the uterus, but not mature eggs from the distal region, which proved to be entirely resistant to infiltration by resin. To make ultrastructural observations of these mature eggs, we resorted to prepare individual egg by the process of high-pressure freezing (Jones et al 2008;Świderski et al 2010). Eggs that had been dissected from the distal third of the uterus were fixed in glutaraldehyde/paraformaldehyde, as described above.…”

Ultra structural study of the Embryonic Development in the Intrauterine Eggs of Acanthostomum (atrophocaecum) aswaninesis Wannas, 1977 (Digenea, Acanthostomatidae) with evidence of early miracidium development

“…The ultra-structural aspects of embryonic envelope and associated developmental stages of intrauterine eggs of trematodes (Fujino et a.l 2000, Ashton et al 2001, Jones et al 2008, Pinhero et al 2015, Swiderski et al 2010a, 2013a, b, 2014, Khampoosa et a.l 2012, aspidogastreans (Swiderski et al 2011(Swiderski et al , 2012, cestodes (Burt 1986, Conn 2008, Mlocicki et al 2005, 2006 and trematodes with cestodes (Conn 2007, Swiderski 1996, Swiderski and Conn 2000, 2001 were studied.…”

Molecular interactions of proteins associated with surface membrane biogenesis and renewal in the tegument of Schistosoma mansoni

“…Here, we demonstrated that I-EM can be successfully performed using a combination of cryopreparation methods and fixation in uranyl acetate. Use of cryopreservation methods for ultrastructural studies of parasitic helminths has only previously been applied to investigations of eggs such as those of schistosomes and other fluke species, and taeniid cestodes (Jones et al, 2008;Jabbar et al, 2010a,b;Ś widerski et al, 2010;. We believe this report constitutes the first description of its utilisation in adult schistosomes.…”