The embryonic development of Schistosoma mansoni eggs: proposal for a new staging system

Abstract

Schistosomiasis is a water-borne parasitic illness caused by neoophoran trematodes of the genus Schistosoma. Using classical histological techniques and whole-mount preparations, the present work describes the embryonic development of Schistosoma mansoni eggs in the murine host and compares it with eggs maintained under in vitro conditions. Two pre-embryonic stages occur inside the female worm: the prezygotic stage is characterized by the release of mature oocytes from the female ovary until its fertilization. The zygotic stage encompasses the migration of the zygote through the ootype, where the eggshell is formed, to the uterus. Fully formed eggs are laid still undeveloped, without having suffered any cleavage. In the outside environment, eight embryonic stages can be defined: stage 1 refers to early cleavages and the beginning of yolk fusion. Stage 2 represents late cleavage, with the formation of a stereoblastula and the onset of outer envelope differentiation. Stage 3 is defined by the elongation of the embryonic primordium and the onset of inner envelope formation. At stage 4, the first organ primordia arise. During stages 5 to 7, tissue and organ differentiation occurs (neural mass, epidermis, terebratorium, musculature, and miracidial glands). Stage 7 is characterized by the nuclear condensation of neurons of the central neural mass. Stage 8 refers to the fully formed larva, presenting muscular contraction, cilia, and flame-cell beating. This staging system was compared to a previous classification and could underlie further studies on egg histoproteomics (morphological localizome). The differentiation of embryonic structures and their probable roles in granulomatogenesis are discussed herein.

Gonad RNA-specific qRT-PCR analyses identify genes with potential functions in schistosome reproduction such as SmFz1 and SmFGFRs

“…Eggs laid by treated worms were cultured for 3–4 days (at 37°C and 5% CO 2 ) and observed by bright-field microscopy (Figure 5). At this time point, control eggs had reached stages II and III according to the definition provided by Jurberg et al (2009). This is evidenced by the increased size of both the egg and the embryo, which fills 50–70% of the egg and is transparent in appearance.…”

Immunostimulatory property of a synthetic peptide belonging to the soluble ATP diphosphohydro-lase isoform (SmATPDase 2) and immunolocalisation of this protein in the Schistosoma mansoni egg

“…The soluble ATP diphosphohydrolase was detected on miracidium at stages 5-7 of embryonic development of the S. mansoni egg, which is when tissue and organ differentiation occurs, and the embryo occupies the internal volume of the egg-shell almost entirely (Jurberg et al 2009). Intense fluorescence was also detected in the region between the miracidium and the inner side of the egg-shell, located in von Lichtenberg's envelope, which is a region of production of immunogenic components.…”

Suppression of Schistosoma japonicum Acetylcholinesterase Affects Parasite Growth and Development

“…The stained eggs were then visualized by fluorescence microscopy (IM1000, Leica, Cambridge, UK) using UV illumination to visualize nuclei. Embryonic development of intestinal eggs obtained from the vaccinated and control mice was compared using a published staging system [52]. …”