The Molluscan Intermediate Host and Schistosomiasis Japonica. I. Observations on the Conditions Governing the Hatching of the Eggs of Schistosoma japonicum

Ingalls, James W.; Huntér, George W.; McMullen, Donald B.; Bauman, Preston M.

doi:10.2307/3273117

Cited by 21 publications

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“…Schistosome eggs are fully embryonated as when passed in the feces or urine and, as a consequence, miracidia can hatch immediately from the egg in the environment [54]. Osmotic changes that occur as the egg enters freshwater are the primary cue for emergence of the miracidia from the eggshell [55–57]. Downstream of the osmotic changes, physiological and molecular events leading to hatching include calcium ion fluxes and the activity of LAP [56–58].…”

Section: Discussionmentioning

confidence: 99%

RNA interference targeting leucine aminopeptidase blocks hatching of Schistosoma mansoni eggs

Rinaldi

Morales

Alrefaei

et al. 2009

Molecular and Biochemical Parasitology

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Schistosoma mansoni leucine aminopeptidase (LAP) is thought to play a central role in hatching of the miracidium from the schistosome egg. We identified two discrete LAPs genes in the Schistosoma mansoni genome, and their orthologs in S. japonicum. The similarities in sequence and exon/intron structure of the two genes, LAP1 and LAP2, suggest that they arose by gene duplication and that this occurred before separation of the mansoni and japonicum lineages. The SmLAP 1 and 2 genes have different expression patterns in diverse stages of the cycle; whereas both are equally expressed in the blood dwelling stages (schistosomules and adult), SmLAP 2 expression was higher in free living larval (miracidia) and in parasitic intra-snail (sporocysts) stages. We investigated the role of each enzyme in hatching of schistosome eggs and the early stages of schistosome development by RNA interference (RNAi). Using RNAi, we observed marked and specific reduction of mRNAs, along with a loss of exopeptidase activity in soluble parasite extracts against the diagnostic substrate Lleucine-7-amido-4-methylcoumarin hydroxide. Strikingly, knockdown of either SmLAP1 or SmLAP2, or both together, was accompanied by ≥ 80% inhibition of hatching of schistosome eggs showing that both enzymes are important to the escape of miracidia from the egg. The methods employed here refine the utility of RNAi for functional genomics studies in helminth parasites and confirm these can be used to identify potential drug targets, in this case schistosome aminopeptidases.

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Section: Discussionmentioning

confidence: 99%

RNA interference targeting leucine aminopeptidase blocks hatching of Schistosoma mansoni eggs

Rinaldi

Morales

Alrefaei

et al. 2009

Molecular and Biochemical Parasitology

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“…Schistosome eggs are fully embryonated as they escape the host, and as a consequence, miracidia can hatch immediately upon appropriate stimuli in the external environment. The primary cue for miracidial emergence is the osmotic changes that occur as the egg enters freshwater [12] – [14] . Although the physiological and molecular cascades leading to hatching are poorly understood, it has been, hypothesised that they involve, in addition to osmotic changes, calcium fluxes, and the activity of leucine aminopeptidases [3] , [13] , [14] .…”

Section: Introductionmentioning

confidence: 99%

Correlative and Dynamic Imaging of the Hatching Biology of Schistosoma japonicum from Eggs Prepared by High Pressure Freezing

et al. 2008

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BackgroundSchistosome eggs must traverse tissues of the intestine or bladder to escape the human host and further the life cycle. Escape from host tissues is facilitated by secretion of immuno-reactive molecules by eggs and the formation of an intense strong granulomatous response by the host which acts to exclude the egg into gut or bladder lumens. Schistosome eggs hatch on contact with freshwater, but the mechanisms of activation and hatching are poorly understood. In view of the lack of knowledge of the behaviour of egg hatching in schistosomes, we undertook a detailed dynamic and correlative study of the hatching biology of Schistosoma japonicum. Methodology/Principal FindingsHatching eggs of S. japonicum were studied using correlative light and electron microscopy (EM). The hatching behaviour was recorded by video microscopy. EM preparative methods incorporating high pressure freezing and cryo-substitution were used to investigate ultrastructural features of the miracidium and extra-embryonic envelopes in pre-activated and activated eggs, and immediately after eggshell rupture. Lectin cytochemistry was performed on egg tissues to investigate subcellular location of specific carbohydrate groups.Conclusions/SignificanceThe hatching of S. japonicum eggs is a striking phenomenon, whereby the larva is liberated explosively while still encapsulated within its sub-shell envelopes. The major alterations that occur in the egg during activation are scission of the outer envelope-eggshell boundary, autolysis of the cellular inner envelope, and likely hydration of abundant complex and simple polysaccharides in the lacunal space between the miracidial larva and surrounding envelopes. These observations on hatching provide insight into the dynamic activity of the eggs and the biology of schistosomes within the host.

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“…However, there was no effect of light and darkness in S. japonicum eggs (Ingalls et al 1949 ) . Hatching occurs only in hypotonic solution and varied with salinity of water.…”

Section: Miracidia Detection Methodsmentioning

confidence: 80%

Schistosomes and Schistosomiasis in South Asia

Agrawal¹

2012

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The Molluscan Intermediate Host and Schistosomiasis Japonica. I. Observations on the Conditions Governing the Hatching of the Eggs of Schistosoma japonicum

Cited by 21 publications

References 0 publications

RNA interference targeting leucine aminopeptidase blocks hatching of Schistosoma mansoni eggs

RNA interference targeting leucine aminopeptidase blocks hatching of Schistosoma mansoni eggs

Correlative and Dynamic Imaging of the Hatching Biology of Schistosoma japonicum from Eggs Prepared by High Pressure Freezing

Schistosomes and Schistosomiasis in South Asia

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