Viney ME (1994) Parasitology "A genetic analysis of reproduction in Strongyloides ratti."

Viney ME

[Parasitology, 1994]

Strongyloides ratti has a complex life-cycle with two adult generations, one free-living and dioecious and one parasitic and female only. The parasitic females reproduce by parthenogenesis, but it is unclear whether this is mitotic or meiotic in nature. This question has been addressed genetically by analysing the progeny of parasitic females that were heterozygous at an actin locus for evidence of allelic segregation. Such progeny were similarly heterozygous showing that segregation had not occurred. It was therefore concluded that reproduction in the parasitic female of S. ratti is functionally mitotic.

Viney ME (1995) International C. elegans Meeting "DEVELOPMENT OF Strongyloides ratti."

Viney ME

[International C. elegans Meeting, 1995]

S. ratti is a rhabditid parasitic nematode which has a free-living generation outside of the host. This can develop in one of two ways. In heterogonic development larvae develop into free-living adults, these mate and their progeny develop into infective L3s. In homogonic development larvae develop directly into infective L3s. These routes may have analogies with the alternative (dauer) development of C. elegans. In Strongyloides which developmental path is followed depends on many factors. Here I will describe the development of isofemale lines of S. ratti under different conditions.

Wilson PA (1979) Parasitology "Tracking radioactive larvae of Strongyloides ratti in the host."

Wilson PA

[Parasitology, 1979]

Infective larvae of homogonic Strongyloides ratti grown in faecal culture with 32P or 75Se acquired a significant amount of radioactivity which was firmly attached to them. Heating removed most of the 32P but left 75Se in place. Subcutaneous injection of virgin and nursing mother rats with living and heat-killed radioactive larvae resulted in a pattern of labelling in the small intestine of injected animals and, in the case of 75Se, those of suckling pups, which can only be explained if labelled worms follow the natural migratory routes. The use of this tool in migratory studies is discussed, with precautions to allow for flaws in the technique.

Murrell KD (1981) J Parasitol "Protective role of immunoglobulin G in immunity to Strongyloides ratti."

Murrell KD

[J Parasitol, 1981]

Serum transfer from hyperimmune rats provided a significant degree of protection against Strongyloides ratti in mature, recipient rats. Eight immune serum pools tested were effective; however, the level of protection, as measured by challenge worm recoveries, ranged from 32 to 91%. Protection did not increase consistently with increasing volumes of immune serum, although as little as 5.0 ml/100 g of body weight afforded consistent protection against challenge infection. The protective effect was exerted against the early migrating tissue stages of the larvae; immune serum given 24 hr after challenge or later had no effect. The specificity of the immune serum's protection was suggested by the removal of this activity by absorption with heat-killed larvae, which have been shown to induce protection by immunization. Fractionation of immune serum showed that a heat-stable 7S component was responsible for protection; no protective activity could be detected in the 19S fraction. Further resolution of the 7S fraction by DEAE ion-exchange chromatography confirmed that the serum's protective activity was in the IgG component. The greatest protection was obtained with the fraction containing predominantly IgG1. In vitro sensitization of infective larvae with rat antibody failed to alter in vivo viability.

Kawanabe M et al. (1988) Parasitol Res "Transmammary transmission of Strongyloides ratti."

Uchikawa R, Kawanabe M, Nojima H

[Parasitol Res, 1988]

The rate of transmammary transmission of Stronglyloides ratti was examined in albino rats in terms of the route of subcutaneous (s.c.) migration from the infection site (the skin) to the cranium. Inoculation sites nearer the cranium resulted in less frequent transmammary infection. The maximum number of adult worms was recovered from the sucklings when the mother was inoculated in her hindquarter and sucklings were allowed to feed for 30-36 h after inoculation (AI). Few worms were recovered from sucklings when they were allowed to nurse during periods of less than 24 h AI or greater than 42 h AI. In lactating mothers, larval infection of the mammary glands was commonly observed, and these larvae showed an increased esophagus length. In nonlactating mothers, most larvae completed their migration to the cranium within 36 h AI.

Wilson PA et al. (1978) Parasitology "Patterns of milk transmission of Strongyloides ratti."

Wilson PA, Cameron M, Scott DS

[Parasitology, 1978]

Eight days after mother rats were injected with 4000 infective larvae of Strongyloides ratti at different stages of lactation the numbers of adult worms in their intestines were uniformly low (less than 3% of the dose) compared with unmated controls (mean = 25%). Those in their litters varied from 12% on day 5 to a maximum of 47% on day 17 post partum. These data, which do not correlate with lactational performance, imply that parasite movements in lactating rats are controlled by qualitative, not quantitative, consequences of humoral events. The numbers of worms in litters are concluded to be the result of the interaction of dynamic determinants of larval routes in the mother and changes in the suitability of the neonatal gut as an environment for worm development. The timing of events leading to milk-borne infection is defined. Injected larvae were closely synchronized in their movements, which were completed in 36 h. Larvae experimentally diverted into the mother's tissues during her first lactation were not available for the infection of a second litter.

Viney ME (1996) Proc Biol Sci "Developmental Switching in the Parasitic Nematode Strongyloides ratti"

Viney ME

[Proc Biol Sci, 1996]

Strongyloides ratti is a nematode parasite of rats. It is able to undergo two types of development outside the host: heterogonic (free-living adults and sexual reproduction) and homogonic (direct larval development). Homogonic development has a number of similarities with the development of the dauer stage of free-living nematodes, including Caenorhabditis elegans. Using isofemale lines of the parasite, factors that control this developmental choice have been investigated. Isofemale lines can be selected for both heterogonic and homogonic development, but are still able to respond to environmental conditions. By using temperature shift experiments it has been possible to determine when larvae become developmentally committed. All larvae are developmentally committed after 24 h at 19 degrees C.

Castelletto, M. et al. (2019) International Worm Meeting "Optimization of CRISPR/Cas9 mutagenesis in Strongyloides ratti."

Castelletto, M., Hallem, E.

[International Worm Meeting, 2019]

The CRISPR/Cas9 system of genetic manipulation is widely used in many systems. We recently demonstrated the use of CRISPR/Cas9 to introduce targeted mutations in the human-parasitic nematode Strongyloides stercoralis and the closely related rat-parasitic nematode Strongyloides ratti. Using the unc-22 gene as a proof-of-concept, we created both F1 homozygous knockouts and F3 mutants via host passage in S. stercoralis. However, the rate of mutagenesis was much lower for S. ratti than for S. stercoralis. Our current project is to optimize CRISPR/Cas9 mutagenesis in S. ratti. The specific goals include increasing the survival of F1 progeny, improving the selection process for potential integrants, designing a generic site for targeted integration of transgenes, and creating a usable system to establish targeted stable mutant lines in Strongyloides ratti. To improve selection and increase the number of integrants in the F1 generation, we varied parameters such as the components and the ratios of these components in microinjection mixes and the use of different fluorescent markers. We identified optimized conditions that increase the overall rate of transgenesis in S. ratti. For the generic targeting platform, we chose to disrupt the Strongyloides nas-4 gene. We have designed homology-directed repair constructs for the insertion into the Ss-nas-4 site of genes encoding fluorescent markers, calcium indicators, and genetic silencers under the control of neuron-specific promoters. Transgenes incorporated into the genome of Strongyloides species are expressed in successive generations, allowing for functional experimentation at all life stages. With this work, we hope to develop a versatile CRISPR/Cas9 toolkit for Strongyloides species that will enable functional studies of genes and neurons required for parasitic behaviors.

Grove DI et al. (1987) J Parasitol "Oral transfer of Strongyloides ratti adult worms to mice."

Grove DI, Northern C

[J Parasitol, 1987]

Murrell KD et al. (1983) J Parasitol "Shedding of antibody complexes by Strongyloides ratti (Nematoda) larvae."

Graham CE, Murrell KD

[J Parasitol, 1983]

Antigens on the epicuticular surface of Strongyloides ratti infective third-stage larvae (L3) could be demonstrated by an indirect fluorescent antibody technique under certain conditions. Infective L3 shed anti-antibody complexes at room temperature, but not at 4 C or in the presence of sodium azide or colchicine. Shedding of antibody did not appear to involve epicuticular antigens, and only occurred when anti-rat IgG was complexed to rat anti-larval antibody. However, parasitic L3 removed from rats did not exhibit this shedding reaction, suggesting that an important developmental change in cuticle physiology occurs during the transition from a free-living existence to a parasitic mode. The ability to shed foreign objects from the epicuticle of free-living infective L3 may be a defensive or protective response to soil microorganisms.