Snail / schistosome compatibility

Réunion Scientifique mardi 3 Avril 2007

Université de Perpignan Via Domitia

E

HP

E

CENTRE NATIONAL

de la RECHERCHE

SCIENTIFIQUE

ECOLE PRATIQUE

des HAUTES

ETUDES

WHO

COLLABORATING

CENTER

André THERON

UMR 5244 BIOLOGIE ET ECOLOGIE TROPICALE ET MEDITERRANEENNEUniversity of Perpignan - 66860 Perpignan - France

from populations to mechanisms

Mollusc / Trematode models

Trematodelife cycles

Schistosoma mansoni

Biomphalaria glabrata

Mollusc / Trematode models

Adults

Egg

Miracidium

Cercariae

Schistosomelife cycle

Schistosoma mansoni

Biomphalariaglabrata

rainy season rainy season

Snail infection in Field populations

dry season

The typically low Infection rates

Most of the field surveys on natural populations

of Biomphalaria snails report :

(1-5%)

variations of population size high mortality rates

genetic bottleneck (extinction /

recolonisation, founder effect)

Ecologie moléculaire de la transmission : recrutement et diversité génétique

Théron et al., 2004. Parasitology.

Génotypage intra-hôte :- parasites adultes HD (microsatellites)- Parasite larvaires HI (microsatellites)

1%

100%

?

1 2

Limitedcontact

RESISTANT/SUSCEPTIBLE

SUSCEPTIBLEHOST

RESISTANTHOST

Resistance / Susceptibility

Polymorphism of hostsusceptibility/resistance

Laboratory strainsExperimental infections

50 - 60 %

2

0 %

50 %

100 %

504030201012 nMi

selected «SUSCEPTIBLE»

strain

Selected«RESISTANT»

strain

… Evolutionary inferences

(Co-evolution, Life history and Red Queen theories, …)

Fitness Cost associated

with resistance(Webster & Woolhouse, 2001 ).

Mating behaviour associated with resistance

(Webster et al., 2003 ).

Molecular markers associated with resistance

(Spada et al., 2002 ).

EVOLUTIONARY IMPLICATIONS >>

Maintenance ofresistance/susceptibility

polymorphism

Resistance is heritable and

dominant(Richards et al., 1992 ).

Routinely used to investigate :

-host defence mechanisms-Genetics of resistance-Genes of resistance

2 Selected “Resistant“strains:

selected «RESISTANT» strain

trade-offs between the FITNESS COST associated with

RESISTANCE (reduced fertility) and the fitness costs

resulting from parasitism (increased mortality).

(Webster & Davis, Parasitology , 123, 2001)

Laboratory selected “resistant“strains: use and limitation.

However, despite extensive efforts and use of various complementary biomolecular approaches, no linkage group, no genetic or functional marker has been assigned to any locus controlling resistance.

Théron & Coustau (J. Helminthol., 2005) raised the question :

Are Biomphalaria snails RESISTANT to Schistosoma mansoni ?

based on some arguments …

B. glabrata resistance : a relative concept

Developed sporocystSUSCEPTIBLE HOST

Encapsulated sporocysts

SUCCESSFUL INFECTION

FAILURE of INFECTION

RESISTANT HOST

Compatibility is tested independently for each entering miracidium.

We conclude that …

The phenotype (resistant vs susceptible) of the host is expressed as a function of the parasite genotype it harbors.

The phenotype (un-infective vs infective) of the parasite is expressed as a function of the host genotype it enters.

This means that the CONCEPT of RESISTANCE (and its evolutionary implication) appears un-adapted to the B. glabrata / S. mansoni system

… Evolutionary inferences

(co-evolution, life history and Red Queen theories, …)

Molecular markers associated with resistance

Fitness Cost associated

with resistance

Mating behaviour associated with resistance

“Resistant“selected

(Webster & Woolhouse, 2001 ).

(Webster et al., 2003 ).

(Spada et al., 2002 ).

EVOLUTIONARY IMPLICATIONS >>

Resistance is heritable and

dominant(Richards et al., 1992 ).

2 Selected “Resistant“strains:

Apparent R

esista

nce

Warn

ing

“Resistance“ / Infectivity in Field populations

Going back to the field ……,

2

RESISTANT/SUSCEPTIBLE

Genotype-by-genotypeInteraction

3

GENETICDIVERSITY

Compatible Un-Compatible

Polymorphism of

compatibility

Genotype-by-Genotype interactionMatching genotype

Parasitegenotypic diversity

- - - +

+ - - +

+ + + +

Snailgenotypic diversity

Compatibility polymorphism andB. glabrata « resistance » in the field ?

3

100 %

0 %

50 %

100 %

50403020101 2 nMi

- exposed snails directly collected in the site

- S. mansoni eggs obtained from a substantial number of naturally infected vertebrate hosts

- increasing miracidial dose exposures

Populational validation

Dans Fond

Dubelloy

Belle Plaine

100 % compatibility

Among Biomphalaria and S. mansoni associations, susceptibility of snails in the field is general if we take into account the total amount of genetic diversity present within the whole population of parasites within vertebrate hosts.

Snail genetic diversity Parasite genetic diversity

Field situation

100 % matching

We conclude that …

Meeting probability

1-5% infection rates

+Matching

probability

Snail genetic diversity Parasite genetic diversity

Field situation

100 % matching

Apparent resistance in Laboratory strains …

Laboratory Strains

0 à 60% matching

The functional point of view :

Schistosomes use molecular mimicry as infectivity strategy and are confronted to self/non-self recognition processes of the host (general immune defence)

success

MatchedMolecularVariants

failure

Un-MatchedMolecularVariant

A genetically determined mechanism theoretically

consistent with a matching genotype

model

Host Host

ParasiteParasite

CONCLUSION …

Matched vs Un-matched status of host-parasite combinations :

?

What phenotypic factors interact between host and parasite ?

What genomic mechanisms generate diversity ?

from populations to mechanisms (André THERON)

from mechanisms to populations (Guillaume MITTA)

Biomphalaria glabrata

Schistosoma mansoni

IncompatibleCompatible

Recherche des gènes acteurs de la compatibilité: Approches moléculaires comparatives entre

souches de S. mansoni

Sporocyste I installé chez le

mollusque

Sporocyste I en dégénérescence

Capsule hémocytaire

Approche protéomique comparative et identification de candidats prometteurs, les MSPPs

25015010075

50

37

25

20

15

Mw

pI (NL)3 10

25015010075

50

37

25

20

15

Mw

pI (NL)3 10

Parasites compatibles Parasites incompatibles

Mother Sporocyst Polymorphic Proteins

(MSPPs)répétitions de 9 aa en tandem 234 aaEtc..

analogies de structure pour des protéines immuno-

dominantes de Plasmodium et Coccidioides :

rôle «écran de fumée»

O-glycosylations

Les MSPPs et les variants au niveau cDNA

REPET B: GGTGACCTCGCATCAGACAAACCCACA B G D L A S D K P T

REPET BMOD: GGTGGCCTCGCATCAGACAAACCCACA B G G L A S D K P T

REPET G: GATGACTATGCATTGAGCGAACCAACA G D D Y A L S E P T

REPET GMOD: GATTACTATGCATTGAGCGAACCAACA G D Y Y A L S E P T

REPET M: GGTGACCTCGCATTAGACGAACCAACA M G D L A L D E P T

Compatible Incompatible

BBBBBBBBBBBBBBBBBBBBBBBBBB

BBBBBBBBBBBBBBBBBBBB

BBBBBBBBBBBBBBBBBBBB

BBBBBB

BBBBBBBBBBB BBBBBBBBBBBBBBB

BBBBB

GGGGGGGGGGG

GGGGGGGGG

GGGG

GGG

GG

BBBBBB

BBBBBBBB BBBBBBBB

GGGGGGGGGGG

GGGGGGGG

GGGGG

GG

GG

GGMGG

GGBBBBBBBBBBB

GGBBGG

GGBBGG

GGBBG

GGBBBBG

0

0,05

0,1

0,15

0,2

0,25

eggs

miracidiasporocystscercariaemale worms

female worms

Ratio/28S

Les MSPPs: ume famille multigénique

MSPP1a 3 4 5 6 7 8 9 10 11 12 13 14 152

3 4 5 6 7 8 9 11 12 13 14 15MSPP2a 2 10

3 4 5 6 7 8 9 11 12 13 14 15MSPP3 2 10

3 432MSPP6

MSPP8 11 12 13 14 15

3 4 5 6 7 8 9MSPP1b 2 10

4 5 6 7 8 9 11 12 13*

14 15MSPP2b 10

11 12 13 14 155 6MSPP9

3 4 5 6 7 8 9MSPP4 2 10

3 7 8 9MSPP5 2 10

11 12 13 14MSPP7 9 10 15

3 gènes

8 pseudogènes

Retrotransposons (RT)

Gènes soumis à des insertions, remaniements fréquents médiés par ces RT

exons

- Protéines potentiellement impliquées dans le contournement du système de défense de B. glabrata

par S. mansoni

- Polymorphisme et organisation génomique génératrice de diversité

Le modèle B. glabrata/S. mansoni: les MSPPs des candidats de choix

Candidats de choix en tant que facteurs clefs de la compatibilité

Candidats pour une 1ère « approche populationnelle »

Comparaison des MSPPs:

Protéines « actrices » de la compatibilité en

populations naturelles?

Compatible Compatibles

Pop Nat LaboGuadeloupe Brésil

Isolats de S. mansoni

de Guadeloupe

4%

6%

Polymorphisme de compatibilité et MSPPs en populations naturelles