7 Genomic Approaches in Aquaculture and Fisheries
245
2007a) and C1q-domain-containing proteins (Zhang et al. 2008a). The interactions
between PRRs and PAMPs trigger the defence mechanisms.
In the Pacific oyster Crassostrea gigas, the characterization of six genes related
to the Rel/NF-κB pathway support the concept of a conserved signalling pathway
(Gueguen et al. 2003, Escoubas et al. 1999, Montagnani et al. 2004, 2008). In others
bivalves, components like the Toll receptor, MyD88 and Rel were also characterized
(Tanguy et al. 2004, Qiu et al. 2007a, b, Wu et al. 2007, Bettencourt et al. 2007).
The homology between Rel/NF-κB pathways in bivalves and insects suggest a role
for this pathway in the regulation of genes involved in innate defence (Lemaitre
et al. 1995, Silverman and Maniatis 2001). Similarly, TGF-β or TGF-beta pathway
could be involved in the activation of inducible defence systems (Lelong et al. 2007).
Finally, the third step of the immune response leads to the expression of effectors
characterized by an antimicrobial activity. These molecules are mainly produced
by the immune-competent cells, the hemocytes, but also by some epithelial tissues
(e.g. gills and mantle), which constitute, in bivalves, the first line of defence. Among
these effectors, inhibitors of proteases and antimicrobial peptides have been studied.
The inhibitors are known to target microorganism proteases to prevent host infection (Labreuche et al. 2006a,b). In bivalves, several of these molecules have been
identified such as α2-macroglobuline (Gueguen et al. 2003, Ma et al. 2005), serine
proteases inhibitor (serpin; Gueguen et al. 2003, Tanguy et al. 2004) and metalloprotease inhibitor (TIMP; Montagnani et al. 2001). The first antimicrobial peptides
characterized were found in Mytilus (Charlet et al. 1996, Hubert et al. 1996) and
include four families of peptides: defensin (Hubert et al. 1996, Mitta et al. 1999b),
myticin (Mitta et al. 1999a), mytilin (Mitta et al. 2000b) and mytimicin (Mitta
et al. 2000a). More recently, antimicrobial peptides were also isolated from other
bivalves (Seo et al. 2005, Gueguen et al. 2006, Zhao et al. 2007, Gestal et al. 2007,
Bettencourt et al. 2007) supporting the concept that these effectors are present in
all phyla of the living kingdom. The amplification of immune effector production in
response to infection is likely to be related to transcriptional or post-transcriptional
regulation but also to an activation of haematopoiesis, which increases the number
of hemocytes (Tirape et al. 2007).
7.6.4.3 Immune Response to Perkinsus Infection
Molecular mechanisms involved in bivalve–Perkinsus interaction remain largely
unknown. A well-characterised mechanism in bivalves is the one triggered by
lectins. Bivalves rely on lectins to recognize infectious agents and trigger resistance
mechanisms to prevent invasion. Because this recognition has proven to be highly
specific it has been used to monitor Perkinsus infection (Kim et al. 2006, 2008). For
example, Perkinsus olseni (Bulgakov et al. 2004, Kang et al. 2006, Kim et al. 2006,
2008) and Perkinsus marinus (Gauthier et al. 2004, Tasumi and Vasta 2007) are not
recognized by the same lectins in clam and oyster, respectively. A new galectin was
also recently shown to recognize P. marinus in particular trophozoites, the virulent
stage of the parasite (Tasumi and Vasta 2007).
245
2007a) and C1q-domain-containing proteins (Zhang et al. 2008a). The interactions
between PRRs and PAMPs trigger the defence mechanisms.
In the Pacific oyster Crassostrea gigas, the characterization of six genes related
to the Rel/NF-κB pathway support the concept of a conserved signalling pathway
(Gueguen et al. 2003, Escoubas et al. 1999, Montagnani et al. 2004, 2008). In others
bivalves, components like the Toll receptor, MyD88 and Rel were also characterized
(Tanguy et al. 2004, Qiu et al. 2007a, b, Wu et al. 2007, Bettencourt et al. 2007).
The homology between Rel/NF-κB pathways in bivalves and insects suggest a role
for this pathway in the regulation of genes involved in innate defence (Lemaitre
et al. 1995, Silverman and Maniatis 2001). Similarly, TGF-β or TGF-beta pathway
could be involved in the activation of inducible defence systems (Lelong et al. 2007).
Finally, the third step of the immune response leads to the expression of effectors
characterized by an antimicrobial activity. These molecules are mainly produced
by the immune-competent cells, the hemocytes, but also by some epithelial tissues
(e.g. gills and mantle), which constitute, in bivalves, the first line of defence. Among
these effectors, inhibitors of proteases and antimicrobial peptides have been studied.
The inhibitors are known to target microorganism proteases to prevent host infection (Labreuche et al. 2006a,b). In bivalves, several of these molecules have been
identified such as α2-macroglobuline (Gueguen et al. 2003, Ma et al. 2005), serine
proteases inhibitor (serpin; Gueguen et al. 2003, Tanguy et al. 2004) and metalloprotease inhibitor (TIMP; Montagnani et al. 2001). The first antimicrobial peptides
characterized were found in Mytilus (Charlet et al. 1996, Hubert et al. 1996) and
include four families of peptides: defensin (Hubert et al. 1996, Mitta et al. 1999b),
myticin (Mitta et al. 1999a), mytilin (Mitta et al. 2000b) and mytimicin (Mitta
et al. 2000a). More recently, antimicrobial peptides were also isolated from other
bivalves (Seo et al. 2005, Gueguen et al. 2006, Zhao et al. 2007, Gestal et al. 2007,
Bettencourt et al. 2007) supporting the concept that these effectors are present in
all phyla of the living kingdom. The amplification of immune effector production in
response to infection is likely to be related to transcriptional or post-transcriptional
regulation but also to an activation of haematopoiesis, which increases the number
of hemocytes (Tirape et al. 2007).
7.6.4.3 Immune Response to Perkinsus Infection
Molecular mechanisms involved in bivalve–Perkinsus interaction remain largely
unknown. A well-characterised mechanism in bivalves is the one triggered by
lectins. Bivalves rely on lectins to recognize infectious agents and trigger resistance
mechanisms to prevent invasion. Because this recognition has proven to be highly
specific it has been used to monitor Perkinsus infection (Kim et al. 2006, 2008). For
example, Perkinsus olseni (Bulgakov et al. 2004, Kang et al. 2006, Kim et al. 2006,
2008) and Perkinsus marinus (Gauthier et al. 2004, Tasumi and Vasta 2007) are not
recognized by the same lectins in clam and oyster, respectively. A new galectin was
also recently shown to recognize P. marinus in particular trophozoites, the virulent
stage of the parasite (Tasumi and Vasta 2007).