Abstract
BackgroundThe cell suicide pathway of apoptosis is a necessary event in the life of multicellular organisms. It is involved in many biological processes ranging from development to the immune response. Evolutionarily conserved proteases, called caspases, play a central role in regulating apoptosis. Reception of death stimuli triggers the activation of initiator caspases, which in turn activate the effector caspases. In Lepidoptera, apoptosis is crucial in processes such as metamorphosis or defending against baculovirus infection. The discovery of p35, a baculovirus protein inhibiting caspase activity, has led to the characterization of the first lepidopteran caspase, Sf-Caspase-1. Studies on Sf-Caspase-1 mode of activation suggested that apoptosis in Lepidoptera requires a cascade of caspase activation, as demonstrated in many other species.ResultsIn order to get insights into this gene family in Lepidoptera, we performed an extensive survey of lepidopteran-derived EST datasets. We identified 66 sequences distributed among 27 species encoding putative caspases. Phylogenetic analyses showed that Lepidoptera possess at least 5 caspases, for which we propose a unified nomenclature. According to homology to their Drosophila counterparts and their primary structure, we determined that Lep-Caspase-1, -2 and -3 are putative effector caspases, whereas Lep-Caspase-5 and -6 are putative initiators. The likely function of Lep-Caspase-4 remains unclear. Lep-Caspase-2 is absent from the silkworm genome and appears to be noctuid-specific, and to have arisen from a tandem duplication of the Caspase-1 gene. In the tobacco hawkmoth, 3 distinct transcripts encoding putative Caspase-4 were identified, suggesting at least 2 duplication events in this species.ConclusionsThe basic repertoire of five major types of caspases shared among Lepidoptera seems to be smaller than for most other groups studied to date, but gene duplication still plays a role in lineage-specific increases in diversity, just as in Diptera and mammals.
Highlights
The cell suicide pathway of apoptosis is a necessary event in the life of multicellular organisms
A Bayesian inferred phylogenetic analysis clustered these sequences into six distinct clades (Figure 3), revealing an extra caspase gene family that was not found in the B. mori genome (Caspase-2)
This observed number of caspase genes in Lepidoptera is similar to the seven genes found in Drosophila species: Drice, Dcp-1, Decay, Damm, Dronc, Dredd and Strica [13]
Summary
The cell suicide pathway of apoptosis is a necessary event in the life of multicellular organisms It is involved in many biological processes ranging from development to the immune response. Conserved proteases, called caspases, play a central role in regulating apoptosis. Development of holometabolous insects is characterized by a complete metamorphosis between the wingless larval stage, mostly dedicated to nutrient acquisition and growth, and the winged adult form, dedicated to reproduction. These drastic modifications in appearance and physiology require massive histolysis and histogenesis. A major family of evolutionarily conserved cysteinedependent aspartate-specific proteases, called caspases, plays a central role in apoptosis. It has been hypothesized that the host-pathogen interaction has been one of the major evolutionary forces shaping the apoptotic machinery and the caspase repertoire [17,18]
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