Apoptosis, or programmed cell death, is a widespread biological phenomenon in multicellular organisms that plays important roles during development, immune response, elimination of damaged cells, and maintenance of homeostasis. The mechanism of apoptosis was well illustrated, but the knowledge of apoptosis in the species between vertebrate and invertebrate is rather limited. Here we have characterized FADD from amphioxus Branchiostoma belcheri.
FADD (Fas-associated death domain), also termed MORT1, plays a critical role in both CD95 (Fas/APO-1) or certain members of the tumor necrosis factor receptor (TNFR) superfamily (called ‘death receptors’) apoptotic signaling pathway, is well conserved in vertebrate species. To reveal the features of FADD in lower species, we have cloned and identified bbFADD (Branchiostoma belcheri FADD) cDNA and genomic DNA sequences by using the methods of RACE-PCE and Genomic Walking. The full length cDNA of bbFADD is 1239 base pairs (bp), encoding 217 amino acids (aa). bbFADD contains two protein interaction domains that are structurally similar to those of vertebrate FADDs, a death effector domain (DED) and a death domain (DD) at its N-terminus and C-terminus, respectively. The reported FADD genomic structure in both human and mouse contain two exons while bbFADD contains three ones. Phylogenetic relationship analysis showed that although amphioxus is at the evolutional intermediate stage from invertebrate to vertebrate, its FADD is more similar to its sea urchin orthologue at the amino acid level. Over-expression of bbFADD in human HeLa cells was able to induce apoptosis indicating that the bbFADD may perform its function by participating in the human apoptotic signaling pathway and the apoptosis system is evolutionarily conserved from amphioxus to mammal.