Ferritin is widely distributed throughout the plant and animal kingdoms in a highly conserved conformation,which plays a key role in cellular iron metabolism including iron storage and detoxification.Vertebrate ferritin has been indirectly linked to innate immune response since their synthesis is regulated by proinflammatory cytokines.In invertebrate,ferritin has also been shown to be relevant to innate immune defense via ironwithholding strategy because it can be elevated by LPS challenge.To be better understand the sequences information and do further research on the function of ferritin,the cDNA sequence is characterized and the gene expression pattern is profiled.In this study,a fulllength ferritin cDNA sequence was obtained by constructing cDNA libraries of sea cucumber(Apostichopus japonicus),which was 792 bp long,and includes a 133 bp long 5′untranslated region(UTR),0RF encoding 173 amino acids,and a 137 bp long 3′UTR; the molecular weight predicted was 20 ku.The 5′UTR contains a highly conserved iron responsive element(IRE)sequence.The amino acids have a conserved motif for ferroxidase center typical of heavy chains of vertebrate ferritins.Sequence comparison showed that it reached the highest similarities of 84% with sea cucumber Holothuria glaberrima and shared more identity to H-chains of vertebrate ferritins than to the Lchains.It also shared 74%-34% identity with invertebrate ferritins compared with sea star,abalone,oyster,sea anemone,nematode,crayfish and drosophila.Phylogenetic analysis revealed the A.japonicus ferritin was grouped together with the invertebrate ferritin cluster.The ferritin mRNA were identified by using RT-PCR at development stages of sea cucumber including unfertilized egg,fertilized egg,cellulous stages,blastula,gastrula,early auricularia,auricularia,late auricularia,doliolaria,pentactula,juvenile and in different tissues of young sea cucumbers including intestines,coelomocytes,respiratory trees and body walls.Quantitative realtime PCR results showed that ferritin messages were low in unfertilized eggs through gastrula,however,a pronounced increase in transcript levels was observed from early auricularia to juvenile; The lowest expression level was found in the respiratory trees of young sea cucumbers; Moreover, ferritin mRNA showed no significant changes in expression after a LPS challenge in the four tissues of young sea cucumbers.This result suggests that ferritin expression might be regulated posttranscriptionally in sea cucumber.