Functional characterization of STATa/b genes encoding transcription factors from Branchiostoma belcheri

The signal transducer and activator of transcription (STAT), as an important transcription factor of the Janus kinase (JAK)-STAT signaling pathway, is pivotal for development and immunity and well documented in vertebrates. However, the STAT gene has not been reported in chordate amphioxus (Branchiostoma belcheri). In this study, we firstly identify and characterize two STAT genes from Branchiostoma belcheri (designed as AmphiSTATa and AmphiSTATb). Secondly, our results reveal that AmphiSTATa is clustered with vertebrate STAT1, STAT2, STAT3 and STAT4, whereas AmphiSTATb is grouped with STAT5 and STAT6 based on phylogenetic analysis. Thirdly, AmphiSTATa and AmphiSTATb are found to widely express in five representative tissues of amphioxus (gill, hepatic cecum, intestine, muscle and notochord) by RT-qPCR analysis. Importantly, both AmphiSTATa and AmphiSTATb can be involved in innate immune responses to LPS stimulation. Fourthly, we demonstrate that AmphiSTATa and AmphiSTATb can form homodimers or heterodimers by Co-IP and Native-PAGE assay, and that AmphiSTATa and AmphiSTATb proteins can also distribute in cytoplasm and nucleus by the subcellular localization. Taken together, our findings not only reveal the roles of AmphiSTATa and AmphiSTATb in amphioxus innate immune responses to LPS stimulation, but provide a new insight into further elucidating the evolution and function of STATs in animals.