Cloning and the expression pattern of Spätzle gene during embryonic development and bacterial challenge in Artemia sinica.

Spätzle gene codes for a NGF-like protein, it involves in the embryonic development and innate immune response of insects and other invertebrate. In dorsal ventral axis differentiation, proSpätzle is activated by serine endoproteases Easter and then binds to the Toll receptor in ventral axis of oocyte which initiates the ventral axis development. Besides, it could also be activated by another protease named Spätzle-processing enzyme (SPZ) to mediate Toll pathway which involves in innate immune response in fungal and Gram-positive bacterial infection of invertebrate. In this paper, a full-length cDNA of Spätzle was firstly isolated from Artemia sinica which belonged to Spätzle-4 family. The expression of Spätzle was investigated at various stages during the embryonic development of A. sinica using real-time PCR and immunohistochemistry assays. The result showed that the high expression level of Spätzle appeared at 7 and 10 days of the embryo. A gradual increased level of Spätzle transcript occurred after being challenged with Gram-positive bacteria. Immunohistochemistry assay showed that Spätzle was mainly expressed in the cephalothorax and on the alimentary canal surface during embryonic development. This new Spätzle member showed a constitutive and regional expression during the embryonic development of A. sinica. It may play an important role in dorsal-ventral differentiation at the early development stages and in immune response pathway at the pseudoadult and adult stage, as well as during infection.