B52 is a member of the classical serine/arginine (SR)-rich proteins, which are phylogenetically conserved and
play significant roles in mRNA maturation, including alternative splicing. In the present study, the docking site,
selector sequences and locus control region of the Chinese mitten crab (Eriocheir sinensis) Down syndrome cell
adhesion molecule (EsDscam) were identified. Alternative splicing of Dscam is essential to generate different
isoforms. We also isolated and characterised the B52 gene from E. sinensis (EsB52). The 876 bp open reading
frame of EsB52 encodes a 291 amino acid residue polypeptide, and EsB52 has two RNA recognition motifs
(RRMs) at the N-terminus and an arginine/serine-rich domain at the C-terminus. Each RRM contains two degenerate
short submotifs, RNP-1 and RNP2. Analysis of tissue distribution revealed that EsB52 mRNA expression
was widespread in all tested tissues, and especially high in brain and hemocytes. In hemocytes, EsB52 was
upregulated significantly after stimulation with pathogen-associated molecular patterns and bacteria.
Furthermore, EsB52 RNAi decreased the number of Ig7 inclusion in mRNA rather than Ig2 or Ig3. Taken together,
these findings suggest that EsB52 acts as an alternative splicing activator of EsDscam.