Crustacea, the subphylum of Arthropoda which dominates the aquatic environment, is of major importance in ecology and fisheries. Here we report the genome sequence of the Pacific white shrimp Litopenaeus vannamei, covering ~1.66 Gb (scaffold N50 605.56 Kb) with 25,596 protein-coding genes and a high proportion of simple sequence repeats (>23.93%). The expansion of genes related to vision and locomotion is probably central to its benthic adaptation. Frequent molting of the shrimp may be explained by an intensified ecdysone signal pathway through gene expansion and positive selection. As an important aquaculture organism, L. vannamei has been subjected to high selection pressure during the past 30 years of breeding, and this has had a considerable impact on its genome. Decoding the L. vannamei genome not only provides an insight into the genetic underpinnings of specific biological processes, but also provides valuable information for enhancing crustacean aquaculture.

B1 cells are an important cell population for the production of natural antibodies and for antibacterial immunoglobulin responses. Here we identified the mouse protein Siglec-G as a B1 cell inhibitory receptor. Siglec-G was expressed in a B cell-restricted way, with large amounts present in B1 cells. When overexpressed, Siglec-G inhibited B cell receptor-mediated calcium signaling. Siglec-G-deficient mice had massive expansion of the B1a cell population, which began early in development and was B cell intrinsic. Siglec-G-deficient mice had higher titers of natural IgM antibodies but not a higher penetrance of IgG autoantibodies. Siglec-G-deficient B1 cells showed a strongly enhanced calcium signaling. Our results demonstrate that Siglec-G-dependent negative regulation exists in B1 cells, which may explain the naturally muted signaling response of B1 cells.