B cell development

Transcripts of Rag-1 and/or Igµ are detectable on sections in adult zebrafish in the spleen, kidney and intestine, consistent with other teleost species and higher vertebrates, where B cells are produced in the bone marrow and are also found in the spleen and intestine. Intestinal B lymphocytes in teleosts are found in the loosely organized gut associated lymphoid tissue. Surprisingly, Rag-1 and Igµ are expressed in the pancreas of adult zebrafish. Tracing this gene expression pattern back in ontogeny, the pancreas was shown to be the initial site of B cell development in zebrafish larvae, initiating as early as 10 days post fertilization (dpf) by sectioning and 4 dpf by in-situ hybridization (for figures and text, go to: http://www.pnas.org/cgi/content/full/99/21/13711). By RT-PCR, membrane Igµ is first expressed on day 7 pf. These findings provide the first suggestion of initial B cell development in pancreatic tissue in a vertebrate.