the online version of this article ( doi:10.1007/s00251 - 009 - 0416 - 5 ) contains supplementary material , which is available to authorized users . peptide sequences encoded by nitr amplicons detected from various zebrafish tissues ( figs .  2 and 3 ) . identical residues are highlighted in black , similar residues are highlighted in gray and gaps are indictaed by a dash ( - ) . sequence identity numbers ( i d ) are shown on the left and are color coded to the tissue source ( bottom ) . blast searches identified known alleles for certain nitr sequences which are indicated on the right : sequences without a listed allele are considered new alleles . the peptide domains are shown at the top of the alignments ( leader sequence ; v , variable domain ; i , intermediate domain ; j , joining - like domain . ) primers used to generate amplicons are described in table  1 and fig . 1 . sequences have been deposited in genbank with accession numbers gu193985gu194163 ( pdf 47  kb )
novel immune - type receptors ( nitrs ) are encoded by large multi - gene families and share structural and signaling similarities to mammalian natural killer receptors ( nkrs ) . 
 nitrs have been identified in multiple bony fish species , including zebrafish , and may be restricted to this large taxonomic group . 
 thirty - nine nitr genes that can be classified into 14 families are encoded on zebrafish chromosomes 7 and 14 . 
 herein , we demonstrate the expression of multiple nitr genes in the zebrafish ovary and during embryogenesis . 
 all 14 families of zebrafish nitrs are expressed in hematopoietic kidney , spleen and intestine as are immunoglobulin and t cell antigen receptors . 
 furthermore , all 14 families of nitrs are shown to be expressed in the lymphocyte lineage , but not in the myeloid lineage , consistent with the hypothesis that nitrs function as nkrs . 
 sequence analyses of nitr amplicons identify known alleles and reveal additional alleles within the nitr1 , nitr2 , nitr3 , and nitr5 families , reflecting the recent evolution of this gene family.electronic supplementary materialthe online version of this article ( doi:10.1007/s00251 - 009 - 0416 - 5 ) contains supplementary material , which is available to authorized users .