Expression of sox11 gene duplicates in zebrafish suggests the reciprocal loss of ancestral gene expression patterns in development

To investigate the role of sox genes in vertebrate development, we have iso lated sox11 from zebrafish (Danio rerio), Two distinct classes of sox11-rel ated cDNAs were identified, sox11a and sox11b, The predicted protein sequen ces shared 75% identity. In a gene phylogeny, both sox11a and sox11b cluste r with human, mouse, chick, and Xenopus Sox11, indicating that zebrafish, l ike Xenopus, has two orthologues of tetrapod Sox11, The work reported here investigates the evolutionary origin of these two gene duplicates and the c onsequences of their duplication for development. The sox11a and sox11b gen es map to linkage groups 17 and 20, respectively, together with other loci whose orthologues are syntenic with human SOX11, suggesting that during the fish lineage, a large chromosome region sharing conserved syntenies with m ammals has become duplicated. Studies in mouse and chick have shown that So x11 is expressed in the central nervous system during development. Expressi on patterns of zebrafish sox11a and sox11b confirm that they are expressed in the developing nervous system, including the forebrain, midbrain, hindbr ain, eyes, and ears from an early stage. Other sites of expression include the fin buds and somites, The two sox genes, sox11a and sox11b, are express ed in both overlapping and distinct sites. Their expression patterns sugges t that sox11a and sox11b may share the developmental domains of the single Sox11 gene present in mouse and chick. For example, zebrafish sox11a is exp ressed in the anterior somites, and zebrafish sox11b is expressed in the po sterior somites, but the single Sox11 gene of mouse is expressed in all the somites, Thus, the zebrafish duplicate genes appear to have reciprocally l ost expression domains present in the sox11 gene of the last common ancesto r of tetrapods and zebrafish. This splitting of the roles of Sox11 between two paralogues suggests that regulatory elements governing the expression o f the sox11 gene in the common ancestor of zebrafish and tetrapods may have been reciprocally mutated in the zebrafish gene duplicates. This is consis tent with duplicate gene evolution via a duplication-degeneration-complemen tation process. Dev Dyn 2000;217:279-292. (C) 2000 Wiley-Liss, Inc.