Two sox9 genes on duplicated zebrafish chromosomes: Expression of similar transcription activators in distinct sites

Sox9 is a transcription factor required for cartilage formation and testis determination in mammals. We have cloned from zebrafish two sox9 genes, ter med sox9a and sox9b. Gene phylogenies showed that both genes are orthologou s to tetrapod SOX3 genes. Genetic mapping showed that these two loci reside on chromosome segments that were apparently duplicated in a large-scale ge nomic duplication event in ray fin fish phylogeny. Both Sox9a and Sox9b pro teins bind to the HMG consensus DNA sequences in vitro. We tested different domains for transactivation potential and identified a potential activatio n domain located in the middle of both Sox9a and Sox9b. During embryogenesi s, sox9a and sox9b expression patterns are distinct but overlap in some reg ions of the brain, head skeleton, and fins. Expression of sox9a/b correlate s well with that of col2a1 in chondrogenic elements. In the adults, sox9a i s expressed in many tissues including brain, muscle, fin, and testis, where as sox9b expression is restricted to previtellogenic oocytes of the ovary. This expression pattern predicts that sox9a and sox9b may have unique funct ions in some specific tissues during development. The role of gene duplicat ion for the evolution of developmental gene function is discussed. (C) 2001 Academic Press.