COMPARISON OF SEQUENCE AND FUNCTION OF THE OCT-6 GENES IN ZEBRAFISH, CHICKEN AND MOUSE

To examine the role of the Oct-6 gene in Schwann cell differentiation we have cloned and characterized the chicken and zebrafish homologues of the mouse Oct-6 gene. While highly homologous in the Pit1-Oct1/2-Un c86 (POU) domain, sequence similarities are limited outside this domai n. Both genes are intronless and both proteins lack the amino acid rep eats that are a characteristic feature of the mammalian Oct-6 proteins . However as in mammals, the aminoterminal parts of the chicken and ze brafish Oct-6 proteins are essential for transactivation of octamer co ntaining promoters. By immunohistochemistry we have found that the chi cken Oct-6 protein is expressed in late embryonic ensheathing Schwann cells of the sciatic nerve and is rapidly downregulated when myelinati on proceeds. This expression profile in glial cells is identical to th at in the mouse and rat. Furthermore the zebrafish Oct-6 homolog is ex pressed in the posterior lateral nerve at a time when it contains acti vely myelinating Schwann cells. Thus despite extensive primary sequenc e divergence among the vertebrate Oct-6 proteins, the expression of th e chicken and zebrafish Oct-6 proteins is consistent with the notion t hat Oct-6 functions as a 'competence factor' in promyelin cells to exe cute the myelination program. (C) 1998 Elsevier Science Ireland Ltd. A ll rights reserved.