Zebrafish evx1 is dynamically expressed during embryogenesis in subsets ofinterneurones, posterior gut and urogenital system

The even-skipped-related homeobox genes (evx) are widely distributed throug h animal kingdom and are thought to play key role in posterior body pattern ing and neurogenesis. We have cloned and analyzed the expression of evx1 in zebrafish (see also Borday et al. (Dev. Dyn, 220 (2001) in press) which di splays a dynamic and restricted expression pattern during neurogenesis. In spinal cord, rhombencephalon, and epiphysis, evx1 is expressed in several s ubsets of emerging interneurones prior to their axonal outgrowth, identifie d as primary interneurones and a subset of Pax2.1(+) commissural interneuro nes. In the hindbrain, evx1 is expressed in reticulospinal interneurones of rhombomeres 5 and 6 as well as in rhombomere 7 interneurones. The latest e merging evx1(+) interneurones in the hindbrain correspond to commissural in terneurones. evx1 is also dynamically transcribed during the formation of t he posterior gut and the uro-genital system in mesenchymal cells that borde r the pronephric ducts, the wall of the pronephric duct, and later in the p osterior gut and the wall of the urogenital opening. In larvae, the ano-rec tal epithelium and the muscular layer that surrounds the analia-genitalia r egion remain stained up to 27 days. In contrast other vertebrates, evx1 dis plays no early nor caudal expression in zebrafish. (C) 2000 Elsevier Scienc e Ireland Ltd. All rights reserved.