Distinct expression patterns for two Xenopus Bar homeobox genes

The BarH1 and BarH2 homeobox genes are coexpressed in cells of the fly reti na and in the central and peripheral nervous systems. The fly Bar genes are required for normal development of the eye and external sensory organs. In Xenopus we have identified two distinct vertebrate Bar-related homeobox ge nes, XBH1 and XBH2. XBH1 is highly related in sequence and expression patte rn to a mammalian gene, MBH1, suggesting that they are orthologues. XBH2 ha s not previously been identified but is clearly related to the Drosophila B ar genes. During early Xenopus embryogenesis XBH1 and XBH2 are expressed in overlapping regions of the central nervous system. XBH1, but not XBH2, is expressed in the developing retina. By comparing the expression of XBH1 wit h that of hermes, a marker of differentiated retinal ganglion cells, we sho w that XBH1 is expressed in retinal ganglion cells during the differentiati on process, but is down-regulated as cells become terminally differentiated .