mirror encodes a novel PBX-class homeoprotein that functions in the definition of the dorsal-ventral border in the Drosophila eye.

Abstract

The Drosophila eye is composed of dorsal and ventral mirror-image fields of opposite chiral forms of ommatidia. The boundary between these fields is known as the equator. We describe a novel gene, mirror (mrr), which is expressed in the dorsal half of the eye and plays a key role in forming the equator. Ectopic equators can be generated by juxtaposing mrr expressing and nonexpressing cells, and the path of the normal equator can be altered by changing the domain of mrr expression. These observations suggest that mrr is a key component in defining the dorsal-ventral boundary of tissue polarity in the eye. In addition, loss of mrr function leads to embryonic lethality and segmental defects, and its expression pattern suggests that it may also act to define segmental borders. Mirror is a member of the class of homeoproteins defined by the human proto-oncogene PBX1. mrr is similar to the Iroquois genes ara and caup and is located adjacent to them in this recently described homeotic cluster.

The Complex Tale of the achaete–scute Complex: A Paradigmatic Case in the Analysis of Gene Organization and Function During Development

“…The first mutation identified as a candidate to participate in the position-specific activation of the AS-C in the thorax was named iroquois (iro), because it caused a phenotype in which several of the lateral macrochaetae were missing (Dambly-Chaudière and Leyns 1992; Leyns et al 1996). The genetic and molecular analysis of iro uncovered yet another gene complex, the iro-C, formed by three genes, caupolican, araucan, and mirror (GomezSkarmeta et al 1996;McNeill et al 1997;Kehl et al 1998). These genes encoded related nuclear proteins characterized by the presence of a conserved homeodomain.…”

The zebrafish Iroquois geneiro7positions the r4/r5 boundary and controls neurogenesis in the rostral hindbrain

“…In several cases, these boundaries act as secondary signalling centres (Araki and Nakamura, 1999;Matsunaga et al, 2000;Kobayashi et al, 2002) (reviewed by Rhinn and Brand, 2001;Wurst and BallyCuif, 2001). Iroquois genes have been implicated in boundary formation both in Drosophila and vertebrates: in Drosophila, Iro genes act as dorsal selector genes in the eye/antenna imaginal disc and are involved in the formation of the DV organiser that prefigures the future equator in the adult eye (McNeill et al, 1997;Cavodeassi et al, 1999;Yang et al, 1999;Cavodeassi et al, 2000). In the chick forebrain, Irx3 is involved in the positioning of the zona limitans intrathalamica by mutual repression with Six3, another homeodomain transcription factor (Kobayashi et al, 2002).…”

Planar Cell Polarity: Keeping Hairs Straight Is Not So Simple

“…Another set of genes are only needed in subsets of tissues to direct planar polarity: These tissue-specific PCP genes include genes such as multiple wing hair (mwh) (Strutt and Warrington 2008), fuzzy ( fy) (Collier and Gubb 1997), and inturned (in) (Park et al 1996), which are only needed for wing PCP, and mirror, fringe, and roulette, which are only necessary for PCP in the eye (Choi and Benzer 1994;McNeill et al 1997;Cho and Choi 1998;Dominguez and de Celis 1998;Yang et al 1999;Strutt and Strutt 2003).…”