Dorsal eye selector pannier (pnr) suppresses the eye fate to define dorsal margin of the Drosophila eye

University of Dayton, Dayton, OH 45469, USA.
Developmental Biology (Impact Factor: 3.55). 10/2010; 346(2):258-71. DOI: 10.1016/j.ydbio.2010.07.030
Source: PubMed


Axial patterning is crucial for organogenesis. During Drosophila eye development, dorso-ventral (DV) axis determination is the first lineage restriction event. The eye primordium begins with a default ventral fate, on which the dorsal eye fate is established by expression of the GATA-1 transcription factor pannier (pnr). Earlier, it was suggested that loss of pnr function induces enlargement in the dorsal eye due to ectopic equator formation. Interestingly, we found that in addition to regulating DV patterning, pnr suppresses the eye fate by downregulating the core retinal determination genes eyes absent (eya), sine oculis (so) and dacshund (dac) to define the dorsal eye margin. We found that pnr acts downstream of Ey and affects the retinal determination pathway by suppressing eya. Further analysis of the "eye suppression" function of pnr revealed that this function is likely mediated through suppression of the homeotic gene teashirt (tsh) and is independent of homothorax (hth), a negative regulator of eye. Pnr expression is restricted to the peripodial membrane on the dorsal eye margin, which gives rise to head structures around the eye, and pnr is not expressed in the eye disc proper that forms the retina. Thus, pnr has dual function, during early developmental stages pnr is involved in axial patterning whereas later it promotes the head specific fate. These studies will help in understanding the developmental regulation of boundary formation of the eye field on the dorsal eye margin.

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    • "Prior to the imposition of dorsal identity, the entire eye disc expresses the ventral selector gene fringe ( fng). During the late first/early second instar, expression of pannier ( pnr), which encodes a GATA transcription factor, is activated via an unknown mechanism in a small group of cells within the peripodial membrane along the dorsal margin (Heitzler et al., 1996; Maurel-Zaffran and Treisman, 2000; Oros et al., 2010). Pnr is then responsible for inducing the expression of wingless (wg) (Maurel-Zaffran and Treisman, 2000), which in turn activates expression of the Iroquois complex (Iro-C) genes within the dorsal half of the eye (McNeill et al., 1997; Heberlein et al., 1998). "
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    • "Loss-of-function clones of pnrexhibit ectopic dorsal eyes, which are restricted within the clones, and suggests that absence of pnrfunction promotes ectopic eye formation in the dorsal eye margin. Thus, Pnr defines the boundary between the head cuticle and the dorsal margin of the developing eye field (Fig. 7; Oros et al., 2010). Since pnris not expressed in the ventral eye, there is a different mechanism to define the boundary of the eye field on the ventral margin. "
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