Deposited in PMC for release after 12 months

Deposited in PMC for release after 12 months. Author contributions C.M.S. at the midline can be eliminated when D/V patterning is usually disrupted and can be induced in situations in which ectopic boundaries are artificially generated. We also show that functions downstream of Notch signaling to maintain the expression of along the midline. vision to examine the role that this helix-loop-helix (HLH) protein Extramacrochaetae (Emc) plays in patterning across the D/V axis. The adult vision contains 750 unit eyes, or ommatidia, that are evenly placed within dorsal and ventral compartments. Each ommatidium contains eight photoreceptors (R1-8) that appear as an asymmetric trapezoid, Uramustine with the R3 and R4 cells Uramustine occupying unbalanced positions within the unit (Dietrich, 1909; Chen, 1929; Waddington and Perry, 1960). The ommatidia in the dorsal and ventral halves FGF1 are mirror images of each other and where they meet in the adult retina is referred to as the equator (Ready et al., 1976). In order to generate these mirror-image plans, the photoreceptor clusters must first adopt different chiralities and then rotate in reverse directions. D/V patterning in the developing vision takes place during the larval stages and can be divided into early and late phases. In the early phase (late first/early second instar) the unpatterned vision is usually subdivided into dorsal, ventral, and midline compartments. In the latter phase (third instar), ommatidia adopt the correct chirality and rotate in the direction that is appropriate for their location in either the dorsal or ventral compartment. In nearly all imaginal discs, the D/V axis is usually laid down during the late first/early second larval instar (Bohn, 1967; Bryant, 1970; Garcia-Bellido and Merriam, 1971a,b; Lawrence and Morata, 1976; Williams et al., 1993). Prior to the imposition of dorsal identity, the entire vision disc expresses the ventral selector gene ((((in the dorsal half of the eye field (Cho and Choi, 1998; Cavodeassi et al., 1999; Yang et al., 1999; Sato and Tomlinson, 2007). In the ventral half of the eye, (expression and ventral identity (Sato and Tomlinson, 2007). The confrontation of (dorsal) and (ventral) tissue leads to the differential activation of (((exhibit defects in chirality as well as in the direction and degree of rotation. In many mutant ommatidia, the R4 precursor adopts an R3 fate (Zheng et al., 1995). Similarly, in ommatidia with reduced Notch signaling, both precursors adopt the R3 fate, whereas hyperactivation of the pathway induces both cells to adopt the R4 fate (Cooper and Bray, 1999; Fanto and Mlodzik, 1999; Tomlinson and Struhl, 1999). Thus, maintaining appropriate levels of Fz and Notch activity in the R3/4 photoreceptor pair is crucial for the establishment of PCP in the eye. Two additional factors that influence PCP are the transmembrane cadherins Fat (Ft) and Dachsous (Ds) (Mahoney et al., 1991; Clark et al., 1995; Ishikawa et al., 2008). These proteins affect PCP in part by maintaining higher Fz receptor levels in the presumptive R3 cell as compared with the R4 precursor (Yang et al., 2002). is usually expressed in a relatively uniform pattern throughout the vision disc, whereas is expressed in a gradient Uramustine with highest levels at the poles. Mutations in the Excess fat/Ds system cause strong PCP defects throughout the entire disc (Yang et al., 2002; Rawls et al., 2002; Simon, 2004; Brittle et al., 2012; Thomas and Strutt, 2012; Sharma and McNeill, 2013; Ayukawa et al., 2014). By contrast, the eyes of homozygous loss-of-function mutant alleles are characterized by relatively weak PCP defects (Zeidler et al., 1999). Although mutant clones show somewhat stronger phenotypes, including nonautonomous effects (Zeidler et al., 1999), these are still relatively moderate compared with disruptions of the Ft/Ds or Fz/Notch systems. Once the R3/4 cells have adopted their individual fates, their positions in relation to each other will shift slightly, thus breaking the symmetry of the photoreceptor cluster. Ommatidia in the dorsal and ventral halves of the eye then rotate 90 in reverse directions, forming.

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