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  • Title: Specification of primary pigment cell and outer photoreceptor fates by BarH1 homeobox gene in the developing Drosophila eye.
    Author: Hayashi T, Kojima T, Saigo K.
    Journal: Dev Biol; 1998 Aug 15; 200(2):131-45. PubMed ID: 9705222.
    Abstract:
    In the developing Drosophila eye, BarH1 and BarH2, paired homeobox genes expressed in R1/R6 outer photoreceptors and primary pigment cells, are essential for normal eye morphogenesis. Here, we show evidence that BarH1 ectopically expressed under the control of the sevenless enhancer (sev-BarH1) causes two types of cone cell transformation: transformation of anterior/posterior cone cells into outer photoreceptors and transformation of equatorial/polar cone cells into primary pigment cells. sev-BarH1repressed the endogenous expression of the rough homeobox gene in R3/R4 photoreceptors, while the BarH2 homeobox gene was activated by sev-BarH1 in an appreciable fraction of extra outer photoreceptors. In primary pigment cells generated by cone cell transformation, the expression of cut, a homeobox gene specific to cone cells, was completely replaced with that of Bar homeobox genes. Extra outer photoreceptor formation was suppressed and enhanced, respectively, by reducing the activity of Ras/MAPK signaling and by dosage reduction of yan, a negative regulator of the pathway, suggesting interactions between Bar homeobox genes (cell fate determinants) and Ras/MAPK signaling in eye development.
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