Hayashi T, Kojima T, Saigo K
Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
Dev Biol. 1998 Aug 15;200(2):131-45. doi: 10.1006/dbio.1998.8959.
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.
在发育中的果蝇眼睛里，BarH1和BarH2这两个配对的同源异型盒基因在R1/R6外部光感受器和初级色素细胞中表达，它们对于正常的眼睛形态发生至关重要。在这里，我们展示了证据表明，在无七受体增强子（sev-BarH1）控制下异位表达的BarH1会导致两种类型的视锥细胞转化：前后视锥细胞转化为外部光感受器，赤道/极视锥细胞转化为初级色素细胞。sev-BarH1抑制了R3/R4光感受器中粗糙同源异型盒基因的内源性表达，而BarH2同源异型盒基因在相当一部分额外的外部光感受器中被sev-BarH1激活。在由视锥细胞转化产生的初级色素细胞中，视锥细胞特有的同源异型盒基因cut的表达完全被Bar同源异型盒基因的表达所取代。分别通过降低Ras/MAPK信号通路的活性和减少该通路的负调节因子yan的剂量，额外的外部光感受器形成受到抑制和增强，这表明Bar同源异型盒基因（细胞命运决定因子）与Ras/MAPK信号通路在眼睛发育中存在相互作用。
