Retina: The control of photoreceptor cell fate

描述（由申请人提供）：视网膜发育中的一个关键问题是不同类型的光感受器如何在视网膜中被指定和定位。果蝇的眼睛是一个有价值的模型系统，可以用来解决这个问题。苍蝇的眼睛是由数百个称为小眼的亚单位组成的复合集合体。在每一个小眼中都有不同的光感受器类型，小眼有不同的类别，包含不同的光感受器类型。不同类型的光感受器视蛋白表达、轴突投射和在小眼内的位置不同。我们在这里要解决的主要问题是：(i)每个小眼内的光感受器是如何被唯一指定的？（ii）如何指明不同种类的小豆？

DESCRIPTION (provided by applicant): A critical question in retinal development is how different photoreceptor types are specified and positioned within a retina. The Drosophila eye is a valuable model system with which to address this question. The fly eye is a compound aggregate of many hundred sub-units called ommatidia. Within each ommatidium there are distinct photoreceptor types and ommatidia occur as different classes containing varying photoreceptor types. The photoreceptor types differ by their opsin expressions, their axonal projections, and their positions within the ommatidia. The major questions we are addressing here are: (i) how the photoreceptors within each ommatidium are uniquely specified? (ii) How the different types of ommatidia are specified? (1) Specification of the R7 photoreceptor: The UV sensitive photoreceptor in each ommatidium is the R7 cell. Signals from differentiating photoreceptors that contact the presumptive R7 and activate two distinct intracellular signals within the cell - the Ras and Notch (N) pathways. We wish to understand how these two pathways interact to specify the R7 cell. Do they act combinatorially to provide the R7 precursor with a unique developmental cue, or do they act in a different manner? For example could N pathway activation allow the activation of the Ras pathway and have no other function? Once these questions are answered we will examine the nature of the molecular interaction, and or integration of the two pathways. (2) Specification of asymmetry within the ommatidia: The photoreceptors in each ommatidium are arrayed in an asymmetric manner that is critically related to the optical properties of the eye. Ommatidia decode graded information in the retina to establish an initial asymmetry that is then communicated to the other cells of the ommatidium. The questions here are how the graded information is established, and how it is decoded and communicated to all cells of the unit. (3) The specification of the dorsal rim: The dorsal rim ommatidia are polarized light detector cells found in the dorsal extreme of the eye and contain specializations of the R7 and R8 cells. Signals emanating from the neighboring head tissue induce these ommatidia in only dorsal tissues. We wish to understand how signals from the head tissue organize the dorsal rim ommatidia and other associated retinal specializations.