Although development of the adult Drosophila compound eye is very well understood, little is known about development of photoreceptors (PRs) in the simple larval eye. We show here that the larval eye is composed of 12 PRs, four of which express blue-sensitive rhodopsin5 (rh5) while the other eight contain green-sensitive rh6. This is similar to the 30:70 ratio of adult blue and green R8 cells. However, the stochastic choice of adult color PRs and the bistable loop of the warts and melted tumor suppressor genes that unambiguously specify rh5 and rh6 in R8 PRs are not involved in specification of larval PRs. Instead, primary PR precursors signal via EGFR to surrounding tissue to develop as secondary precursors, which will become Rh6-expressing PRs. EGFR signaling is required for the survival of the Rh6 subtype. Primary precursors give rise to the Rh5 subtype. Furthermore, the combinatorial action of the transcription factors Spalt, Seven-up, and Orthodenticle specifies the two PR subtypes. Therefore, even though the larval PRs and adult R8 PRs express the same rhodopsins (rh5 and rh6), they use very distinct mechanisms for their specification.

中文翻译：

---

成虫和幼虫感光器使用不同的机制来指定相同的视紫红质命运。

尽管对成年果蝇复眼的发育非常了解，但对简单幼虫眼中光感受器 (PR) 的发育知之甚少。我们在这里展示了幼虫眼由 12 个 PR 组成，其中四个表达对蓝色敏感的视紫红质 (rh5)，而另外八个则包含对绿色敏感的 rh6。这类似于成人蓝色和绿色 R8 细胞的 30:70 比例。然而，成人颜色 PRs 的随机选择和疣的双稳态环和融化的肿瘤抑制基因明确指定 R8 PRs 中的 rh5 和 rh6 不参与幼虫 PRs 的指定。相反，初级 PR 前体通过 EGFR 向周围组织发出信号，发展为次级前体，这将成为表达 Rh6 的 PR。Rh6 亚型的生存需要 EGFR 信号传导。初级前体产生Rh5亚型。此外，转录因子 Spalt、Seven-up 和 Orthodenticle 的组合作用指定了两种 PR 亚型。因此，即使幼虫 PR 和成年 R8 PR 表达相同的视紫红质（rh5 和 rh6），它们使用非常不同的机制来规范它们。