French V, Brakefield P M
Institute of Cell, Animal and Population Biology, University of Edinburgh, United Kingdom.
Dev Biol. 1995 Mar;168(1):112-23. doi: 10.1006/dbio.1995.1065.
The eyespot colour pattern on butterfly wings is specified in the early pupal epidermis by signals from a central "focus." In Bicyclus anynana we show that a small square of focal epidermis, grafted to a range of distal wing sites, induces eyespot formation in surrounding host tissue. Signaling is limited to the focus, and even an adjacent (parafocal) graft does not maintain its normal fate (of contributing to the eyespot) and does not influence its surroundings. Along the wing, there is an abrupt change in the epidermis, as a focus grafted to a proximal site provokes no host response. The results of several grafting experiments demonstrate that their different response properties are autonomous to small areas of the distal and proximal epidermis and that the nonresponding proximal tissue can nonetheless transmit the focal sign. The Bicyclus dorsal forewing has a small anterior and a large posterior eyespot, and we show that this results mainly from a difference in focal signals, not in the epidermal response. A grafted posterior focus induces a large eyespot, whereas an anterior focus induces a small eyespot. Furthermore, the anterior and posterior eyespots differ in proportions, and this difference also depends on the identity of the focus, not on the responding epidermis. Eyespots are specified over many cell diameters from the focus by a mechanism which could consist of one long-range signal, such as a morphogen gradient or of a cascade of short-range interactions initiated by the focus. Focal control of the difference in size and proportion between the anterior and posterior eyespot is more readily compatible with a gradient mechanism. Neither model, however, readily explains why the pattern induced by a grafted focus is smaller, but its peripheral gold annulus is broader than in the corresponding control eyespot. Also, there is no direct evidence for long-range gradients, in the butterfly wing or any other insect epithelium.
蝴蝶翅膀上眼斑的颜色图案是在蛹早期表皮中由来自一个中央“焦点”的信号所指定的。在猫眼蛱蝶中，我们发现一小块焦点表皮移植到一系列翅膀远端部位时，会诱导周围宿主组织形成眼斑。信号传导仅限于焦点，即使是相邻的（副焦点）移植组织也不会维持其正常命运（对眼斑形成有贡献），也不会影响其周围环境。沿着翅膀，表皮存在突然变化，因为移植到近端部位的焦点不会引发宿主反应。多个移植实验的结果表明，它们不同的反应特性对于远端和近端表皮的小区域是自主的，并且无反应的近端组织仍然可以传递焦点信号。猫眼蛱蝶的前翅背面有一个小的前眼斑和一个大的后眼斑，我们发现这主要是由于焦点信号的差异，而非表皮反应的差异。移植的后焦点会诱导形成大的眼斑，而前焦点会诱导形成小的眼斑。此外，前眼斑和后眼斑在比例上存在差异，这种差异也取决于焦点的特性，而非反应表皮的特性。眼斑是通过一种机制在距离焦点多个细胞直径的范围内被指定的，该机制可能由一种长距离信号组成，例如形态发生素梯度，或者由焦点引发的一系列短距离相互作用组成。对前眼斑和后眼斑大小和比例差异的焦点控制更容易与梯度机制相契合。然而，这两种模型都不容易解释为什么移植焦点诱导的图案较小，但其外围的金色环带却比相应的对照眼斑更宽。此外，在蝴蝶翅膀或任何其他昆虫上皮中，都没有长距离梯度的直接证据。
