形态发生素是发育过程中在生长和模式形成中起重要作用的分泌蛋白。形态发生素的一个关键特征是，它能通过一个扩散梯度在距原点一定距离处发挥作用。本文作者直接评估了果蝇的Wingless (wg)蛋白的扩散的功能。他们发现，那些其固有wg 基因被编码一种膜系留Wg蛋白的（该基因的）一个人工形式取代的果蝇是可以存活并具有生殖能力的。这些发现与认为Wingless起一个长距离信号作用的观点是一致的，但却对一个扩散梯度的必要作用提出了质疑。
Wnts are evolutionarily conserved secreted signalling proteins that, in various developmental contexts, spread from their site of synthesis to form a gradient and activate target-gene expression at a distance. However, the requirement for Wnts to spread has never been directly tested. Here we used genome engineering to replace the endogenous wingless gene, which encodes the main Drosophila Wnt, with one that expresses a membrane-tethered form of the protein. Surprisingly, the resulting flies were viable and produced normally patterned appendages of nearly the right size, albeit with a delay. We show that, in the prospective wing, prolonged wingless transcription followed by memory of earlier signalling allows persistent expression of relevant target genes. We suggest therefore that the spread of Wingless is dispensable for patterning and growth even though it probably contributes to increasing cell proliferation.