Genome editing in butterflies reveals that spalt promotes and Distal-less represses eyespot colour patterns

Butterfly eyespot colour patterns are a key example of how a novel trait can appear in association with the co-option of developmental patterning genes. Little is known, however, about how, or even whether, co-opted genes function in eyespot development. Here we use CRISPR/Cas9 genome editing to determine the roles of two co-opted transcription factors that are expressed during early eyespot determination. We found that deletions in a single gene, spalt, are sufficient to reduce or completely delete eyespot colour patterns, thus demonstrating a positive regulatory role for this gene in eyespot determination. Conversely, and contrary to previous predictions, deletions in Distal-less (Dll) result in an increase in the size and number of eyespots, illustrating a repressive role for this gene in eyespot development. Altogether our results show that the presence, absence and shape of butterfly eyespots can be controlled by the activity of two co-opted transcription factors.

蝴蝶眼斑色彩图案是阐释全新性状如何伴随发育模式基因的共招募而产生的关键范例。然而，目前对于共招募的基因如何乃至是否在眼斑发育中发挥功能，仍知之甚少。在此，我们利用CRISPR/Cas9基因组编辑技术，探究两个在眼斑早期决定阶段表达的共招募转录因子的功能。我们发现，仅对单个基因spalt进行缺失突变，即可削弱乃至完全消除眼斑色彩图案，由此证实该基因在眼斑决定过程中发挥正向调控作用。与之相反且与此前预测相悖的是，对Distal-less (Dll)基因进行缺失突变后，眼斑的尺寸与数量均出现增加，这表明该基因在眼斑发育过程中发挥抑制性功能。综合来看，我们的研究结果表明，蝴蝶眼斑的有无与形态均可通过两个共招募转录因子的活性实现调控。