Department of Biological Sciences, National University of Singapore, 117543 Singapore, Singapore.
Science Division, Yale-NUS College, 138609 Singapore, Singapore.
Genetics. 2021 Mar 3;217(1):1-9. doi: 10.1093/genetics/iyaa005.
The eyespot patterns found on the wings of nymphalid butterflies are novel traits that originated first in hindwings and subsequently in forewings, suggesting that eyespot development might be dependent on Hox genes. Hindwings differ from forewings in the expression of Ultrabithorax (Ubx), but the function of this Hox gene in eyespot development as well as that of another Hox gene Antennapedia (Antp), expressed specifically in eyespots centers on both wings, are still unclear. We used CRISPR-Cas9 to target both genes in Bicyclus anynana butterflies. We show that Antp is essential for eyespot development on the forewings and for the differentiation of white centers and larger eyespots on hindwings, whereas Ubx is essential not only for the development of at least some hindwing eyespots but also for repressing the size of other eyespots. Additionally, Antp is essential for the development of silver scales in male wings. In summary, Antp and Ubx, in addition to their conserved roles in modifying serially homologous segments along the anterior-posterior axis of insects, have acquired a novel role in promoting the development of a new set of serial homologs, the eyespot patterns, in both forewings (Antp) and hindwings (Antp and Ubx) of B. anynana butterflies. We propose that the peculiar pattern of eyespot origins on hindwings first, followed by forewings, could be due to an initial co-option of Ubx into eyespot development followed by a later, partially redundant, co-option of Antp into the same network.
眼斑模式在蛱蝶翅膀上的出现是新颖的特征，首先出现在后翅，随后出现在前翅，这表明眼斑的发育可能依赖于 Hox 基因。后翅与前翅在 Ultrabithorax（Ubx）的表达上存在差异，但该 Hox 基因在眼斑发育中的功能，以及另一个 Hox 基因 Antennapedia（Antp）在两翼眼斑中心的特异性表达，仍不清楚。我们使用 CRISPR-Cas9 靶向 Bicyclus anynana 蝴蝶中的这两个基因。我们表明，Antp 对于前翅眼斑的发育以及后翅白色中心和较大眼斑的分化是必不可少的，而 Ubx 不仅对于至少一些后翅眼斑的发育是必不可少的，而且对于抑制其他眼斑的大小也是必不可少的。此外，Antp 对于雄性翅膀中银鳞的发育也是必不可少的。总之，Antp 和 Ubx 除了在昆虫前后轴的串列同源节段的修饰中具有保守作用外，还在促进一组新的串列同源体（眼斑模式）的发育中获得了新的作用，这些模式在前翅（Antp）和后翅（Antp 和 Ubx）中都存在。我们提出，后翅首先出现眼斑，然后在前翅出现眼斑的特殊模式可能是由于 Ubx 最初被纳入眼斑发育，随后 Antp 被部分冗余地纳入同一网络。
