"Researchers have uncovered that butterfly and moth wing color variations, previously attributed to the cortex gene, are actually regulated by a microRNA, mir-193, which represses pigmentation genes. This discovery, consistent across species, emphasizes the critical role of non-coding RNAs in driving phenotypic diversity.
Lepidopterans, including butterflies and moths, display a vast range of wing color patterns, often featuring black-and-white or dark-and-bright variations due to melanin. These variations are considered key examples of natural selection and evolution, such as the British peppered moth's adaptation to an industrialized, soot-darkened environment and the diverse mimetic patterns of Heliconius butterflies.
While ecological factors influencing melanin-based coloration are well understood, the genetic mechanisms behind these changes have remained elusive.
For years, scientists believed that the cortex gene controlled melanic wing color variations. However, a team of international researchers, led by Professor Antónia Monteiro and Dr. Shen Tian from the National University of Singapore (NUS), discovered that the cortex gene does not directly influence melanic coloration. Instead, a microRNA, mir-193, located near cortex, serves as the actual color switch.
The research, published in Science on December 5, 2024, revealed that disrupting mir-193 using CRISPR-Cas9 technology in three butterfly species—African squinting bush brown (Bicyclus anynana), Indian cabbage white (Pieris canidia), and common Mormon (Papilio polytes)—resulted in the loss of dark wing colors. In contrast, disrupting cortex or other nearby genes had no effect on wing color, confirming mir-193’s role as the key melanic color regulator across Lepidoptera species.
The study also found that mir-193 is processed from a long non-coding RNA called ivory and works by repressing multiple pigmentation genes. Notably, mir-193 is conserved across the animal kingdom, as its role in melanic coloration was also observed in Drosophila flies, highlighting its evolutionary significance.
Professor Monteiro explained that while earlier studies focused on the cortex gene, this work reveals that a small non-protein-coding RNA, mir-193, plays a central role in generating the diversity of melanic wing color variations. The study underscores the importance of considering non-coding RNAs, such as miRNAs, in genotype-phenotype research to avoid misleading conclusions.
Dr. Tian emphasized that the contribution of non-coding RNAs to phenotypic diversification remains underexplored, and this study paves the way for further investigations into how miRNAs and similar molecules shape phenotypic diversity in other organisms."
