Divergent expression of aristaless1 and aristaless2 is associated with embryonic appendage and pupal wing development in butterflies

Abstract

Aristaless is a major regulator of developmental processes. It is well known for its role during appendage specification and extension across animals. Butterflies and moths have two copies of aristaless, aristaless1 (al1) and aristaless2 (al2), as a result of a gene duplication event. Previous work in Heliconius has shown that both copies appear to have novel functions related to wing color patterning. Here we expand our knowledge on the expression profiles associated with both ancestral and novel functions of Al1 across embryogenesis and wing pigmentation. Furthermore, we characterize Al2 expression, providing a comparative framework for understanding the role of gene duplicates in novel and ancestral roles. Our work shows that both Al1 and Al2 expression are associated with developing sensory appendages (leg, mouth, spines, and eyes) in embryos. Interestingly, Al1 appears to show higher expression earlier in embryogenesis while the highest levels of Al2 expression are shifted to later stages of embryonic development. Furthermore, Al1 localization appears extranuclear while Al2 co-localizes tightly with nuclei earlier, and then also expands outside the nucleus later in development. We observed similar cellular expression patterns for Al1 and Al2 in pupal wings when examining their roles in pigmentation. We also describe, for the first time, how Al1 localization appear to correlates with zones of Anterior/Posterior elongation of the body during embryonic growth, showcasing a possible new function related to Aristaless previously described role in appendage extension. Overall, these data suggest similar developmental roles associated with the extension/formation of specific appendages for both duplicates. However, we describe that such functions might be regulated by spatially and temporally complex patterns of expression for al1 and al2. This work expands our knowledge of Aristaless function and expression following gene duplication and the implications of the duplication on butterfly development. Finally, and more fundamentally, our study helps clarify principles behind sub-functionalization and gene expression evolution associated with developmental functions following gene duplication events.