Project description:Butterfly wings display a diversity of cell types, including large polyploid scale cells, yet the molecular basis of such diversity is poorly understood. To explore scale cell diversity at a transcriptomic level, we employ single-cell RNA sequencing of ∼5,200 large cells (>6 μm) from 22.5- to 25-h male pupal forewings of the butterfly Bicyclus anynana. Using unsupervised clustering, followed by in situ hybridization, immunofluorescence, and CRISPR-Cas9 editing of candidate genes, we annotate various cell types on the wing. We identify genes marking non-innervated scale cells, pheromone-producing glandular cells, and innervated sensory cell types. We show that senseless, a zinc-finger transcription factor, and HR38, a hormone receptor, determine the identity, size, and color of different scale cell types and are important regulators of scale cell differentiation. This dataset and the identification of various wing cell-type markers provide a foundation to compare and explore scale cell-type diversification across arthropod species.
Project description:The loss of discrete morphological traits, the most common evolutionary transition, is typically driven by changes in expression of developmental genes. Mutations accumulating in regulatory elements of these genes can disrupt DNA binding sites for transcription factors patterning their spatial expression, or delete entire enhancers. Regulatory elements, however, may in principle be silenced through other mechanisms, including changes in chromatin accessibility, or the emergence of repressive elements. Here, we show that an increase in chromatin accessibility at the pigmentation gene yellow, combined with the gain of a repressor site, underlie the evolutionary loss of a spot pigmentation pattern on the wings of a Drosophila species. The evolutionary gain of accessibility of this repressive element is regulated by E93, a transcription factor governing the progress of metamorphosis. This convoluted evolutionary scenario contrasts with the classical parsimonious mutational paths generally envisioned and often documented for morphological losses. It illustrates for the first time how evolutionary changes in chromatin accessibility may directly contribute to morphological diversification. We profiled chromatin accessibility at selected stages in the pupal wings of D. melanogaster and D. biarmipes using ATAC-seq.
Project description:Bicyclus anynana butterflies were reared at 17°C and 27°C to produce the dry and wet season forms. RNA was extracted using TRIzol from the heads of 12 individual animals ~0-3 hours after eclosing; 3 dry season females, 3 wet season females, 3 dry season males, and 3 wet season males. A TruSeq RNA Sample Preparation Kit v2 was used to make 12 double stranded cDNA libraries from polyadenylated RNA. We size selected for DNA at ~280-340 bp. Libraries were sequenced using a HiSeq 2500, paired end 100-cycle sequence run.