A Genetic Approach to Creating Asymmetric Brains in Drosophila melanogaster

Most animals, including humans and fruit flies, are Bilateria, a major branch of the animal kingdom characterized by bilateral symmetry. This symmetry extends to the brain, where the left and right hemispheres are near-perfect mirror images. The brain's structural symmetry poses challenges for genetic manipulation; current tools cannot selectively alter gene expression in just one hemisphere. This study extends the Sparse Predictive Activity through Recombinase Competition (SPARC) genetic toolkit to induce asymmetrical gene expression in Drosophila melanogaster. SPARC operates through probabilistic recombination, generating unique mosaics of gene expression in each individual fly. Here, I apply SPARC to create left-right asymmetry in the brain by targeting early embryonic development via maternal genetic reserves, deposited to the embryo. To standardize split-expression patterns, I investigate how environmental and genetic factors influence the likelihood of achieving lateralized gene expression and explore the resulting asymmetry. Data are collected from dissected, immunolabeled, and imaged brains. My findings suggest that SPARC, when maternally supplied, induces brain left/right asymmetry in roughly 58% of flies. Maternal age, progeny order, and environmental temperature did not significantly affect asymmetry probability, though larger asymmetries may be more common as the mother ages. SPARC successfully targeted a range of neuronal and glial cell types, with no significant differences in asymmetry rates across them. These results establish SPARC as a reliable tool for inducing asymmetric gene expression across diverse biological conditions and establish a framework for future applications of SPARC for asymmetrical manipulation studies of the fly brain.