Deciphering the cellular heterogeneity of the insect brainwith single-cell RNA sequencing

Insects show highly complicated adaptive and sophisticated behaviors, includ-ing spatial orientation skills, learning ability, and social interaction. These behaviors arecontrolled by the insect brain, the central part of the nervous system. The tiny insect brainconsists of millions of highly differentiated and interconnected cells forming a complexnetwork. Decades of research has gone into an understanding of which parts of the insectbrain possess particular behaviors, but exactly how they modulate these functional conse-quences needs to be clarified. Detailed description of the brain and behavior is required todecipher the complexity of cell types, as well as their connectivity and function. Single-cell RNA-sequencing (scRNA-seq) has emerged recently as a breakthrough technologyto understand the transcriptome at cellular resolution. With scRNA-seq, it is possible touncover the cellular heterogeneity of brain cells and elucidate their specific functions andstate. In this review, we first review the basic structure of insect brains and the links toinsect behaviors mainly focusing on learning and memory. Then the scRNA applicationson insect brains are introduced by representative studies. Single-cell RNA-seq has allowedresearchers to classify cell subpopulations within different insect brain regions, pinpointsingle-cell developmental trajectories, and identify gene regulatory networks. These devel-opments empower the advances in neuroscience and shed light on the intricate problemsin understanding insect brain functions and behaviors.