Insights into the genetic regulatory network underlying neurogenesis in the parthenogenetic marbled crayfish Procambarus virginalis

Abstract

Nervous system development has been intensely studied in insects (especially Drosophila melanogaster), providing detailed insights into the genetic regulatory network governing the formation and maintenance of the neural stem cells (neuroblasts) and the differentiation of their progeny. Despite notable advances over the last two decades, neurogenesis in other arthropod groups remains by comparison less well understood, hampering finer resolution of evolutionary cell type transformations and changes in the genetic regulatory network in some branches of the arthropod tree of life. Although the neurogenic cellular machinery in malacostracan crustaceans is well described morphologically, its genetic molecular characterization is pending. To address this, we established an in situ hybridization protocol for the crayfish Procambarus virginalis and studied embryonic expression patterns of a suite of key genes, encompassing three SoxB group transcription factors, two achaete-scute homologs, a Snail family member, the differentiation determinants Prospero and Brain tumor, and the neuron marker Elav. We document cell type expression patterns with notable similarities to insects and branchiopod crustaceans, lending further support to the homology of hexapod-crustacean neuroblasts and their cell lineages. Remarkably, in the crayfish head region, cell emigration from the neuroectoderm coupled with gene expression data points to a neuroblast-independent initial phase of brain neurogenesis. Further, SoxB group expression patterns suggest an involvement of Dichaete in segmentation, in concordance with insects. Our target gene set is a promising starting point for further embryonic studies, as well as for the molecular genetic characterization of subregions and cell types in the neurogenic systems in the adult crayfish brain.

Combining Old and New Tricks: The Study of Genes, Neurons, and Behavior in Crayfish

“…Early work focused on the development of the nervous system and some of its neurotransmitters ( Vilpoux et al, 2006 ; Polanska et al, 2007 ; Fabritius-Vilpoux et al, 2008 ; Rieger and Harzsch, 2008 ). More recently, studies have investigated adult neurogenesis ( Brenneis et al, 2021 ), operant conditioning ( Okada et al, 2021 ), phototaxis ( Shiratori et al, 2017 ), and psychostimulant actions on marbled crayfish behavior ( Jackson and van Staaden, 2019 ). However, most of these studies used traditional non-genetic methods.…”

“…The axons of the new sensory neurons must find their way to the brain, where they must be integrated into the already existing neuronal network of the olfactory lobe. Most recently, first insight into the genetic regulatory network underlying neurogenesis has been provided ( Brenneis et al, 2021 ), but generally speaking, very little is known about the molecular, genetic, and physiological profiles of these processes. Further combining these approaches in marbled crayfish will open new avenues to investigate neurogenesis, axonal path-finding, and regeneration of neurons.…”