UC San Diego

The use of model organisms has been instrumental in furthering our understanding of biology as a whole; however, the use of additional organisms among different phylogenetic branches are needed to better understand the evolution of biological processes, traits, cell types, and genes. In recent years, due to its feasibility in culturing and established molecular techniques, the molluscan nudibranch Berghia stephanieae has emerged as a “non-model organism” to study a wide variety of biological processes. One barrier to Berghia research is the lack of a foundational understanding of Berghia biology, including the molecular mechanisms underlying novel tissue and cell type development. To lessen this barrier, this study combines three NGS datasets with in situ hybridization chain reaction to identify and characterize tissue and cell types in juvenile Berghia. Three novel tissues, the digestive gland, cnidosac, and rhinophore, were characterized through marker gene expression. A literature review of all single-cell RNA sequencing studies performed in molluscs was done, and a workflow for identifying cell types in our Berghia scRNA-seq data was established. From this data, four different cell types, including two hemocyte populations, neurons, ectomesoderm-derived secretory cells, were identified and characterized. Identification of these cell types will allow for future comparisons with additional scRNA-seq datasets to address questions about the evolution of these cell types. Overall, this work provides a foundational understanding of the molecular mechanisms behind tissues and cell types in juvenile development in the nudibranch Berghia stephanieae, enhancing its usefulness as a model organism.