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要旨:
A longstanding prediction of evolutionary theory is that phenotypic plasticity, the ability of one genotype to produce different phenotypes based on environmental input during development, plays a significant role in the evolution of morphological novelty. Nematodes of the Diplogastridae family are characterized by the presence of such a novelty: they possess cuticular teeth at the base of their mouths. Additionally, these structures are also polyphenic; different environmental cues can induce development of either a predatory form with two large teeth or a bacterivorous morph with only one dorsal tooth. Previous work demonstrated that two nuclear receptors, Ppa-NHR-1 and Ppa-NHR-40, regulate the morphogenesis of these teeth in Pristionchus pacificus. Interestingly, nematodes outside of the Diplogastridae, like Caenorhabditis elegans, lack this morphological novelty and the associated phenotypic plasticity entirely. Instead, these worms are monomorphic with simple, triangular flaps at the base of their mouths. However, Ppa-nhr-1 and Ppa-nhr-40 are the only genes of the P. pacificus mouth-form regulatory network that retain 1:1 orthologs in C. elegans. Therefore, we investigate whether these transcription factors also have a conserved function in regulating the development of the C. elegans mouth. Using the CRISPR/Cas9 system, we generated small indels in the coding sequences of Cel-nhr-1 and Cel-nhr-40 and isolated frameshift mutants to ensure a loss-of-function. Additionally, we aim to investigate the localization of both nuclear receptors by tagging them with fluorescent protein markers (e.g., mNeonGreen). In order to identify potential mutant phenotypes, we quantify differences in mouth shape between wildtype and CRISPR-edited strains by applying landmark-based geometric morphometrics in combination with k-medoid and model-based clustering.This data will be complemented with future RNA-seq experiments, which will identify the regulatory targets of Cel-NHR-1 and Cel-NHR-40. Taken together, this data will allow a comparison of the cellular localization, the regulatory targets, and the functional relevance of NHR-1 and NHR-40 for stoma development between C. elegans and P. pacificus. Ultimately, this study will reveal whether these nuclear receptors share a conserved function in stoma development that predates the evolution of the morphological novelty, or if a neo-functionalization accompanied its origin.
