Neural tube closure in Ciona intestinalis: Investigating the gene regulatory network of Lmx

Abstract

Neural tube formation is an intricate process that requires proper regulation of cell division, movement, and shape changes. It is influenced by both environmental cues and genetic factors. Perturbation of its closure leads to neural tube defects (NTD’s) such as spina bifida. However, a comprehensive gene regulatory network has yet to be fully elucidated due to the complexity of vertebrate systems. Ciona intestinalis serves as a model organism for the purpose of this research because of its highly simplified neural tube and fixed embryonic cell lineage. The transcription factor Lmx, expressed in the dorsal neural tube cells in Ciona, has shown an intercalation defect when down-regulated. To gain more insight into the role for Lmx during neural tube formation, I ectopically expressed the gene in the epidermis adjacent to the neural plate. Lmx overexpression in this region results in dorsal curvature of the tail instead of ventral, and in most cases, the tube fails to close. The overexpression of Lmx did not affect the epidermal identity of the cells in triggering them to adopt a neural fate. In a single cell transcriptomic screen of Lmx overexpressing embryos, Lmx, DCDC2, and PIM3 expression were affected by the Lmx misexpression. Fluorescence intensity quantifications of reporter gene expression suggested Lmx activation of itself and inhibition of DCDC2 and PIM3, although results were not statistically significant and thus failed to conclusively confirm their regulation by Lmx.