The Mystery of the Delta Phenotype: the Role of the Notch Signaling Pathway in Tribolium castaneum Embryogenesis

Abstract

Vertebrates, annelids, and arthropods have evolved to form their body plans via segmentation. The question is whether this process stems from a common, segmented ancestor or if segmentation in these three phyla evolved from a series of independent events. To determine which of these theories is true, we look to determining whether these phyla share any pathways in the development of their segments. The Notch signaling pathway is a well-known pathway that vertebrates utilize for segmentation. Without it, somitogenesis does not occur properly as the segmentation oscillator is not functioning. Drosophila does not use this pathway for segmentation, but several other arthropods have recently been found to utilize it in the formation and maintenance of their segments (17-24). There has been debate as to whether Tribolium castaneum also uses the Notch pathway during segmentation as previous knockdowns of the Notch and Delta genes have led to a loss of segments and appendages/mouthparts (25-27). To determine this pathway’s involvement in Tribolium segmentation, I knocked down the Delta gene via eRNAi and attempted to determine Notch and Delta expression patterns via in situ hybridization. My results were inconclusive for determining the role of the Notch signaling pathway in segmentation. In the Delta dsRNA embryos, a loss of the labial segment, head and mouthpart defects, a loss of leg formation, and midline defects were seen. Future experiments need to be performed to determine whether an overexpression of mesoderm, ectoderm, or both is the cause of the defective ventral midline and whether this could lead to a loss of segments later in development. Overall, I can conclude that the Notch signaling pathway plays a role in mouthpart/leg development, the labial segment, and what I believe to be lateral inhibition between mesoderm and ectoderm determination.