Apoptosis as Potential Cause for Notochord Cell Loss in Molgula occulta

Abstract

The evolution of the chordate body plan is still unresolved. Notochord evolution can be studied with two tunicates—the tailed M. oculata and the tailless M. occulta. The tailed M. oculata has 40 notochord cells that are converged and extended. The tailless M. occulta does not form a tail in their larval stage as it only has 20 notochord cells that have not converged or extended. A hypothesis for the loss of notochord cells in M. occulta is that the notochord cells are being destroyed by apoptosis (programmed cell death). In this study, preparations for studying programmed cell death (PCD) using two genes Programmed cell death 2 (PDCD2) and Programmed cell death interacting protein 6 (PCDIP6) were made for in situ hybridizations. A cell death assay and in situ hybridizations will be done in the future on a variety of developmental stages of both the tailed and tailless species to assess differential regulation of the PCD genes. These studies elucidate if differential regulation of PCD is potentially the cellular mechanism for the loss of a tail in M. occulta.