Title: Characterizing Axon Guidance in Mouse Palate
Michael Chen (Presenter)
Audrey O'Neill, UCSF
Jeffrey Bush, UCSF
Objectives: The secondary palate is a sensory organ housing the nasopalatine, greater palatine, and lesser palatine nerves, which are critical for general and taste sensation, and are anesthetic targets for maxillary dental procedures. However, nerve development in the palate has not be studied extensively. Hence, this study aims to characterize axonal phenotypes and their interactions with Ephs/ephrins, which are signaling cues that have been shown to be involved in axon guidance in other parts of the body. We aim to characterize the architecture of palatal axons in wildtype and mutant murine embryos at various embryonic stages.
Methods: Wildtype and mutant embryos of various stages were harvested at various stages (E11.5-E15.5). The palates were dissected, stained with a 2H3 (anti-neurofilament) antibody, an anti-ephrin-B1 antibody, and DAPI, cleared in SeeDB, and visualized using confocal microscopy.
Results: Wildtype E11.5 embryos lack any branches. Wildtype E12.5 embryos exhibit small lateral branches. In wildtype E13.5 embryos, the greater palatine nerve has parallel lateral branches and lacks branches at the anterior-medial border, where ephrin-B1 is strongly expressed. At E14.5 and E15.5, the greater palatine nerve branches into the anterior-medial palate. Efnb1 heterozygous mutants display fewer parallel branches and ephrinB1 patches that axons seem to track along. EphA3;EphA7 double mutants appear similar to controls.
Conclusions: In wildtype mice, the greater palatine nerve first branches laterally and then medially. This could be due to high ephrin-B1 expression in the anterior-medial palate acting as a repulsive force for axon guidance. Consistent with this, disorganized ephrin-B1 expression leads to disorganization of the axon tree. Though EphA3 and EphA7 are expressed in the palate, they appear not to affect axon guidance. Elucidating these cellular mechanisms could enhance our understanding of axon guidance mechanisms in secondary palate development and improve diagnosis of failed axon patterning, which is important for understanding dental anesthesia.