Samantha Luk was invited by Professor Cramer to work in her lab. A highlight of Samantha’s research experience was her development of an understanding of what it is like to be a researcher. Through her participation in all of the steps of her project, she developed independence, organization, leadership, and networking skills that will help her throughout her future career. Samantha was very active outside of her classes at UCI, serving as Co-Vice President of UNICEF at UCI, Treasurer of WHOS (World Health of Students), and Co-President of the Neurobiology Club.

Eph and ephrin proteins play an important role in many areas of brain development, such as in the auditory system, which has several precise pathways. One auditory pathway that is necessary for sound localization is found between the ventral cochlear nucleus (VCN) and the medial nucleus of the trapezoid body (MNTB). Based on previous studies of ephrin-B2, we hypothesized that this ephrin protein plays an important part in creating the specific axonal connections between the VCN and the MNTB. We investigated this hypothesis by studying the anatomy of this pathway. Fluorescent dye was used to trace the axonal connections from the VCN to the MNTB in wild type mice and mutant ephrin-B2 mice. Normally, the axons coming from the VCN project primarily to the contralateral, or opposite, MNTB. However, it was found that the mutant ephrin-B2 mice formed abnormal axonal connections from the VCN to the ipsilateral (same side) MNTB. This abnormality in the auditory pathway suggests an inhibitory role for ephrin-B2 in axonal guidance during the development of the auditory system.

Karina S. Cramer School of Biological Sciences

Brain functions, including perception and behavior, depend critically on accurately ordered connections between nerve cells. A principle goal of developmental neuroscience is to determine how these connections form during embryonic and postnatal development. This can be studied in the auditory system, in which remarkable precision allows us to identify sound sources and their locations. Sound waves produce vibrations in receptor cells in the ear. These are converted to nervous system signals, which are in turn relayed by nerve cell connections in the brain. This study evaluated the molecular signals that assemble this circuitry when auditory nerve cells make their initial connections. The auditory connectivity was studied in mice lacking candidate genes. Using this approach, a key molecule role in establishing auditory circuitry was identified.