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Sensitive periods of olfactory imprinting in lake sturgeon
Chunbo Zhang1,2, That Dang2, Yating Chen2, and Xin Sui2
1 Combi-Blocks, Inc., 7949 Silverton Ave, #915, San Diego, CA 92126
2 Department of Biological and Chemical Sciences, Illinois Institute of Technology, 3101S Dearborn St., Chicago, IL 60616
Lake sturgeon Acipenser fulvenscens is a freshwater sturgeon species indigenous to North America. We followed ontogeny of lake sturgeon to gain morphological and molecular biological information of the olfactory epithelium and forebrain (the olfactory system including the relay station) to predict when the olfactory system is vulnerable for olfactory imprinting. Morphogenesis studies of the forebrain differentiation and development indicated that lake sturgeon has more ancient structures than other actinopterygian species studied thus far, making lake sturgeon the most valuable model for unrevealing forebrain evolution in actinopterygii. Our data stimulate our searching for novel insights into actinopterygian forebrain evolution. After obtaining novel genetic information for genes expressed in the olfactory epithelium and the forebrain, we analyzed trends of gene expression along the development and determined that several key genes, we hypothesized that can be used to predict the time window of olfactory imprinting, showed expression patterns illustrative. These genes included orthodenticle vertebrate orthologue Otx2, glutamic acid decarboxylase (GAD) 65 and GAD67, NMDA receptors NR1, NR2A, NR2B, deiodinases D1 and D2, thyroid hormone receptors TRa and TR_, cyclin-dependent kinase 5 (Cdk5), and proliferating cell nuclear antigen (PCNA). Elevation of Otx2 signals the beginning of the sensitive period; D1, D2, TRa, and TR_ peak at the center of the period; and NR2 off the peak high and winding down of Cdk5 expression indicate ending of the sensitive period. The gene expression patterns suggest that there are two time windows for olfactory imprinting during the period we investigated. The first one takes whole Laval Stage at the Week 3 and 4 after hatching when fish are around 2-4 cm in total length. The second window likely starts in August or later of the 0-year in fish larger than 8 cm in total length. We predict that when the winter approaches, it becomes increasingly critical for olfactory imprinting. Out study suggest that current strategy of releasing 0-year fingering lake sturgeon to the Great Lakes in autumn is a recommend practice.