Photoperiod regulates genes encoding melanocortin 3 and serotonin receptors, and secretogranins expressed in the dmpARC of the Siberian hamster

The mechanism(s) involved in the regulation of the seasonal-appropriate body weight of the Siberian hamster is currently unknown. We have identified photoperiodically regulated genes including VGF in a sub-region of the arcuate nucleus termed the dorsomedial posterior arcuate (dmpARC). Gene expression changes in this nucleus so far account for a significant number of those reported as photoperiodically regulated and are therefore likely to contribute to seasonal physiological responses of the hamsters. The present study was conducted to identify additional genes expressed in the dmpARC regulated by photoperiod that could be involved in regulating the activity of this nucleus with respect to seasonal physiology of the Siberian hamster. Using laser capture microdissection coupled with a microarray analysis and a candidate gene approach, we have identified in the dmpARC several photoperiodically regulated genes that are known to have roles in secretory and intracellular signaling pathways. These include secretogranin III (SgIII) and SgVI (secretory pathway), melanocortin 3 receptor (MC3-R) and serotonin (5-HT) receptors 2A and 7 (signaling pathway), all of which increase in expression in short photoperiod. The spatial relationship between receptor signaling and potential secretory pathways was investigated by dual in situ hybridization, which revealed that 5-HT2A and 5-HT7 receptors are expressed in neurons expressing VGF mRNA and that a sub-population (approximately 40%) of these neurons express MC3-R. These gene expression changes in dmpARC neurons may reflect the functional requirement of these neurons for seasonal physiology responses of the hamster Samples were taken from 10 individual animals, 5 of which had lived under a short day (SD) photoperiod, the other 5 under a long day (LD) photoperiod. Each hybridisation compared a LD sample (labelled with Cy5) with a SD sample (labelled with Cy3).