Cloning and developmental expression analysis of prokineticin 2 and its receptor PKR2 in the Syrian hamster surpachiasmatic nucleus

Prokineticin 2 (PK2) and its receptor (PKR2) may play important roles in transmitting circadian rhythm information from the suprachiasmatic nucleus (SCN) to downstream neural targets. In this study, we identified PK2 and PKR2 genes in the Syrian hamster through a homologous cloning approach by performing 5′ and 3′-RACE. Sequence alignments indicate significant homology between the mouse, rat and Syrian hamster sequences. In situ hybridization experiments indicate that PK2 and PKR2 are expressed in the SCN, with the expression of PK2 with a pronounced amplitude change across the daily cycle under DD conditions. Recent studies indicate that the molecular machinery of the central clock in the suprachiasmatic nucleus only mature gradually during development. We thus studied the developmental expression of PK2 and PKR2 in the surpachiasmatic nuclei of the perinatal animals. PKR2 is expressed in the Syrian hamster SCN at all time points examined, while the expression of PK2 remains undetectable at prenatal time points. Expression of PK2 begins to be detectable on postnatal day 3 and onwards on day 5 and day 7. The developmental appearance of the PK2 expression rhythm may reflect the maturation process of the central clock's molecular machinery.