Recent advances on the circadian gene PER2 and metabolic rhythm of lactation of mammary gland

Ruminal epithelial cell proliferation and short-chain fatty acid transporters in vitro are associated with abundance of period circadian regulator 2 (PER2)

The major circadian clock gene PER2 is closely related to cell proliferation and lipid metabolism in various nonruminant cell types. Objectives of the study were to evaluate circadian clock-related mRNA abundance in cultured goat ruminal epithelial cells (REC), and to determine effects of PER2 on cell proliferation and mRNA abundance of short-chain fatty acid (SCFA) transporters, genes associated with lipid metabolism, cell proliferation, and apoptosis. Ruminal epithelial cells were isolated from weaned Boer goats (n = 3; 2 mo old; ∼10 kg of body weight) by serial trypsin digestion and cultured at 37°C for 24 h. Abundance of CLOCK and PER2 proteins in cells was determined by immunofluorescence. The role of PER2 was assessed through the use of a knockout model with short interfering RNA, and sodium butyrate (15 mM) was used to assess the effect of upregulating PER2. Both CLOCK and PER2 were expressed in REC in vitro. Sodium butyrate stimulation increased mRNA and protein abundance of PER2 and PER3. Furthermore, PER2 gene silencing enhanced cell proliferation and reduced cellular apoptosis in isolated REC. In contrast, PER2 overexpression in response to sodium butyrate led to lower cellular proliferation and ratio of cells in the S phase along with greater ratio of cells in the G₂/M phase. Those responses were accompanied by downregulated mRNA abundance of CCND1, CCNB1, CDK1, and CDK2. Among the SCFA transporters, PER2 silencing upregulated mRNA abundance of MCT1 and MCT4. However, it downregulated mRNA abundance of PPARA and PPARG. Overexpression of PER2 resulted in lower mRNA abundance of MCT1 and MCT4, and greater PPARA abundance. Overall, data suggest that CLOCK and PER2 might play a role in the control of cell proliferation, SCFA, and lipid metabolism. Further studies should be conducted to evaluate potential mechanistic relationships between circadian clock and SCFA absorption in vivo.

Discovery of the indicator role of period 2 in yellow catfish (Pelteobagrus fulvidraco) food intake during early life development stages

The early development stages of fish are a highly ordered and tightly regulated, involving many circadian rhythm-related gene and protein processes. Nonetheless, there are few reports on the effects of circadian clock genes on the early development stages of fish. We studied Pelteobagrus fulvidraco Period 2 (Pf-Per 2) gene structures and expression patterns during the early life stages of development, including the fertilized embryo, yolk absorption, preliminary food, rotifer breeding, and mixed food stages. cDNA of Pf-Per 2 is 4593 bp in length, with 357 bp 5'-untranslated region (5'UTR), 216 bp 3'UTR. The 4020 bp open reading frame consists of 1339 encoded amino acids. By multiple sequence alignment and phylogenetic analysis, the sequence was found to demonstrate high similarity to humans, rodents, microorganisms, and other fish species. Expression patterns of mRNA transcripts showed existence of rhythmic oscillations in the yellow catfish during the early development phase. The higher expression level of Per 2 is obviously present in the early embryonic development stage; the continuous downward trend of Per 2 was observed in the embryonic development and yolk nutrition absorption stages; additionally, the expression of Per 2 mRNA was significantly increased during individual development, rotifer breeding, and mixed food stages. Moreover, immunohistochemistry studies revealed strongest immune-labeled positive signals of Per 2 proteins mainly located in the cytoplasm of the olfactory bulb cell. Our findings reveal Pf-Per 2 serves important functions and may be useful as an indicator of P. fulvidraco early life development and initial food intake process stages.