Period 2: A Regulator of Multiple Tissue-Specific Circadian Functions

Abstract

The zebrafish represents a powerful model for exploring how light regulates the circadian clock due to the direct light sensitivity of its peripheral clocks, a property that is retained even in organ cultures as well as zebrafish-derived cell lines. Light-inducible expression of the per2 clock gene has been predicted to play a vital function in relaying light information to the core circadian clock mechanism in many organisms, including zebrafish. To directly test the contribution of per2 to circadian clock function in zebrafish, we have generated a loss-of-function per2 gene mutation. Our results reveal a tissue-specific role for the per2 gene in maintaining rhythmic expression of circadian clock genes, as well as clock-controlled genes, and an impact on the rhythmic behavior of intact zebrafish larvae. Furthermore, we demonstrate that disruption of the per2 gene impacts on the circadian regulation of the cell cycle in vivo. Based on these results, we hypothesize that in addition to serving as a central element of the light input pathway to the circadian clock, per2 acts as circadian regulator of tissue-specific physiological functions in zebrafish.

Contribution of the eye and ofopn4xafunction to circadian photoentrainment in the diurnal zebrafish

“…A loss of dec1 using morpholino antisense technology suggests a role for this gene in controlling circadian rhythms of locomotor activity induced by a light pulse but a role for this gene in period control in LL has not been addressed (Ben-Moshe et al, 2014). Along the same line a double mutant line for per2 and cry1a exhibit deficits in the generation of rhythms following a light pulse but the role of cry1a during period control in LL has not been addressed (Hirayama et al, 2019) In contrast, per2 regulates period length in constant light but its transcription is not affected in opn4xa -/- larvae ((Ruggiero et al, 2021; Wang et al, 2015); Figure 5G)); it is however possible that affecting the level of CRY1A could modify PER2 activity therefore leading to the observed phenotype. Further experiments will be required to address this question.…”

Genetic ablation of the Bsx homeodomain transcription factor in zebrafish: Impact on mature pineal gland morphology and circadian behavior

“…Following two‐way ANOVA, differences for heterozygote ( bsx +/ − ) and mutant ( bsx −/− ) fish compared to those of wildtype ( bsx +/+ ) controls were determined by multiplicity‐adjusted Dunnett's multiple comparisons tests. For the analysis of rhythmic locomotor activity, the data were normalized, and the period, phase, and amplitude were calculated as recently described 31 . Statistical differences in period and amplitude between groups were determined by ANOVA (followed by Tukey's multiple comparisons tests), and statistical differences in phase were determined by Watson–Williams test for the homogeneity of means by use of R software.…”

“…For the analysis of rhythmic locomotor activity, the data were normalized, and the period, phase, and amplitude were calculated as recently described. 31 Statistical differences in period and amplitude between groups were determined by ANOVA (followed by Tukey's multiple comparisons tests), and statistical differences in phase were determined by Watson–Williams test for the homogeneity of means by use of R software. Values are presented as mean with standard error (SEM).…”

Blind fish have cells that see light

“…Cells were entrained for 4 days on a 12 : 12 LD cycle prior to the experiment, and ZT21 was chosen as the time of the light pulse, as previous phase response curve data in zebrafish has shown that this is the time of day that the zebrafish cells are robustly light responsive [35]. The light-responsive clock genes cry1a and per2a, as well as the light-sensitive DNA repair gene cyclobutane pyrimidine dimer photolyase (CPD-Ph), were selected as marker genes for light sensitivity, as these genes appear to be activated using different pathways [36][37][38][39].…”