Does the Precision of a Biological Clock Depend upon Its Period? Effects of the Duper and tau Mutations in Syrian Hamsters

Mutations which alter the feedback loops that generate circadian rhythms may provide insight into their insensitivity to perturbation robustness) and their consistency of period (precision). I examined relationships between endogenous period, activity and rest (τDD, α and ρ) in Syrian hamsters using two different mutations, duper and tau, both of which speed up the circadian clock. I generated 8 strains of hamsters that are homozygous or heterozygous for the tau, duper, and wild type alleles in all combinations. The endogenous period of activity onsets among these strains ranged from 17.94+0.04 to 24.13±0.04 h. Contrary to predictions, the variability of period was unrelated to its absolute value: all strains showed similar variability of τDD when activity onsets and acrophase were used as phase markers. The τDD of activity offsets was more variable than onsets but also differed little between genotypes. Cycle variation and precision were not correlated with τDD within any strain, and only weakly correlated when all strains are considered together. Only in animals homozygous for both mutations (super duper hamsters) were cycle variation and precision reduced. Rhythm amplitude differed between strains and was positively correlated with τDD and precision. All genotypes showed negative correlations between α and ρ. This confirms the expectation that deviations in the duration of subjective day and night should offset one another in order to conserve circadian period, even though homeostatic maintenance of energy reserves predicts that longer intervals of activity or rest would be followed by longer durations of rest or activity. Females consistently showed greater variability of the period of activity onset and acrophase, and of α, but variability of the period of offset differed between sexes only in super duper hamsters. Despite the differences between genotypes in τDD, ρ was consistently more strongly correlated with the preceding than the succeeding α

The Circadian Clock Protein CRY1 Is a Negative Regulator of HIF-1 alpha

The circadian clock and the hypoxia-signaling pathway are regulated by an integrated interplay of positive and negative feedback limbs that incorporate energy homeostasis and carcinogenesis. We show that the negative circadian regulator CRY1 is also a negative regulator of hypoxia-inducible factor (HIF). Mechanistically, CRY1 interacts with the basic-helix-loop-helix domain of HIF-1a via its tail region. Subsequently, CRY1 reduces HIF-1a half-life and binding of HIFs to target gene promoters. This appeared to be CRY1 specific because genetic disruption of CRY1, but not CRY2, affected the hypoxia response. Furthermore, CRY1 deficiency could induce cellular HIF levels, proliferation, and migration, which could be reversed by CRISPR/Cas9- or short hairpin RNA-mediated HIF knockout. Altogether, our study provides a mechanistic explanation for genetic association studies linking a disruption of the circadian clock with hypoxia-associated processes such as carcinogenesis

Rubus parthenocissus (Rosaceae) in Poland

Rubus parthenocissus, recently described species, known mainly from the southern part of Central Europe, has been found on 23 localities in S Poland

New localities of Rubus clusii (Rosaceae) seriously expanding it range towards the East

Rubus clusii Borbás is a species which occurs in Central Europe, from southern Germany, Czech Republic, southwestern Slovakia, through western Hungary andAustria to Slovenia. Nine new localities of this taxon were found in southeastern Poland, which considerably extends its geographical range. The results of one study suggest that the present definition of the species range was based on incomplete data, missing its potential localities. Therefore, we expect further extension with more localities identified

Restoration of self-sustained circadian rhythmicity by the mutant Clock allele in mice in constant illumination

Mice mutant for the Clock gene display abnormal circadian behavior characterized by long circadian periods and a tendency to become rapidly arrhythmic in constant darkness (DD). To investigate whether this result is contingent on the absence of light, the authors studied the circadian behavior of homozygous Clock mutant mice under conditions of both constant light and DD. Fourteen of 15 Clock/Clock mice stayed rhythmic in constant light of 70 to 170 lux, where 10 of 15 wild-type mice became arrhythmic. In contrast, only 5 of 15 Clock/Clock mice and 15 of 15 wild-type mice remained rhythmic after 60 cycles when released in DD (dim red light of < 1.5 lux) after 8 days of entrainment. The restoration of self-sustained rhythmicity by the Clock allele cannot be attributed to reduced sensitivity of the system to light. It underscores the fact that self-sustainment is not a secure guide to functional organization