Influence of temperature on the liver circadian clock in the ruin lizard Podarcis sicula

Hibernation with rhythmicity: the circadian clock and hormonal adaptations of the hibernating Asiatic toads (Bufo gargarizans)

Hibernation is one of the fundamental strategies in response to cold environmental temperatures. During hibernation, the endocrine and circadian systems ensure minimal expenditure of energy for survival. The circadian rhythms of key hormones, melatonin (MT), corticosterone (CORT), triiodothyronine (T₃ ), and thyroxine (T₄ ), and the underlying molecular regulatory mechanisms of hibernation have been well determined in mammals but not in ectotherms. Here, a terrestrial hibernating species, Asiatic toad (Bufo gargarizans), was employed to investigate the plasma CORT, MT, T₃ , and T₄ ; and the retina, brain, and liver mRNA expression of the core clock genes, including circadian locomotor output cycles kaput (Clock), brain and muscle ARNT-like 1 (Bmal1), cryptochrome (Cry) 1 and 2, and period (Per) 1 and 2, at 7-time points over a 24-h period under acute cold (1 day at 4°C), and hibernation (45 days at 4°C). Our results showed that the circadian rhythms of the core clock genes were rather unaffected by acute cold exposure in the retina, unlike the brain and liver. In contrast, during hibernation, the liver clock genes displayed significant circadian oscillations, while those in the retina and brain stopped ticking. Furthermore, plasma CORT expressed circadian oscillations in both groups, and T₃ in acute cold exposure group, whereas T₄ and MT did not. Our results reveal that the plasma CORT and the liver sustain rhythmicity when the brain was not, indicating that the liver clock along with the adrenal clock synergistically maintains the metabolic requirements to ensure basic survival in hibernating Asiatic toads.

RNA/MBNL1-containing foci in myoblast nuclei from patients affected by myotonic dystrophy type 2: an immunocytochemical study

Myotonic dystrophy type 2 (DM2) is a dominantly inherited autosomal disease with multi-systemic clinical features and it is caused by expansion of a CCTG tetranucleotide repeat in the first intron of the zinc finger protein 9 (ZNF9) gene in 3q21.The expanded-CCUG-containing transcripts are retained in the cell nucleus and accumulate in the form of focal aggregates which specifically sequester the muscleblind-like 1 (MBNL1) protein, a RNA binding factor involved in the regulation of alternative splicing. The structural organization and composition of the foci are still incompletely known. In this study, the nuclear foci occurring in cultured myoblasts from DM2 patients were characterised at fluorescence and transmission electron microscopy by using a panel of antibodies recognizing transcription and processing factors of pre-mRNAs. MBNL1 proved to co-locate in the nuclear foci with snRNPs and hnRNPs, whereas no co-location was observed with RNA polymerase II, the non-RNP splicing factor SC35, the cleavage factor CStF and the PML protein. At electron microscopy the MBNL1-containing nuclear foci appeared as roundish domains showing a rather homogeneous structure and proved to contain snRNPs and hnRNPs. The sequestration of splicing factors involved in early phases of pre-mRNA processing supports the hypothesis of a general alteration in the maturation of several mRNAs, which could lead to the multiple pathological dysfunctions observed in dystrophic patients.

Dynamic relocation of nuclear proteins during the execution phase of apoptosis

In the apoptotic program of controlled cell dismantling, the most characteristic nuclear changes involve chromatin, which condenses and often collapses against the nuclear envelope in the form of crescents. A severe reorganization also occurs in ribonucleoprotein (RNP)-containing structures which are involved in the synthesis and processing of transcripts: already during early apoptosis, the nucleoplasmic RNPs (namely, perichromatin fibrils, perichromatin granules, and interchromatin granules) coalesce in the interchromatin space where they associate with segregated nucleolar components, to ectopically form fibro-granular heterogeneous clusters. This was found to occur in cell systems in vivo and in cultured cell lines, after different apoptogenic stimuli. These RNP aggregates we have called heterogeneous ectopic RNP-derived structures (HERDS) move from the nucleus to the cytoplasm, and may be found in apoptotic bodies, in late apoptosis. Immunolabeling experiments demonstrated that several other proteins which are normally located inside the nucleus also move into the cytoplasm, during apoptosis, independently from HERDS. Apoptotic cells have been suggested to be a powerful source of nuclear auto-antigens, which are produced by the partial proteolytic or nucleolytic cleavage of a wide variety of nuclear substrates. In the presence of defective phagocytosis (or when massive apoptosis overwhelms the clearance capability of the tissue scavenger cells), the disposal of apoptotic cells becomes insufficient and unphagocytosed late apoptotic cells may accumulate in the tissue where they may be engulfed by antigen-presenting cells (such as dendritic cells); an autoimmune response may thus be elicited, by which apoptosis-derived auto-antigens are recognized and presented to the immune system.

Effects of ageing on the fine distribution of the circadian CLOCK protein in reticular formation neurons

Many biochemical, physiological and behavioural processes, from bacteria to human, exhibit roughly 24 h cyclic oscillations defined as circadian rhythms. However, during ageing, numerous aspects of the circadian biology undergo alterations; in particular, the sleep pattern changes, with more frequent awakenings and shorter sleep time. The basic mechanism of the circadian clock relies on intracellular molecular pathways involving interlocking transcriptional/translational feedback loops, and CLOCK protein, a transcription factor, is essential for normal circadian rhythms. In this study, the fine distribution of CLOCK protein has been analysed, in adult and old rats, at different phases of the daily cycle in the neurons of the medullary reticular formation, involved in the control of the sleep-wake cycle. The results demonstrate quali-quantitative modifications of CLOCK protein in the neurons of old animals, suggesting that such a deregulation of the intracellular clock mechanism may play some role in the degeneration of the sleep-wake circadian cycle.