Eylem Seç
Study of the impact of the circadian mutation tau on the biological clock of the Syrian hamster (Mesocricetus auratus)
Başlık:
Study of the impact of the circadian mutation tau on the biological clock of the Syrian hamster (Mesocricetus auratus)
Yazar:
Dey, Joita, author.
ISBN:
9780438085091
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (329 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Özet:
The tau mutation in the Syrian hamster shortens the circadian period of locomotor activity from 24 h to 20. The mutation affects the casein kinase 1 epsilon (CK1epsilon) locus. A molecular basis for period shortening in the pacemaker in tau SCN has not been reported and the impact of the mutation on peripheral oscillators are yet to be defined. Tau mutants exhibit abnormal entrainment to light, especially following prolonged exposure to darkness, when the light-induced phase-shifts in behaviour resemble "Type 0" re-setting. Tau mutation has also affected the temporal organisation of a number of physiological and neuroendocrine processes. This thesis has two main aims. 1) To investigate the molecular basis of abnormal photic-resetting response in tau mutants. 2) To uncover the impact of the mutation on the molecular clock in the SCN and peripheral tissues. In order to characterise photic re-setting in wild types and tau mutants, light-induced phase-delays in wheel running activity was monitored and the expression of c-Fos, Per 1 and Bmall mRNA in the SCN quantified, using immunohistochemistry (IHC) and in-situ hybridisation (ISH) methods. Prolonged exposure to darkness resulted in larger phase-delays in tau mutants, both in response to a 1 h saturating light-pulse and at lower irradiances of 5 min duration given at CT 14. The phase-delays in tau mutants induced by 1 h light-pulse were typical of "type 0" re-setting. The duration of activity (a) in tau mutants was unaffected by photic history, instead the intensity of activity declined with progressive exposure to darkness. Light-induced c-fos mRNA in the SCN did not differ in kinetics or peak level between wild type and tau mutants, and it was also unaffected by photic history. Similarly, light-induced c-Fos-imnumoreactivity in the SCN did not differ between the two genotypes. Bmall mRNA was also characterised in both genotypes. A significant reduction in Bmall was observed in the tau SCN following prolonged exposure to darkness, this was correlated with a reduced intensity of wheel running activity observed in the animals. Light-pulses at CT 14 resulted in an accelerated rate of induction of Perl in the tau SCN, implying photic signalling might be altered in the mutants. In response to saturating light pulses of 15 min and 1 h duration, peak expression of Perl occurred at a similar time and with equivalent amplitude as in wild types. Photic history did not alter the maximal level of Perl and it did not correlate with "type 0" re-setting behaviour. However, following increased exposure to darkness (14 cycles) a higher level of Perl was induced and larger phase-delays in behaviour observed in tau mutants at sub-maximal irradiances. At this stage, behaviour and gene expression correlated. Augmented induction of Perl and increased behavioural phase-delays at sub-maximal irradiances implied that photic sensitivity increased in tau mutants following prolonged exposure to darkness. A light pulse at CT 14 significantly increased c-Fos-ir and Perl mRNA in tau retina, although the level of neither product differed from that in wild types. The circadian profile of clock gene mRNA and proteins in the SCN was characterised using ISH and IHC. The circadian peak of Perl mRNA was reduced by 20% in tau SCN compared to wild types. Nuclear PERI and PER2 proteins declined significantly earlier in tau SCN, suggesting that a clock phase at that time has been compressed or deleted in tau mutants, which underlies the shortened period. Additionally, Reverba mRNA was up-regulated, and Bmall mRNA dampened in the tau SCN during the earlier declining phase of PER proteins. Clock gene expression in the lung and heart were examined using TaqMan RT PCR. In tau heart, Perl and Bmall mRNA rhythms were dampened, whilst Dbp expression phase-advanced. Similarly, in the tau lung, Perl and Dbp expression was also phase-advanced by 4-6 h compared to wild type profile. Aberrant amplitude and phasing of clock gene expression in the peripheral oscillators possibly resulted from an abnormal output from the SCN. This misalignment of circadian oscillators in the SCN and peripheral tissues may therefore underlie the widespread effects of tau mutation on physiology. The initial aims of the project were to map the tau mutation and then clone a murine orthologue of tau. Amplified fragment length polymoiphism method was used to identify genomic and cDNA markers, a number of that showed homology to sequences in humans and mouse genomes. This part of the work was discontinued since the mutation was mapped to human chromosome 22q at the CKls locus. It is noteworthy that markers identified from the AFLP screen showed homology to sequences on chromosome 22q11-13 in humans, where tau mutation was mapped (Lowrey et al., 2000). The tau mutant hamster is the best-described vertebrate circadian model in terms of any clock gene affecting behaviour and physiology. The present study has demonstrated how a shortened period might have arisen in tau mutants and also provided suitable explanation for impaired behaviour and physiology in these animals. The data from the present study has further advanced the current understanding of the molecular basis of circadian rhythms and the mechanisms that control timed physiology, behaviour and entrainment.
Notlar:
School code: 1543
Konu Başlığı:
Tüzel Kişi Ek Girişi:
Mevcut:*
Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(686927.1) | 686927-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
On Order
Liste seç
Bunu varsayılan liste yap.
Öğeler başarıyla eklendi
Öğeler eklenirken hata oldu. Lütfen tekrar deneyiniz.
:
Select An Item
Data usage warning: You will receive one text message for each title you selected.
Standard text messaging rates apply.