Induction of chromosome abnormalities by reversal of colcemid inhibition in leucocyte cultures

Zusammenfassung Menschliche Leukozyten, die vorher 2 resp. 4 h der Wirkung von Colcemid ausgesetzt worden waren, ergaben in Zellkulturen 45 resp. über 50% Zellen mit 45 oder weniger Chromosomen im Vergleich zu 10% in Kontrollkulturen ohne Colcemid.

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This work is supported financially by Schering Chemicals Ltd., Burgess Hill, Sussex. We would like to thank Dr.A. G. Pitchford for advice and MissE. Gristwood for technical assistance.     

Tritium analyses of groundwater from the Gort Lowland of Western Ireland

Zusammenfassung Grundwasserproben aus der Gort-Ebene (West-Irland) wurden auf Tritium-Gehalt analysiert und die Ergebnisse mit dem bereits bekannten Tritium-Einstrom dieser Gegend verglichen. Registrierungen des «World Precipitation Network» in Wien ergaben den Nachweis eines offenbar langsamen Durchflusses in das Grundwasser-Aquifer-System.

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Acknowledgments. The authors are indebted to the Nuclear Physics Division, Atomic Energy Research Establishment, Harwell (England) for tritium analyses and to Mr.B. R. Payne, Section of Isotope Hydrology, IAEA, Wien (Austria) for providing unpublished tritium data from Valentia for the period 1966 to 1971.     

Cadherin 23 is a component of the tip link in hair-cell stereocilia

Mechanoelectrical transduction, the conversion of mechanical force into electrochemical signals, underlies a range of sensory phenomena, including touch, hearing and balance. Hair cells of the vertebrate inner ear are specialized mechanosensors that transduce mechanical forces arising from sound waves and head movement to provide our senses of hearing and balance; however, the mechanotransduction channel of hair cells and the molecules that regulate channel activity have remained elusive. One molecule that might participate in mechanoelectrical transduction is cadherin 23 (CDH23), as mutations in its gene cause deafness and age-related hearing loss. Furthermore, CDH23 is large enough to be the tip link, the extracellular filament proposed to gate the mechanotransduction channel. Here we show that antibodies against CDH23 label the tip link, and that CDH23 has biochemical properties similar to those of the tip link. Moreover, CDH23 forms a complex with myosin-1c, the only known component of the mechanotransduction apparatus, suggesting that CDH23 and myosin-1c cooperate to regulate the activity of mechanically gated ion channels in hair cells.     

Instability of Hes7 protein is crucial for the somite segmentation clock

During somitogenesis, a pair of somites buds off from the presomitic mesoderm every 2 hours in mouse embryos, suggesting that somite segmentation is controlled by a biological clock with a 2-hour cycle. Expression of the basic helix-loop-helix factor Hes7, an effector of Notch signaling, follows a 2-hour oscillatory cycle controlled by negative feedback; this is proposed to be the molecular basis for the somite segmentation clock. If the proposal is correct, this clock should depend crucially on the short lifetime of Hes7. To address the biological importance of Hes7 instability, we generated mice expressing mutant Hes7 with a longer half-life (approximately 30 min compared with approximately 22 min for wild-type Hes7) but normal repressor activity. In these mice, somite segmentation and oscillatory expression became severely disorganized after a few normal cycles of segmentation. We simulated this effect mathematically using a direct autorepression model. Thus, instability of Hes7 is essential for sustained oscillation and for its function as a segmentation clock.     

Physiology: hibernation in a tropical primate

The Madagascan fat-tailed dwarf lemur, Cheirogaleus medius, hibernates in tree holes for seven months of the year, even though winter temperatures rise to over 30 degrees C. Here we show that this tropical primate relies on a flexible thermal response that depends on the properties of its tree hole: if the hole is poorly insulated, body temperature fluctuates widely, passively following the ambient temperature; if well insulated, body temperature stays fairly constant and the animal undergoes regular spells of arousal. Our findings indicate that arousals are determined by maximum body temperatures and that hypometabolism in hibernating animals is not necessarily coupled to a low body temperature.