Oestrus induction in unisexually grouped mice by multiple short-term exposures to males

Oestrus induction and synchronization (the Whitten effect) were achieved in unisexually grouped female mice by short-term (10 and 30 min) exposure to conspecific males.     

Human ES-cell-derived cardiomyocytes electrically couple and suppress arrhythmias in injured hearts

Transplantation studies in mice and rats have shown that human embryonic-stem-cell-derived cardiomyocytes (hESC-CMs) can improve the function of infarcted hearts, but two critical issues related to their electrophysiological behaviour in vivo remain unresolved. First, the risk of arrhythmias following hESC-CM transplantation in injured hearts has not been determined. Second, the electromechanical integration of hESC-CMs in injured hearts has not been demonstrated, so it is unclear whether these cells improve contractile function directly through addition of new force-generating units. Here we use a guinea-pig model to show that hESC-CM grafts in injured hearts protect against arrhythmias and can contract synchronously with host muscle. Injured hearts with hESC-CM grafts show improved mechanical function and a significantly reduced incidence of both spontaneous and induced ventricular tachycardia. To assess the activity of hESC-CM grafts in vivo, we transplanted hESC-CMs expressing the genetically encoded calcium sensor, GCaMP3 (refs 4, 5). By correlating the GCaMP3 fluorescent signal with the host ECG, we found that grafts in uninjured hearts have consistent 1:1 host–graft coupling. Grafts in injured hearts are more heterogeneous and typically include both coupled and uncoupled regions. Thus, human myocardial grafts meet physiological criteria for true heart regeneration, providing support for the continued development of hESC-based cardiac therapies for both mechanical and electrical repair.     

Abrupt reversal in ocean overturning during the Palaeocene/Eocene warm period

An exceptional analogue for the study of the causes and consequences of global warming occurs at the Palaeocene/Eocene Thermal Maximum, 55 million years ago. A rapid rise of global temperatures during this event accompanied turnovers in both marine and terrestrial biota, as well as significant changes in ocean chemistry and circulation. Here we present evidence for an abrupt shift in deep-ocean circulation using carbon isotope records from fourteen sites. These records indicate that deep-ocean circulation patterns changed from Southern Hemisphere overturning to Northern Hemisphere overturning at the start of the Palaeocene/Eocene Thermal Maximum. This shift in the location of deep-water formation persisted for at least 40,000 years, but eventually recovered to original circulation patterns. These results corroborate climate model inferences that a shift in deep-ocean circulation would deliver relatively warmer waters to the deep sea, thus producing further warming. Greenhouse conditions can thus initiate abrupt deep-ocean circulation changes in less than a few thousand years, but may have lasting effects; in this case taking 100,000 years to revert to background conditions.     

A hypothesized unifying mechanism in neural function

Zusammenfassung Es wird die Hypothese aufgestellt, wonach alle nervösen Prozesse auf Ligandenkomplexierung mit Rezeptordisulfiden und/oder Sulfhydrylprotomeren der Nervenmembranen beruhen und diese Prozesse mit Reduktions- bzw. Oxydationsprozessen gekoppelt sein könnten. Lernprozesse würden auf dem gleichen Mechanismus beruhen.

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Approved for publication by the Director of the Research Division, College of Agricultural and Life Sciences. This research was supported in part by research grants No. GB-6580 and No. GB-8756 from the U.S. National Science Foundation, and by funds from the Elm Research Institute, the Wisconsin Department of Natural Resources, the Alleghany Foundation, the Schoenleber Foundation, and the Acme Chemical Co.     

The buffer effect and large-scale population regulation in migratory birds

Buffer effects occur when sites vary in quality and fluctuations in population size are mirrored by large changes in animal numbers in poor-quality sites but only small changes in good-quality sites. Hence, the poor sites 'buffer' the good sites, a mechanism that can potentially drive population regulation if there are demographic costs of inhabiting poor sites. Here we show that for a migratory bird this process can apply on a country-wide scale with consequences for both survival and timing of arrival on the breeding grounds (an indicator of reproductive success). The Icelandic population of the black-tailed godwit, Limosa limosa islandica, wintering in Britain has increased fourfold since the 1970s (ref. 5) but rates of change within individual estuaries have varied from zero to sixfold increases. In accordance with the buffer effect, rates of increase are greater on estuaries with low initial numbers, and godwits on these sites have lower prey-intake rates, lower survival rates and arrive later in Iceland than godwits on sites with stable populations. The buffer effect can therefore be a major process influencing large-scale population regulation of migratory species.     

Role of paternal and maternal genomes in mouse development

There has been much speculation on whether mammalian eggs with two male pronuclei can develop normally. Eggs with two female pronuclei can sometimes develop as far as the 25-somite stage but with only very meagre extraembryonic tissues. We suggested that the genome undergoes specific imprinting during gametogenesis and that some paternal genes may be necessary for normal development of the extraembryonic tissues, in which only the maternal X chromosome remains active. However, the need for the maternal genome for development to term is not yet unequivocally established. The detailed study described here demonstrates that while between 40 and 50% of heterozygous reconstituted eggs with a male and a female pronucleus develop to term, none of the eggs with two male pronuclei does so. Furthermore, embryos in the latter case are very retarded, even though the trophoblast develops relatively well compared with embryos having two female pronuclei. Our combined results indicate that while the paternal genome is essential for the normal development of extraembryonic tissues, the maternal genome may be essential for some stages of embryogenesis.     

Two stellar components in the halo of the Milky Way

The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, and this information can be used to tightly constrain models of galaxy formation and evolution. Although the halo was once considered a single component, evidence for its dichotomy has slowly emerged in recent years from inspection of small samples of halo objects. Here we show that the halo is indeed clearly divisible into two broadly overlapping structural components--an inner and an outer halo--that exhibit different spatial density profiles, stellar orbits and stellar metallicities (abundances of elements heavier than helium). The inner halo has a modest net prograde rotation, whereas the outer halo exhibits a net retrograde rotation and a peak metallicity one-third that of the inner halo. These properties indicate that the individual halo components probably formed in fundamentally different ways, through successive dissipational (inner) and dissipationless (outer) mergers and tidal disruption of proto-Galactic clumps.