Every year, a committee of experts sits down with a tough job to do: from among all ICREA publications, they must find a handful that stand out from all the others. This is indeed a challenge. The debates are sometimes heated and always difficult but, in the end, a shortlist of 24 publications is produced. No prize is awarded, and the only additional acknowledge is the honour of being chosen and highlighted by ICREA. Each piece has something unique about it, whether it be a particularly elegant solution, the huge impact it has in the media or the sheer fascination it generates as a truly new idea. For whatever the reason, these are the best of the best and, as such, we are proud to share them here.


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  • Binucleated epicardial cells key in heart regeneration (2019)

    Trepat, Xavier (IBEC)
    Raya Chamorro, Ángel (IDIBELL)

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    Binucleated epicardial cells key in heart regeneration

    After an acute heart lesion, such as a myocardial infarction, the human heart is unable to regenerate. The adult cardiac cells cannot grow and divide to replace the damaged ones, and the lesion becomes irreversible. But this does not happen in all animals. For example, zebrafish can completely regenerate its heart even after 20% ventricular amputation.

    This extraordinary regenerative capacity has attracted the attention of researchers from all over the world, who see the range of possibilities that would be opened up if this mechanism of cell regeneration could be applied in human therapies. In collaboration with the team led by Angel Raya, we discovered a surprising mechanism by which zebrafish heart cells move and divide during regeneration.

    We focused on the epicardium, which is the layer of cells on the outer surface of the heart. Although the epicardium cells represent only a small fraction of the heart’s mass, they play a fundamental role in its regeneration. This tissue is the origin of several of the heart’s cell types, and secretes biochemical signals that tell the cells what they have to do at all times. It’s a kind of regeneration ‘hub’.

    After a heart lesion, the epicardium cells begin to divide and move en masse to cover the wound. We observed that, during this process, the cells become binucleated: they duplicate the genetic material and separate it into two nuclei, but they are not divided into two independent cells.

    We discovered that the mechanism by which cells become binucleated has a biomechanical origin. Once DNA has already separated into two nuclei, most animal cells form a contractile ring at its centre. As it contracts, this ring divides the mother cell into two daughter cells. In the case of the heart cells of the zebrafish, our study shows that the ring adheres to the fibres of its environment so that it cannot contract. The result is that the two daughter cells cannot separate despite having duplicated their DNA.

    Multinucleation is a well-known phenomenon in cancer, because it is a cause of genetic instability. In the zebrafish heart, multinucleation is physiological and may be advantageous.

  • Analysing the pledges of the Paris-Agreement (2019)

    van den Bergh, Jeroen (UAB)

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    Analysing the pledges of the Paris-Agreement

    The Paris Agreement takes a bottom-up approach to tackling climate change with countries submitting pledges in the form of nationally determined contributions (NDCs). Based on analysing such pledges, we classified them into 4 categories:

    1. Absolute emission reduction: for a target year in % terms relative to a historic base year, set by the country. The base year ranges from 1990 to 2014.

    2. Business-as-usual reduction (BAU): a % reduction in emissions relative to a no-policy scenario. BAU is defined by countries, causing large variance in emissions growth.

    3. Emission intensity reductions: a reduction in emission intensity per GDP relative to a base year. Effective emissions targets are then uncertain as they are dependent on future GDP growth.

    4. Projects absent of GHG-emission targets: no explicit GHG emission target but mention of projects intended to reduce emissions, like investment in renewable energy.

    These four categories cause a lack of consistency and transparency, which we correct for by normalisation. This involves calculating changes in emissions by 2030 – hence transforming categories 2-4 pledges to category 1 – using as the base year 2015. The result is shown in the figure. We find that pledges framed in terms of absolute emission reductions against historical base years generally produce the greatest ambition, with average emission reductions of 16% by 2030. Pledges defined as GDP intensity targets perform the worst with average emission increases of 61% by 2030.

    To illustrate, Russia, India and Pakistan all frame their NDCs in terms of % reductions: Russia relative to a base year, India to emissions per GDP, and Pakistan to a BAU scenario. This makes associated pledges hard to compare and causes a psychological effect of reducing ambition. Russia might have offered a more ambitious pledge if it was unable to frame its actual 13% emissions increase as a 25% decrease against a base year of choice.

    We advise to bar countries from presenting their pledges in a frame of own choice, or to let the UNFCCC normalise (updates of) pledges. Experiments demonstrate how aversion from shame is a powerful motivator of contributing to the commons.

  • A climate club for effective global governance (2019)

    van den Bergh, Jeroen (ICTA-UAB)

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    A climate club for effective global governance

    The Paris Climate Agreement relies on voluntary action by countries as it was impossible to achieve global policy coordination among all countries. As a result, national climate policies remain weak. A climate club or coalition of countries has been suggested as a means to move towards more effective global governance. It would involve uniform policy, most likely carbon pricing. The club could attract further membership by imposing penalties on imports from non-members, to limit competition from unregulated sources. Through economic and moral pressure, it would then expand. In addition, it could speak with a single, powerful voice at UN climate summits.

    We take this idea a step further by extending a club to comprise sub-national states or provinces. This is especially relevant to the US, given its withdrawal from the Paris Agreement. Our study used 4 measures to predict the likelihood of involvement for governments at multiple levels.

    We identified a group of nine countries likely to be receptive to club membership (Figure 1). The EU appears as the preferred initiator of the club, given its high emissions and history of climate leadership. China could likely be convinced to join given its recent sharp rise in concern about local and global emissions.

    As US states have significant control over their economies, we evaluated the likelihoods of individual states joining the club. The results indicate that 10 of the 50 states are ‘very likely’ to do so, with a further 13 ‘moderately likely’ to do so. Further analysis (Figure 2) shows that 10 less motivated US states could be persuaded through strong export dependencies with the EU, Canada, Mexico and China, likely members of an initial climate club. In all, we find that states covering 69.9 % of US emissions may be amenable to club membership via either of these mechanisms.

    While a climate club evidently has to overcome political hurdles, the limitations of Paris and the urgency of effective climate solutions suggest the time is ripe for debating daring solutions.

  • Seeing Single Nanocrystals by Stimulated Emission (2019)

    van Hulst, Niek F. (ICFO)

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    Seeing Single Nanocrystals by Stimulated Emission

    Detection and imaging of single-molecules has become routine over the last 3 decades, with a wide range of applications, particularly in biology, but also in physics and chemistry. To date such imaging relies almost fully on detection of fluorescence as the red-shifted photons are easily counted and the background is virtually zero. Yet fluorescence imaging has its limits: first, only fluorescent (or labelled) samples can be perceived; second fluorescence is prone to bleaching; and finally fluorescence, spontaneous emission, is a slow, occurring on a timescale of nanoseconds. As a result one misses out on all coherences, vibrational dynamics, and ultrafast energy or charge transfer.

    At ICFO, we have developed a complementary approach, based on the detection of stimulated emission, with several advantages. All molecules can be stimulated to emit a photon, also those that do not fluoresce. Most importantly the stimulation is ultrafast, in fact instantaneous, such that bleaching is avoided, while femto-picosecond dynamics of excited states is traced. The downside is that the stimulating laser beam also produces a significant amount of background light. We have overcome this challenge by using synchronized pump and probe pulses from the same broadband laser, ultrafast modulation, balanced and phase sensitive detection.

    In a first application, we show stimulated emission imaging of individual colloidal quantum dots at room temperature, while simultaneously recording the depleted spontaneous emission, enabling us to trace the carrier population through the entire photocycle. By capturing the femtosecond evolution of the stimulated emission signal, together with the nanosecond fluorescence, we disentangle the ultrafast charge trajectories in the excited state and determine the populations that experience stimulated emission, spontaneous emission, and excited-state absorption processes.

    Next we would like to extend our stimulated microscopy of single quantum systems to molecules and biomolecular complexes.

  • Neuromelanin: When darkness is the light to follow.   (2019)

    Vila Bover, Miquel (VHIR)

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    Neuromelanin: When darkness is the light to follow.  

    In Parkinson’s disease (PD) there is a preferential degeneration of neurons containing the dark-brown cytoplasmic pigment neuromelanin (NM), especially dopaminergic neurons of the substantia nigra the loss of which leads to the classical motor symptoms of PD. In humans, NM appears in early childhood and accumulates progressively with age, and increasing age is the main risk factor for developing PD. While the loss of pigmented nigral neurons in PD was first established a century ago and constitutes the cardinal pathologic diagnostic criteria for the disease, the potential contribution of NM to PD pathogenesis has remained largely unknown because, in contrast to humans, laboratory animal species commonly used in experimental research, such as rodents, lack NM. Thus, a factor so intimately linked to PD such as NM has been surprisingly neglected to date in experimental in vivo paradigms of the disease.

    To overcome this major limitation, we developed the first genetically-engineered rodent model exhibiting age-dependent production and accumulation of human-like NM within PD-vulnerable nigral neurons, at levels up to those reached in elderly humans. Using this unique animal model, we found that progressive intracellular build-up of NM with age ultimately compromised neuronal function when allowed to accumulate above a specific threshold, eventually triggering in an age-dependent manner all the main pathological features of PD. Relevant to humans, intracellular NM levels reached this pathogenic threshold in PD patients and pre-PD subjects but not in healthy elderly individuals. Importantly, the lowering of intracellular NM by gene therapy to levels below this pathogenic threshold reversed PD symptoms and pathology in NM-producing rodents. These results suggest that progressive, age-dependent intracellular NM accumulation above a pathogenic threshold might be responsible for the initiation of PD. Accordingly, strategies to maintain or decrease intracellular NM to levels below its pathogenic threshold may provide unprecedented therapeutic opportunities to prevent, halt or delay neuronal dysfunction and degeneration linked to PD and, in a broader sense, brain aging.

  • Rivers as main pathway of microplastic pollution to the ocean (2019)

    Ziveri, Patrizia (ICTA-UAB)

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    Rivers as main pathway of microplastic pollution to the ocean

    Rivers are considered the main pathway for microplastic pollution to reach oceans.  Microplastics are particles or fibers smaller than 5 mm. They can be “primary” microplastics such as raw material used to create plastic products (pellets), small particles used for cosmetic purposes, beads for industrial abrasive blasting media or fibers for textile purposes, or “secondary” microplastics, originating from the degradation of larger plastic items. Until now, studies on microplastic pollution have focused on their presence in oceans and seas, with little consideration given to rivers and estuaries as main sources of these pollutants. A recent study focussing on the Ebro Delta shows that Ebro's  surface waters annually discharge approximately 2.2 billion microplastics into the Mediterranean Sea.

    In the study, the values found in benthic sediments are 3-6 X higher than on sandy beaches of the estuarine system. This concentration is due to the influence of the salt wedge - spacing between fresh water and ocean water - where the flow velocity is lower and the retention time is longer. Overall, 70% of the microplastics found in the Ebro River Delta are synthetic fibers, followed by plastic fragments and films. Most of these fibers arrive to the river through wastewater effluents and treatment plants as a consequence of domestic and commercial laundry. Up to 2000 fibers can be released washing a single garment of clothing. Wastewater treatment plants are not able to remove all the textile fibers. 

    Transitional fresh and marine water systems - particularly near urbanized areas - are critical for microplastic research. Estimating the residence times of microplastics in this dynamic corridor to the ocean can help evaluate the hazard of these pollutants to organisms and ecosystems and, by extension, to human health.