Asteroseismology and Interferometry

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within Astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume 14, Issue 3-4, pp. 217-36

Codon Size Reduction as the Origin of the Triplet Genetic Code

The genetic code appears to be optimized in its robustness to missense errors and frameshift errors. In addition, the genetic code is near-optimal in terms of its ability to carry information in addition to the sequences of encoded proteins. As evolution has no foresight, optimality of the modern genetic code suggests that it evolved from less optimal code variants. The length of codons in the genetic code is also optimal, as three is the minimal nucleotide combination that can encode the twenty standard amino acids. The apparent impossibility of transitions between codon sizes in a discontinuous manner during evolution has resulted in an unbending view that the genetic code was always triplet. Yet, recent experimental evidence on quadruplet decoding, as well as the discovery of organisms with ambiguous and dual decoding, suggest that the possibility of the evolution of triplet decoding from living systems with non-triplet decoding merits reconsideration and further exploration. To explore this possibility we designed a mathematical model of the evolution of primitive digital coding systems which can decode nucleotide sequences into protein sequences. These coding systems can evolve their nucleotide sequences via genetic events of Darwinian evolution, such as point-mutations. The replication rates of such coding systems depend on the accuracy of the generated protein sequences. Computer simulations based on our model show that decoding systems with codons of length greater than three spontaneously evolve into predominantly triplet decoding systems. Our findings suggest a plausible scenario for the evolution of the triplet genetic code in a continuous manner. This scenario suggests an explanation of how protein synthesis could be accomplished by means of long RNA-RNA interactions prior to the emergence of the complex decoding machinery, such as the ribosome, that is required for stabilization and discrimination of otherwise weak triplet codon-anticodon interactions

Transfection of large plasmids in primary human myoblasts

NRC publication: Ye

Silencing SERCA1b in a few fibers stimulates growth in the entire regenerating soleus muscle

The neonatal isoform of the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 1 (SERCA1b) is a dominant Ca2+ pump in the young Wbers of regenerating muscle. In vivo transfection of about 1% of the Wbers with SERCA1b RNAi plasmid resulted in no apparent change in the transfected Wbers, but enhanced the increase of fresh weight and Wber size in the whole regenerating rat soleus muscle, until the normal size was reached. Co-transfection of calcineurin inhibitor cain/cabin-1 with SERCA1b RNAi was suYcient to cut down the widespread growth stimulation, but the subsequent transfection of cain into the SERCA1b RNAi transfected muscle did not inhibit muscle growth. The SERCA1b RNAi preferably upregulated the expression of the NFAT reporter lacZ compared to controls when co-transfected into the Wbers. Notably, perimuscular injection of interleukin-4 (IL-4) antibody but not that of an unrelevant antibody completely abolished the growth-promoting eVect of SERCA1b RNAi. This indicates that silencing SERCA1b in a few Wbers stimulates the calcineurin- NFAT-IL-4 pathway and Wber growth in the whole regenerating soleus. These results suggest the presence of an autocrine–paracrine coordination of growing muscle Wbers, and put forward a new method to stimulate skeletal muscle regeneration