Rapid advances in DNA synthesis techniques have made it possible to engineer viruses, biochemical pathways and assemble bacterial genomes. Here, we report the synthesis of a functional 272,871 bp designer eukaryotic chromosome, synIII, which is based on the 316,617 bp native Saccharomyces cerevisiae chromosome III. Changes to synIII include TAG/TAA stop-codon replacements, deletion of subtelomeric regions, introns, tRNAs, transposons and silent mating loci as well as insertion of loxPsym sites to enable genome scrambling. SynIII is functional in S. cerevisiae. Scrambling of the chromosome in a heterozygous diploid reveals a large increase in “a mater” derivatives resulting from loss of the MATα allele on synIII. The total synthesis of synIII represents the first complete design and synthesis of a eukaryotic chromosome, establishing S. cerevisiae as the basis for designer eukaryotic genome biology.

The generation of human pluripotent stem cell (hPSC)-derived ventricular progenitors and their assembly into a 3-dimensional in vivo functional ventricular heart patch has remained an elusive goal. Herein, we report the generation of an enriched pool of hPSC-derived ventricular progenitors (HVPs), which can expand, differentiate, self-assemble, and mature into a functional ventricular patch in vivo without the aid of any gel or matrix. We documented a specific temporal window, in which the HVPs will engraft in vivo. On day 6 of differentiation, HVPs were enriched by depleting cells positive for pluripotency marker TRA-1-60 with magnetic-activated cell sorting (MACS), and 3 million sorted cells were sub-capsularly transplanted onto kidneys of NSG mice where, after 2 months, they formed a 7 mm × 3 mm × 4 mm myocardial patch resembling the ventricular wall. The graft acquired several features of maturation: expression of ventricular marker (MLC2v), desmosomes, appearance of T-tubule-like structures, and electrophysiological action potential signature consistent with maturation, all this in a non-cardiac environment. We further demonstrated that HVPs transplanted into un-injured hearts of NSG mice remain viable for up to 8 months. Moreover, transplantation of 2 million HVPs largely preserved myocardial contractile function following myocardial infarction. Taken together, our study reaffirms the promising idea of using progenitor cells for regenerative therapy.

Sick sinus syndrome (SSS) encompasses a group of disorders whereby the heart is unable to perform its pacemaker function, due to genetic and acquired causes. Tachycardia-bradycardia syndrome (TBS) is a complication of SSS characterized by alternating tachycardia and bradycardia. Techniques such as genetic screening and molecular diagnostics together with the use of pre-clinical models have elucidated the electrophysiological mechanisms of this condition. Dysfunction of ion channels responsible for initiation or conduction of cardiac action potentials may underlie both bradycardia and tachycardia; bradycardia can also increase the risk of tachycardia, and vice versa. The mainstay treatment option for SSS is pacemaker implantation, an effective approach, but has disadvantages such as infection, limited battery life, dislodgement of leads and catheters to be permanently implanted in situ. Alternatives to electronic pacemakers are gene-based bio-artificial sinoatrial node and cell-based bio-artificial pacemakers, which are promising techniques whose long-term safety and efficacy need to be established. The aim of this article is to review the different ion channels involved in TBS, examine the three-way relationship between ion channel dysfunction, tachycardia and bradycardia in TBS and to consider its current and future therapies.

Although biomimetic stimuli, such as microgroove-induced alignment (µ), triiodothyronine (T3) induction, and electrical conditioning (EC), have been reported to promote maturation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs), a systematic examination of their combinatorial effects on engineered cardiac tissue constructs and the underlying molecular pathways has not been reported. Herein, human embryonic stem cell-derived ventricular cardiomyocytes (hESC-VCMs) were used to generate a micro-patterned human ventricular cardiac anisotropic sheets (hvCAS) for studying the physiological effects of combinatorial treatments by a range of functional, calcium (Ca 2+)-handling, and molecular analyses. High-resolution optical mapping showed that combined µ-T3-EC treatment of hvCAS increased the conduction velocity, anisotropic ratio, and proportion of mature quiescent-yet-excitable preparations by 2. 3-, 1. 8-, and 5-fold (>70%), respectively. Such electrophysiological changes could be attributed to an increase in inward sodium current density and a decrease in funny current densities, which is consistent with the observed upand downregulated SCN1B and HCN2/4 transcripts, respectively. Furthermore, Ca 2+-handling transcripts encoding for phospholamban (PLN) and sarco/endoplasmic reticulum Ca 2+-ATPase (SERCA) were upregulated, and this led to faster upstroke and decay kinetics of Ca 2+-transients. RNA-sequencing and pathway mapping of T3-EC-treated hvCAS revealed that the TGF-β signaling was downregulated; the TGF-β receptor agonist and antagonist TGF-β1 and SB431542 partially reversed T3-EC induced quiescence and reduced spontaneous contractions, respectively. Taken