Alejandro De Los Angeles

• DPhil MPH MS
• Postdoctoral Research Fellow at Harvard University

Naive human pluripotent stem cells (hPSCs) closely mirror the pre-implantation epiblast but risk imprint erosion under strong MEK/ERK inhibition, jeopardizing disease modeling and regenerative applications. In Stem Cell Reports, Fischer et al. show that partial MEK/ERK inhibition plus ZFP57 overexpression crucially preserves parent-of-origin DNA me...

Since the revolutionary discovery of induced pluripotent stem cells (iPSCs) by Shinya Yamanaka, the comparison between iPSCs and embryonic stem cells (ESCs) has revealed significant differences in their epigenetic states and developmental potential. A recent compelling study published in Nature by Buckberry et al.1 demonstrated that a transient-nai...

Exploring the early stages of human embryonic development poses significant difficulties owing to ethical and technical limitations. Two recent studies in Nature report the self-organization of human stem cells into 3D embryoids that model features of the early post-implantation stages of human development.1,2.

(Abstracted from Cell 2022;185:2988.e20–3007.e20) Spontaneous DNA damage, such as double-strand breaks (DSBs), affects cell-cycle progression and contributes to embryo attrition. There is a strong correlation among mitotic cell-cycle progression, ploidy, the quality of the blastocyst formed, and successful implantation from in vitro fertilization.

A role for voltage-gated calcium channels (VGCCs) in psychiatric disorders has long been postulated as part of a broader involvement of intracellular calcium signalling. However, the data were inconclusive and hard to interpret. We review three areas of research that have markedly advanced the field. First, there is now robust genomic evidence that...

Human cleavage-stage embryos frequently acquire chromosomal aneuploidies during mitosis due to unknown mechanisms. Here, we show that S phase at the 1-cell stage shows replication fork stalling, low fork speed, and DNA synthesis extending into G2 phase. DNA damage foci consistent with collapsed replication forks, DSBs, and incomplete replication fo...

The study of human–animal chimeras is fraught with technical and ethical challenges. In this Comment, we discuss the importance and future of human–monkey chimera research within the context of current scientific and regulatory obstacles.

Background Alternative splicing is a key mechanism underlying cellular differentiation and a driver of complexity in mammalian neuronal tissues. However, understanding of which isoforms are differentially used or expressed and how this affects cellular differentiation remains unclear. Long read sequencing allows full-length transcript recovery and...

Totipotency refers to single cells' developmental capacity to form an entire organism. Understanding how totipotent stem cells form has implications for chimera generation. In a recent Cell study, Shen et al. (2021) report that inhibition of spliceosomes resets conventional pluripotent stem cells to a cellular state with totipotency features.

Alternative splicing (AS) is a key mechanism underlying cellular differentiation and a driver of complexity in mammalian neuronal tissues. However, understanding of which isoforms are differentially used or expressed and how this affects cellular differentiation remains unclear. Long read sequencing allows full-length transcript recovery and quanti...

A key challenge in psychiatry research is the development of high-fidelity model systems that can be experimentally manipulated to explore and test pathophysiological mechanisms of illness. In this respect, the emerging capacity to derive neural cells and circuits from human induced pluripotent stem cells (iPSCs) has generated significant excitemen...

A key challenge in psychiatry research is the development of high-fidelity model systems that can be experimentally manipulated to explore and test pathophysiological mechanisms of illness. In this respect, the emerging capacity to derive neural cells and circuits from human induced pluripotent stem cells (iPSCs) has generated significant excitemen...

Gastrulation is a phase in early mammalian development when the three germ layers are generated and body plan is formed. Although well-studied in mice, much less is known about gastrulation in humans. Due to the lack of access to primary human tissue for study and experimental manipulation, as well as legal and ethical constraints surrounding the u...

Cerebral organoids are stem cell-derived, self-organizing three-dimensional cultures. Owing to the remarkable degree to which they recreate the cellular diversity observed in the human brain, they have attracted significant interest as a novel model system for research and drug development, as well as capturing the public imagination. However, many...

Rare heterozygous deletions in the neurexin 1 (NRXN1) gene robustly increase an individual's risk of developing neurological and psychiatric disorders. However, the molecular bases by which different mutations result in different clinical presentations, with variable penetrance are unknown. To better understand the molecular and cellular consequenc...

Pluripotency refers to the potential of single cells to form all cells and tissues of an organism. The observation that pluripotent stem cells can chimerize the embryos of evolutionarily distant species, albeit at very low efficiencies, could with further modifications, facilitate the production of human-animal interspecies chimeras. The generation...

The search for a better animal model to simulate human disease has been a “holy grail” of biomedical research for decades. Recent identification of different types of pluripotent stem cells (PS cells) and advances in chimera research might soon permit the generation of interspecies chimeras from closely related species, such as those between humans...

Pluripotency refers to the potential of cells to generate all cell types of the embryo proper. Pluripotency spans a spectrum of cellular states. At one polar extreme is naïve pluripotency, which is identified based on the potential to form germline chimeras. At the other polar extreme is primed pluripotency, in which pluripotent cells are primed to...

Human pluripotent stem (PS) cells can be isolated from preimplantation embryos or by reprogramming of somatic cells or germline progenitors. Human PS cells are considered the “holy grail” of regenerative medicine because they have the potential to form all cell types of the adult body. Because of their similarity to humans, nonhuman primate (NHP) P...

Humans develop from a unique group of pluripotent cells in early embryos that can produce all cells of the human body. While pluripotency is only transiently manifest in the embryo, scientists have identified conditions that sustain pluripotency indefinitely in the laboratory. Pluripotency is not a monolithic entity, however, but rather comprises a...

Stroke is the fifth leading cause of death among Americans each year. Current standard-of-care treatment for stroke deploys intravenous tissue-type plasminogen activator (tPA), mechanical thrombolysis, or delivery of fibrinolytics. Although these therapies have reduced stroke-induced damage, therapeutic options still remain limited. Transplantation...

Pluripotency refers to the capacity of single cells to form derivatives of the three germ layers—ectoderm, mesoderm, and endoderm. Pluripotency can be captured in vitro as a spectrum of pluripotent stem cell states stabilized in specialized laboratory conditions. The recent discovery that pluripotent stem cells can colonize the embryos of distantly...

The production of human organs inside human‐animal interspecies chimeras might one day comprise a viable strategy for generating patient‐specific organs, but such experiments will require human chimera‐competent pluripotent stem (PS) cells. The stabilization of PS cell self‐renewal in serum‐free medium and ERK blockade might be critical for capturi...

Generating human organs inside interspecies chimeras might one day produce patient-specific organs for clinical applications, but further advances in identifying human chimera-competent pluripotent stem (PS) cells are needed. Moreover, the potential for human PS cells to contribute to the brains in human-animal chimeras raises ethical questions. Th...

This volume addresses challenging new questions surrounding stem cell-based chimera research. This book is organized into three parts: Part One provides readers with a summary of different human donor cell types. The chapters in this section discuss ways to evaluate new types of pluripotent stem cells; the derivation of naïve and primed pluripotent...

The search for a better animal model to simulate human disease has been a "holy grail" of biomedical research for decades. Recent identification of different types of pluripotent stem (PS) cells and advances in chimera research might soon permit the generation of interspecies chimeras from closely related species, such as those between humans and o...

The shortage of human organs for transplantation is a devastating medical problem. One way to expand organ supply is to derive functional organs from patient-specific stem cells. Due to their capacity to grow indefinitely in the laboratory and differentiate into any cell type of the human body, patient-specific pluripotent stem (PS) cells harbor th...

Stem cells self-renew and generate specialized progeny through differentiation, but vary in the range of cells and tissues they generate, a property called developmental potency. Pluripotent stem cells produce all cells of an organism, while multipotent or unipotent stem cells regenerate only specific lineages or tissues. Defining stem-cell potency...

Polycomb Repressive Complex 2 (PRC2) function and DNA methylation (DNAme) are typically correlated with gene repression. Here, we show that PRC2 is required to maintain expression of maternal microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) from the Gtl2-Rian-Mirg locus, which is essential for full pluripotency of iPSCs. In the absence of PRC2...

Primordial germ cells (PGCs) share many properties with embryonic stem cells (ESCs) and innately express several key pluripotency-controlling factors, including OCT4, NANOG, and LIN28. Therefore, PGCs may provide a simple and efficient model for studying somatic cell reprogramming to induced pluripotent stem cells (iPSCs), especially in determining...

Self-renewal and pluripotency of embryonic stem cells (ESCs) are established by multiple regulatory pathways operating at several levels. The roles of histone demethylases (HDMs) in these programs are incompletely defined. We conducted a functional RNAi screen for HDMs and identified five potential HDMs essential for mouse ESC identity. In-depth an...

Cellular reprogramming to a stem-cell state has now been achieved in tissues of genetically engineered mice. This work signals a future for regenerative medicine in which tissue fates might be manipulated in living organisms. See Article p.340

Pluripotency can be experimentally induced from somatic cells by nuclear transfer, fusion with embryonic stem cells, or ectopic transcription factor induction, but attempts to recapitulate this process by chemical means alone have previously failed. In a recent paper published in Science, Hou et al. pursue a rational, albeit laborious approach to i...

Efficient strategies for precise genome editing in human-induced pluripotent cells (hiPSCs) will enable sophisticated genome engineering for research and clinical purposes. The development of programmable sequence-specific nucleases such as Transcription Activator-Like Effectors Nucleases (TALENs) and Cas9-gRNA allows genetic modifications to be ma...

During development, the hematopoietic lineage transits through hemogenic endothelium, but the signaling pathways effecting this transition are incompletely characterized. Although the Hedgehog (Hh) pathway is hypothesized to play a role in patterning blood formation, early embryonic lethality of mice lacking Hh signaling precludes such analysis. To...

Human embryonic germ cells (EGCs) provide a powerful model for identifying molecules involved in the pluripotent state when compared to their progenitors, primordial germ cells (PGCs), and other pluripotent stem cells. Microarray and Principal Component Analysis (PCA) reveals for the first time that human EGCs possess a transcription profile distin...

The generation of patient-specific induced pluripotent stem (iPS) cells provides an invaluable resource for cell therapy, in vitro modeling of human disease, and drug screening. To date, most human iPS cells have been generated with integrating retro- and lenti-viruses and are limited in their potential utility because residual transgene expression...

Pluripotency manifests during mammalian development through formation of the epiblast, founder tissue of the embryo proper. Rodent pluripotent stem cells can be considered as two distinct states: naïve and primed. Naïve pluripotent stem cell lines are distinguished from primed cells by self-renewal in response to LIF signaling and MEK/GSK3 inhibiti...

Intravascular delivery of neural stem cells (NSCs) after stroke has been limited by the low efficiency of transendothelial migration. Vascular cell adhesion molecule-1 is an endothelial adhesion molecule known to be upregulated early after stroke and is responsible for the firm adhesion of inflammatory cells expressing the surface integrin, CD49d....

Endogenous neural stem cells normally reside in their niche, the subventricular zone, in the uninjured rodent brain. Upon stroke, these cells become more proliferative and migrate away from the subventricular zone into the surrounding parenchyma. It is not known whether this stroke-induced behavior is due to changes in the niche or introduction of...

The use of stem cell transplantation to restore neurological function after stroke is being recognized as a potential novel therapy. Before stem cell transplantation can become widely applicable, however, questions remain about the optimal site of delivery and timing of transplantation. In particular, there seems to be increasing evidence that intr...