Binding requirements for latent transforming growth factor Beta2 activation.

Although the mechanism for activation of latent TGFß1 and TGFß3 is understood to involve the binding of the TGFß propeptide (LAP) to both an integrin and an insoluble substrate, the activation of latent TGFß2 has been unclear because the TGFß2 LAP does not have the classical integrin binding sequence found in the other two TGFß isoform LAPs. To assess the potential requirement for covalent linkage with a matrix or cell surface protein for the activation of latent TGFß2, we generated mice in which the TGFß2 Cys residue predicted to be involved in binding was mutated to Ser (Tgfb2C24S). We reasoned that, if covalent interaction with a second molecule is required for latent TGFß2 activation, mutant mice should display a Tgfb2 null (Tgfb2-/-)-like phenotype. Tgfb2C24S mice closely phenocopy Tgfb2-/- mice with death in utero between E18 and P1 and with congenital heart and kidney defects similar to those described for Tgfb2-/- mice. The mutant latent TGFß2 is secreted at levels similar to WT, yet TGFß signaling monitored as nuclear pSmad2 is suppressed. We conclude that, like latent TGFß1, latent TGFß2 activation requires binding to an immobilized matrix or plasma membrane molecule.

A Pregnant Adolescent with COVID-19 and Multisystem Inflammatory Syndrome in Children.

Multisystem inflammatory syndrome in children (MIS-C), a new condition related to coronavirus disease 2019 (COVID-19) in the pediatric population, was recognized by physicians in the United Kingdom in April 2020. Given those up to the age of 21 years can be affected, pregnant adolescents and young adults are susceptible. However, there is scant information on how MIS-C may affect pregnancy and whether the presentation differs in the pregnant population. We report a case of a pregnant adolescent with COVID-19 and MIS-C with a favorable outcome. This case highlights the considerations in managing a critically ill pregnant patient with a novel illness and the importance of a multidisciplinary team in coordinating care.

Cardiolipin prolongs the lifetimes of respiratory proteins in Drosophila flight muscle.

Respiratory complexes and cardiolipins have exceptionally long lifetimes. The fact that they co-localize in mitochondrial cristae raises the question of whether their longevities have a common cause and whether the longevity of OXPHOS proteins is dependent on cardiolipin. To address these questions, we developed a method to measure side-by-side the half-lives of proteins and lipids in wild-type Drosophila and cardiolipin-deficient mutants. We fed adult flies with stable isotope-labeled precursors (13C615N2-lysine or 13C6-glucose) and determined the relative abundance of heavy isotopomers in protein and lipid species by mass spectrometry. To minimize the confounding effects of tissue regeneration, we restricted our analysis to the thorax, the bulk of which consists of post-mitotic flight muscles. Analysis of 680 protein and 45 lipid species showed that the subunits of respiratory complexes I-V and the carriers for phosphate and ADP/ATP were among the longest-lived proteins (average half-life of 48 ± 16 days) while the molecular species of cardiolipin were the longest-lived lipids (average half-life of 27 ± 6 days). The remarkable longevity of these crista residents was not shared by all mitochondrial proteins, especially not by those residing in the matrix and the inner boundary membrane. Ablation of cardiolipin synthase, which causes replacement of cardiolipin by phosphatidylglycerol, and ablation of tafazzin, which causes partial replacement of cardiolipin by monolyso-cardiolipin, decreased the lifetimes of the respiratory complexes. Ablation of tafazzin also decreased the lifetimes of the remaining cardiolipin species. These data suggest that an important function of cardiolipin in mitochondria is to protect respiratory complexes from degradation.

An Anterior Second Heart Field Enhancer Regulates the Gene Regulatory Network of the Cardiac Outflow Tract.

BACKGROUND: Conotruncal defects due to developmental abnormalities of the outflow tract (OFT) are an important cause of cyanotic congenital heart disease. Dysregulation of transcriptional programs tuned by NKX2-5 (NK2 homeobox 5), GATA6 (GATA binding protein 6), and TBX1 (T-box transcription factor 1) have been implicated in abnormal OFT morphogenesis. However, there remains no consensus on how these transcriptional programs function in a unified gene regulatory network within the OFT. METHODS: We generated mice harboring a 226-nucleotide deletion of a highly conserved cardiac enhancer containing 2 GATA-binding sites located ≈9.4 kb upstream of the transcription start site of Nkx2-5 (Nkx2-5∆enh) using CRISPR-Cas9 gene editing and assessed phenotypes. Cardiac defects in Nkx2-5∆enh/∆enh mice were structurally characterized using histology and scanning electron microscopy, and physiologically assessed using electrocardiography, echocardiography, and optical mapping. Transcriptome analyses were performed using RNA sequencing and single-cell RNA sequencing data sets. Endogenous GATA6 interaction with and activity on the NKX2-5 enhancer was studied using chromatin immunoprecipitation sequencing and transposase-accessible chromatin sequencing in human induced pluripotent stem cell-derived cardiomyocytes. RESULTS: Nkx2-5∆enh/∆enh mice recapitulated cyanotic conotruncal defects seen in patients with NKX2-5, GATA6, and TBX1 mutations. Nkx2-5∆enh/∆enh mice also exhibited defects in right Purkinje fiber network formation, resulting in right bundle-branch block. Enhancer deletion reduced embryonic Nkx2-5 expression selectively in the right ventricle and OFT of mutant hearts, indicating that enhancer activity is localized to the anterior second heart field. Transcriptional profiling of the mutant OFT revealed downregulation of important genes involved in OFT rotation and septation, such as Tbx1, Pitx2, and Sema3c. Endogenous GATA6 interacted with the highly conserved enhancer in human induced pluripotent stem cell-derived cardiomyocytes and in wild-type mouse hearts. We found critical dose dependency of cardiac enhancer accessibility on GATA6 gene dosage in human induced pluripotent stem cell-derived cardiomyocytes. CONCLUSIONS: Our results using human and mouse models reveal an essential gene regulatory network of the OFT that requires an anterior second heart field enhancer to link GATA6 with NKX2-5-dependent rotation and septation gene programs.

Autoimmune Congenital Complete Heart Block: How Late Can It Occur?

Objective Maternal anti-Ro (SSA) and/or anti-La (SSB) antibodies are a risk factor for congenital complete heart block (CHB). Because detailed analysis of the incidence of CHB after 24 weeks of gestational age (GA) is lacking, we aimed to ascertain the risk of "later-onset" CHB among offspring of SSA/SSB-positive mothers in the published literature. Study Design Using search terms "neonatal lupus heart block" and "autoimmune congenital heart block" on PubMed and Ovid, we gathered prospective studies of SSA/SSB-positive mothers with fetal echo surveillance starting from before CHB diagnosis and retrospective cases of fetal CHB diagnosis after 24 weeks of GA (if there was prior normal heart rate) or after birth. Results Ten prospective studies included 1,248 SSA/SSB-positive pregnancies with 24 cases of CHB diagnosed during pregnancy (1.9%). Among these, three (12.5%) were after 24 weeks-at weeks 25, 26, and 28. Our retrospective studies revealed 50 patients with CHB diagnosis in late fetal life and neonatal period and 34 in the nonneonatal childhood period. An additional four cases were diagnosed after age 18 years. Conclusion Later-onset autoimmune CHB in offspring of SSA/SSB-positive mothers does occur. Our analysis suggests that prenatal surveillance should continue beyond 24 weeks of GA but is limited by inconsistent published surveillance data.

TGFß-2 haploinsufficiency causes early death in mice with Marfan syndrome.

To assess the contribution of individual TGF-ß isoforms to aortopathy in Marfan syndrome (MFS), we quantified the survival and phenotypes of mice with a combined fibrillin1 (the gene defective in MFS) hypomorphic mutation and a TGF-ß1, 2, or 3 heterozygous null mutation. The loss of TGF-ß2, and only TGF-ß2, resulted in 80% of the double mutant animals dying earlier, by postnatal day 20, than MFS only mice. Death was not from thoracic aortic rupture, as observed in MFS mice, but was associated with hyperplastic aortic valve leaflets, aortic regurgitation, enlarged aortic root, increased heart weight, and impaired lung alveolar septation. Thus, there appears to be a relationship between loss of fibrillin1 and TGF-ß2 in the postnatal development of the heart, aorta and lungs.

Characteristics of Cardiac Abnormalities in Pediatric Patients With Acute COVID-19.

Introduction Coronavirus disease 2019 (COVID-19) is known to cause cardiac abnormalities in adults. Cardiac abnormalities are well-described in multisystem inflammatory syndrome in children, but effects in children with acute COVID-19 are less understood. In this multicenter study, we assessed the cardiac effects of acute COVID-19 among hospitalized children (<21 years) admitted to three large healthcare systems in New York City. Methods We performed a retrospective observational study. We examined electrocardiograms, echocardiograms, troponin, or B-type natriuretic peptides. Results Of 317 admitted patients, 131 (41%) underwent cardiac testing with 56 (43%) demonstrating cardiac abnormalities. Electrocardiogram abnormalities were the most common (46/117 patients (39%)), including repolarization abnormalities and QT prolongation. Elevated troponin occurred in 14/77 (18%) patients and B-type natriuretic peptide in 8/39 (21%) patients. Ventricular dysfunction was identified in 5/27 (19%) patients with an echocardiogram, all of whom had elevated troponin. Ventricular dysfunction resolved by first outpatient follow-up. Conclusion Electrocardiogram and troponin can assist clinicians in identifying children at risk for cardiac injury in acute COVID-19.

Why Don't More Mitochondrial Diseases Exhibit Cardiomyopathy?

BACKGROUND: Although the heart requires abundant energy, only 20-40% of children with mitochondrial diseases have cardiomyopathies. METHODS: We looked for differences in genes underlying mitochondrial diseases that do versus do not cause cardiomyopathy using the comprehensive Mitochondrial Disease Genes Compendium. Mining additional online resources, we further investigated possible energy deficits caused by non-oxidative phosphorylation (OXPHOS) genes associated with cardiomyopathy, probed the number of amino acids and protein interactors as surrogates for OXPHOS protein cardiac "importance", and identified mouse models for mitochondrial genes. RESULTS: A total of 107/241 (44%) mitochondrial genes was associated with cardiomyopathy; the highest proportion were OXPHOS genes (46%). OXPHOS (p = 0.001) and fatty acid oxidation (p = 0.009) defects were significantly associated with cardiomyopathy. Notably, 39/58 (67%) non-OXPHOS genes associated with cardiomyopathy were linked to defects in aerobic respiration. Larger OXPHOS proteins were associated with cardiomyopathy (p < 0.05). Mouse models exhibiting cardiomyopathy were found for 52/241 mitochondrial genes, shedding additional insights into biological mechanisms. CONCLUSIONS: While energy generation is strongly associated with cardiomyopathy in mitochondrial diseases, many energy generation defects are not linked to cardiomyopathy. The inconsistent link between mitochondrial disease and cardiomyopathy is likely to be multifactorial and includes tissue-specific expression, incomplete clinical data, and genetic background differences.

Knockout of cardiolipin synthase disrupts postnatal cardiac development by inhibiting the maturation of mitochondrial cristae.

Background: Cardiomyocyte maturation requires a massive increase in respiratory enzymes and their assembly into long-lived complexes of oxidative phosphorylation (OXPHOS). The molecular mechanisms underlying the maturation of cardiac mitochondria have not been established. Methods: To determine whether the mitochondria-specific lipid cardiolipin is involved in cardiac maturation, we created a cardiomyocyte-restricted knockout (KO) of cardiolipin synthase ( Crls1 ) in mice and studied the postnatal development of the heart. We also measured the turnover rates of proteins and lipids in cardiolipin-deficient flight muscle from Drosophila, a tissue that has mitochondria with high OXPHOS activity like the heart. Results: Crls1KO mice survived the prenatal period but failed to accumulate OXPHOS proteins during postnatal maturation and succumbed to heart failure at the age of 2 weeks. Turnover measurements showed that the exceptionally long half-life of OXPHOS proteins is critically dependent on cardiolipin. Conclusions: Cardiolipin is essential for the postnatal maturation of cardiomyocytes because it allows mitochondrial cristae to accumulate OXPHOS proteins to a high concentration and to shield them from degradation.

The critical role of cardiolipin in metazoan differentiation, development, and maturation.

Cardiolipins are phospholipids that are central to proper mitochondrial functioning. Because mitochondria play crucial roles in differentiation, development, and maturation, we would also expect cardiolipin to play major roles in these processes. Indeed, cardiolipin has been implicated in the mechanism of three human diseases that affect young infants, implying developmental abnormalities. In this review, we will: (1) Review the biology of cardiolipin; (2) Outline the evidence for essential roles of cardiolipin during organismal development, including embryogenesis and cell maturation in vertebrate organisms; (3) Place the role(s) of cardiolipin during embryogenesis within the larger context of the roles of mitochondria in development; and (4) Suggest avenues for future research.

Condensed Mitochondria Assemble Into the Acrosomal Matrix During Spermiogenesis.

Mammalian spermatogenesis is associated with the transient appearance of condensed mitochondria, a singularity of germ cells with unknown function. Using proteomic analysis, respirometry, and electron microscopy with tomography, we studied the development of condensed mitochondria. Condensed mitochondria arose from orthodox mitochondria during meiosis by progressive contraction of the matrix space, which was accompanied by an initial expansion and a subsequent reduction of the surface area of the inner membrane. Compared to orthodox mitochondria, condensed mitochondria respired more actively, had a higher concentration of respiratory enzymes and supercomplexes, and contained more proteins involved in protein import and expression. After the completion of meiosis, the abundance of condensed mitochondria declined, which coincided with the onset of the biogenesis of acrosomes. Immuno-electron microscopy and the analysis of sub-cellular fractions suggested that condensed mitochondria or their fragments were translocated into the lumen of the acrosome. Thus, it seems condensed mitochondria are formed from orthodox mitochondria by extensive transformations in order to support the formation of the acrosomal matrix.

Genetic Basis of Left Ventricular Noncompaction.

BACKGROUND: Left ventricular noncompaction (LVNC) is the third most common pediatric cardiomyopathy characterized by a thinned myocardium and prominent trabeculations. Next-generation genetic testing has led to a rapid increase in the number of genes reported to be associated with LVNC, but we still have little understanding of its pathogenesis. We sought to grade the strength of the gene-disease relationship for all genes reported to be associated with LVNC and identify molecular pathways that could be implicated. METHODS: Following a systematic PubMed review, all genes identified with LVNC were graded using a validated, semi-quantitative system based on all published genetic and experimental evidence created by the Clinical Genome Resource (ClinGen). Genetic pathway analysis identified molecular processes and pathways associated with LVNC. RESULTS: We identified 189 genes associated with LVNC: 11 (6%) were classified as definitive, 21 (11%) were classified as moderate, and 140 (74%) were classified as limited, but 17 (9%) were classified as no evidence. Of the 32 genes classified as definitive or moderate, the most common gene functions were sarcomere function (n=11; 34%), transcriptional/translational regulator (n=6; 19%), mitochondrial function (n=3; 9%), and cytoskeletal protein (n=3; 9%). Furthermore, 18 (56%) genes were implicated in noncardiac syndromic presentations. Lastly, 3 genetic pathways (cardiomyocyte differentiation via BMP receptors, factors promoting cardiogenesis in vertebrates, and Notch signaling) were found to be unique to LVNC and not overlap with pathways identified in dilated cardiomyopathy and hypertrophic cardiomyopathy. CONCLUSIONS: LVNC is a genetically heterogeneous cardiomyopathy. Distinct from dilated or hypertrophic cardiomyopathies, LVNC appears to arise from abnormal developmental processes.

LPGAT1 controls the stearate/palmitate ratio of phosphatidylethanolamine and phosphatidylcholine in sn-1 specific remodeling.

Most mammalian phospholipids contain a saturated fatty acid at the sn-1 carbon atom and an unsaturated fatty acid at the sn-2 carbon atom of the glycerol backbone group. While the sn-2 linked chains undergo extensive remodeling by deacylation and reacylation (Lands cycle), it is not known how the composition of saturated fatty acids is controlled at the sn-1 position. Here, we demonstrate that lysophosphatidylglycerol acyltransferase 1 (LPGAT1) is an sn-1 specific acyltransferase that controls the stearate/palmitate ratio of phosphatidylethanolamine (PE) and phosphatidylcholine. Bacterially expressed murine LPGAT1 transferred saturated acyl-CoAs specifically into the sn-1 position of lysophosphatidylethanolamine (LPE) rather than lysophosphatidylglycerol and preferred stearoyl-CoA over palmitoyl-CoA as the substrate. In addition, genetic ablation of LPGAT1 in mice abolished 1-LPE:stearoyl-CoA acyltransferase activity and caused a shift from stearate to palmitate species in PE, dimethyl-PE, and phosphatidylcholine. Lysophosphatidylglycerol acyltransferase 1 KO mice were leaner and had a shorter life span than their littermate controls. Finally, we show that total lipid synthesis was reduced in isolated hepatocytes of LPGAT1 knockout mice. Thus, we conclude that LPGAT1 is an sn-1 specific LPE acyltransferase that controls the stearate/palmitate homeostasis of PE and the metabolites of the PE methylation pathway and that LPGAT1 plays a central role in the regulation of lipid biosynthesis with implications for body fat content and longevity.

Strain in children with MIS-C and acute COVID-19.

Context: Cardiac injury has been described in both acute COVID-19 and the multisystem inflammatory syndrome in children (MIS-C). Echocardiographic strain has been shown to be a sensitive measure of systolic function. Aims: We sought to describe strain findings in both the groups on initial presentation and follow-up. Settings and Design: A retrospective study analyzing echocardiograms of all patients presenting with acute COVID-19 infection and MIS-C at our institution between March 2020 and December 2020 was performed. Subjects and Methods: TOMTEC software was used for strain analysis in both the study groups (COVID-19 and MIS-C) and age-matched healthy controls. Strain was correlated with LV ejection fraction (EF) and serum troponin levels. Results: Forty-five patients (34 - MIS-C and 11 - COVID-19) met the inclusion criteria. There was a statistically significant decrease in LV longitudinal strain (P < 0.001), LV circumferential strain (P < 0.001), and left atrial strain (P = 0.014) in the MIS-C group when compared to the control group. There was a statistically significant decrease in LV longitudinal strain (P = 0.028) in the acute COVID-19 group. All patients with abnormal left ventricular EF (LVEF) had abnormal strain. However, 14 (41%) patients in the MIS-C group and 3 (27%) in the acute COVID-19 group had preserved LVEF but abnormal strain. There was a significant correlation with LV longitudinal strain (P = 0.005) and LVEF (P = 0.002) and troponin in patients with MIS-C. Abnormal strain persisted in one-third of patients in the MIS-C and acute COVID-19 groups on outpatient follow-up. Conclusions: Patients with MIS-C and acute COVID-19 can develop myocardial dysfunction as seen by abnormal strain. LV longitudinal strain correlates with cardiac injury as measured by serum troponin in patients with MIS-C. Strain may provide an additional tool in detecting subtle myocardial dysfunction. It can be routinely employed at diagnosis and at follow-up evaluation of these patients.

A simple mechanistic explanation for Barth syndrome and cardiolipin remodeling.

Barth syndrome is a multisystem disorder caused by an abnormal metabolism of the mitochondrial lipid cardiolipin. In this review, we discuss physical properties, biosynthesis, membrane assembly, and function of cardiolipin. We hypothesize that cardiolipin reduces packing stress in the inner mitochondrial membrane, which arises as a result of protein crowding. According to this hypothesis, patients with Barth syndrome are unable to meet peak energy demands because they fail to concentrate the proteins of oxidative phosphorylation to a high surface density in the inner mitochondrial membrane.

Cardiolipin remodeling enables protein crowding in the inner mitochondrial membrane.

Mitochondrial cristae are extraordinarily crowded with proteins, which puts stress on the bilayer organization of lipids. We tested the hypothesis that the high concentration of proteins drives the tafazzin-catalyzed remodeling of fatty acids in cardiolipin, thereby reducing bilayer stress in the membrane. Specifically, we tested whether protein crowding induces cardiolipin remodeling and whether the lack of cardiolipin remodeling prevents the membrane from accumulating proteins. In vitro, the incorporation of large amounts of proteins into liposomes altered the outcome of the remodeling reaction. In yeast, the concentration of proteins involved in oxidative phosphorylation (OXPHOS) correlated with the cardiolipin composition. Genetic ablation of either remodeling or biosynthesis of cardiolipin caused a substantial drop in the surface density of OXPHOS proteins in the inner membrane of the mouse heart and Drosophila flight muscle mitochondria. Our data suggest that OXPHOS protein crowding induces cardiolipin remodelling and that remodeled cardiolipin supports the high concentration of these proteins in the inner mitochondrial membrane.

Neurological & psychological aspects of Barth syndrome: Clinical manifestations and potential pathogenic mechanisms.

Barth syndrome is a rare X-linked multisystem mitochondrial disease that is caused by variants in the tafazzin gene leading to deficient and abnormal cardiolipin. Previous research has focused on the cardiomyopathy and neutropenia in individuals with Barth syndrome, yet just as common are the least explored neurological aspects of Barth syndrome. This review focuses on the major neuropsychological and neurophysiological phenotypes that affect the quality of life of individuals with Barth syndrome, including difficulties in sensory perception and feeding, fatigue, and cognitive and psychological challenges. We propose selected pathogenetic mechanisms underlying these phenotypes and draw parallels to other relevant disorders. Finally, avenues for future research are also suggested.

Is My Mouse Pregnant? High-Frequency Ultrasound Assessment.

The mouse is the mammalian animal model of choice for many human diseases and biological processes. Developmental biology often requires staged-pregnant mice to determine evolving processes at various timepoints. Moreover, optimal and efficient breeding of model mice requires an assessment of timed pregnancies. Most commonly, mice are mated overnight, and the presence of a vaginal plug is determined; however, the positive predictive value of this technique is suboptimal, and one needs to wait to know if the mouse is truly pregnant. High-resolution ultrasound biomicroscopy is an effective and efficient tool for imaging: 1) Whether a mouse is pregnant; 2) What gestational stage the mouse has reached; and 3) Whether there are intrauterine losses. In addition to the embryos and fetuses, the investigator must also recognize common artifacts in the abdominal cavity so as not to mistake these for a gravid uterus. This article provides a protocol for imaging along with illustrative examples.

Effect of In utero Non-steroidal anti-inflammatory drug therapy for severe ebstein anomaly or tricuspid valve dysplasia (NSAID therapy for fetal ebstein anomaly)

Abstract: Ebstein anomaly (EA) and tricuspid valve dysplasia (TVD) are rare congenital malformations associated with nearly 50% mortality when diagnosed in utero. The diseases often produce severe tricuspid regurgitation (TR) in the fetus and in some cases, pulmonary regurgitation (PR) and circular shunting ensue. Since the ductus arteriosus (DA) plays a critical role in the circular shunt and may be constricted by transplacental non-steroidal anti-inflammatory drugs (NSAIDs), we sought to assess the effect of NSAIDs on fetuses with EA/TVD. We reviewed mothers of singleton fetuses with EA/TVD and PR, indicative of circular shunting, who were offered NSAIDs at multiple centers from 2010-2018. Initial dosing consisted of indomethacin, followed by ibuprofen in most cases. Twenty-one patients at 10 centers were offered therapy 4 at a median gestational age (GA) of 30.0 weeks (range: 20.9-34.9). Most (15/21=71%) mothers received NSAIDs, and 12/15 (80%) achieved DA constriction after a median of 2.0 days (1.0-6.0). All fetuses with DA constriction had improved PR; 92% had improved Doppler patterns. Median GA at pregnancy outcome was 36.1 weeks (30.7-39.0) in fetuses with DA constriction vs. 33 weeks (23.3-37.3) in fetuses who did not receive NSAIDs or achieve DA constriction (p=0.040). Eleven of 12 patients (92%) with DA constriction survived to live-birth, whereas 4/9 patients (44%) who did not receive NSAIDs or achieve DA constriction survived (p=0.046). In conclusion, our findings demonstrate the proof of concept that NSAIDs mitigate circular shunt physiology by DA constriction and improve PR among fetuses with severe EA/TVD. Although the early results are encouraging, further investigation is necessary to determine safety and efficacy.

Not yet a dinosaur: the chalk talk.

This article discusses the chalk talk's potential as an active learning method. Although chalk talks are a form of interactive lecture, they have received little attention in the medical education literature compared with other active learning methods such as team-based learning and simulation. One of the authors (C. K. L. Phoon) has used chalk talks to teach congenital heart defects to first- and third-year NYU medical students for many years. His chalk talks have consistently earned among the highest teaching scores, and students have noted their strengths of being more interesting, clear, and tangible than didactic lectures. Using the teacher and student perspectives, we examine the chalk talk's strengths and weaknesses compared with common passive and active learning methods. Chalk talks create a real-time, shared space that facilitates the active learning goals of helping students build, test, and revise mental models (conceptual frameworks). The limited amount of information that can be presented and the ability to solicit and arrange students' ideas on the board lead to the cocreation of valuable conceptual frameworks. Chalk talks require less restructuring of teaching sessions than other active learning methods and are best suited to topics that hinge on understanding of concepts. We advocate for the chalk talk to be reexamined as a promising educational tool given its strengths and the successes that other active learning methods have shown. Furthermore, we provide guidance to help educators deliver chalk talks and discuss future studies that would advance understanding of this powerful teaching tool.