Heart field origin of great vessel precursors relies on nkx2.5-mediated vasculogenesis

The pharyngeal arch arteries (PAAs) are transient embryonic blood vessels that make indispensable contributions to the carotid arteries and great vessels of the heart, including the aorta and pulmonary artery1, 2. During embryogenesis, the PAAs appear in a craniocaudal sequence to connect pre-existing segments of the primitive circulation after de novo vasculogenic assembly from angioblast precursors3, 4. Despite the unique spatiotemporal characteristics of PAA development, the embryonic origins of PAA angioblasts and the genetic factors regulating their emergence remain unknown. Here, we identify the embryonic source of PAA endothelium as nkx2.5+ progenitors in lateral plate mesoderm long considered to adopt cell fates within the heart exclusively5, 6. Further, we report that PAA endothelial differentiation relies on Nkx2.5, a canonical cardiac transcription factor not previously implicated in blood vessel formation. Together, these studies reveal the heart field origin of PAA endothelium and attribute a novel vasculogenic function to the cardiac transcription factor nkx2.5 during great vessel precursor development

Real-Time Light Field 3D Microscopy via Sparsity-Driven Learned Deconvolution

Light Field Microscopy (LFM) is a scan-less 3D imaging technique capable of capturing fast biological processes, such as neural activity in zebrafish. However, current methods to recover a 3D volume from the raw data require long reconstruction times hampering the usability of the microscope in a closed-loop system. Moreover, because the main focus of zebrafish brain imaging is to isolate and study neural activity, the ideal volumetric reconstruction should be sparse to reveal the dominant signals. Unfortunately, current sparse decomposition methods are computationally intensive and thus introduce substantial delays. This motivates us to introduce a 3D reconstruction method that recovers the spatio-temporally sparse components of an image sequence in real-time. In this work we propose a combination of a neural network (SLNet) that recovers the sparse components of a light field image sequence and a neural network (XLFMNet) for 3D reconstruction. In particular, XLFMNet is able to achieve high data fidelity and to preserve important signals, such as neural potentials, even on previously unobserved samples. We demonstrate successful sparse 3D volumetric reconstructions of the neural activity of live zebrafish, with an imaging span covering 800 × 800 × 250µm3 at an imaging rate of 24 − 88Hz, which provides a 1500 fold speed increase against prior work and enables real-time reconstructions without sacrificing imaging resolution

Notch signaling regulates cardiomyocyte proliferation during zebrafish heart regeneration

The human heart’s failure to replace ischemia-damaged myocardium with regenerated muscle contributes significantly to the worldwide morbidity and mortality associated with coronary artery disease. Remarkably, certain vertebrate species, including the zebrafish, achieve complete regeneration of amputated or injured myocardium through the proliferation of spared cardiomyocytes. Nonetheless, the genetic and cellular determinants of natural cardiac regeneration remain incompletely characterized. Here, we report that cardiac regeneration in zebrafish relies on Notch signaling. Following amputation of the zebrafish ventricular apex, Notch receptor expression becomes activated specifically in the endocardium and epicardium, but not the myocardium. Using a dominant negative approach, we discovered that suppression of Notch signaling profoundly impairs cardiac regeneration and induces scar formation at the amputation site. We ruled out defects in endocardial activation, epicardial activation, and dedifferentiation of compact myocardial cells as causative for the regenerative failure. Furthermore, coronary endothelial tubes, which we lineage traced from preexisting endothelium in wild-type hearts, formed in the wound despite the myocardial regenerative failure. Quantification of myocardial proliferation in Notch-suppressed hearts revealed a significant decrease in cycling cardiomyocytes, an observation consistent with a noncell autonomous requirement for Notch signaling in cardiomyocyte proliferation. Unexpectedly, hyperactivation of Notch signaling also suppressed cardiomyocyte proliferation and heart regeneration. Taken together, our data uncover the exquisite sensitivity of regenerative cardiomyocyte proliferation to perturbations in Notch signaling.Stem Cell and Regenerative Biolog

Sparse decomposition light-field microscopy for high speed imaging of neuronal activity

One of the major challenges in large scale optical imaging of neuronal activity is to simultaneously achieve sufficient temporal and spatial resolution across a large volume. Here, we introduce sparse decomposition light-field microscopy (SDLFM), a computational imaging technique based on light-field microscopy (LFM) that takes algorithmic advantage of the high temporal resolution of LFM and the inherent temporal sparsity of spikes to improve effective spatial resolution and signal-to-noise ratios (SNRs). With increased effective spatial resolution and SNRs, neuronal activity at the single-cell level can be recovered over a large volume. We demonstrate the single-cell imaging capability of SDLFM with in vivo imaging of neuronal activity of whole brains of larval zebrafish with estimated lateral and axial resolutions of ∼3.5 µm and ∼7.4 µm, respectively, acquired at volumetric imaging rates up to 50 Hz. We also show that SDLFM increases the quality of neural imaging in adult fruit flies.National Science Foundation (Grant 1848029)U. S. Army Research Laboratory and the U. S. Army Research Office (Contract W911NF1510548)National Institutes of Health (Grants 1R01DA045549, 1R41MH112318, 1R43MH109332, 1RM1HG008525, 1DP1NS087724

Failed Progenitor Specification Underlies the Cardiopharyngeal Phenotypes in a Zebrafish Model of 22q11.2 Deletion Syndrome

Microdeletions involving TBX1 result in variable congenital malformations known collectively as 22q11.2 deletion syndrome (22q11.2DS). Tbx1-deficient mice and zebrafish recapitulate several disease phenotypes, including pharyngeal arch artery (PAA), head muscle (HM), and cardiac outflow tract (OFT) deficiencies. In zebrafish, these structures arise from nkx2.5⁺ progenitors in pharyngeal arches 2–6. Because pharyngeal arch morphogenesis is compromised in Tbx1-deficient animals, the malformations were considered secondary. Here, we report that the PAA, HM, and OFT phenotypes in tbx1 mutant zebrafish are primary and arise prior to pharyngeal arch morphogenesis from failed specification of the nkx2.5⁺ pharyngeal lineage. Through in situ analysis and lineage tracing, we reveal that nkx2.5 and tbx1 are co-expressed in this progenitor population. Furthermore, we present evidence suggesting that gdf3-ALK4 signaling is a downstream mediator of nkx2.5⁺ pharyngeal lineage specification. Collectively, these studies support a cellular mechanism potentially underlying the cardiovascular and craniofacial defects observed in the 22q11.2DS population. Microdeletions encompassing the TBX1 locus cause 22q11.2 deletion syndrome (DS), which is characterized by congenital heart, aorta, and craniofacial malformations. Using a zebrafish model of 22q11.2DS, Guner-Ataman et al. demonstrate that tbx1-mutant animals fail to specify the nkx2.5⁺ progenitor population that gives rise to the affected structures. Keywords: Tbx1; cardiopharyngeal; zebrafish; nkx2.5; heart; DiGeorge; 22q11; progenitor; arch arter

Precision Calcium Imaging of Dense Neural Populations via a Cell-Body-Targeted Calcium Indicator

Methods for one-photon fluorescent imaging of calcium dynamics can capture the activity of hundreds of neurons across large fields of view at a low equipment complexity and cost. In contrast to two-photon methods, however, one-photon methods suffer from higher levels of crosstalk from neuropil, resulting in a decreased signal-to-noise ratio and artifactual correlations of neural activity. We address this problem by engineering cell-body-targeted variants of the fluorescent calcium indicators GCaMP6f and GCaMP7f. We screened fusions of GCaMP to natural, as well as artificial, peptides and identified fusions that localized GCaMP to within 50 μm of the cell body of neurons in mice and larval zebrafish. One-photon imaging of soma-targeted GCaMP in dense neural circuits reported fewer artifactual spikes from neuropil, an increased signal-to-noise ratio, and decreased artifactual correlation across neurons. Thus, soma-targeting of fluorescent calcium indicators facilitates usage of simple, powerful, one-photon methods for imaging neural calcium dynamics

Precision Calcium Imaging of Dense Neural Populations via a Cell-Body-Targeted Calcium Indicator

© 2020 Elsevier Inc. One-photon fluorescent imaging of calcium signals can capture the activity of hundreds of neurons across large fields of view but suffers from crosstalk from neuropil. Shemesh et al. engineer cell-body-targeted variants of fluorescent calcium indicators and show in mice and zebrafish that artifactual spikes and correlations are greatly reduced