Avian ovaries develop asymmetrically apart from prey birds, with only the left ovary growing more towards functional organs. Here, we analyze over 135,000 cells from chick\'s left and right ovaries at six distinct embryonic developmental stages utilizing single-cell transcriptome sequencing. We delineate gene expression patterns across 15 cell types within these embryo ovaries, revealing side-specific development. The left ovaries exhibit cortex cells, zygotene germ cells, and transcriptional changes unique to the left side. Differential gene expression analysis further identifies specific markers and pathways active in these cell types, highlighting the asymmetry in ovarian development. A fine-scale analysis of the germ cell meiotic transcriptome reveals seven distinct clusters with gene expression patterns specific to various meiotic stages. The study also identifies signaling pathways and intercellular communications, particularly between pre-granulosa and germ cells. Spatial transcriptome analysis shows the asymmetry, demonstrating cortex cells exclusively in the left ovary, modulating neighboring cell types through putative secreted signaling molecules. Overall, this single-cell analysis provides insights into the molecular mechanisms of the asymmetric development of avian ovaries, particularly the significant role of cortex cells in the left ovary.

Asymmetric vertebrate heart development is driven by an intricate sequence of morphogenetic cell movements, the coordination of which requires precise interpretation of signaling cues by heart primordia. Here we show that Nodal functions cooperatively with FGF during heart tube formation and asymmetric placement. Both pathways act as migratory stimuli for cardiac progenitor cells (CPCs), but FGF is dispensable for directing heart tube asymmetry, which is governed by Nodal. We further find that Nodal controls CPC migration by inducing left-right asymmetries in the formation of actin-based protrusions in CPCs. Additionally, we define a developmental window in which FGF signals are required for proper heart looping and show cooperativity between FGF and Nodal in this process. We present evidence FGF may promote heart looping through addition of the secondary heart field. Finally, we demonstrate that loss of FGF signaling affects proper development of the atrioventricular canal (AVC), which likely contributes to abnormal chamber morphologies in FGF-deficient hearts. Together, our data shed insight into how the spatiotemporal dynamics of signaling cues regulate the cellular behaviors underlying organ morphogenesis.

Heart development is a complex process that requires asymmetric positioning of the heart, cardiac growth and valve morphogenesis. The mechanisms controlling heart morphogenesis and valve formation are not fully understood. The pro-convertase FurinA functions in heart development across vertebrates. How FurinA activity is regulated during heart development is unknown. Through computational analysis of the zebrafish transcriptome, we identified an RNA motif in a variant FurinA transcript harbouring a long 3\' untranslated region (3\'UTR). The alternative 3\'UTR furina isoform is expressed prior to organ positioning. Somatic deletions in the furina 3\'UTR lead to embryonic left-right patterning defects. Reporter localisation and RNA-binding assays show that the furina 3\'UTR forms complexes with the conserved RNA-binding translational repressor, Ybx1. Conditional ybx1 mutant embryos show premature and increased Furin reporter expression, abnormal cardiac morphogenesis and looping defects. Mutant ybx1 hearts have an expanded atrioventricular canal, abnormal sino-atrial valves and retrograde blood flow from the ventricle to the atrium. This is similar to observations in humans with heart valve regurgitation. Thus, the furina 3\'UTR element/Ybx1 regulon is important for translational repression of FurinA and regulation of heart development.

Correct intestinal morphogenesis depends on the early embryonic process of gut rotation, an evolutionarily conserved program in which a straight gut tube elongates and forms into its first loops. However, the gut tube requires guidance to loop in a reproducible manner. The dorsal mesentery (DM) connects the gut tube to the body and directs the lengthening gut into stereotypical loops via left-right (LR) asymmetric cellular and extracellular behavior. The LR asymmetry of the DM also governs blood and lymphatic vessel formation for the digestive tract, which is essential for prenatal organ development and postnatal vital functions including nutrient absorption. Although the genetic LR asymmetry of the DM has been extensively studied, a divider between the left and right DM has yet to be identified. Setting up LR asymmetry for the entire body requires a Lefty1+ midline barrier to separate the two sides of the embryo-without it, embryos have lethal or congenital LR patterning defects. Individual organs including the brain, heart, and gut also have LR asymmetry, and while the consequences of left and right signals mixing are severe or even lethal, organ-specific mechanisms for separating these signals are not well understood. Here, we uncover a midline structure composed of a transient double basement membrane, which separates the left and right halves of the embryonic chick DM during the establishment of intestinal and vascular asymmetries. Unlike other basement membranes of the DM, the midline is resistant to disruption by intercalation of Netrin4 (Ntn4). We propose that this atypical midline forms the boundary between left and right sides and functions as a barrier necessary to establish and protect organ asymmetry.

Myosin-1D (myo1D) is important for Drosophila left-right asymmetry, and its effects are modulated by myosin-1C (myo1C). De novo expression of these myosins in nonchiral Drosophila tissues promotes cell and tissue chirality, with handedness depending on the paralog expressed. Remarkably, the identity of the motor domain determines the direction of organ chirality, rather than the regulatory or tail domains. Myo1D, but not myo1C, propels actin filaments in leftward circles in in vitro experiments, but it is not known if this property contributes to establishing cell and organ chirality. To further explore if there are differences in the mechanochemistry of these motors, we determined the ATPase mechanisms of myo1C and myo1D. We found that myo1D has a 12.5-fold higher actin-activated steady-state ATPase rate, and transient kinetic experiments revealed myo1D has an 8-fold higher MgADP release rate compared to myo1C. Actin-activated phosphate release is rate limiting for myo1C, whereas MgADP release is the rate-limiting step for myo1D. Notably, both myosins have among the tightest MgADP affinities measured for any myosin. Consistent with ATPase kinetics, myo1D propels actin filaments at higher speeds compared to myo1C in in vitro gliding assays. Finally, we tested the ability of both paralogs to transport 50 nm unilamellar vesicles along immobilized actin filaments and found robust transport by myo1D and actin binding but no transport by myo1C. Our findings support a model where myo1C is a slow transporter with long-lived actin attachments, whereas myo1D has kinetic properties associated with a transport motor.

Left-right asymmetry is an essential feature in bilateral animals. The mechanism underlying the left-right asymmetrical organ morphogenesis is a central question in developmental biology. Studies in vertebrates show that left-right asymmetry formation needs three essential steps: the initial left-right symmetry breaking, the left-right asymmetrical gene expression, and the left-right asymmetrical organ morphogenesis. Many vertebrates use cilia to produce directional fluid flow to break symmetry during embryonic development, asymmetric Nodal-Pitx2 signaling to pattern the left-right asymmetry, and Pitx2 and other genes to control the morphogenesis of asymmetrical organs. In invertebrates, there are left-right mechanisms independent of cilia and even others more different from that of vertebrates. In this review, we summarize the major steps and relevant molecular mechanisms of left-right asymmetric development in vertebrates and invertebrates, aiming to provide a reference for the understanding of the origin and evolution of the left-right developmental mechanism.
左右不对称是两侧对称动物的重要特征，其形成机制一直是发育生物学领域备受关注的科学问题之一。脊椎动物的左右不对称发生经过3个重要阶段：左右对称性的打破，左右不对称信号的建立和维持，以及左右不对称器官的形态发生。多数脊椎动物在胚胎发育阶段依赖纤毛产生定向液流打破胚胎的左右对称性，随后建立Nodal-Pitx2左右不对称信号，最后由Pitx2等基因指导左右不对称器官的形态发生过程。无脊椎动物中存在不依赖纤毛介导的Nodal-Pitx不对称信号表达机制，甚至具有完全独立的左右不对称发育机制。本文结合最新的左右不对称器官发育机制的研究进展，综述了脊椎动物和无脊椎动物胚胎左右不对称的发生过程及相关基因和信号通路，有助于深入理解左右不对称器官发育的过程，以期为追溯左右不对称器官发育机制的起源演化提供参考。.

The developmental potential of the animal cap (consisting of eight mesomeres) recombined with micromeres or of micromere progeny was examined in sea urchin embryos. The embryos derived from the animal cap recombined with a quartet of micromeres or their descendants developed into four-armed plutei. After feeding, the larvae developed into eight-armed plutei. The left-right polarity of the larvae, recognized by the location of the echinus rudiment, was essentially normal, regardless of the orientation of animal-vegetal polarity in micromeres combining with the animal cap. The larvae had sufficient potential to metamorphose into complete juvenile sea urchins with five-fold radial symmetry. Cell lineage tracing experiments showed that: (i) macromere progeny were not required for formation of the typical pattern of primary mesenchyme cells derived exclusively from large micromeres; (ii) the progeny of large micromeres did not contribute to cells in the endodermal gut with three compartments of normal function; (iii) the presumptive ectoderm had the potential to differentiate into endodermal gut and mesodermal secondary mesenchyme cells, from which pigment cells likely differentiated; and (iv) behavior of the progeny of small micromeres was the same as that in normal embryos through the gastrula stage. These results indicate that the mesomeres respecify their fate under the inductive influence of micromeres so perfectly that complete juvenile sea urchins are produced.

Left-right (LR) asymmetry of the brain is fundamental to its higher-order functions. The Drosophila brain\'s asymmetrical body (AB) consists of a structural pair arborized from AB neurons and is larger on the right side than the left. We find that the AB initially forms LR symmetrically and then develops LR asymmetrically by neurite remodeling that is specific to the left AB and is dynamin dependent. Additionally, neuronal ecdysone signaling inhibition randomizes AB laterality, suggesting that ecdysone signaling determines AB\'s LR polarity. Given that AB\'s LR asymmetry relates to memory formation, our research establishes AB as a valuable model for studying LR asymmetry and higher-order brain function relationships.

Wnt signaling plays essential roles in multiple steps of left-right (L-R) determination in development. First, canonical Wnt signaling is required to form the node, where L-R symmetry breaking takes place. Secondly, planar cell polarity (PCP) driven by non-canonical Wnt signaling polarizes node cells along the anterio-posterior (A-P) axis and provides the tilt of rotating cilia at the node, which generate the leftward fluid flow. Thus, reciprocal expression of Wnt5a/5b and their inhibitors Sfrp1, 2, 5 generates a gradient of Wnt5 activity along the embryo\'s anterior-posterior (A-P) axis. This polarizes cells at the node, by placing PCP core proteins on the anterior or posterior side of each node cell. Polarized PCP proteins subsequently induce asymmetric organization of microtubules along the A-P axis, which is thought to push the centrally localized basal body toward the posterior side of a node cell. Motile cilia that extend from the posteriorly-shifted basal body is tilted toward the posterior side of the embryo. Thirdly, canonical-Wnt signaling regulates the level and expansion of Nodal activity and establishes L-R asymmetric Nodal activity at the node, the first molecular asymmetry in the mouse embryo. Overall, both canonical and non-canonical Wnt signalings are essential for L-R symmetry breaking.

As magnetic resonance imaging (MRI) scanners with ultra-high field (UHF) have optimal performance, scientists have been working to develop high-performance devices with strong magnetic fields to improve their diagnostic potential. However, whether an MRI scanner with UHF poses a risk to the safety of the organism require further evaluation. This study evaluated the effects of 11.4 Tesla (T) UHF on embryonic development using a zebrafish model. Multiple approaches, including morphological parameters, physiological behaviors, and analyses of the transcriptome at the molecular level, were determined during 5 days after laboratory-controlled exposure from 6 hour post fertilization (hpf) to 24 hpf. No significant effects were observed in embryo mortality, hatching rate, body length, Left-Right patterning, locomotor behavior, etc. RNA-sequencing analysis revealed up-regulated tumor necrosis factor (TNF) inflammatory factors and activated TNF signaling pathways in the 11.4 T exposure group. The results were further validated using qPCR. Our findings indicate that although UHF exposure under 11.4 T has no effect on the development of zebrafish embryos, it has specific effects on the immune response that require further investigation.