Morphogenic, molecular, and cellular adaptations for unidirectional airflow in the chicken lung.

Unidirectional airflow in the avian lung enables gas exchange during both inhalation and exhalation. The underlying developmental process and how it deviates from that of the bidirectional mammalian lung are poorly understood. Sampling key developmental stages with multiscale 3D imaging and single-cell transcriptomics, we delineate morphogenic, molecular, and cellular features that accommodate the unidirectional airflow in the chicken lung.

BMP3 inhibits TGFβ2-mediated myofibroblast differentiation during wound healing of the embryonic cornea.

Often acute damage to the cornea initiates drastic tissue remodeling, resulting in fibrotic scarring that disrupts light transmission and precedes vision impairment. Very little is known about the factors that can mitigate fibrosis and promote scar-free cornea wound healing. We previously described transient myofibroblast differentiation during non-fibrotic repair in an embryonic cornea injury model.

Cell-independent matrix configuration in early corneal development.

Mechanisms controlling the spatial configuration of the remarkably ordered collagen-rich extracellular matrix of the transparent cornea remain incompletely understood. We previously described the assembly of the emerging corneal matrix in the mid and late stages of embryogenesis and concluded that collagen fibril organisation was driven by cell-directed mechanisms. Here, the early stages of corneal morphogenesis were examined by serial block face scanning electron microscopy of embryonic chick corneas starting at embryonic day three (E3), followed by a Fourier transform analysis of three-dimensional datasets and theoretical considerations of factors that influence matrix formation.

Knockdown of CXCL14 disrupts neurovascular patterning during ocular development.

The C-X-C motif ligand 14 (CXCL14) is a recently discovered chemokine that is highly conserved in vertebrates and expressed in various embryonic and adult tissues. CXCL14 signaling has been implicated to function as an antiangiogenic and anticancer agent in adults. However, its function during development is unknown.

PlexinD1 is required for proper patterning of the periocular vascular network and for the establishment of corneal avascularity during avian ocular development.

The anterior eye is comprised of an avascular cornea surrounded by a dense periocular vascular network and therefore serves as an excellent model for angiogenesis. Although signaling through PlexinD1 underlies various vascular patterning events during embryonic development, its role during the formation of the periocular vascular network is yet to be determined. Our recent study showed that PlexinD1 mRNA is expressed by periocular angioblasts and blood vessels during ocular vasculogenesis in patterns that suggest its involvement with Sema3 ligands that are concurrently expressed in the anterior eye.

Corneal Development: Different Cells from a Common Progenitor.

Development of the vertebrate cornea is a multistep process that involves cellular interactions between various ectodermal-derived tissues. Bilateral interactions between the neural ectoderm-derived optic vesicles and the cranial ectoderm give rise to the presumptive corneal epithelium and other epithelia of the ocular surface. Interactions between the neural tube and the adjacent ectoderm give rise to the neural crest cells, a highly migratory and multipotent cell population.

Quail-chick chimeras and eye development.

The quail-chick chimera is a stable and precise labeling technique that allows tracing of definite cells and their progeny without interfering with normal development of two related avian species. This technique utilizes the transplantation of quail tissues into chick embryo or vice versa. The region of interest (graft) is removed from the donor and replaced in the stage-matched host embryo.

Sema3A maintains corneal avascularity during development by inhibiting Vegf induced angioblast migration.

Corneal avascularity is important for optical clarity and normal vision. However, the molecular mechanisms that prevent angioblast migration and vascularization of the developing cornea are not clear. Previously we showed that periocular angioblasts and forming ocular blood vessels avoid the presumptive cornea despite dynamic ingression of neural crest cells.

Wounded embryonic corneas exhibit nonfibrotic regeneration and complete innervation.

Purpose: Wound healing in adult corneas is characterized by activation of keratocytes and extracellular matrix (ECM) synthesis that results in fibrotic scar formation and loss of transparency. Since most fetal wounds heal without scaring, we investigated the regenerative potential of wounded embryonic corneas.

Methods: On embryonic day (E) 7 chick corneas were wounded by making a linear incision traversing the epithelium and anterior stroma.

Expression of CXCL12 and CXCL14 during eye development in chick and mouse.

Vertebrate eye development is a complex multistep process coordinated by signals from the lens, optic cup and periocular mesenchyme. Although chemokines are increasingly being recognized as key players in cell migration, proliferation, and differentiation during embryonic development, their potential role during eye development has not been examined. In this study, we demonstrate by section in situ hybridization that CXCL12 and CXCL14 are expressed during ocular development.

Human fetal keratocytes have multipotent characteristics in the developing avian embryo.

The human cornea contains stem cells that can be induced to express markers consistent with multipotency in cell culture; however, there have been no studies demonstrating that human corneal keratocytes are multipotent. The objective of this study is to examine the potential of human fetal keratocytes (HFKs) to differentiate into neural crest-derived tissues when challenged in an embryonic environment. HFKs were injected bilaterally into the cranial mesenchyme adjacent to the neural tube and the periocular mesenchyme in chick embryos at embryonic days 1.

Expression of pro- and anti-angiogenic factors during the formation of the periocular vasculature and development of the avian cornea.

Background: During embryonic development, endothelial precursor cells (angioblasts) migrate relatively long distances to form the primary vascular plexus. The migratory behavior of angioblasts and localization of the primitive blood vessels is tightly regulated by pro-angiogenic and anti-angiogenic factors encountered in the embryonic environment. Despite the importance of corneal avascularity to proper vision, it is not known when avascularity is established in the developing cornea and how pro- and anti-angiogenic factors regulate this process.

Distinct roles for neuropilin1 and neuropilin2 during mouse corneal innervation.

Trigeminal sensory innervation of the cornea is critical for protection and synthesis of neuropeptides required for normal vision. Little is known about axon guidance during mammalian corneal innervation. In contrast to the chick where a pericorneal nerve ring forms via Npn/Sema signaling, mouse corneal axons project directly into the presumptive cornea without initial formation of an analogous nerve ring.

Analysis of neural crest migration and differentiation by cross-species transplantation.

Avian embryos provide a unique platform for studying many vertebrate developmental processes, due to the easy access of the embryos within the egg. Chimeric avian embryos, in which quail donor tissue is transplanted into a chick embryo in ovo, combine the power of indelible genetic labeling of cell populations with the ease of manipulation presented by the avian embryo. Quail-chick chimeras are a classical tool for tracing migratory neural crest cells (NCCs).

Nerve repulsion by the lens and cornea during cornea innervation is dependent on Robo-Slit signaling and diminishes with neuron age.

The cornea, the most densely innervated tissue on the surface of the body, becomes innervated in a series of highly coordinated developmental events. During cornea development, chick trigeminal nerve growth cones reach the cornea margin at embryonic day (E)5, where they are initially repelled for days from E5 to E8, instead encircling the corneal periphery in a nerve ring prior to entering on E9. The molecular events coordinating growth cone guidance during cornea development are poorly understood.

Innervation of the mouse cornea during development.

Purpose: Dense innervation of the cornea is important for maintaining its homeostasis and transparency. Although corneal nerves have been well studied in adults, little is known about mammalian corneal innervation during development. This study provides a detailed profile of nerves at various stages of mouse cornea development.

Semaphorin3A/neuropilin-1 signaling acts as a molecular switch regulating neural crest migration during cornea development.

Cranial neural crest cells migrate into the periocular region and later contribute to various ocular tissues including the cornea, ciliary body and iris. After reaching the eye, they initially pause before migrating over the lens to form the cornea. Interestingly, removal of the lens leads to premature invasion and abnormal differentiation of the cornea.

Robo2-Slit1 dependent cell-cell interactions mediate assembly of the trigeminal ganglion.

Vertebrate cranial sensory ganglia, responsible for sensation of touch, taste and pain in the face and viscera, are composed of both ectodermal placode and neural crest cells. The cellular and molecular interactions allowing generation of complex ganglia remain unknown. Here, we show that proper formation of the trigeminal ganglion, the largest of the cranial ganglia, relies on reciprocal interactions between placode and neural crest cells in chick, as removal of either population resulted in severe defects.

Lens-derived Semaphorin3A regulates sensory innervation of the cornea.

The cornea, one of the most highly innervated tissues of the body, is innervated by trigeminal sensory afferents. During development, axons are initially repelled at the corneal margin, resulting in the formation of a circumferential nerve ring. The nature and source of guidance molecules that regulate this process remain a mystery.

Corneal keratocytes retain neural crest progenitor cell properties.

Corneal keratocytes have a remarkable ability to heal the cornea throughout life. Given their developmental origin from the cranial neural crest, we asked whether this regenerative ability was related to the stem cell-like properties of their neural crest precursors. To this end, we challenged corneal stromal keratocytes by injecting them into a new environment along cranial neural crest migratory pathways.

Graded potential of neural crest to form cornea, sensory neurons and cartilage along the rostrocaudal axis.

Neural crest cells arising from different rostrocaudal axial levels form different sets of derivatives as diverse as ganglia, cartilage and cornea. These variations may be due to intrinsic properties of the cell populations, different environmental factors encountered during migration or some combination thereof. We test the relative roles of intrinsic versus extrinsic factors by challenging the developmental potential of cardiac and trunk neural crest cells via transplantation into an ectopic midbrain environment.