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.

Expression of Nephronectin in the Descemet's membrane of mouse corneas during development and adult homeostasis.

Nephronectin (Npnt) is an extracellular matrix (ECM) protein with pleiotropic functions during organogenesis, disease, and homeostasis. Although the ECM plays a crucial role during development and homeostasis of the adult cornea, little is known about the expression of Npnt in the mammalian cornea. Here, we investigated the expression of Npnt during early embryonic and postnatal development, and in adult mouse corneas.

Visualization of RNA virus infection in a marine protist with a universal biomarker.

Half of the marine virosphere is hypothesized to be RNA viruses (kingdom Orthornavirae) that infect abundant micro-eukaryotic hosts (e.g. protists).

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.

Investigating Scarless Tissue Regeneration in Embryonic Wounded Chick Corneas.

Chick embryonic corneal wounds display a remarkable capacity to fully and rapidly regenerate, whereas adult wounded corneas experience a loss of transparency due to fibrotic scarring. The tissue integrity of injured embryonic corneas is intrinsically restored with no detectable scar formation. Given its accessibility and ease of manipulation, the chick embryo is an ideal model for studying scarless corneal wound repair.

Nephronectin-integrin α8 signaling is required for proper migration of periocular neural crest cells during chick corneal development.

During development, cells aggregate at tissue boundaries to form normal tissue architecture of organs. However, how cells are segregated into tissue precursors remains largely unknown. Cornea development is a perfect example of this process whereby neural crest cells aggregate in the periocular region prior to their migration and differentiation into corneal cells.

Recapitulation of normal collagen architecture in embryonic wounded corneas.

Wound healing is characterized by cell and extracellular matrix changes mediating cell migration, fibrosis, remodeling and regeneration. We previously demonstrated that chick fetal wound healing shows a regenerative phenotype regarding the cellular and molecular organization of the cornea. However, the chick corneal stromal structure is remarkably complex in the collagen fiber/lamellar organization, involving branching and anastomosing of collagen bundles.

Periocular neural crest cell differentiation into corneal endothelium is influenced by signals in the nascent corneal environment.

During ocular development, periocular neural crest cells (pNC) migrate into the region between the lens and presumptive corneal epithelium to form the corneal endothelium and stromal keratocytes. Although defects in neural crest cell development are associated with ocular dysgenesis, very little is known about the molecular mechanisms involved in this process. This study focuses on the corneal endothelium, a monolayer of specialized cells that are essential for maintaining normal hydration and transparency of the cornea.

Primary cilia deficiency in neural crest cells models anterior segment dysgenesis in mouse.

Defects affecting tissues of the anterior segment (AS) of the eye lead to a group of highly debilitating disorders called Anterior Segment Dysgenesis (ASD). Despite the identification of some causative genes, the pathogenesis of ASD remains unclear. Interestingly, several ciliopathies display conditions of the AS.

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.

Transcriptomic analysis of differential gene expression during chick periocular neural crest differentiation into corneal cells.

Background: Multipotent neural crest cells (NCC) contribute to the corneal endothelium and keratocytes during ocular development, but the molecular mechanisms that underlie this process remain poorly understood. We performed RNA-Seq analysis on periocular neural crest (pNC), corneal endothelium, and keratocytes and validated expression of candidate genes by in situ hybridization.

Results: RNA-Seq profiling revealed enrichment of genes between pNC and neural crest-derived corneal cells, which correspond to pathways involved in focal adhesion, ECM-receptor interaction, cell adhesion, melanogenesis, and MAPK signaling.

Expression of the heparin-binding growth factors Midkine and pleiotrophin during ocular development.

Midkine (MDK) and Pleiotrophin (PTN) belong to a group of heparin-binding growth factors that has been shown to have pleiotropic functions in various biological processes during development and disease. Development of the vertebrate eye is a multistep process that involves coordinated interactions between neuronal and non-neuronal cells, but very little is known about the potential function of MDK and PTN in these processes. In this study, we demonstrate by section in situ hybridization, the spatiotemporal expression of MDK and PTN during ocular development in chick and mouse.

Transformation of the Transcriptomic Profile of Mouse Periocular Mesenchyme During Formation of the Embryonic Cornea.

Purpose: Defects in neural crest development are a major contributing factor in corneal dysgenesis, but little is known about the genetic landscape during corneal development. The purpose of this study was to provide a detailed transcriptome profile and evaluate changes in gene expression during mouse corneal development.

Methods: RNA sequencing was used to uncover the transcriptomic profile of periocular mesenchyme (pNC) isolated at embryonic day (E) 10.

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.

A technique to increase accessibility to late-stage chick embryos for in ovo manipulations.

Background: During early development, avian embryos are easily accessible in ovo for transplantations and experimental perturbations. However, these qualities of the avian embryonic model rapidly wane shortly after embryonic day (E)4 when the embryo is obscured by extraembryonic membranes, making it difficult to study developmental events that occur at later stages in vivo.

Results: In this study, we describe a multistep method that involves initially windowing eggs at E3, followed by dissecting away extraembryonic membranes at E5 to facilitate embryo accessibility in ovo until later stages of development.

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.