Improvements in histological quality and signal retention following in situ hybridization in early chick embryos using plastic resin and recolorization

Use of AgNOR staining to determine the effect of metoclopramide on neural tube development in early chick embryos

Nausea and vomiting during pregnancy are common problems and prolonged pharmacological treatment often is needed; however, the teratogenic effects of anti-emetic drugs on neural tube (NT) development are not clear. We investigated the effects of different doses of metoclopramide on NT development in 48 and 72 h chick embryos using an argyrophilic nucleolar organizing region (AgNOR) staining method. We used 150 fertile, specific pathogen-free eggs incubated for 28 h, then randomly divided into five equal groups: group A, sham control was administered 0.9% saline; groups B - E were administered 0.15 mg/egg, 0.3 mg/egg, 0.6 mg/egg and 1.2 mg/egg, respectively. Half of the eggs in each group were taken from the incubator at 48 h incubation and the other half at 72 h incubation. After incubation, eggs were opened, embryos were dissected from their membranes, fixed with 10% formalin and examined by light microscopy. The NT status, i.e., open or closed, and somite number, crown-rump length, morphological features and gross developmental abnormalities were recorded. Excised embryos were sectioned and stained using hematoxylin and eosin or the AgNOR procedure and examined for morphology and histopathology. Delayed NT closure was observed in all 48 h drug exposed embryos, but in the 72 h groups, this occurred only in high-dose groups. Somite number was reduced significantly in groups C - E compared to the control group. Crown-rump length was decreased in both 48 and 72 h embryos. We found a decreased total AgNOR area:nuclear area ratio in 48 and 72 h embryos of all experimental groups. We found that metoclopramide delayed NT closure in chick embryos in a dose-dependent manner.

Platelet-derived growth factor is involved in the differentiation of second heart field-derived cardiac structures in chicken embryos

For the establishment of a fully functional septated heart, addition of myocardium from second heart field-derived structures is important. Platelet-derived growth factors (PDGFs) are known for their role in cardiovascular development. In this study, we aim to elucidate this role of PDGF-A, PDGF-C, and their receptor PDGFR-alpha. We analyzed the expression patterns of PDGF-A, -C, and their receptor PDGFR-alpha during avian heart development. A spatiotemporal pattern of ligands was seen with colocalization of the PDGFR-alpha. This was found in second heart field-derived myocardium as well as the proepicardial organ (PEO) and epicardium. Mechanical inhibition of epicardial outgrowth as well as chemical disturbance of PDGFR-alpha support a functional role of the ligands and the receptor in cardiac development.

Dysregulation of the PDGFRA gene causes inflow tract anomalies including TAPVR: integrating evidence from human genetics and model organisms

Total anomalous pulmonary venous return (TAPVR) is a congenital heart defect inherited via complex genetic and/or environmental factors. We report detailed mapping in extended TAPVR kindreds and mutation analysis in TAPVR patients that implicate the PDGFRA gene in the development of TAPVR. Gene expression studies in mouse and chick embryos for both the Pdgfra receptor and its ligand Pdgf-a show temporal and spatial patterns consistent with a role in pulmonary vein (PV) development. We used an in ovo function blocking assay in chick and a conditional knockout approach in mouse to knock down Pdgfra expression in the developing venous pole during the period of PV formation. We observed that loss of PDGFRA function in both organisms causes TAPVR with low penetrance (approximately 7%) reminiscent of that observed in our human TAPVR kindreds. Intermediate inflow tract anomalies occurred in a higher percentage of embryos (approximately 30%), suggesting that TAPVR occurs at one end of a spectrum of defects. We show that the anomalous pulmonary venous connection seen in chick and mouse is highly similar to TAPVR discovered in an abnormal early stage embryo from the Kyoto human embryo collection. Whereas the embryology of the normal venous pole and PV is becoming understood, little is known about the embryogenesis or molecular pathogenesis of TAPVR. These models of TAPVR provide important insight into the pathogenesis of PV defects. Taken together, these data from human genetics and animal models support a role for PDGF-signaling in normal PV development, and in the pathogenesis of TAPVR.

Semi-thin sections of epoxy resin-embedded mouse embryos in morphological analysis of whole mount in situ RNA hybridization

Descriptive morphological studies are often combined with gene expression pattern analyses. Unembedded vibratome or cryotome sections are compatible with in situ RNA hybridization, but spatial resolution is rather low for precise microscopic studies necessary in embryology. Therefore, use of plastic embedding media, which allow semi-thin and ultra-thin sectioning for light and electron microscopy, could be an important advantage. This work suggested a new approach based on the whole mount hybridization of mouse embryos and subsequent epoxy resin embedding. Epoxy resin allowed serial sectioning of semi-thin sections with preserved in situ RNA hybridization signal, which was a necessary prerequisite for precise morphological analysis of embryo development.