Editorial highlights

Every organism is a model organism for understanding development, evolution, disease, and regeneration, and we have only begun to scratch the surface of the interdisciplinary genetic, molecular, cellular, and developmental mechanisms that regulate these biological processes. These “Highlights” denote exciting advances recently reported in Developmental Dynamics that illustrate the complex dynamics of developmental biology.

Preimplantation Mammalian Development. “Maternal exposure to hyperbaric oxygen at the preimplantation stages increases apoptosis and ectopic Cdx2 expression and decreases Oct4 expression in mouse blastocysts via Nrf2-Notch1 upregulation and Nf2 downregulation” by Yu-Ming Li, Yu Lang Chung, Yung-Fu Wu, Chien-Kuo Wang, Chieh-Min Chen, and Yi-Hui Chen; DevDyn 253:5, pp. 467–489. https://doi.org/10.1002/dvdy.671. Environmental oxygen tension during preimplantation development in vivo and in vitro is a critical regulator of blastomere cleavage, blastocyst implantation, and pregnancy. Therefore, the use of hyperbaric oxygen in pregnant women is limited due to potential adverse risks. In this study, maternal hyperbaric oxygen exposure during preimplantation embryo development, resulted in increased DNA damage and apoptosis in the inner cell mass, abnormal lineage specification, and impaired lineage segregation between the inner cell mass and trophectoderm. The domain and levels of both Nf2 and Yap gene expression, are pivotal regulators of early lineage segregations in both mouse and human preimplantation embryos and here the authors show that Nf2-Yap and Nrf2-Notch1 signaling are two critical regulatory pathways that mediate hyperbaric oxygen-induced aberrant lineage specification. Thus, hyperbaric oxygen-induced oxidative stress is associated with aberrant first lineage segregation in the preimplantation embryo development.

Retina Development. “Kdm7a expression is spatiotemporally regulated in developing Xenopus laevis embryos, and its overexpression influences late retinal development” by Davide Martini, Matteo Digregorio, Ilaria Anna Pia Voto, Giuseppe Morabito, Andrea Degl'Innocenti, Guido Giudetti, Martina Giannaccini and Massimiliano Andreazzoli; DevDyn 253:5, pp. 508–518. https://doi.org/10.1002/dvdy.670. Epigenetics is the study of complex and dynamically reversible chemical modification of DNA and histone proteins that remodel heterochromatin and euchromatin, and their effects on gene transcription. Posttranslational histone modifications are among the most common epigenetic modifications that regulate gene activity during embryonic development and in the pathogenesis of disease. KDM7A is a histone lysine demethylase that catalyzes the demethylation of H3K9me1/2 and H3K27me1/2. This study shows that kdm7a is dynamically expressed during embryonic development, and that overexpression of kdm7a alters the late stages of retinal development, and in particular, ganglion cells and horizontal cell formation during retinogenesis. This suggest that kdm7a and histone lysine demethylation play critical roles in the molecular machinery that regulated the spatiotemporally ordered generation of retinal neuronal subtypes.

Vascular Development. “Identification of distinct vascular mural cell populations during zebrafish embryonic development” by Sarah Colijn, Miku Nambara, Gracie Malin, Elena Sacchetti, and Amber Stratman; DevDyn 253:5, pp. 519–541. https://doi.org/10.1002/dvdy.681. Blood vessels initially consist of a single layer of endothelial cells that recruit mural cells to assist in basement membrane deposition, vessel contractility, and cellular communication. Mural cells can vary widely in their origin and function, and include pericytes, which are associated with small vessels such as capillaries, and vascular smooth muscle cells (vSMCs) which associate with large vessels. vSMCs accumulate on arteries and, to a lesser extent, on veins during vascular development to provide tensile strength to vessels and promote basement membrane deposition. This study reports the discovery of two previously unreported sources of mural cells. First, in the hypochord, which is a transient structure in fish and amphibians, that contributes tagln-positive cells, indicative of mature vSMC, to the dorsal aorta. Second, a likely sclerotome-derived mural cell progenitor population that resides along the midline at the notochord-neural tube interface and contributes to the intersomitic vessels. These results further improve our understanding of the site-specific and temporal regulation of mural cell biology.