Editorial highlights

Abstract

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.

“Elp1 function in placode-derived neurons is critical for proper trigeminal ganglion development” by Margaret and Hines and Lisa Taneyhill, DevDyn 254.6, pp. 494–512. https://doi.org/10.1002/dvdy.749.

Cranial sensory nerves are part of the peripheral nervous system and are responsible for relaying sensory information to the central nervous system. The trigeminal (V), epibranchial (geniculate (facial VII)), petrosal (glossopharyngeal IX), and nodose (vagal X) ganglia house neuronal cell bodies and supporting glia of the sensory nerves, which innervate the face, tongue, mouth, and digestive tract. The ganglia are derived from two embryonic cell populations, cranial neural crest and neurogenic placodes, however, the molecules and pathways that mediate reciprocal interactions between them during ganglion development remain poorly understood. Recently, the authors identified Elongator acetyltransferase complex subunit 1 (Elp1) as a potential regulator of trigeminal ganglion development, which when perturbed can cause familial dysautonomia, a neurodevelopmental and neurodegenerative disease. Here the authors characterize the spatiotemporal expression of Elp1 in avian embryos as the trigeminal ganglion initially assembles. Elp1 is expressed in migratory cranial neural crest cells and later in undifferentiated neural crest cells and placode-derived neurons that contribute to the trigeminal ganglion. Knockdown of Elp1 in trigeminal placode cells reveal its critical functions in placode-derived neurons during trigeminal ganglion development, providing additional insight into the etiology of trigeminal nerve deficits in familial dysautonomia.

“Spatiotemporal distribution of neural crest cells in the common wall lizard Podarcis muralis” by Robin Pranter and Nathalie Feiner, DevDyn 254.6, pp. 551–567. https://doi.org/10.1002/dvdy.758. Neural crest cells are a migratory cell population considered unique to vertebrates and fundamentally important for their evolution and variation. Reptiles which comprise ~12,000 species, are renowned for their numerous morphological adaptions, many of which are neural crest cell derived, which have facilitated their radiation and adaption to nearly every ecological niche on the plant. Hence there is considerable interest in the evolutionary origins of neural crest cells and while studies in squamates have increased our understanding of neural crest cell specification, migration, and differentiation across vertebrates, evolutionary changes in neural crest cell behavior and potentially associated phenotypic changes are currently underexplored. This study describes neural crest cell development in the common wall lizard, Podarcis muralis, which exhibit substantial variation in predominantly neural crest cell derived traits, including coloration, morphology and social behavior. The authors reveal conservation of neural crest cell specification, migration, and differentiation, but taxonomic differences in the expression patterns of individual markers, which help to shape micro-evolutionary patterns.

“Stat stimulates histone H3K4 methylation via KDM5 inhibition in adult stem cells of budding tunicates” by Yuri Kimura-Nagano, Kanoko Kishimoto, Satoko Sekida and Kaz Kawamura, DevDyn 254.6, pp. 538–550. https://doi.org/10.1002/dvdy.754. The budding tunicate, Polyandrocarpa misakiensis is a single animal with a lifespan of several months. However, Polyandrocarpa misakiensis produces buds that also live for several months, thus budding may facilitate cell renewal of asexual animals. Polyandrocarpa misakiensis belongs to the order Stolidobranchiata, which is characterized by the complexity of the branchial basket, which bends into four pharyngeal folds on each side of the body and is decorated by numerous spikes that develop from inner longitudinal vessels. The authors previously reported histone trimethylation at H3K4 and H3K27 in the branchial epithelium of Polyandrocarpa misakiensis, however, the roles of histone methylation in the structure and function of the branchial sac remain unclear. Histone modification plays an important role in regulating cell differentiation and dedifferentiation during animal development and homeostasis. In general, Histone H3K4 trimethylation (H3K4me3) is associated with active chromatin, which facilitates transcription factor binding and gene expression, whereas histone H3K27 trimethylation (H3K27me3) is indicative of heterochromatic regions that are typically associated with downregulation of gene expression. This study reveals that JAK/STAT signaling mediates epigenetic histone H3K4 methylation and consequently regulates gene activity critical for adult stem cells during budding and regeneration.

“Spatiotemporal characteristics of eustachian tube development in C57BL/6 mice: Correlation between morphological and functional maturation” by Xuan Yu, Huimin Zhang, Hejie Li, Xingqian Shen, Wenting Yu, Ting Li, Xiaoye Chen, Shimin Zong, and Hongjun Xiao, DevDyn 254.6, pp. 513–537. https://doi.org/10.1002/dvdy.753. The eustachian tube connects the middle ear and nasopharynx and is essential for normal middle ear function. It helps to equalize pressure inside and outside the middle ear, clear the middle ear of mucosal secretions, and protect the middle ear from pathogens and secretions from the nasopharynx. Despite our comprehensive understanding of the anatomical structure, physiological functions, and pathologies affecting the eustachian tube in adult mammals, comparatively less is known about its embryonic morphogenesis. This study investigated the development of the eustachian tube during embryogenesis and early postnatal period. Immunofluorescence and scanning electron microscopy revealed at both the molecular and ultrastructural levels, that ciliated cells first appear in the eustachian tube only a couple of days before birth. Subsequent analysis of lumen morphology and the development of the epithelium identified postnatal day 9 as the developmental time point at which the initial division of the cartilaginous and membranous parts of the eustachian tube occurs. Notably, this coincides with the stages of the middle ear cavity and the normalization of auditory function. Furthermore, Muc5b plays a foundational role during early stages, while Muc5ac enhances function in later stages.

“EphB2, EphB4, and ephrin-B1 expression and localization in postnatal developing epididymis in mice” by Md. Royhan Gofur, Kazushige Ogawa, DevDyn 254.6, pp. 478–493. https://doi.org/10.1002/dvdy.752. The efferent ductules and the ductus epididymis make up the male genital excurrent duct system in the epididymis. Derived from the mesonephric tubules and the mesonephric duct respectively, these progenitor tissues constitute a developmental and histological boundary. But what keeps these tissues segregated and allows them to developmentally integrate during the formation of the epididymis? Ephrin ligands and their Eph receptors function to facilitate communication between cells, and they also control migration, adhesion, and repulsion between cells, however a role for Eph-ephrin signaling during the development of the epididymis had not been previously explored. The authors studied the expression of EphB and ephrin-B in the adult mouse epididymis revealing EphB2/B4 and ephrin-B1 expression compartments positioned along the epididymal excurrent duct system aligned with ductule/duct-specific epithelia. Here they studied the expression and localization of EphB2/B4 and ephrin-B1 in the epithelium as well as stromal cells of postnatal developing epididymis in mice. The results suggest that EphB4/ephrin-B1 bidirectional signaling may influence the proliferation, and maturation and, or differentiation, of epididymal epithelium during early and late postnatal development, respectively.