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.

“Neural induction: New insight into the default model and an extended four-step model in vertebrate embryos” by Mohsen Saghal, DevDyn 254.7, pp. 785-811, https://doi.org/10.1002/dvdy.70002. Neural induction is the process by which naive or uncommitted ectodermal cells differentiate into neural progenitor cells and ultimately give rise to the central and peripheral nervous systems. In vertebrates, this is thought to involve the inhibition of BMP signaling, mediated by the underlying mesoderm. Neural differentiation was therefore considered the default fate of naïve ectoderm unless instructed to acquire an epidermal cell fate in the presence of BMP signaling. However, both FGF signaling activation and Wnt inhibition were subsequently found to be required to suppress the BMP signaling, leading to a “pro-FGF” model of neural induction. This review highlights historical and recent findings that elucidate the mechanism of neural induction in vertebrates, and the author proposes a more refined four-step Activation, Stabilization, Transformation, and Elongation model of neural induction.

“Urodele amphibian newt bridges the missing link in evo-devo of the pancreas” by Ryosuke Morozumi, Kazuko Okamoto, Eriko Enomoto, Yuta Tsukamoto, Mitsuki Kyakuno, Nanoka Suzuki, Ichiro Tazawa, Nobuaki Furuno, Hajime Ogino, Yasuhiro Kamei, Masatoshi Matsunami, Shuji Shigenobu, Kenichi Suzuki, Hitoshi Uemasu, Noriyuki Namba, and Toshinori Hayashi, DevDyn 254.7, pp. 812-828. https://doi.org/10.1002/dvdy.763. The pancreas in mammals, performs an exocrine function by producing pancreatic juice containing various digestive enzymes, and an endocrine function, by producing several hormones that regulate blood glucose levels. The acquisition of an endocrine function occurred during the fish to amphibian transition, highlighting the evolutionary significance of amphibians in pancreas development. To date, most studies on amphibian pancreas development and physiology have centered on anurans, and most notably Xenopus. By comparison, pancreas development and function in urodeles, such as newts, remains underexplored. This study investigated the development of the pancreas in the urodele, Pleurodeles waltl, revealing that the pancreas in the newt comprises a single organ with exocrine tissue characterized by acinar structures and endocrine tissue forming islets. Furthermore, the newt possesses unique pancreas-like tissues on their intestines. Thus, the newt pancreas exhibits a morphology similar to that of the mammalian pancreas, which includes both exocrine and endocrine tissues, highlighting the intermediate evolutionary position of the newt in the evolution of pancreatic development and function.

“The link of FOXO1 and FOXO4 transcription factors to development of the lens” by Rifah Gheyas, Ruby Williams, Kelly Ryan, and A. Sue Menko, DevDyn 254.7, pp. 829-852. https://doi.org/10.1002/dvdy.766. The lens of the eye is a transparent structure that sits behind the iris and pupil, where it refracts light, focusing it onto the retina, to enable clear vision. The function of the mature lens depends on its complex structure, which is composed of two cell types, the epithelial cells and fiber cells. Localized proliferation in the anterior region of the lens equatorial epithelium known as the germinative zone, occurs during early development. For these cells to exit this zone and initiate their differentiation program they must first express p27, a cyclin dependent kinase inhibitor, which is a well-known FOXO1/FOXO4 transcriptional target. In this study, the lens is used to investigate the importance of FOXO1 and FOXO4 as mediators of the commitment of undifferentiated cells to a differentiation pathway. The authors show that expression of p27 is central to the initiation of lens differentiation and dependent upon the transcriptional activation of FOXO1, which is mediated by PI3K/Akt signaling.

“Interaction between perfluoro-octanoic sulfonate and common antibiotics induces developmental anomalies and lethality in Xenopus laevis” by Emma Harrison, Shreya Chattapadhyay, Ganad Neka, Maya Baskin, Nora Richmond, Quynh Nguyen, Isabel Wade, Arya Anekal, Olive Lucanish, and John Young, DevDyn 254.7, pp. 853-864. https://doi.org/10.1002/dvdy.764. “Forever Chemicals” are a family of chemicals that do not occur naturally in the environment. Perfluoroalkyl substances (PFAS) are one such example of forever chemicals and are known to bioaccumulate in various organisms. However, the long-term consequences of such bioaccumulation are poorly understood. Therefore, in this study, the authors use the frog, Xenopus laevis, to investigate the developmental consequences of exposure to the PFAS molecule perfluoro-octanoic sulfonate (PFOS). Exposure to high levels of PFOS results in significant axial shortening and dose-dependent formation of a cellular masses in the dorsal fin of developing tadpoles. Surprisingly, these developmental phenotypes are exacerbated upon co-exposure with commonly used antibiotics such as gentamicin, which results in increased apoptosis, possibly as a consequence of mitochondrial toxicity, together with loss of cellular integrity and increased overall lethality. The work adds to our understanding of PFOS exposure to vertebrate development and highlights additional concerns when potential interactions with antibiotics are also taken into consideration.

“Assessing candidate DLX-regulated genes in the first pharyngeal arch of chick embryos” by Afshan Sohail, Olivia Nicoll, and Andrew Bendall, DevDyn 254.7, pp. 865-878. https://doi.org/10.1002/dvdy.765. The shift from a cyclostome-like ancestor to vertebrates with asymmetric and articulating jaws was a major transition in animal evolution that facilitated the radiation and adaptation of vertebrates throughout aquatic, terrestrial, and aerial environments. At a molecular level, the evolution of asymmetrical jaws is associated with differential Endothelin-Dlx signaling and gene expression, which lies near the top of the regulatory hierarchy that distinguishes the patterning of upper and lower jaw-forming tissues. Defining the next tier of gene regulation, the direct targets of Dlx regulation is important for understanding how paralogous proteins such as Dlx5 and Dlx6 elicit their mechanistic effect in the realization of the “Dlx code.” This study investigates the expression and regulatory activity of Gsc, Hand2, Pitx1, and Gbx2, a core group of ventral identity genes whose expression in the first pharyngeal arch in avian embryos depends on the combined action of Dlx5 and Dlx6. The evidence presented in this study supports the hypothesis that these four genes are direct targets of DLX transcription factors in the lower jaw-forming tissue and were important for jaw evolution and subsequent function.