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.

“Stage-by-stage exploration of normal embryonic development in the Arabian killifish, Aphanius dispar” by Amena Alsakran, Rashid Minhas, Atyaf Hamied, Rod Wilson, Mark Ramsdale, and Tetsuhiro Kudoh Fan, DevDyn 254.5, pp. 380–395, https://doi.org/10.1002/dvdy.738.

Teleost fish such as zebrafish and medaka are attractive models for studying developmental processes due to their small size and transparency. In addition, zebrafish and medaka have classically been used to model genetic diseases and infection. However, it is still desirable to develop new fish models that can facilitate the investigation of environmental changes and pollution in estuarine, marine, and high-salinity environments. The Arabian killifish (Aphanius dispar) is a small teleost fish in which the embryo and chorion are very transparent, which facilitates high resolution and high throughput imaging. A. dispar has been used as an effective biological control agent for mosquito larvae. This study investigated the step-by-step development of A. dispar embryos, delineating key developmental milestones from the maternal to hatching stages, and demonstrated that temperature has a significant effect on embryonic development, with accelerated development at higher temperatures. A. dispar exhibits broad thermal tolerance and extended independent feeding capabilities, making it a promising model organism for ecotoxicology and disease pathogenesis studies.

“Effects of life history strategies and habitats on limb regeneration in plethodontid salamanders” by Vivien Bothe, Hendrik Müller, Neil Shubin, and Nadia Fröbisch Fan, DevDyn 254.5, pp. 396–419, https://doi.org/10.1002/dvdy.742.

Salamanders are renowned as the only tetrapod capable of fully regenerating its limbs. Indeed, in addition to their limbs and tails, salamanders are the only tetrapod able to regenerate various other anatomical structures, including organs such as the lens, heart, and liver, repeatedly and throughout their entire life. However, salamanders are a highly diverse clade of tetrapods with around 850 currently known species, and yet research on tetrapod regeneration has largely been based on a small number of salamander species, primarily the Mexican axolotl Ambystoma mexicanum and, to a lesser extent, Pleurodeles waltl and Notophthalmus viridescens. Interestingly, some studies have suggested that certain salamanders may not be able to regenerate their limbs at all. Therefore, it remains to be determined how limb regeneration varies across salamanders and how factors like variable life histories, ecologies, and limb functions have influenced and shaped regenerative capacities throughout evolution. This study focused on six species of plethodontid salamanders representing distinct life histories and habitats that were examined for their regeneration ability after bite injuries or controlled amputations. Considerable regenerative capacity was evident in all species investigated; however, history, habitat, and mode of locomotion all influence the speed and accuracy of limb regeneration.

“Knockout of rbm24a and rbm24b genes in zebrafish impairs skeletal and cardiac muscle integrity and function during development” by Audrey Saquet, Ziwei Ying, De-Li Shi, and Raphaëlle Grifone Fan, DevDyn 254.5, pp. 420–435, https://doi.org/10.1002/dvdy.743.

Skeletal and cardiac muscles are contractile tissues whose development and function are dependent on precisely orchestrated genetic programs. RNA-binding proteins are critical regulators of gene expression, and dysregulation of RNA-binding proteins can compromise cellular health and function. Rbm24 has been identified as a key regulator of skeletal myogenesis and cardiomyogenesis in several vertebrates, through its effects on post-transcriptional regulation, including pre-mRNA alternative splicing and mRNA stabilization. This study used gene editing to generate rbm24a and rbm24b single mutants as well as double mutants in zebrafish. rbm24a single mutants displayed weak skeletal muscle defects and strong cardiac abnormalities, whereas rbm24b single mutants exhibit no obvious phenotype. However, the combinatorial loss of rbm24a and rbm24b severely disrupted sarcomere organization and muscle tissue integrity, and impaired contractility and motility of skeletal and cardiac muscle function. This illustrates the functional redundancy between rbm24a and rbm24b and provides new genetic tools to evaluate the function of Rbm24 in skeletal and cardiac muscle development and function in vertebrates. In summary, skeletal and cardiac muscles are contractile tissues whose development, homeostasis, and function require specific post-transcriptional networks that are regulated by RNA-binding proteins.

“Developmental cochlear defects are involved in early-onset hearing loss in A/J mice” by Lihong Kui, Peng Ma, Wenben Zhao, Bin Yan, Xiaojing Kuang, Bo Li, Ruishuang Geng, Tihua Zheng, and Qingyin Zheng Fan, DevDyn 254.5, pp. 436–449, https://doi.org/10.1002/dvdy.741.

Hearing loss is one of the most common forms of sensory impairment and affects about 430 million worldwide. Mechanosensory hair cells in the cochlea convert the mechanical movement generated by sound waves into electrical signals. Although it is generally thought that degeneration of hair cells and auditory neurons is the main cause of hearing loss, it is becoming more apparent that anomalies or disruptions in any stage of the conductive hearing process can contribute to hearing loss. A/J inbred mice, which are a commonly used model of age-related hearing loss, carry a mutant allele of Cdh23. Cdh23 encodes the Cadherin23 protein, which is a key component of stereocilia tips, essential for hair cell stereocilia bundle development and function. Previous analyses of cochlear pathology in A/J mice focused on structural hair bundle defects and the loss of hair cells and spiral ganglion neurons, but severe hearing loss in A/J mice is already evident at 3 weeks of age. In this study, the authors detected defects in cochlear hair cell stereocilia and mechanoelectrical transduction channel function as early as 3 days of age, with abnormal localization and reduction in the number of ribbon synapses by 2 weeks of age, and anomalies in cochlear nerve innervation and terminal swellings by 3 weeks of age. Thus, all of the cochlear abnormalities were prevalent prior to hair cell and auditory nerve loss, suggesting that developmental defects and subsequent cochlear degeneration are responsible for early onset hearing loss in A/J mice.

“Analysis pipeline to quantify uterine gland structural variations” by Sameed Khan, May Shen, Aishwarya Bhurke, Adam Alessio, and Ripla Arora, DevDyn 254.5, pp. 450–469, https://doi.org/10.1002/dvdy.757.

Three-dimensional (3D) imaging continues to uncover new details about the shape and structure of tissues and organs, and technical advances in whole tissue imaging and clearing have allowed 3D reconstruction of novel morphological features associated with physiological and pathological changes. In this study, the authors describe a deep imaging pipeline for segmenting and analyzing uterine gland shape, length, and branching patterns, and reconstruct exocrine uterine glands deep-seated in the endometrium during the elusive window of mouse embryo implantation. Their analysis reveals that at the time of embryo or egg entry into the uterus, the uterine glands undergo changes in length, tortuosity, and proximity to the uterine lumen while gland branch number stays the same. Eventually, these shape changes aid in the reorganization of the glands around the embryo implantation site, and the feasibility of this approach extends to uterine glandulogenesis in human and other mammalian species. This study therefore serves as a resource for defining quantitative and reproducible morphological features from three-dimensional uterine gland images to reveal insights about functional and structural patterns during uterine development and glandulogenesis.