The International journal of developmental biology最新文献

Invertebrate and vertebrate species have many unusual cellular structures, such as long- or short-lived cell-in-cell structures and coenocytes. Coenocytes (often incorrectly described as syncytia) are multinuclear cells derived, unlike syncytia, not from the fusion of multiple cells but from multiple nuclear divisions without cytokinesis. An example of a somatic coenocyte is the coenocytic blastoderm in Drosophila. An astonishing property of coenocytes is the ability to differentiate the nuclei sharing a common cytoplasm into different subpopulations with different fate trajectories. An example of a germline coenocyte is the oogenic precursor of appendicularian tunicates, which shares many features with the somatic coenocyte of Drosophila. The germline coenocyte (coenocyst) is quite an unexpected structure because in most animals, including Drosophila, Xenopus, and mice, oogenesis proceeds within a group (cyst, nest) of sibling cells (cystocytes) connected by the intercellular bridges (ring canals, RCs) derived from multiple divisions with incomplete cytokinesis of a progenitor cell called the cystoblast. Here, I discuss the differences and similarities between cystocyte-based and coenocyst-based oogenesis, and the resemblance of coenocystic oogenesis to coenocytic somatic blastoderm in Drosophila. I also describe cell-in-cell structures that although not mechanistically, cytologically, or molecularly connected to somatic or germline coenocytes, are both unorthodox and intriguing cytological phenomena rarely covered by scientific literature.

During embryonic development, the vertebrate embryonic epiblast is divided into two parts including neural and superficial ectoderm. The neural plate border (NPB) is a narrow transitional area which locates between these parts and contains multipotent progenitor cells. Despite its small size, the cellular heterogeneity in this region produces specific differentiated cells. Signaling pathways, transcription factors, and the expression/repression of certain genes are directly involved in these differentiation processes. Different factors such as the Wnt signaling cascade, fibroblast growth factor (FGF), bone morphogenetic protein (BMP) signaling, and Notch, which are involved in various stages of the growth, proliferation, and differentiation of embryonic cells, are also involved in the determination and differentiation of neural plate border stem cells. Therefore, it is essential to consider the interactions and temporospatial coordination related to cells, tissues, and adjacent structures. This review examines our present knowledge of the formation of the neural plate border and emphasizes the requirement for interaction between different signaling pathways, including the BMP and Wnt cascades, the expression of its special target genes and their regulations, and the precise tissue crosstalk which defines the neural crest fate in the ectoderm at the early human embryonic stages.

Mutations in the gene encoding Tre2/Bub2/Cdc16 (TBC)1 domain family member 24 (TBC1D24) protein are associated with a variety of neurological disorders, ranging from non-syndromic hearing loss to drug-resistant lethal epileptic encephalopathy and DOORS syndrome [Deafness, Onychodystrophy, Osteodystrophy, intellectual disability (formerly referred to as mental Retardation), and Seizures]. TBC1D24 is a vesicle-associated protein involved in neural crest cell and neuronal migration, maturation, and neurotransmission. In the cochlea, TBC1D24 has been detected in auditory neurons, but few reliable and convergent data exist about the sensory epithelium. Here, the expression of TBC1D24 has been characterized via immunolabelling throughout the postnatal maturation of the mouse cochlear sensory epithelium. TBC1D24 was detected in glia-like non-sensory epithelial cells during early developmental stages. In contrast, TBC1D24 was virtually absent in adjacent sensory hair cells. This expression distinguishing non-sensory from sensory epithelial cells almost disappears around the onset of hearing. Until now, TBC1D24 was mainly described as a neuronal protein either in the brain or in the cochlea. The present observations suggest that TBC1D24 could also regulate vesicle trafficking in cochlear glia-like non-sensory epithelial cells. For a long time, research about epilepsy has been mainly neurocentric. However, there is now evidence proving that glial cell dysregulation contribute to pathogenesis of epilepsy and neurodevelopmental disorders. As a consequence, exploring the possibility that TBC1D24 could also have a role in glial cells of the central nervous system could help to gain insight into TBC1D24-related neurological pathogenesis.

Enhancers play an essential role in gene regulation by receiving cues from transcription factors and relaying these signals to modulate transcription from target promoters. Enhancer-promoter communications occur across large linear distances of the genome and with high specificity. The molecular mechanisms that underlie enhancer-mediated control of transcription remain unresolved. In this review, we focus on research in Drosophila uncovering the molecular mechanisms governing enhancer-promoter communication and discuss the current understanding of developmental gene regulation. The functions of protein acetylation, pausing of RNA polymerase II, transcriptional bursting, and the formation of nuclear hubs in the induction of tissue-specific programs of transcription during zygotic genome activation are considered.

Understanding the evolution of body plans has been one of the major areas of investigation in developmental and evolutionary biology. Cnidaria, the sister group to bilaterians, provides an opportunity to elucidate the origin and evolution of body axes. Hydra, a freshwater cnidarian, is a useful model to study signaling pathways governing pattern formation, which are conserved up to vertebrates including humans. The transforming growth factor β (TGF-β) signaling pathway is one of the fundamental pathways that regulate axis formation and organogenesis during embryonic development. In this article, we discuss the TGF-β pathway members identified in Hydra along with other cnidarians with an emphasis on bone morphogenetic proteins (BMPs) and their inhibitors. TGF-β members, especially those involved in BMP signaling pathway, are mainly involved in maintaining the Organizer region and patterning the body axis in Hydra. Identification of other members of this pathway in Hydra and fellow cnidarians would provide insights into the evolution of body axes and pattern formation in more complex metazoans.

During the initial days of development, the embryo gradually shifts from reliance on maternally provided RNAs and proteins to regulation of its own development. This transition is marked by embryonic genome activation (EGA). While the factors driving human EGA remain poorly characterized, accumulating evidence suggests that double homeobox 4 (DUX4) is an important regulator of this process. Despite advances in single-cell methods which have allowed studies in early human embryos, fundamental questions regarding the function and regulation of DUX4 persist. Here, we review current knowledge of DUX4 with a focus on EGA in humans.

The development of skin appendages, including hair follicles, teeth and mammary glands is initiated through the formation of the placode, a local thickening of the epithelium. The Wnt/β-catenin signaling cascade is an evolutionary conserved pathway with an essential role in placode morphogenesis, but its downstream targets and their exact functions remain ill defined. In this study, we identify Achaete-scute complex-like 4 (Ascl4) as a novel target of the Wnt/β-catenin pathway and demonstrate its expression pattern in the signaling centers of developing hair follicles and teeth. Ascl transcription factors belong to the superfamily of basic helix-loop-helix transcriptional regulators involved in cell fate determination in many tissues. However, their specific role in the developing skin remains largely unknown. We report that Ascl4 null mice have no overt phenotype. Absence of Ascl4 did not impair hair follicle morphogenesis or hair shaft formation suggesting that it is non-essential for hair follicle development. No tooth or mammary gland abnormalities were detected either. We suggest that other transcription factors may functionally compensate for the absence of Ascl4, but further research is warranted to assess this possibility.

Differentiation of human induced pluripotent stem cells towards pancreatic islet endocrine cells is a complex process, involving the stepwise modulation of key developmental pathways, such as the Hedgehog signaling inhibition during early differentiation stages. In tandem with this active inhibition, key transcription factors for the islet endocrine cell fate, such as HNF1A, show specific changes in their expression patterns. Here we designed a pilot study aimed at investigating the potential interconnection between HH-signaling inhibition and the increase in the HNF1A expression during early regeneration, by inducing changes in the GLI code. This unveiled a link between the two, where GLI3-R mediated Hedgehog target genes inhibition is apparently required for HNF1A efficient expression.

Keratin 17 (K17) is thought to be a candidate target gene for regulation by Lymphoid Enhancer Factor-1 (Lef-1). K17 is a marker that distinguishes junctional epithelium (JE) from epithelial rests of Malassez (ERM). However, the relationship of Lef-1 to K17 is not clear in this context. Moreover, the expression of other keratins such as K5, K6, K7 and K16 is not reported. Therefore, the aim of our study was to assay the expression of K5, K6, K7, K14, K16, K17 and Lef-1 in postnatal developing teeth, and clarify the corresponding immunophenotypes of the JE and ERM. Upper jaws of Wistar rats aged from postnatal (PN) day 3.5 to PN21 were used and processed for immunohistochemistry. K5 and K14 were intensely expressed in inner enamel epithelium (IEE), reduced enamel epithelium (REE), ERM and JE. There was no staining for K16 in the tissue, except for strong staining in the oral epithelium. Specifically, at PN3.5 and PN7, K17 was initially strongly expressed and then negative in the IEE. At PN16 and PN21, both REE and ERM were strongly stained for K17, whereas K17 was negative in the JE. In addition, K6, K7 and Lef-1 were not detected in any tissue investigated. REE and ERM have an identical keratin expression pattern before eruption, while JE differs from ERM in the expression of K17 after eruption. The expression of K17 does not coincide with that of Lef-1. These data indicate that JE has a unique phenotype different from ERM, which is of odontogenic origin.

In vertebrate development, ectoderm is specified into neural plate (NP), neural plate border (NPB), and epidermis. Although such patterning is thought to be achieved by molecular concentration gradients, it has been revealed, mainly by in vitro analysis, that mechanical force can regulate cell specification. During in vivo patterning, cells deform and migrate, and this applies force to surrounding tissues, shaping the embryo. However, the role of mechanical force for cell specification in vivo is largely unknown. In this study, with an aspiration assay and atomic force microscopy, we have demonstrated that tension on ectodermal cells decreases laterally from the midline in Xenopus early neurula. Ectopically applied force laterally expanded the neural crest (NC) region, a derivative of the NPB, whereas force relaxation suppressed it. Furthermore, force application activated both the FGF and Wnt pathways, which are required for NC formation during neuroectodermal patterning. Taken together, mechanical force is necessary for NC formation in order to regulate signaling pathways. Furthermore, molecular signals specify the NP and generate force on neighboring tissue, the NPB, with its closure. This force activates signals, possibly determining the appropriate width of a narrow tissue, the NC.