The International journal of developmental biology最新文献

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.

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.

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 structure and function of cells is central to cell biology and physiology. The ability to control cell function may benefit biomedicine, such as cell-replacement therapy or regeneration. If structure defines function and cells are composed of water, lipids, small metabolites, nucleic acids, and proteins, of which the latter are largely encoded by the DNA present in the same cell, then one may assume that the cell types and variation in cellular phenotypes are shaped by differential gene expression. Cells of the same cell type maintain a similar composition. In this review, I will discuss the epigenetic and transcription regulation mechanisms guiding cell fate- specific gene expression in developing neural cells. Differentiation involves processes of cell-fate selection, commitment and maturation, which are not necessarily coupled.

Wnt4 signaling is critical for mammalian female sex determination, in female reproductive organ development, in follicular and oocyte maturation, and in steroid hormone production. When Wnt4 function is impaired, female embryos undergo partial female to male sex-reversal. This phenotype is associated with the expression of a set of somatic genes that are typical for the male differentiation pathways such as those of the Leydig cells. Given the roles of the 3`untranslated region (3`UTR) in control of gene expression, we addressed whether a knock-in of a stop cassette to 3`END of the Wnt4 gene would impact female reproductive system development or function. The 3`UTR^stop cassette indeed affected Wnt4 gene expression in vivo so that the respective mRNA was upregulated in the ovaries of a three month-old female. The homozygous Wnt4 3`UTR<sup>stop</sup> mice were noted to be leaner than their wild type (WT) littermate controls. Analysis of the ovarian follicular count at the age of three months revealed increased pre-antral but reduced ovarian corpus luteum follicular counts. Furthermore, two out of five of the homozygous female Wnt4 3`UTR^stop mice had ovarian cysts, not noted in WT controls. RT-qPCR and in situ hybridization analysis depicted changes in the expression of a panel of genes which encode enzymes that mediate the synthesis of female steroid hormones or their receptors due to the Wnt4 3`UTR<sup>stop</sup> knock-in. Thus, female mice which had the homozygous construct exhibited elevated ovarian Wnt4 mRNA expression and the corresponding knock-in was associated with changes in ovarian development and folliculogenesis. Our data reinforce the conclusion that deregulated Wnt4 expression impacts female sex organogenesis, ovary development and function, and that the Wnt4 3`UTR^stop knock-in mouse provides a model to explore in more detail the roles of Wnt4 signaling in the process.

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.

The megasporangium serves as a model system for understanding the concept of individual cell identity, and cell-to-cell communication in angiosperms. As development of the ovule progresses, three distinct layers, the epidermal (L1), the subepidermal or the hypodermal (L2) and the innermost layers (L3) are formed along the MMC (megaspore mother cell). The MMC, which is the primary female germline cell, is initiated as a single subepidermal cell amongst several somatic cells. MMC development is governed by various regulatory pathways involving intercellular signaling, small RNAs and DNA methylation. The programming and reprograming of a single nucellar cell to enter meiosis is governed by 'permissive' interacting processes and factors. Concomitantly, several nucellar sister cells are prevented from germline fate also by a set of 'repressive' factors. However, in certain angiosperms, anomalies in development of the female gametophyte have been observed. The sporophytic tissue surrounding the female gametophyte affects the gametophyte in multiple ways. The role of genes and transcription factors in the development of the MMC and in the regulation of various processes studied in selected model plants such as Arabidopsis is explained in detail in this paper. However, as angiosperms display enormous diversity, it is important to investigate early stages of megasporogenesis in other plant systems as well. Such studies provide valuable insights in understanding the regulation of megasporogenesis and the evolution of the female gametophyte from gymnosperms to flowering plants.

The midbrain-hindbrain boundary (MHB), also known as the isthmic organizer (IsO), plays a critical role in the developmental patterning of the posterior midbrain and anterior hindbrain. Understanding the wiring of this organizer's deeply conserved gene regulatory network is of significant interest for both evolutionary and neurodevelopmental biology. Various secreted signalling molecules and transcription factors have been identified as being important components for the formation and function of the MHB. Among these, FGF8 is considered a primary mediator of IsO activity; it directs anterior-posterior patterning and promotes the specification and maintenance of the MHB. While the core gene regulatory network governing MHB development is well-characterized, the direct interactions between key regulatory genes and the cis-regulatory elements that control their spatiotemporal expression remain poorly understood. This review summarizes the current knowledge of the gene regulatory network underlying the formation of the vertebrate midbrain-hindbrain boundary. We focus in particular on Fgf8 and its regulatory landscape from an evolutionary perspective.

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.