Development Of Non-neural Tissues Research Articles

Foxn4: A multi-faceted transcriptional regulator of cell fates in vertebrate development

Vertebrate development culminates in the generation of proper proportions of a large variety of different cell types and subtypes essential for tissue, organ and system functions in the right place at the right time. Foxn4, a member of the forkhead box/winged-helix transcription factor superfamily, is expressed in mitotic progenitors and/or postmitotic precursors in both neural (e.g., retina and spinal cord) and non-neural tissues (e.g., atrioventricular canal and proximal airway). During development of the central nervous system, Foxn4 is required to specify the amacrine and horizontal cell fates from multipotent retinal progenitors while suppressing the alternative photoreceptor cell fates through activating Dll4-Notch signaling. Moreover, it activates Dll4-Notch signaling to drive commitment of p2 progenitors to the V2b and V2c interneuron fates during spinal cord neurogenesis. In development of non-neural tissues, Foxn4 plays an essential role in the specification of the atrioventricular canal and is indirectly required for patterning the distal airway during lung development. In this review, we highlight current understanding of the structure, expression and developmental functions of Foxn4 with an emphasis on its cell-autonomous and non-cell-autonomous roles in different tissues and animal model systems.

Netrin-4 Promotes Glioblastoma Cell Proliferation through Integrin β4 Signaling

Netrin-4 is a laminin-related secreted molecule originally found to have roles in neuronal axon migration. Recent studies have indicated that netrin-4 also participates in the development of nonneural tissues and modulates tumor cell proliferation and tumor metastasis. Here we have explored the functions and molecular mechanisms of netrin-4 in glioblastoma multiforme. The suppression of netrin-4 expression in glioblastoma cell lines significantly reduced cell proliferation and motility and increased serum deprivation-induced apoptosis. Using tandem affinity purification combined with protein identification by mass spectrometry, we found that integrin β(4) interacts with netrin-4 and that it mediates mitogenic effects as well as AKT and mammalian target of rapamycin phosphorylation induced by netrin-4. Interestingly, netrin-4 acted as an inhibitor of cell proliferation in integrin β(4)-silenced glioblastoma cells, and high concentrations of netrin-4 reduced cell proliferation. The negative effects of netrin-4 on proliferation were mediated by UNC5B. Analysis of more than 400 primary tumors from The Cancer Genome Atlas repository revealed that the expression of netrin-4 is significantly downregulated in glioblastoma and that the reduced expression is linked to poor patient survival time. The expression of integrin β(4) is increased in glioblastoma, and it predicts poor patient survival time. Current results illustrate a novel mechanism for glioma progression, where glioma cells reduce netrin-4 expression to decrease its inhibitory effects. In parallel, the expression of integrin β(4) is upregulated to sensitize the cells to low concentrations of netrin-4 for maintaining cell proliferation.

Developmental expression of prion protein and its ligands stress‐inducible protein 1 and vitronectin

Prion protein (PrP(C)) is the normal isoform of PrP(Sc), a protein involved in neurodegenerative disorders. PrP(C) participates in neuritogenesis, neuroprotection, and memory consolidation through its interaction with the secreted protein stress-inducible protein 1 (STI1) and the extracellular matrix protein vitronectin (Vn). Although PrP(C) mRNA expression has been documented during embryogenesis, its protein expression patterns have not been evaluated. Furthermore, little is known about either Vn or STI protein expression. In this study, PrP(C), STI1, and Vn protein expression was explored throughout mouse embryonic life. We found that the distributions of the three proteins were spatiotemporally related. STI1 and Vn expression became evident at E8, earlier than PrP(C), in the nervous system and heart. At E10, we observed, in the spinal cord, a gradient of expression of the three proteins, more abundant in the notochord and floor plate, suggesting that they can have a role in axonal growth. As development proceeded, the three proteins were detected in other organs, suggesting that they may play a role in the development of nonneural tissues as well. Finally, although STI1 and Vn are PrP(C) ligands, their expression was not altered in PrP(C)-null mice.

Sema3D, Sema3F, and Sema5A are expressed in overlapping and distinct patterns in chick embryonic heart

An increasing number of axon guidance cues have been shown recently to play important roles in the development of non-neural tissues. Semaphorins comprise one of the largest conserved families of axon guidance factors. We analyzed the expression patterns of Sema3D, Sema3F, and Sema5A genes in the chick embryonic heart by in situ hybridization. All three genes are expressed in the cardiac cushion regions, both in the mesenchymal cells, and epithelial cells in the endocardial layer, during the period of cardiac remodeling. In addition to the overlapping expression patterns in the cardiac cushion regions, these genes also exhibit distinct expression patterns in the developing heart: Sema3D is additionally expressed in the tips of the ventricular trabeculae; Sema3F is expressed in a subset of cells scattered throughout the ventricles; and Sema5A is expressed in the newly formed atrioventricular valves. The overlapping and distinct expression patterns of these genes suggest that they may play important roles in heart development.

Embryology of the Neural Crest: Its Inductive Role in the Neurocutaneous Syndromes

Neural crest cells are first recognized at the lateral margin of the neural placode shortly after gastrulation, although they are not committed to their diverse fates until later. After dorsal closure of the neural tube, neural crest cells separate and migrate throughout the embryo to form many structures of ectodermal origin (eg, dorsal root and autonomic ganglia, peripheral nerve sheaths) and mesodermal origin (eg, blood vessels, melanocytes, adipose tissue, membranous bone, connective tissue, most of the ocular globe). Terminal differentiation occurs after migration is complete. Three regions of the neural tube generate neural crest: rhombencephalon, mesencephalon, and prosencephalon, each with a different migratory pattern. The most important genes promoting neural crest differentiation and migration are those with a dorsalizing influence in the vertical axis of the neural tube (eg, PAX3, BMP4, ZIC2), some segmentation genes (eg, WNT1), genes that inhibit neural crest (eg, EGR2), and neural crest-specific differentiating genes (eg, SLUG, SOX10). In the neurocutaneous syndromes, diverse features result from abnormal neural crest differentiation, providing a more encompassing embryologic basis for these disorders than the traditional view that these syndromes are somehow related to skin and brain because both are ectodermal derivatives. Abnormal angiogenesis, areas of abnormal pigmentation that sometimes follow the lines of Blashko, nerve sheath proliferations, disorders of chromaffin tissue, lipomes and benign and malignant tumors are frequent features. Many defective genes in neurocutaneous syndromes have an additional function as tumor suppressors. Interactions between genes associated with these disorders and others essential to neural crest formation, migration, and differentiation, are a likely molecular genetic basis for these diseases. The craniofacial abnormalities associated with many cerebral malformations and cutaneous lesions in some neurocutaneous syndromes emphasize an important inductive role of the neural tube in the development of non-neural tissues, mediated through neural crest.

Semaphorin3a1 regulates angioblast migration and vascular development in zebrafish embryos.

Semaphorins are a large family of secreted and cell surface molecules that guide neural growth cones to their targets during development. Some semaphorins are expressed in cells and tissues beyond the nervous system suggesting the possibility that they function in the development of non-neural tissues as well. In the trunk of zebrafish embryos endothelial precursors (angioblasts) are located ventral and lateral to the somites. The angioblasts migrate medially and dorsally along the medial surface of the somites to form the dorsal aorta just ventral to the notochord. Here we show that in zebrafish Sema3a1 is involved in angioblast migration in vivo. Expression of sema3a1 in somites and neuropilin 1, which encodes for a component of the Sema3a receptor, in angioblasts suggested that Sema3a1 regulates the pathway of the dorsally migrating angioblasts. Antisense knockdown of Sema3a1 inhibited the formation of the dorsal aorta. Induced ubiquitous expression of sema3a1 in hsp70:(gfp)sema3a1(myc) transgenic embryos inhibited migration of angioblasts ventral and lateral to the somites and retarded development of the dorsal aorta, resulting in severely reduced blood circulation. Furthermore, analysis of cells that express angioblast markers following induced expression of sema3a1 or in a mutant that changes the expression of sema3a1 in the somites confirmed these results. These data implicate Sema3a1, a guidance factor for neural growth cones, in the development of the vascular system.

The slice overlay assay: a versatile tool to study the influence of extracellular signals on neuronal development.

We have developed a technique that allows characterization and identification of extracellular signals that regulate various aspects of neuronal differentiation. In this in vitro assay, dissociated cells isolated from the developing cerebral wall are labeled and cultured over organotypic cortical slices. We have used this slice overlay assay to identify some of the extracellular cues that regulate differentiation and patterning of axons and dendrites in the cerebral cortex. This assay can be easily adapted to identify factors that control other aspects of neuronal development, such as proliferation and survival, and can also be used to evaluate the role of extracellular signals in the development of nonneural tissues.

歯はい形成を助けるＮＧＦシグナルはｐ７５を介して伝達される

Cranial neural crest cells considerably contribute to the formation of craniofacial structures during embryogenesis. Like many other organs, teeth develop through a series of reciprocal interactions between two adjacent tissues, the epithelium and the mesenchyme, most of which are cranial neural crest cells migrated from neural folds. Cranial neural crest cells migrate from dorsal to ventral under the epithelium, and some of them reside into the developing first pharyngeal arch. It has been suggested that NGF is required for the migration and/or differentiation of cranial neural crest cells. The expression patterns of neurotrophins including NGF and their cognate receptors suggest that they have some effects on tooth formation. However, the biological role of neurotrophins in the development of non-neural tissues such as tooth germ remains unclear. An low-affinity receptor for NGF, p75 is expressed in many embryonic organs, and has been proposed to have regulatory roles or functions during the development of non-neural tissues. High-affinity NGF receptor trkA is not expressed in the region of tooth formation, while p75 low-affinity NGF receptor is expressed in the mesenchyme of first pharyngeal arch at the stage of tooth initiation.In this study, organ culture system of E9 mouse mandibles and antisense inhibition technique of p75 low-affinity neurotrophin receptors have been used to study the effects of NGF signals on the cranial neural crest cells. Cultured for 10 days, control groups supplemented with p75 random oligonucleotides and groups with no supplementation formed tongue, Meckel's cartilage and cap stage tooth germ, while no tooth germs were observed in the explants cultured with the antisense oligonucleotides. Results of this study suggest that NGF signal is required for the cranial neural crest cells, which form dental mesenchyme, and is mediated through p75.

The enkephalinergic osteoblast.

The enkephalinergic osteoblast.

Gene expression of CD24 core peptide molecule in developing brain and developing non‐neural tissues

CD24 is a signal transducing molecule on the surface of most human B cells, murine immature T cells, myeloid and erythroid lineage cells. We isolated rat CD24 gene from embryonic brain cDNA library and characterized the gene expression during rat embryogenesis. Rat CD24 cDNA is homologous to murine and human CD24 gene with respect to the structure of signal peptide, N-glycosylation sites, and possible glycosyl phosphatidylinositol (GPI) linker attaching site, suggesting that rat CD24 is a transducing glycoprotein anchoring membrane via GPI linker. In the developing embryo, in situ hybridization analyses revealed that CD24 transcript was detected in primitive ectoderm, mesoderm, and ventral endoderm of day 9 postcoitum (p.c.) embryo. In central nervous systems CD24 transcript was strongly expressed in postmitotic cells of spinal cord, hindbrain, midbrain, and forebrain from day 11 p.c. embryo to day 21 p.c. embryo but was dramatically down regulated in adult brain. Furthermore, expression was also detected in epithelium during development of non-neural tissues, such as intestinal mucosal epithelium, nasal epithelium, ductal epithelium of salivary gland, bronchial epithelium, renal tubular epithelium, and hair follicles. In tooth development, where correct epithelium requires epithelial-mesenchymal interactions, CD24 mRNA was specifically induced in mesenchymal cells differentiating into odontoblast in dental papilla, suggesting the pivotal role of CD24 molecule in cell differentiations in vivo. We suggest that CD24 gene may encode the core peptide molecule of 31 kDa GPI linked molecule which has been known to be important in the migration of neurons on astroglial processes during development.

A homolog of Drosophila Notch expressed during mammalian development

Drosophila Notch and the related Caenorhabditis elegans proteins lin-12 and glp-1 function as mediators of local cell-cell interactions required for cell-fate decisions during invertebrate development. To investigate the possibility that similar proteins play determinative roles during mammalian development, we isolated cDNA clones encoding rat Notch. The deduced amino acid sequence of this protein contains 36 epidermal growth factor (EGF)-like repeats, and is remarkably similar in both its extracellular and cytoplasmic domains to the sequence of Xenopus Xotch and Drosophila Notch. In the developing central nervous system, in situ hybridisation analyses revealed that Notch transcripts were dramatically restricted to the ventricular proliferative zones of embryonic neuroepithelia. Notch was also strongly expressed during development of non-neural tissues, such as hair follicles and tooth buds, whose correct differentiation requires epithelial-mesenchymal interactions. These data support the hypothesis that Notch plays an essential role in mammalian development and pattern formation that closely parallels its role in the development of invertebrates.