frizzled 9 is expressed in neural precursor cells in the developing neural tube

The wnt signaling pathway has important functions in nervous system development. To better understand this process we have cloned and analyzed the expression of the wnt receptor, frizzled 9, in the developing nervous system in mouse, chick and zebrafish. The earliest expression of mouse frizzled 9 mRNA expression begins at E8.5 with expression throughout the entire rostral-caudal neuraxis. This early expression pattern within the neural tube appears to be conserved between chick and zebrafish. Expression becomes restricted to a ventral domain in the mouse ventricular zone at E11.5, a region specified to give rise to neurons and glia. Using a polyclonal antibody to MFZ9 further shows expression limited to neural restricted precursors cells.     

Embryonic expression of three mouse genes with homology to the Drosophila melanogaster prickle gene

The Drosophila melanogaster gene prickle-spiny-legs (pk) functions in an intercellular feedback loop that is central to the establishment of planar cell polarity in the eye and epidermis of the fly, by modulating Frizzled-Disheveled signalling. Here we identify three mouse prickle-related genes (dyxin, testin and prickle) and describe their expression pattern during murine embryogenesis (E7.5-E15.5). We report that the three genes are expressed in restricted areas of the developing mouse brain: dyxin in the most ventral region of the neural tube and in some localized regions of the ventricular layer of the mesencephalon and rhombencephalon, prickle in the pons region, ventrolateral part of rhombencephalon and motoneurons in the spinal cord, and testin in differentiating neurons of the spinal cord and retina. At the stages analyzed, the main site of expression of testin is the migrating cranial neural crest, while the expression of dyxin is noticeable in myotomal cells and its derivatives, with prickle expression being reciprocally localized to some sclerotomal derivatives, like bone primordia. prickle is also expressed in the apical ectodermal ridge and the most distal mesenchyme of the forming limb buds.     

Embryonic expression of three mouse genes with homology to the Drosophila melanogaster prickle gene

The Drosophila melanogaster gene prickle-spiny-legs (pk) functions in an intercellular feedback loop that is central to the establishment of planar cell polarity in the eye and epidermis of the fly, by modulating Frizzled-Disheveled signalling. Here we identify three mouse prickle-related genes (dyxin, testin and prickle) and describe their expression pattern during murine embryogenesis (E7.5-E15.5). We report that the three genes are expressed in restricted areas of the developing mouse brain: dyxin in the most ventral region of the neural tube and in some localized regions of the ventricular layer of the mesencephalon and rhombencephalon, prickle in the pons region, ventrolateral part of rhombencephalon and motoneurons in the spinal cord, and testin in differentiating neurons of the spinal cord and retina. At the stages analyzed, the main site of expression of testin is the migrating cranial neural crest, while the expression of dyxin is noticeable in myotomal cells and its derivatives, with prickle expression being reciprocally localized to some sclerotomal derivatives, like bone primordia. prickle is also expressed in the apical ectodermal ridge and the most distal mesenchyme of the forming limb buds.     

Distinct expression of midkine and pleiotrophin in the spinal cord and placental tissues during early mouse development

Midkine and pleiotrophin comprise a family of heparin-binding growth factors, and are expressed in overlapping tissues during the mid- to late-gestation periods of mouse development. Their distinct expression during early mouse development, as revealed by in situ hybridization, was reported. Midkine was expressed in the embryonic ectoderm from as early as embryonic day (E5.5). In the neural tube midkine was expressed specifically in the neuroepithelium, that is, in the whole area of the neural tube at E9.5, and in the ventricular zone from E10.5-13.5. At E15.5, when the neuroepithelium disappeared, midkine concomitantly became undetectable. In contrast, pleiotrophin expression started exclusively in the neural plate at E8.5, and in the lateral plate of the neural tube at E9.5. It then became restricted to a dorsal ventricular zone from E11.5-13.5, and finally to the central gray neurons at E15.5. Moreover, pleiotrophin was expressed in the ventral horns. Among placental tissues, midkine was detected in the chorion, the fetal component of the placenta, whereas pleiotrophin was found in the decidua basalis, the maternal component of the placenta. The distinct expression of midkine and pleiotrophin suggests their differential role in early development.     

Symposium 8: Regulation of Oligodendrocyte Development. Guidance of oligodendrocyte precursor migration in the developing spinal cord

Oligodendrocyte precursors arise in restricted regions of the developing neuroepithelium due to local signals that include sonic hedgehog. In the spinal cord the founder cells of the oligodendrocyte lineage develop in a specific domain of the ventral ventricular zone. These cells or their progeny subsequently migrate long distances to populate the entire spinal cord and myelinate axons in the peripheral presumptive white matter. The majority of migration in the oligodendrocyte lineage is accomplished by immature precursors, which then stop, proliferate and differentiate in the appropriate location. Several distinct mechanisms appear to regulate this migration. The initial dispersal of cells from the ventral ventricular zone is guided by chemorepellent cues including netrin‐1 present in the ventral ventricular domain. Migratory precursors are arrested in particular locations within the developing spinal cord as the result of the localized expression of the chemokine, CXCL1 by astrocytes. This chemokine, signalling through the CXCR2 receptor combines with PDGF to inhibit cell migration and enhance cell proliferation thereby facilitating the local expansion of the oligodendrocyte lineage and myelination of all relevant axons.     

Developmental expression of the calcium‐activated chloride channels TMEM16A and TMEM16B in the mouse olfactory epithelium

Calcium‐activated chloride channels are involved in several physiological processes including olfactory perception. TMEM16A and TMEM16B, members of the transmembrane protein 16 family (TMEM16), are responsible for calcium‐activated chloride currents in several cells. Both are present in the olfactory epithelium of adult mice, but little is known about their expression during embryonic development. Using immunohistochemistry we studied their expression in the mouse olfactory epithelium at various stages of prenatal development from embryonic day (E) 12.5 to E18.5 as well as in postnatal mice. At E12.5, TMEM16A immunoreactivity was present at the apical surface of the entire olfactory epithelium, but from E16.5 became restricted to a region near the transition zone with the respiratory epithelium, where localized at the apical part of supporting cells and in their microvilli. In contrast, TMEM16B immunoreactivity was present at E14.5 at the apical surface of the entire olfactory epithelium, increased in subsequent days, and localized to the cilia of mature olfactory sensory neurons. These data suggest different functional roles for TMEM16A and TMEM16B in the developing as well as in the postnatal olfactory epithelium. The presence of TMEM16A at the apical part and in microvilli of supporting cells is consistent with a role in the regulation of the chloride ionic composition of the mucus covering the apical surface of the olfactory epithelium, whereas the localization of TMEM16B to the cilia of mature olfactory sensory neurons is consistent with a role in olfactory signal transduction. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 74: 657–675, 2014     

Spatially and temporally restricted expression of Pax2 during murine neurogenesis

The expression of the murine paired-box-containing gene, Pax2, is examined in the developing central nervous system by in situ hybridization. Pax2 expression is detected along the boundaries of primary divisions of the neural tube. Initially, Pax2 is expressed in the ventricular zone in two compartments of cells on either side of the sulcus limitans and along the entire rhombencephalon and spinal cord. At later times, Pax2 is restricted to progeny cells that have migrated to specific regions of the intermediate zone. In the eye, Pax2 expression is restricted to the ventral half of the optic cup and stalk and later to the optic disc and nerve. In the ear, expression is restricted to regions of the otic vesicle that form neuronal components. The transient and restricted nature of Pax2 expression suggests that this murine segmentation gene homologue may also establish compartmental boundaries and contribute to the specification of neuronal identity, as do certain Drosophila segmentation genes.     

Tlx and Pax6 co-operate genetically to establish the pallio-subpallial boundary in the embryonic mouse telencephalon

We have examined the role of Tlx, an orphan nuclear receptor, in dorsal-ventral patterning of the mouse telencephalon. Tlx is expressed broadly in the ventricular zone, with the exception of the dorsomedial and ventromedial regions. The expression spans the pallio-subpallial boundary, which separates the dorsal (i.e. pallium) and ventral (i.e. subpallium) telencephalon. Despite being expressed on both sides of the pallio-subpallial boundary, Tlx homozygous mutants display alterations in the development of this boundary. These alterations include a dorsal shift in the expression limits of certain genes that abut at the pallio-subpallial boundary as well as the abnormal formation of the radial glial palisade that normally marks this boundary. The Tlx mutant phenotype is similar to, but less severe than, that seen in Small eye (i.e. Pax6) mutants. Interestingly, removal of one allele of Pax6 on the homozygous Tlx mutant background significantly worsens the phenotype. Thus Tlx and Pax6 cooperate genetically to regulate the establishment of the pallio-subpallial boundary. The patterning defects in the Tlx mutant telencephalon result in a loss of region-specific gene expression in the ventral-most pallial region. This correlates well with the malformation of the lateral and basolateral amygdala in Tlx mutants, both of which have been suggested to derive from ventral portions of the pallium.     

Ultraviolet light induces the sustained unscheduled expression of cyclin E in the absence of functional p53

Cell cycle progression is regulated through changes in the activity of cyclin-dependent kinases that are, in turn, regulated by the expression of their respective cyclin partners. In primary cells, cyclin E expression increases through the G1 phase of the cell cycle and peaks near the G1/S boundary. The unscheduled expression of cyclin E in primary human fibroblasts leads to chromosomal instability that is greatly increased by loss of the p53 tumour suppressor. Intriguingly, ultraviolet light (UV), the most prevalent environmental carcinogen, is similarly known to induce chromosomal instability more dramatically in the absence of p53. Here we report that UV light transiently increased the expression of cyclin E in normal human fibroblasts. Strikingly, cyclin E levels remained elevated for an extended period of time in the absence of functional p53. UV-induced cyclin E expression was not restricted to the G1/S boundary but remained elevated throughout S phase and this correlated with a massive accumulation of p53-deficient fibroblasts in this phase of the cell cycle. Forced expression of cyclin E alone was insufficient to cause a similar S phase arrest but forced expression of cyclin E led to an increase in the proportion of UV-irradiated cells in S phase. The present work suggests that p53 affects S phase progression following UV exposure by preventing the sustained unscheduled expression of cyclin E and that this may limit the clastogenic and carcinogenic effects of UV light.     

Netrin 1 mediates spinal cord oligodendrocyte precursor dispersal

In spinal cord, oligodendrocyte precursors that give rise to myelin-forming cells originate in a restricted domain of the ventral ventricular zone. During development, these cells migrate widely throughout the spinal cord. Netrin 1 is expressed at the ventral ventricular zone during oligodendrocyte precursors emigration, and, in vitro, netrin 1 acts as chemorepellent and antagonizes platelet-derived growth factor (PDGF) chemoattraction. Oligodendrocyte precursors express the netrin receptors DCC and UNC5 and function-blocking anti-DCC antibody inhibits chemorepulsion of ventral spinal cord explants and netrin-secreting cells. In spinal cord slice preparations, addition of function-blocking anti-DCC antibody or netrin 1 dramatically inhibits oligodendrocyte precursor migration from the ventral ventricular zone. These data indicate the initial dispersal of oligodendrocyte precursors from their localized origin is guided by a chemorepellent response to netrin 1.     

Establishment of vagal sensorimotor circuits during fetal development in rats

The differentiation of vagal motor neurons and their emerging central relationship with vagal sensory afferents was examined in fetal rats. To identify peripherally projecting sensory and motor neurons, 1,1′-dioctadecyl 3,3,3′,3′-tetramethylindocarbocyanine perchloarate (DiI) was inserted into the proximal gut or cervical vagus nerve in fixed preparations. At embryonic day (E) 12, labeled vagal sensory neurons are present in the nodose ganglia and a few sensory axons project into the dorsolateral medulla. Central sensory processes become increasingly prevalent between E13 and E14 but remain restricted to the solitary tract. Vagal motor neurons are first labeled at E13, clustered within a region corresponding to the nucleus ambiguus (NA). Additional motor neurons appear to be migrating toward the NA from the germinal zone of the fourth ventricle. Motor neurons in the dorsal motor nucleus of the vagus (DMV) first project to the gut at E14 and have processes that remain in physical contact with the ventricular zone through E16. Sensory axons emerge from the solitary tract at E15 and project medially through the region of the nucleus of the solitary tract (NST) to end in the ventricular zone. A possible substrate for direct vagovagal, sensorimotor interaction appears at E16, when vagal sensory fibers arborize within the DMV and DMV dendrites extend into the NST. By E18, the vagal nuclei appear remarkably mature. These data suggest specific and discrete targeting of vagal sensory afferents and motor neuron dendrites in fetal rats and define an orderly sequence of developmental events that precedes the establishment of vagal sensorimotor circuits. © 1993 John Wiley & Sons, Inc.     

Expression profiles of Insulin-like growth factor binding protein-like 1 in the developing mouse forebrain

Insulin-like growth factor binding protein-like 1 (IGFBPL-1) has a domain structure that resembles one in the insulin-like growth factor binding proteins (IGFBPs), which is a domain known to be bound by insulin-like growth factors (IGFs) with high affinity and to thereby affect cell growth and metabolism. However, the distribution and functions of IGFBPL-1 in the brain are not known. Thus, to clarify IGFBPL-1 expression profiles during development, we have investigated the expression patterns of IGFBPL-1 mRNA in developing mouse brains using in situ hybridization, focusing especially on the forebrain. On embryonic day (E)12, IGFBPL-1mRNA expressions were localized in the preplate of the neopallium, dorsal thalamus, the differentiating field of the epithalamus, and the hippocampus. On E14, strong expression was recognized in the subventricular zone (SVZ) and intermediate zone (IMZ) in the neopallium, hippocampus, the differentiating field of the epithalamus, and the dorsal thalamus. E14 expressions were generally the strongest among all the stages examined and signals decreased thereafter. At E16 and E18, IGFBPL-1mRNA was strongly detected in the hippocampus and the SVZ of the neopallium. In postnatal stages, mRNA was found only in the granule cell layer of the dentate gyrus (DG). Notably, at P20, expression was restricted to the deep fraction of the granule cell layer, the location of late-born DG neurons.     

Developmental Expression of Transferrin Binding Protein in Oligodendrocyte Lineage Cells of the Embryonic Chick Spinal Cord

Oligodendrocytes develop from precursor cells in the neuroepithelium of the ventral ventricular zone. Oligodendrocytes in the different stages of development are characterized by expression of a number of different marker molecules such as myelin genes, growth factors, and specific antigens. We have previously identified that transferrin binding protein (TfBP), a member of heat shock protein 90 families, is a novel avian ER-associated membrane protein that is specifically localized in oligodendrocytes in adult chicken CNS. In this study we describe the developmental expression of TfBP in the embryonic chick spinal cord. A few, distinct, TfBP+ cells appeared at the lateral margin of the subventricular neuroepithelium of the spinal cord at E7. Thereafter, some TfBP+ cells, exhibited a migrative form of unipolar or bipolar shape occurred around E8 in the mantle layer, midway between the neuroepithelium and the marginal layer of the primitive spinal cord. Thereafter, the TfBP+ cells rapidly increased in number as well as their staining intensity, and overall distribution of TfBP+ cells at E15 was comparable to that of a mature spinal cord. Our observations suggest that TfBP is expressed in the subpopulation of oligodednrcyte lineage in the development and a putative role of TfBP in relation to transferrin and iron trafficking is considered. SW Park and HS Lim contributed equally to this work.