Embryo Nervous System Research Articles

Expanding understanding of chick embryo's nervous system development at HH22-HH41 embryonic stages using X-ray microcomputed tomography.

Assessing the embryotoxicity and teratogenicity of various substances and processes is crucial due to their complexity and resource intensity. The chicken embryo (CE) serves an ideal model for simulating the first months of mammalian embryonic development. This makes the CE a reliable model for testing teratogenic effects, particularly in relation to the nervous system (NS), which experiences developmental abnormalities second in frequency only to cardiovascular teratogenic disorders. Microcomputed tomography (μCT) is a promising method for studying these processes. The advantages of μCT include relatively high research speed, diagnostic accuracy, high resolution and the ability to visualize the entire internal 3D structure of an object while preserving for other types of research. At the same time, there are practically no available databases of normative μCT data, both qualitative and quantitative, which would act as a starting point for screening detection of abnormalities in the development of the NS. In this study, we present a simple method for obtaining very detailed quantitative sets of 2D and 3D μCT data of NS structures of the CE (Gallus Gallus domesticus) at HH22-HH41 embryonic stages with contrasting by 1% phosphotungstic acid. The results of μCT demonstrate the exact boundaries, high general and differentiated contrast of the main and specific structures of the NS of CE, which are quantitatively and qualitatively similar to results of histological analysis. Calculations of the X-ray density and volume of the main structures of the NS at constant exponential growth are presented. In addition to the increase in linear dimensions, significant changes in the structures of various parts of the brain were identified and visualized during the CE development at HH22 to HH41 embryonic stages. The data presented establish the first methodology for obtaining normative data, including subtle localized differences in the NS in CE embryogenesis. The data obtained open up new opportunities for modern embryology, teratology, pharmacology and toxicology.

Nervous System Development and Neuropeptides Characterization in Embryo and Larva: Insights from a Non-Chordate Deuterostome, the Sea Cucumber Apostichopus japonicus.

Simple SummaryPentamerous radial symmetrical echinoderm adults develop from bilaterally symmetrical larvae and are a great model for understanding the origin and evolution of deuterostome nervous systems. Neuropeptides are important neuronal signaling molecules that regulate diverse behavioral and physiological processes in animals including echinoderms. In this study, we revealed the remarkable complexity of embryonic and larval nervous systems, identified the neuropeptide profile, and quantified the expressions of specific neuropeptide precursor genes in Apostichopus japonicus embryo and larvae. Collectively, this research will enable us to have a more comprehensive understanding of the holothuroid embryonic and larval nervous system and gain insights into the potential functions of neuropeptidergic systems in holothuroid larvae.Here, we described the complex nervous system at five early developmental stages (blastula, gastrula, auricularia, doliolaria and pentactula) of a holothurian species with highly economic value, Apostichopus japonicus. The results revealed that the nervous system of embryos and larvae is mainly distributed in the anterior apical region, ciliary bands or rings, and the feeding and attachment organs, and that serotonergic immunoreactivity was not observed until the embryo developed into the late gastrula; these are evolutionarily conserved features of echinoderm, hemichordate and protostome larvae. Furthermore, based on available transcriptome data, we reported the neuropeptide precursors profile at different embryonic and larval developmental stages. This analysis showed that 40 neuropeptide precursors present in adult sea cucumbers were also identified at different developmental stages of embryos and larvae, and only four neuropeptide precursors (SWYG precursor 2, GYWKDLDNYVKAHKT precursor, Neuropeptide precursor 14-like precursor, GLRFAmprecursor-like precursor) predicted in adults were absent in embryos and larvae. Combining the quantitative expression of ten specific neuropeptide precursor genes (NPs) by qRT-PCR, we revealed the potential important roles of neuropeptides in embryo development, feeding and attachment in A. japonicus larvae. In conclusion, this work provides novel perspectives on the diverse physiological functions of neuropeptides and contributes to understanding the evolution of neuropeptidergic systems in echinoderm embryos and larvae.

Expression of Hey marks a subset of enteroendocrine cells in the Drosophila embryonic and larval midgut.

Hey is a conserved transcription factor of the bHLH-Orange family that participates in the response to Notch signaling in certain tissues. Whereas three Hey paralogues exist in mammalian genomes, Drosophila possesses a single Hey gene. Fly Hey is expressed in the subset of newborn neurons that receive a Notch signal to differentiate them from their sibling cells after the asymmetric division of precursors called ganglion-mother-cells. We used a polyclonal anti-Hey serum and a GFP-tagged transgenic duplication of the Hey locus to examine its expression in tissues outside the nervous system in embryos and larvae. We detected robust Hey expression in the embryonic midgut primordium at the time of birth of enteroendocrine cells, identified by expression of Prospero. Approximately half of the Pros-positive cells were also Hey positive at mid-embryogenesis. By the end of embryogenesis, most enteroendocrine cells had downregulated Hey expression, although it was still detectable at low levels after hatching. Low levels of Hey were also detected in subsets of the epithelial enterocytes at different times. Embryo enteroendocrine Hey expression was found to be Notch dependent. In late third-instar larvae, when few new enteroendocrine cells are born, novel Hey expression was detected in one cell of each sibling pair. In conclusion, Hey is strongly expressed in one of each pair of newly-born enteroendocrine cells. This is consistent with a hypothesis that embryonic enteroendocrine cells are born by an asymmetric division of a precursor, where Notch/Hey probably distinguish between the subtypes of these cells upon their differentiation.

Expression of NK genes that are not part of the NK cluster in the onychophoran Euperipatoides rowelli (Peripatopsidae)

BackgroundNK genes are a group of homeobox transcription factors that are involved in various molecular pathways across bilaterians. They are typically divided into two subgroups, the NK cluster (NKC) and NK-linked genes (NKL). While the NKC genes have been studied in various bilaterians, corresponding data of many NKL genes are missing to date. To further investigate the ancestral roles of NK family genes, we analyzed the expression patterns of NKL genes in the onychophoran Euperipatoides rowelli.ResultsThe NKL gene complement of E. rowelli comprises eight genes, including BarH, Bari, Emx, Hhex, Nedx, NK2.1, vax and NK2.2, of which only NK2.2 was studied previously. Our data for the remaining seven NKL genes revealed expression in different structures associated with the developing nervous system in embryos of E. rowelli. While NK2.1 and vax are expressed in distinct medial regions of the developing protocerebrum early in development, BarH, Bari, Emx, Hhex and Nedx are expressed in late developmental stages, after all major structures of the nervous system have been established. Furthermore, BarH and Nedx are expressed in distinct mesodermal domains in the developing limbs.ConclusionsComparison of our expression data to those of other bilaterians revealed similar patterns of NK2.1, vax, BarH and Emx in various aspects of neural development, such as the formation of anterior neurosecretory cells mediated by a conserved molecular mechanism including NK2.1 and vax, and the development of the central and peripheral nervous system involving BarH and Emx. A conserved role in neural development has also been reported from NK2.2, suggesting that the NKL genes might have been primarily involved in neural development in the last common ancestor of bilaterians or at least nephrozoans (all bilaterians excluding xenacoelomorphs). The lack of comparative data for many of the remaining NKL genes, including Bari, Hhex and Nedx currently hampers further evolutionary conclusions. Hence, future studies should focus on the expression of these genes in other bilaterians, which would provide a basis for comparative studies and might help to better understand the role of NK genes in the diversification of bilaterians.

Neural development in the tardigrade Hypsibius dujardini based on anti-acetylated α-tubulin immunolabeling

BackgroundThe tardigrades (water bears) are a cosmopolitan group of microscopic ecdysozoans found in a variety of aquatic and temporarily wet environments. They are members of the Panarthropoda (Tardigrada + Onychophora + Arthropoda), although their exact position within this group remains contested. Studies of embryonic development in tardigrades have been scarce and have yielded contradictory data. Therefore, we investigated the development of the nervous system in embryos of the tardigrade Hypsibius dujardini using immunohistochemical techniques in conjunction with confocal laser scanning microscopy in an effort to gain insight into the evolution of the nervous system in panarthropods.ResultsAn antiserum against acetylated α-tubulin was used to visualize the axonal processes and general neuroanatomy in whole-mount embryos of the eutardigrade H. dujardini. Our data reveal that the tardigrade nervous system develops in an anterior-to-posterior gradient, beginning with the neural structures of the head. The brain develops as a dorsal, bilaterally symmetric structure and contains a single developing central neuropil. The stomodeal nervous system develops separately and includes at least four separate, ring-like commissures. A circumbuccal nerve ring arises late in development and innervates the circumoral sensory field. The segmental trunk ganglia likewise arise from anterior to posterior and establish links with each other via individual pioneering axons. Each hemiganglion is associated with a number of peripheral nerves, including a pair of leg nerves and a branched, dorsolateral nerve.ConclusionsThe revealed pattern of brain development supports a single-segmented brain in tardigrades and challenges previous assignments of homology between tardigrade brain lobes and arthropod brain segments. Likewise, the tardigrade circumbuccal nerve ring cannot be homologized with the arthropod ‘circumoral’ nerve ring, suggesting that this structure is unique to tardigrades. Finally, we propose that the segmental ganglia of tardigrades and arthropods are homologous and, based on these data, favor a hypothesis that supports tardigrades as the sister group of arthropods.Electronic supplementary materialThe online version of this article (doi:10.1186/s13227-015-0008-4) contains supplementary material, which is available to authorized users.

Histamine in brain development

The function of histamine in the adult central nervous system has been extensively studied, but data on its actions upon the developing nervous system are still scarce. Herein, we review the available information regarding the possible role for histamine in brain development. Some relevant findings are the existence of a transient histaminergic neuronal system during brain development, which includes serotonergic neurons in the midbrain and the rhombencephalon that coexpress histamine; the high levels of histamine found in several areas of the embryo nervous system at the neurogenic stage; the presence of histaminergic fibers and the expression of histamine receptors in various areas of the developing brain; and the neurogenic and proliferative effects on neural stem cells following histamine H(1) - and H(2) -receptor activation, respectively. Altogether, the reviewed information supports a significant role for histamine in brain development and the need for further research in this field.

Distinct patterns of human medulloblastoma dissemination in the developing chick embryo nervous system

Medulloblastoma (MB) is the most common malignant primary brain tumor in children. Aggressive tumors that disseminate along the leptomeninges carry extremely poor prognoses. Mechanisms that predict dissemination are poorly understood. Our objective was to develop a reliable and reproducible model to study MB dissemination. We have created a chicken-human xenograft to study features of MB with leptomeningeal dissemination. Human MB cell lines (D283, Daoy), primary human MB cells (SF8113), and primary genetic mouse model (Math1cre:SmoM2 flox/flox) MB cells were either transfected to express green fluorescent protein (GFP) or were labeled with a membrane permeable green fluorescent probe. Cells were then injected as aggregates or implanted as pellets into the developing chicken brain immediately after neural tube closure at embryonic day 2 (E2). Most embryos were harvested three days after implantation (E5) though some were harvested up to E15. The developing brain was analyzed via whole mount fluorescent imaging and tissue section immunohistochemistry. Human and mouse MBs survived in the developing chicken central nervous system (CNS). They exhibited distinct patterns of incorporation and dissemination into the CNS that were consistent with observed phenotypes of the corresponding human patient or mouse host. Specifically, metastatic D283 cells disseminated along the leptomeninges whereas Daoy, primary mouse MB, and primary human MB cells did not. This work supports an avian-human xenograft as a successful model to study patterns of MB dissemination. Our model provides a basis for manipulating cell signaling mechanisms to understand critical targets involved in MB dissemination.

FaRP cell distribution in the developing CNS suggests the involvement of FaRPs in all parts of the chromatophore control pathway in Sepia officinalis (Cephalopoda)

The FMRFamide-related peptide (FaRP) family includes a wide range of neuropeptides that have a role in many biological functions. In cephalopods, these peptides intervene in the peculiar body patterning system used for communication and camouflage. This system is particularly well developed in the cuttlefish and is functional immediately after hatching (stage 30). In this study, we investigate when and how the neural structures involved in the control of body patterning emerge and combine during Sepia embryogenesis, by studying the expression or the production of FaRPs. We detected FaRP expression and production in the nervous system of embryos from the beginning of organogenesis (stage 16). The wider FaRP expression was observed concomitantly with brain differentiation (around stage 22). Until hatching, FaRP-positive cells were located in specific areas of the central and peripheral nervous system (CNS and PNS). Most of these areas were implicated in the control of body patterns, suggesting that FaRPs are involved in all parts of the neural body pattern control system, from the ‘receptive areas’ via the CNS to the chromatophore effectors.

A Single Origin of the Central Nervous System?

As Denes et al. (2007) reveal in this issue, the expression profile and roles of genes that pattern the nervous system in embryos of chordates and annelids are surprisingly similar. This extraordinary conservation suggests that the patterning mechanism has been inherited largely unchanged from the bilaterian common ancestor and that the central nervous system, although dorsal in fish and ventral in worms, is an ancient characteristic of animals.

Development of swimming in the medicinal leech, the gradual acquisition of a behavior

Observing the development of behavior provides an assay for the developmental state of an embryo's nervous system. We have previously described the development of behaviors that were largely confined to one or a few segments. We now extend the work to a kinematic analysis of the development of swimming, a behavior that requires coordination of the entire body. When leech embryos first begin to swim they make little forward progress, but within several days they swim as effectively as adults. This increase in efficacy depends on changes in body shape and on improved intersegmental coordination of the swim central pattern generator. These kinematic details suggest how the swim central pattern generating circuit is assembled during embryogenesis.

Genetic analyses of essential genes in cytological region 61D1-2 to 61F1-2 of Drosophila melanogaster.

We performed a systematic mutagenesis screen for lethals in the genomic region 61D1-2 to 61F1-2 on chromosomal arm 3L of Drosophila melanogaster. Our genetic analyses revealed that this region contains eight essential complementation groups including trio, Glut1 and extra macrochaetae (emc). For the trio locus, 22 mutant alleles were identified, and all of the alleles analyzed resulted in defects in the central nervous system of embryos, indicating that trio functions in the control of axon extension or guidance. Western analysis showed that at least three proteins are derived from trio and also suggested that a polypeptide of over 200 kDa plays a crucial role in embryonic or larval development. In addition, a newly identified emc allele was associated with several defects in embryonic morphogenesis, including abnormalities in head involution, gut formation and dorsal closure, thus revealing multiple roles for emc in embryonic development. We also performed preliminary phenotypic analyses on stocks bearing mutations belonging to the other lethal complementation groups. These genes function in essential biological events, but the mutations do not result in gross morphological changes during embryonic stages. The present study extends our knowledge of the Drosophila gene set, by identifying most of the essential genes in the chromosomal region 61D1-2 to 61F1-2.

Primary culture of neural precursors from the ovine central nervous system (CNS)

The present study demonstrates that bipotential neural precursors isolated from an early developmental stage of the sheep embryo nervous system can be maintained in vitro in an undifferentiated state for a long period. These precursors multiplied under the action of epidermal growth factor and basic fibroblast growth factor and formed free-floating aggregates of nestin-immunoreactive cells, called neurospheres. These precursors can undergo predominantly neural or glial differentiation according to the culture conditions. Medium supplemented with foetal calf serum mainly favoured cell differentiation predominantly into astrocytes, whereas the defined SATO medium favoured neuronal differentiation. Using various immunomarkers of neurones and astroglial cells, we described the course of differentiation of neuronal and astroglial cells in different culture conditions. The ability to grow neural precursors from common laboratory animals has been useful for studying the cellular and molecular mechanisms underlying the development of the central nervous system. Furthermore, neural progenitors are already being used for in vivo cell therapy in various neurodegenerative disorders. The ovine species is a well-known model for prion diseases, since scrapie is endemic in most countries and has been studied for a long time. In this respect, the availability of ovine neural precursors will add a new perspective to the study of the pathogenicity of prion diseases.

Effects and neuro-toxic mechanisms of 2, 2', 4, 4', 5, 5'-hexachlorobiphenyl and endosulfan in neuronal stem cells.

Endocrine disrupters are exogenous compounds thought to mimic the action of estrogen or other hormones and influence endocrine activity in the body (Juberg, 2000). These chemicals have adverse effects not only in the reproductive system but also in the central nervous system during development and throughout life. Polychlorinated biphenyls (PCBs) are a class of environmentally persistent and widespread halogenated hydrocarbons. It has been reported that PCBs are potential neurotoxicants. Endosulfan is an organochlorine insecticide that is extensively used to control pests in vegetables, cotton, and fruits. To determine the effect of 2, 2', 4, 4', 5, 5',-hexachlorobiphenyl(2, 4, 5-HCB) and endosulfan on embryo nervous system, we isolated neural stem cells from rat brain at embryonic day 17. Isolated neural stem cells showed pluripotenty. Stem cells could differentiate into neurons and glia. Neurite formation in endosulfan and 2, 4, 5-HCB treated cells. And it appeared to be decreased as compared with that in untreated cells. In order to know the neuro-toxic mechanisms of 2, 4, 5-HCB and endosulfan in neuronal stem cells, we investigated mitogen-activated protein kinase activity (MAPK) and gap junctional intercellular communication (GJIC). Endosulfan decreased the MAPK activity in dose dependent manner. Endosulfan and 2, 4, 5-HCB inhibited GJIC compared to the untreated cell by scrape loading dye transfer (SL/DT). 2, 4, 5-HCB and endosulfan decreased the expression of connexin 43 in dose dependent manner. These results indicated that 2, 4, 5-HCB and endosulfan may inhibit differentiation and proliferation of neural stem cells and gap junctional intercellular communication which play a crucial role in the maintenance of cellular homeostasis.

Detection of caspase-9 activation in the cell death of the Bcl-x-deficient mouse embryo nervous system by cleavage sites-directed antisera

Caspases, which play crucial roles during apoptosis, are activated from their inactive proforms in a sequential cascade of cleavage by other members of the caspase family. Caspase-9 is autoprocessed by the Apaf-1/cytochrome c pathway and acts at an early point in this cascade, whereas Bcl-xL, an antiapoptotic member of the Bcl-2 family, prevents activation of caspases in vitro. Little is known, however, about the relation between caspase-9 and Bcl-xL during development of the mammalian nervous system. We used antisera against two cleavage sites in mouse caspase-9 that recognize only the activated form of mouse caspase-9, and we examined immunohistochemically the activation of mouse caspase-9 in the nervous system of Bcl-x-deficient mouse embryos. Mouse caspase-9 is processed at both D 353 and D 368, but it is processed preferentially at D 368 during apoptosis of cultured cells induced by various stimuli and in the nervous system of Bcl-x-deficient mouse embryos. We show that Bcl-xL protects against caspase-9- and/or caspase-3-dependent apoptosis in the caudal portion of the ventral hindbrain, anterior horn cells, and dorsal root ganglia neurons of the normal mouse embryos and against caspase-9/caspase-3-independent apoptosis in the dorsal region of the nervous system including the dorsal spinal cord. Furthermore, we demonstrate that Bcl-xL blocks cytochrome c release from mitochondria, causing activation of caspase-9 in anterior horn cells and dorsal root ganglia neurons in mouse embryos at embryonic day 11.5.

A single allatostatin-immunoreactive neuron innervates skeletal muscles of several segments in the locust

In the nervous system of embryos and adult Locusta migratoria, somata, neurites within the ganglia, and axons leaving the thoracic ganglia show allatostatin immunoreactivity. The immunoreactive efferent axons divide to follow different nerve branches and form varicose terminals on skeletal muscles. In the adult locust, one pair of motor neurons is particularly prominent among the allatostatin-immunoreactive neurons. The somata are located symmetrically in a lateral position in the first abdominal neuromere of the fused metathoracic ganglion. Each neuron gives rise to five axon branches projecting into ipsilateral nerves. Three axons project posteriorly and exit through the dorsal nerves of the abdominal neuromeres A1, A2, and A3. One axon extends into the metathoracic neuromere and exits through metathoracic nerve 1 (N1). The fifth axon extends anteriorly through the connective into the mesothoracic ganglion, where it leaves through the mesothoracic N1. The targets of this neuron, among them the mesothoracic and metathoracic muscles M87, M88, M116 and the dorsal longitudinal muscles M81 and M112, are located in five different segments. In addition to supplying skeletal muscles, the neuron forms neurohaemal-like structures in the sheath of nerve branches. The authors call this neuron the common lateral neuron (CLN). The innervation of several muscles by Diploptera allatostatin 7-immunoreactive axon branches with a common cellular origin and the anatomy of one of the corresponding motor neurons in adults, the CLN, suggest that allatostatin acts as a modulator of neuromuscular parameters in insects by multisegmental direct innervation of skeletal muscles.

A single allatostatin‐immunoreactive neuron innervates skeletal muscles of several segments in the locust

In the nervous system of embryos and adult Locusta migratoria, somata, neurites within the ganglia, and axons leaving the thoracic ganglia show allatostatin immunoreactivity. The immunoreactive efferent axons divide to follow different nerve branches and form varicose terminals on skeletal muscles. In the adult locust, one pair of motor neurons is particularly prominent among the allatostatin-immunoreactive neurons. The somata are located symmetrically in a lateral position in the first abdominal neuromere of the fused metathoracic ganglion. Each neuron gives rise to five axon branches projecting into ipsilateral nerves. Three axons project posteriorly and exit through the dorsal nerves of the abdominal neuromeres A1, A2, and A3. One axon extends into the metathoracic neuromere and exits through metathoracic nerve 1 (N1). The fifth axon extends anteriorly through the connective into the mesothoracic ganglion, where it leaves through the mesothoracic N1. The targets of this neuron, among them the mesothoracic and metathoracic muscles M87, M88, M116 and the dorsal longitudinal muscles M81 and M112, are located in five different segments. In addition to supplying skeletal muscles, the neuron forms neurohaemal-like structures in the sheath of nerve branches. The authors call this neuron the common lateral neuron (CLN). The innervation of several muscles by Diploptera allatostatin 7-immunoreactive axon branches with a common cellular origin and the anatomy of one of the corresponding motor neurons in adults, the CLN, suggest that allatostatin acts as a modulator of neuromuscular parameters in insects by multisegmental direct innervation of skeletal muscles. J. Comp. Neurol. 413:507–519, 1999. © 1999 Wiley-Liss, Inc.

Dystrophin localization and gene expression in the developing nervous system of the chick.

The presence and distribution of dystrophin was studied in selected areas of the chick embryo nervous system and in primary cultures. Dystrophin was examined at the protein level by immunocytochemistry and at the transcriptional level by a semiquantitative reverse transcriptase-polymerase chain reaction analysis. Immunofluorescence staining shows that dystrophin is present early during embryogenesis in dorsal root ganglia, spinal cord, and ciliary ganglia and colocalizes with neurofilament subunits. Cultured dorsal root ganglion, spinal cord, and ciliary ganglion neurons show immunoreactivity for dystrophin, both in cell bodies and along fibers. Dystrophin mRNA level in ciliary and dorsal root ganglia is higher than in spinal cord throughout development and shows a tissue-specific pattern of expression. In primary cultures of dorsal root ganglia and ciliary ganglia, dystrophin mRNA level increases with time in vitro. However, in spinal cord cultures, dystrophin mRNA drastically decreases with time in vitro, but it is significantly increased when embryonic muscle extract is added to the cultures. Our results show that dystrophin is present in neurons from different areas of embryonic chick nervous system and that its mRNA level is developmentally regulated both in vivo and in vitro.

Gene expression of MASH-1, MATH-1, neuroD and NSCL-2, basic helix-loop-helix proteins, during neural differentiation in P19 embryonal carcinoma cells.

We examined the gene expression of MASH-1, MATH-1, neuroD and NSCL-2 during neural differentiation of P19 embryonal carcinoma cells using reverse transcription-polymerase chain reaction and high performance liquid chromatography. These proteins are members of basic helix-loop-helix transcription factor family and their expressions are reported to be transient and restricted in the nervous system during early neurogenesis. Retinoic acid (RA-, 1 microM)-treatment and aggregation for 4 days induced and greatly increased MASH-1, neuroD and NSCL-2 mRNA in P19 cells. The increases peaked at day 3, 4 and 5, respectively. RA-treatment increased MATH-1 mRNA slightly. mRNA of MAP2, a neural differentiation marker, were increased by RA-treatment and the increases reached to the plateau at day 5. The results indicate that the gene expression of MASH-1, MATH-1, neuroD and NSCL-2 during neural differentiation in P19 cells is transient and the order is similar to that in the mouse embryo nervous system as previously reported.

A novel serine/threonine kinase gene, Gek1, is expressed in meiotic testicular germ cells and primordial germ cells.

We have isolated a novel serine/ threonine kinase gene designated Gek1 from mouse primordial germ cell-derived embryonic germ cell. Gek1 is preferentially expressed in meiotic testicular germ cells and primordial germ cells. Gek1 mRNA is also detected in several other tissues, including hematopoietic organs in adult mice and central nervous system in embryos. The Gek1 cDNA encodes a protein with the consensus sequence of the catalytic domain of protein kinases in its N-terminal region. The deduced amino acid sequence of Gek1 in the kinase domain is related to those encoded by the Saccharomyces cerevisiae STE20, CDC15, and Drosophila melanogaster ninaC. The patterns of expression and the structural features of Gek1 suggest that the gene product is involved in signal transduction or nuclear division of germ cells and other proliferating cells. We also show that Gek1 locates on chromosome 11, near the wr locus, showing neuronal and reproductive defects.

Wnt expression patterns in chick embryo nervous system

Several lines of evidence suggest that Wnt genes play a critical role in regulating development of the vertebrate embryo. To address the role that this family may play in the development of the chicken central nervous system (CNS), we have used a PCR based strategy to clone partial sequences for Wnt genes. At least six different Wnt genes are expressed in the developing CNS of the chick embryo. The domains of expression overlap either partially or completely, and are expressed in spatial domains that prefigure morphological subunits of the embryonic neural tube. Wnt-1 and Wnt-4 are first expressed in the open neural plate in the region of the presumptive mesencephalon. Wnt-3a expression is first observed in the rhombencephalic regions of the open neural plate. After neural tube closure, when the embryonic subdivisions of the neural tube became apparent, Wnt-1, Wnt-3a and Wnt-4 are all broadly expressed in partially overlapping domains in the mesencephalon and caudal diencephalon, as well as in the rhombencephalon and spinal cord. The mesencephalic expression patterns are subsequently modified such that Wnt-1 and Wnt-4 are expressed in a characteristic ring just rostral to the isthmus, at the mesencephalic/metencephalic junction; and Wnt-1 and Wnt-3a expression become restricted to the dorsal midline. Wnt-1, Wnt-3a, Wnt-4, Wnt-5a and Wnt-8b are expressed in one or two caudal subdivisions of the developing diencephalon, the synencephalon and posterior parencephalon, but do not extend ventral to the zona limitans interparencephalica. In contrast, Wnt-7b is expressed in the anterior parencephalon. Both Wnt-7b and Wnt-8b are expressed in telencephalic portions of the secondary prosencephalon. The timing and spatial distribution of Wnt-gene expression in the chick embryo further support the general hypothesis that Wnt genes play key roles in patterning the developing vertebrate nervous system.