Roles of HNK-1 carbohydrate epitope and its synthetic glucuronyltransferase genes on migration of rat neural crest cells

Effects of local and systemic treatment with human natural killer-1 mimetic peptide (HNK-1) after ventral root avulsion and reimplantation in mice

Background

Spinal ventral root injuries generate significant motoneuron degeneration, which hinders full functional recovery. The poor prognosis of functional recovery can be attributed to the use or combination of different therapeutic approaches. Several molecules have been screened as potential treatments in combination with surgical reimplantation of the avulsed roots, the gold standard approach for such injuries. Among the studied molecules, human natural killer-1 (HNK-1) stands out as it is related to the stimulation of motor axon outgrowth. Therefore, we aimed to comparatively investigate the effects of local administration of an HNK-1 mimetic peptide (mp-HNK-1) and systemic treatment with ursolic acid (UA), another HNK-1 mimetic, after ventral root avulsion and reimplantation with heterologous fibrin biopolymer (HFB).

Methods

Female mice of the isogenic strain C57BL/6JUnib were divided into five experimental groups: Avulsion, Reimplantation, mp-HNK-1 (in situ), and UA (systemic treatment). Mice were evaluated 2 and 12 weeks after surgery. Functional assessment was performed every four days using the Catwalk platform. Neuronal survival was analyzed by cytochemistry, and glial reactions and synaptic coverage were evaluated by immunofluorescence.

Results

Treatment with UA elicited long-term neuroprotection, accompanied by a decrease in microglial reactions, and reactive astrogliosis. The neuroprotective effects of UA were preceded by increased glutamatergic and GABAergic inputs in the ventral spinal cord two weeks after injury. However, a single application of mp-HNK-1 had no significant effects. Functional analysis showed that UA treatment led to an improvement in motor and sensory recovery.

Conclusion

Overall, the results indicate that UA is neuroprotective, acting on glial cells and synaptic maintenance, and the combination of these findings led to a better functional recovery.

Progenitor Cell Heterogeneity in the Adult Carotid Body Germinal Niche

Somatic stem cells confer plasticity to adult tissues, permitting their maintenance, repair and adaptation to a changing environment. Adult germinal niches supporting somatic stem cells have been thoroughly characterized throughout the organism, including in central and peripheral nervous systems. Stem cells do not reside alone within their niches, but they are rather accompanied by multiple progenitor cells that not only contribute to the progression of stem cell lineage but also regulate their behavior. Understanding the mechanisms underlying these interactions within the niche is crucial to comprehend associated pathologies and to use stem cells in cell therapy. We have described a stunning germinal niche in the adult peripheral nervous system: the carotid body. This is a chemoreceptor organ with a crucial function during physiological adaptation to hypoxia. We have shown the presence of multipotent stem cells within this niche, escorted by multiple restricted progenitor cell types that contribute to niche physiology and hence organismal adaptation to the lack of oxygen. Herein, we discuss new and existing data about the nature of all these stem and progenitor cell types present in the carotid body germinal niche, discussing their role in physiology and their clinical relevance for the treatment of diverse pathologies.

Regenerative effects of human embryonic stem cell-derived neural crest cells for treatment of peripheral nerve injury

Surgical intervention is the current gold standard treatment following peripheral nerve injury. However, this approach has limitations, and full recovery of both motor and sensory modalities often remains incomplete. The development of artificial nerve grafts that either complement or replace current surgical procedures is therefore of paramount importance. An essential component of artificial grafts is biodegradable conduits and transplanted cells that provide trophic support during the regenerative process. Neural crest cells are promising support cell candidates because they are the parent population to many peripheral nervous system lineages. In this study, neural crest cells were differentiated from human embryonic stem cells. The differentiated cells exhibited typical stellate morphology and protein expression signatures that were comparable with native neural crest. Conditioned media harvested from the differentiated cells contained a range of biologically active trophic factors and was able to stimulate in vitro neurite outgrowth. Differentiated neural crest cells were seeded into a biodegradable nerve conduit, and their regeneration potential was assessed in a rat sciatic nerve injury model. A robust regeneration front was observed across the entire width of the conduit seeded with the differentiated neural crest cells. Moreover, the up-regulation of several regeneration-related genes was observed within the dorsal root ganglion and spinal cord segments harvested from transplanted animals. Our results demonstrate that the differentiated neural crest cells are biologically active and provide trophic support to stimulate peripheral nerve regeneration. Differentiated neural crest cells are therefore promising supporting cell candidates to aid in peripheral nerve repair.

Simple in vitro migration assay for neural crest cells and the opposite effects of all-trans-retinoic acid on cephalic- and trunk-derived cells

Here, we describe a simple in vitro neural crest cell (NCC) migration assay and the effects of all-trans-retinoic acid (RA) on NCCs. Neural tubes excised from the rhombencephalic or trunk region of day 10.5 rat embryos were cultured for 48 h to allow emigration and migration of NCCs. Migration of NCCs was measured as the change in the radius (radius ratio) calculated from the circular spread of NCCs between 24 and 48 h of culture. RA was added to the culture medium after 24 h at embryotoxic concentrations determined by rat whole embryo culture. RA (10 μM) reduced the migration of cephalic NCCs, whereas it enhanced the migration of trunk NCCs, indicating that RA has opposite effects on these two types of NCCs.

Regulated expression and neural functions of human natural killer-1 (HNK-1) carbohydrate

Human natural killer-1 (HNK-1) carbohydrate, comprising a unique trisaccharide HSO(3)-3GlcAβ1-3Galβ1-4GlcNAc, shows well-regulated expression and unique functions in the nervous system. Recent studies have revealed sophisticated and complicated expression mechanisms for HNK-1 glycan. Activities of biosynthetic enzymes are controlled through the formation of enzyme-complexes and regulation of subcellular localization. Functional aspects of HNK-1 carbohydrate were examined by overexpression, knockdown, and knockout studies of these enzymes. HNK-1 is involved in several neural functions such as synaptic plasticity, learning and memory, and the underlying molecular mechanisms have been illustrated upon identification of the target carrier glycoproteins of HNK-1 such as the glutamate receptor subunit GluA2 or tenascin-R. In this review, we describe recent findings about HNK-1 carbohydrate that provide further insights into the mechanism of its expression and function in the nervous system.

Development of the juxta-oral organ in rat embryo

The aim of this work is to clarify the development and morphology of the juxta-oral organ (JOO) in rat embryos from Day (E)14 to 19. Furthermore, in the region of the JOO, an analysis was made of the expression of the monoclonal antibody HNK-1, which recognizes cranial neural-crest cells. In this study, we report that JOO develops from an epithelial condensation at the end of the transverse groove of the primitive mouth at E14. During E15, it invaginates and is disconnected from the oral epithelium. At E16, the JOO forms an solid epithelial cord with three parts (anterior, middle, and posterior) and is related to the masseter, temporal, medial pterygoid, and tensor veli palatini muscles. During E17-19, no significant changes were detected in their position. Both the mesenchyme caudal to the anlage of the JOO at E14, as well as the mesenchyme that surrounds the bud of the JOO at E15, expressed positivity for HNK-1. Our results suggest that the mesenchyme surrounding the JOO at E15 could emit some inductive signal for the JOO to reach its position at E16. This work shows for the first time that the cranial neural-crest-derived mesenchyme participates in the development of the JOO.

Proteoglycans in stem cells

The remarkable promise of pluripotent and multipotent stem cells (SCs) imparts tremendous optimism for advancement of regenerative medicine, developmental biology, and drug discovery. Perhaps the greatest challenge is to finely direct, control, and command their differentiation. As those processes are managed on many levels, including genomic, transcriptomic, and epigenomic, examination of all of these components will yield powerful tools for manipulation of SCs. Carbohydrates surround all cells, including SCs as a glycocalyx. Of particular interest is the class of carbohydrates known as proteoglycans (PGs), which are a diverse group of glycoconjugates consisting of core protein with one or more glycosaminoglycan (GAG) chains attached. They are primarily located in the extracellular matrix as well as at cell surfaces, where they are bound or anchored to the membrane through their core proteins. GAG chains are linear, anionic, and highly heterogeneous carbohydrates consisting of repeating disaccharides. PGs facilitate interaction of cells with the extracellular environment by interacting with chemokines, growth factors, and other signaling molecules. Core proteins are involved in many signaling pathways, both individually, as well as through attached proteins via GAG-mediated interactions. These essential and accessible functions make PGs an excellent target for manipulating SCs and guiding their fate. Studying the role of PGs in cell development will yield valuable insight into the mechanism of SC differentiation and suggest approaches toward directing those pathways. Such studies may also help identify valuable markers for distinguishing between various cell populations during differentiation.

Prenatal zinc deficiency: influence on heart morphology and distribution of key heart proteins in a rat model

The etiology of congenital heart disease is multifactorial, with genetics and nutritional deficiencies recognized as causative agents. Maternal zinc (Zn) deficiency is associated with an increased risk for fetal heart malformations; however, the contributing mechanisms have yet to be identified. In this study, we fed pregnant rats a Zn-adequate diet (ZnA), a Zn-deficient (ZnD), or a restricted amount of Zn adequate diet (RF) beginning on gestation day (GD) 4.5, to examine whether increased cell death and changes in cardiac neural crest cells (NCC) play a role in Zn deficiency-induced heart defects. Fetuses were collected on GD 13.5, 15.5, and 18.5 and processed for GATA-4, FOG-2, connexin-43 (Cx43), HNK-1, smooth muscle alpha-actin (SMA) and cleaved caspase-3 protein expression. Fetuses from ZnA-fed dams showed normal heart development, whereas fetuses from dams fed with the ZnD diet exhibited a variety of heart anomalies, particularly in the region of the outflow tract. HNK-1 expression was lower than normal in the hearts of GD13.5 and 15.5 ZnD fetuses, particularly in the right atrium and in the distal tip of the interventricular septum. Conversely, Cx43 immunoreactivity was increased throughout the heart in fetuses from ZnD dams compared to fetuses from control dams. The distribution and intensity of expression of SMA, GATA-4, FOG-2, and markers of apoptosis were similar among the three groups. We propose that Zn deficiency induced alterations in the distribution of Cx43 and HNK-1 in fetal hearts contribute to the occurrence of the developmental heart anomalies.

Transferring genes into cultured mammalian embryos by electroporation

Mammalian whole embryo culture (WEC) was developed long before transgenic and gene targeted animals are widely used. Electroporation (EP) into cultured rodent embryos has expanded the potential to analyze gene functions in mammalian embryos by transferring exogenous plasmid vectors or small nucleotides in region- and stage-specific ways. This method is quite simple, and therefore enables us to analyze gene functions more quickly than genetic manipulation. In this review, we introduce combinatorial methods of WEC and EP, and summarize various applications in developmental neurobiology.

Synthesis and Evaluation of Dual Wavelength Fluorescent Benzo[b]thiophene Boronic Acid Derivatives for Sugar Sensing

Cell surface glycoproteins have been known to play very important roles in various physiologic and pathologic processes. Small molecule compounds capable of carbohydrate recognition can be very useful for the development of sensing, diagnostic, and therapeutic agents. Along this line, we are interested in developing water-soluble fluorescent boronic acid compounds for carbohydrate recognition. As such, a series of benzo[b]thiophene boronic acid derivatives have been synthesized and their fluorescent properties analyzed at physiologic pH. Benzo[b]thiophene derivatives were found to be a new type of fluorescent reporter compounds capable of dual fluorescent emission under physiologic pH conditions. Compounds 1, 3, 4, 5, and 6 showed unusual emission wavelength shifts upon binding of sugars. These boronic acids will be useful tools for building glycoprotein biosensors for biologic applications.

Role of a transcription factor Pax6 in the developing vertebrate olfactory system

The olfactory system is responsible for capturing and processing odorant information, which significantly influences a variety of behaviors in animals. The vertebrate olfactory system consists of several neuronal components including the olfactory epithelium, olfactory bulb and olfactory cortex, which originate from distinct embryonic tissues. The transcription factor Pax6 is strongly expressed in the embryonic and postnatal olfactory systems, and regulates neuronal specification, migration and differentiation. Here we review classical and recent studies focusing on the role of Pax6 in the developing olfactory system, and highlight the cellular and molecular mechanisms underlying the highly coordinated developmental processes of the vertebrate olfactory system.

Neurospheres from human adipose tissue transplanted into cultured mouse embryos can contribute to craniofacial morphogenesis: a preliminary report

Adipose-derived stromal cells (ASCs) are one of the most promising stem cell populations that differentiate into the mesodermal as well as neural lineages in vitro. In this study, we examined the neural differentiating potential of human ASCs by a neurosphere culture method. Neurospheres derived from human ASCs expressed Nestin and Musashi-1 genes, which are marker genes for neural stem cells. When these cells were labeled with green fluorescent protein gene transfection by Sendai virus vector and transplanted into the head region of mouse embryos using a whole embryo culture system, these cells were incorporated into the craniofacial development. Some transplanted cells appeared to migrate along the second branchial arches, implicating some similarity to the cranial neural crest cells. Although preliminary, our results support an idea that ASC-derived neurospheres have properties of neural progenitors in vitro and in vivo.

The expression and functions of glycoconjugates in neural stem cells

The mammalian central nervous system is organized by a variety of cells such as neurons and glial cells. These cells are generated from a common progenitor, the neural stem cell (NSC). NSCs are defined as undifferentiated neural cells that are characterized by their high proliferative potential while retaining the capacity for self-renewal and multipotency. Glycoconjugates carrying carbohydrate antigens, including glycoproteins, glycolipids, and proteoglycans, are primarily localized on the plasma-membrane surface of cells and serve as excellent biomarkers at various stages of cellular differentiation. Moreover, they also play important functional roles in determining cell fate such as self-renewal, proliferation, and differentiation. In the present review, we discuss the expression pattern and possible functions of glycoconjugates and carbohydrate antigens in NSCs, with an emphasis on stage-specific embryonic antigen-1, human natural killer antigen-1, polysialic acid-neural cell-adhesion molecule, prominin-1, gp130, chondroitin sulfate proteoglycans, heparan sulfate proteoglycans, cystatin C, galectin-1, glycolipids, and Notch.

Defects in aortic fusion and craniofacial vasculature in the holoprosencephalic mouse embryo under inhibition of sonic hedgehog signaling

Sonic hedgehog (Shh) is a well-known morphogen indispensable in facial and nervous development, and recently it has also garnered much attention as a potent angiogenic factor. We previously created an animal model of holoprosencephaly by administration of cyclopamine, a specific inhibitor of hedgehog signaling, to the mouse embryos cultured in vitro, and found several types of angiogenic defects. In this study, we focused on other angiogenic phenotypes in the same model. When cyclopamine was added for embryonic day (E) 8.0-9.5, a pair of immature dorsal aortae, which normally fuse to form the single aorta by E9.5, remained to be separated. Expressions of vascular endothelial growth factor and bone morphogenetic protein 4, putative mediators of aortic fusion, were also reduced around the aorta by blockade of Shh signaling. When cyclopamine was added for E8.5-10.5, vessels on the surface of craniofacial region (possibly external cardinal veins) were extended and malformed. These results suggest that Shh signaling is essential for some aspects of embryonic angiogenesis, and that pathophysiology of holoprosencephaly may involve, at least in part, the Shh-dependent angiogenesis.

Critical time window of hedgehog-dependent angiogenesis in murine yolk sac

Hedgehog family was reported to be involved in murine yolk sac angiogenesis. However, it has not been clarified whether impaired angiogenesis under hedgehog signaling blockade is attributable to true defect in angiogenic process or just a sequel of earlier vasculogenic abnormalities. In the present study, we examined the effects of stage-specific inhibition of hedgehog cascade on vascular morphogenesis by applying cyclopamine or jervine to culture media of whole embryo culture system from embryonic days 8.0 until 9.5. Whole-mount immunostaining revealed that cyclopamine or jervine treatment in a narrow time window impaired angiogenic remodeling such as ramification into large and small branches and pericyte recruitment, although vasculogenesis was grossly normal. Molecular analyses suggest that indian hedgehog in the yolk sac endoderm regulates the induction of VEGF, Flk-1 and Notch-1. Our results indicate that hedgehog signaling is indispensable for mouse yolk sac angiogenesis, even when vasculogenesis is not perturbed.

Baalc, a marker of mesoderm and muscle

Transcripts of the Brain and Acute Leukemia, Cytoplasmic (BAALC) gene are expressed in human neuroectodermal tissues and in CD34-positive bone marrow cells. High transcript levels occur in leukemic blasts from some patients with acute myeloid leukemia (AML), where high expression is an independent marker of poor prognosis. To gain insight into the hitherto unknown function of BAALC/Baalc, we studied its protein expression in embryonic and adult mouse tissue by immunohistochemical analysis. Baalc protein was mainly expressed in developing and mature muscle cells (cardiac, skeletal, and smooth) beginning on day E9 (heart). Signal was seen in the pre-muscle mesodermal cells of the dermatomyotome regions, and the derivatives of the lateral plate and intermediate mesoderm such as smooth muscle wall of the esophagus, stomach, the gut tube, bronchi, small blood vessels, and urinary bladder. This pattern continued through the late embryonic stages into adulthood. Baalc appeared to localize in the cytoplasm, adjacent to the cell membrane. This is distinctly observed in adult skeletal muscle cells. Baalc co-localized with known muscle-associated proteins but not with neural crest or neuronal markers. Scattered expression in adult bone marrow hematopoietic cells and weak expression in the brain neuropil also occurred. In conclusion, BAALC/Baalc is a marker of the mesodermal lineage, especially muscle.

Characterization of glycoconjugate antigens in mouse embryonic neural precursor cells

Neuronal and glial cells organizing the central nervous system (CNS) are generated from common neural precursor cells (NPCs) during neural development. However, the expression of cell-surface glycoconjugates that are crucial for determining the properties and biological function of these cells at different stages of development has not been clearly defined. In this study, we investigated the expression of several stage-specific glycoconjugate antigens, including several b-series gangliosides GD3, 9-O-acetyl GD3, GT1b and GQ1b, stage-specific embryonic antigen-1 (SSEA-1) and HNK-1, in mouse embryonic NPCs employing immunocytochemistry and flow cytometry. In addition, several of these antigens were positively identified by chemical means for the first time. We further showed that the SSEA-1 immunoreactivity was contributed by both glycoprotein and glycolipid antigens, and that of HNK-1 was contributed only by glycoproteins. Functionally, SSEA-1 may participate in migration of the cells from neurospheres in an NPC cell culture system, and the effect could be repressed by anti-SSEA-1 antibody. Based on this observation, we identified beta1 integrin as one of the SSEA-1 carrier glycoproteins. Our data thus provide insights into the functional role of certain glycoconjugate antigens in NPCs during neural development.

Changes in angiogenic gene expression in a case of expanded capillary malformation: does an expanded capillary malformation grow?

We examined a 59-year-old woman with a capillary malformation (CM) in her thigh, which was serially excised. Interestingly, the remnant CM after the first excision was enlarged at the time of the second excision. To investigate whether this phenomenon was caused by mere passive expansion or regrowth, the CM specimens of the first operation (nonexpanded) and the second operation (expanded) were examined. Expressions of angiogenic genes Tie2 and Angiopoietin-1 were up-regulated within the expanded CM compared with the nonexpanded lesion, suggesting angiogenesis in the expanded CM. Expression pattern of the endothelial marker von Willebrand factor and the capillary densities were unchanged after the excision, suggesting that angiogenesis seen in the expanded CM resulted in reorganization of vascular networks. We consider that our data support a hypothesis that the expanded lesion in this case was caused by regrowth, not a passive expansion, of the CM.

Angiogenesis within the developing mouse neural tube is dependent on sonic hedgehog signaling: possible roles of motor neurons

Embryonic morphogenesis of vascular and nervous systems is tightly coordinated, and recent studies revealed that some neurogenetic factors such as Sonic hedgehog (Shh) also exhibit angiogenetic potential. Vascularization within the developing mouse neural tube depends on vessel sprouting from the surrounding vascular plexus. Previous studies implicated possible roles of VEGF/Flk-1 and Angiopoietin-1(Ang-1)/Tie-2 signaling as candidate molecules functioning in this process. Examining gene expressions of these factors at embryonic day (E) 9.5 and 10.5, we unexpectedly found that both VEGF and Ang-1 were expressed in the motor neurons in the ventral neural tube. The motor neurons were indeed located in the close vicinity of the infiltrating vessels, suggesting involvement of motor neurons in the sprouting. To substantiate this possibility, we inhibited induction of the motor neurons in the cultured mouse embryos by cyclopamine, a Shh signaling blocker. The vessel sprouting was dramatically impaired by inhibition of Shh signaling, together with nearly complete loss of the motor neurons. Expression of Ang-1, but not VEGF, within the neural tube was remarkably reduced in the cyclopamine treated embryos. These results suggest that the neural tube angiogenesis is dependent on Shh signaling, and mediated, at least in part, by the Ang-1 positive motor neurons.

Craniofacial anomalies of the cultured mouse embryo induced by inhibition of sonic hedgehog signaling: an animal model of holoprosencephaly

The pathogenesis of holoprosencephaly is multifactorial, and blockage of Sonic hedgehog signaling is one of the most important causative factors in animal models and human cases. In this study, the authors analyzed facial anomalies of mouse embryos, which were cultured in vitro and exposed to cyclopamine, an alkaloid blocker of Sonic hedgehog signaling. When cultured with cyclopamine for embryonic day 8.5 to 10.5, the whole body size was smaller than normal, and the distance and angle between the nasal placodes were remarkably reduced. Extension of the cranial surface vessels also was noted. No cyclopia was observed. Migration of the cranial neural crest cells seemed to be intact. Expressions of Patched-1 and Gli-1, downstream genes of Sonic hedgehog signaling, also were down-regulated in in situ hybridization and real-time reverse transcriptase-polymerase chain reaction analyses. The authors consider that these facial anomalies represent milder phenotypes of holoprosencephaly.

Identification of a novel type II classical cadherin: Ratcadherin19 is expressed in the cranial ganglia and Schwann cell precursors during development

To identify a novel type II classical cadherin, we searched the genome database and found rat cadherin19 (cad19) with high similarity to human cadherin19. We also found nucleotide sequences corresponding to rat cad19 in mouse and chicken genomes. In situ hybridization of rat cad19 revealed that rat cad19 mRNA was initially expressed in cephalic neural crest cells, and then in the cranial ganglia, migrating trunk neural crest cells, the nascent dorsal root ganglia, and the sympathetic ganglia. Expression of cad19 overlapped with that of neural crest markers, including Sox10 and AP-2, but cad19 expression was confined to subpopulations of the neural crest-derived cells, those typically observed in the satellite glia at the periphery of the ganglia and Schwann cell precursors along the peripheral nerves. cad19 mRNA was not detected in cells expressing Phox2b, an epibranchial placode-derived neurons, nor in those expressing neuronal markers such as Hu protein. These observations suggest that cad19 is expressed in neural crest-derived, non-neuronal cells. Although the expression of cad19 mRNA persisted in Schwann cell precursors at E14.5, it was no longer detected in maturing Schwann cells at later stages. These results suggest that cad19 is an evolutionarily conserved cadherin and may be involved in the early development of Schwann cells in the peripheral nervous system.