RESUMO
The lingual surface potential (LSP), which hyperpolarizes in response to salt and bitter stimuli, is thought to be a bioelectrical signal associated with taste transduction in humans. In contrast, a recent study reported sweet and sour stimuli to evoke a depolarization of the LSP. We questioned the origin of such a depolarization because liquid junction potentials (JPs), which arise at the interfaces of recording electrode and taste solutions, are neglected in the report. We recorded the LSPs to sucrose and NaCl solutions on the human tongue using an Ag/AgCl electrode. To estimate JPs generated by each taste solution, we made an agar model to simulate the human tongue. The lingual surface was rinsed with a 10 mM NaCl solution that mimics the sodium content of the lingual fluid. In the human tongue, sucrose dissolved in distilled water evoked a depolarizing LSP that could be attributed to JPs, resulting from the change in electrolyte concentration of the taste solution. Sucrose dissolved in 10 mM NaCl solution evoked a hyperpolarizing LSP which became more negative in a concentration-dependent manner (300-1500 mM). Lactisole (3.75 mM), an inhibitor of sweet taste, significantly reduced the LSPs and decreased perceived intensity of sweetness by human subjects. The negative JPs generated by 100 mM NaCl in the agar model were not different from the LSPs to 100 mM NaCl. When the electrolyte environment on the lingual surface is controlled for JPs, the bioelectrical signal associated with sweet taste transduction is a hyperpolarizing potential.
Assuntos
Papilas Gustativas , Paladar , Epitélio , Humanos , Cloreto de Sódio/farmacologia , Sacarose/farmacologia , LínguaRESUMO
The corticospinal (CS) tract is essential for voluntary movement, but what we know about the organization and development of the CS tract remains limited. To determine the total cortical area innervating the seventh cervical spinal cord segment (C7), which controls forelimb movement, we injected a retrograde tracer (fluorescent microspheres) into C7 such that it would spread widely within the unilateral gray matter (to >80%), but not to the CS tract. Subsequent detection of the tracer showed that, in both juvenile and adult mice, neurons distributed over an unexpectedly broad portion of the rostral two-thirds of the cerebral cortex converge to C7. This even included cortical areas controlling the hindlimbs (the fourth lumbar segment, L4). With aging, cell densities greatly declined, mainly due to axon branch elimination. Whole-cell recordings from spinal cord cells upon selective optogenetic stimulation of CS axons, and labeling of axons (DsRed) and presynaptic structures (synaptophysin) through cotransfection using exo utero electroporation, showed that overgrowing CS axons make synaptic connections with spinal cells in juveniles. This suggests that neuronal circuits involved in the CS tract to C7 are largely reorganized during development. By contrast, the cortical areas innervating L4 are limited to the conventional hindlimb area, and the cell distribution and density do not change during development. These findings call for an update of the traditional notion of somatotopic CS projection and imply that there are substantial developmental differences in the cortical control of forelimb and hindlimb movements, at least in rodents.
Assuntos
Envelhecimento/fisiologia , Medula Cervical/fisiologia , Tratos Piramidais/crescimento & desenvolvimento , Medula Espinal/fisiologia , Animais , Animais Recém-Nascidos , Axônios/fisiologia , Contagem de Células , Membro Anterior/inervação , Membro Posterior/inervação , Vértebras Lombares , Camundongos , Movimento/fisiologia , Tratos Piramidais/fisiologiaRESUMO
KEY POINTS: Direct connections between corticospinal (CS) axons and motoneurons (MNs) appear to be present only in higher primates, where they are essential for discrete movement of the digits. Their presence in adult rodents was once claimed but is now questioned. We report that MNs innervating forearm muscles in infant rats receive monosynaptic input from CS axons, but MNs innervating proximal muscles do not, which is a pattern similar to that in primates. Our experiments were carefully designed to show monosynaptic connections. This entailed selective electrical and optogenetic stimulation of CS axons and recording from MNs identified by retrograde labelling from innervated muscles. Morphological evidence was also obtained for rigorous identification of CS axons and MNs. These connections would be transient and would regress later during development. These results shed light on the development and evolution of direct CS-MN connections, which serve as the basis for dexterity in humans. Recent evidence suggests there is no direct connection between corticospinal (CS) axons and spinal motoneurons (MNs) in adult rodents. We previously showed that CS synapses are present throughout the spinal cord for a time, but are eliminated from the ventral horn during development in rodents. This raises the possibility that CS axons transiently make direct connections with MNs located in the ventral horn of the spinal cord. This was tested in the present study. Using cervical cord slices prepared from rats on postnatal days (P) 7-9, CS axons were stimulated and whole cell recordings were made from MNs retrogradely labelled with fluorescent cholera toxin B subunit (CTB) injected into selected groups of muscles. To selectively activate CS axons, electrical stimulation was carefully limited to the CS tract. In addition we employed optogenetic stimulation after injecting an adeno-associated virus vector encoding channelrhodopsin-2 (ChR2) into the sensorimotor cortex on P0. We were then able to record monosynaptic excitatory postsynaptic currents from MNs innervating forearm muscles, but not from those innervating proximal muscles. We also showed close contacts between CTB-labelled MNs and CS axons labelled through introduction of fluorescent protein-conjugated synaptophysin or the ChR2 expression system. We confirmed that some of these contacts colocalized with postsynaptic density protein 95 in their partner dendrites. It is intriguing from both phylogenetic and ontogenetic viewpoints that direct and putatively transient CS-MN connections were found only on MNs innervating the forearm muscles in infant rats, as this is analogous to the connection pattern seen in adult primates.
Assuntos
Membro Anterior/inervação , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Neurogênese , Tratos Piramidais/fisiologia , Sinapses/fisiologia , Animais , Axônios/fisiologia , Feminino , Membro Anterior/fisiologia , Masculino , Músculo Esquelético/crescimento & desenvolvimento , Músculo Esquelético/inervação , Tratos Piramidais/crescimento & desenvolvimento , Ratos , Ratos WistarRESUMO
The GluN2B (GluRepsilon2/NR2B) and GluN2A (GluRepsilon1/NR2A) NMDA receptor (NMDAR) subtypes have been differentially implicated in activity-dependent synaptic plasticity. However, little is known about the respective contributions made by these two subtypes to developmental plasticity, in part because studies of GluN2B KO [Grin2b(-/-) (2b(-/-))] mice are hampered by early neonatal mortality. We previously used in vitro slice cocultures of rodent cerebral cortex (Cx) and spinal cord (SpC) to show that corticospinal (CS) synapses, once present throughout the SpC, are eliminated from the ventral side during development in an NMDAR-dependent manner. To study subtype specificity of NMDAR in this developmental plasticity, we cocultured Cx and SpC slices derived from postnatal day 0 (P0) animals with different genotypes [2b(-/-), Grin2a(-/-) (2a(-/-)), or WT mice]. The distribution of CS synapses was studied electrophysiologically and with a voltage-sensitive dye. Synapse elimination on the ventral side was blocked in WT(Cx)-2b(-/-)(SpC) pairs but not in WT(Cx)-2a(-/-)(SpC) or 2b(-/-)(Cx)-WT(SpC) pairs. CS axonal regression was also observed through live imaging of CS axons labeled with enhanced yellow fluorescent protein (EYFP) through exo utero electroporation. These findings suggest that postsynaptic GluN2B is selectively involved in CS synapse elimination. In addition, the elimination was not blocked in 2a(-/-) SpC slices, where Ca(2+) entry through GluN2B-mediated CS synaptic currents was reduced to the same level as in 2b(-/-) slices, suggesting that the differential effect of GluN2B and GluN2A in CS synapse elimination might not be explained based solely on greater Ca(2+) entry through GluN2B-containing channels.
Assuntos
Córtex Cerebral/fisiologia , Córtex Cerebral/ultraestrutura , Receptores de N-Metil-D-Aspartato/fisiologia , Medula Espinal/fisiologia , Medula Espinal/ultraestrutura , Sinapses/fisiologia , Animais , Córtex Cerebral/crescimento & desenvolvimento , Técnicas de Cocultura , Fenômenos Eletrofisiológicos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos ICR , Camundongos Knockout , Plasticidade Neuronal/fisiologia , Ratos , Receptores de N-Metil-D-Aspartato/deficiência , Receptores de N-Metil-D-Aspartato/genética , Medula Espinal/crescimento & desenvolvimentoRESUMO
Although corticospinal neurons are known to be distributed in both the primary motor and somatosensory cortices (S1), details of the projection pattern of their fibers to the lumbar cord gray matter remain largely uncharacterized, especially in rodents. We previously investigated the cortical area projecting to the gray matter of the fourth lumbar cord segment (L4) (L4 Cx) in mice. In the present study, we injected an anterograde tracer into multiple sites to cover the entire L4 Cx. We found that (1) the rostromedial part of the L4 Cx projects to the intermediate and ventral zones of the lumbar cord gray matter, (2) the lateral part projects to the medial dorsal horn, and (3) the caudal part projects to the lateral dorsal horn. We also found that the border between the rostromedial and caudolateral parts corresponds to the border between the agranular and granular cortex. Analysis of the somatotopic patterns formed by the cortical projection cells and the primary sensory neurons innervating the skin of the hindlimb and its related area suggests that the lateral part corresponds to the S1 hindlimb area and the caudal part to the S1 trunk area. Examination of thalamic innervation by the L4 Cx revealed that the caudolateral L4 Cx focally projects to the ventrobasal complex (VB) and the posterior complex (PO), while the medial L4 Cx widely projects to the PO but little to the VB. These findings suggest that the L4 Cx is parceled into subregions defined by the cytoarchitecture and subcortical projection.
Assuntos
Córtex Somatossensorial , Medula Espinal , Animais , Substância Cinzenta , Membro Posterior/inervação , Camundongos , Medula Espinal/fisiologia , TálamoRESUMO
We previously observed in rodents that during the 2nd postnatal week corticospinal axons make monosynaptic connections with motoneurons. Prior to that finding, it had been believed that such contacts only occur in higher primates. Although an in vitro electrophysiological study is prerequisite for studying the developmental time course of synaptic connections, the technical difficulty of reliably recording synaptic responses from spinal motoneurons in animals over 2â¯weeks old hampered the study. Instead, we used retrograde transsynaptic labeling with a genetically modified rabies virus to confirm the presence of direct corticomotoneuronal connections at an early developmental stage and to show that these connections were subsequently eliminated. However, determination of an accurate elimination time course and quantitative evaluation of synaptic connectivity cannot be achieved through viral-tracing experiments. For the present study, we improved the slice preparation procedure and maintenance of slice viability, which enabled us to record postsynaptic responses using the whole cell patch-clamp technique from retrogradely labeled forearm motoneurons up until postnatal week 7. We examined the extent of corticomotoneuronal monosynaptic connections and studied the time course of their accumulation and loss. Positive ratios of monosynaptic corticomotoneuronal EPSCs increased from P6 to P8 and then plateaued (P8-P13: 65%). Thereafter, the monosynaptic connections declined until P21, at which time they were no longer detected. The time course of the falling phase and elimination was confirmed by experiments using optogenetic stimulation. The timing of the elimination fell within the same range (P18-22) estimated in our earlier study using retrograde transsynaptic labeling.
Assuntos
Tratos Piramidais , Roedores , Animais , Axônios , Neurônios Motores , Técnicas de Patch-Clamp , SinapsesRESUMO
Here we describe methods for (a) collecting starfish during their breeding period; (b) maintaining adults with fully grown gonads in laboratory aquaria; (c) rearing fertilized eggs to brachiolaria larvae, and (d) inducing larvae to metamorphose into juveniles under laboratory conditions. Such protocols should facilitate various analyses of starfish development throughout the entire life cycle of these model organisms.
Assuntos
Asterina/crescimento & desenvolvimento , Animais , Aquicultura/instrumentação , Aquicultura/métodos , Asterina/embriologia , Desenho de Equipamento , Feminino , Larva/crescimento & desenvolvimento , Masculino , Metamorfose Biológica , Oócitos/citologia , OogêneseRESUMO
The corticospinal (CS) neurons projecting to the cervical cord distribute not only in motor-related cortical areas, but also in somatosensory areas, including the primary somatosensory cortex (S1). The exact functions of these widely distributed CS neurons are largely unknown, however. In this study, we injected mice with adeno-associated virus encoding membrane-binding fluorescent proteins to investigate the distribution of axons from CS neurons in different regions within a broad cortical area. We found that CS axons from the primary motor cortex (M1), the rostral part of S1 (S1r), and the caudal part of S1 (S1c) differentially project to specific compartments within the spinal gray matter of the seventh cervical cord segment: (a) M1 projects mainly to intermediate and ventral areas, (b) S1r to the mediodorsal area, and (c) S1c to the dorsolateral area. We also found that the projection from S1r, which corresponds to the forelimb area, largely overlaps the cutaneous afferent terminals from the forepaw (hand) in the dorsal horn, and we detected a similar relation between S1c and the trunk. Our findings suggest the existence of considerably fine somatotopic compartments within the dorsal horn that process somatosensation and descending information, which is provided mainly by S1 CS neurons and contribute to delicate control of sensory information in generation of movement.
Assuntos
Vias Aferentes/citologia , Substância Cinzenta/citologia , Tratos Piramidais/citologia , Córtex Somatossensorial/citologia , Medula Espinal/citologia , Animais , CamundongosRESUMO
The corticospinal (CS) tract emerged and evolved in mammals, and is essentially involved in voluntary movement. Over its phylogenesis, CS innervation gradually invaded to the ventral spinal cord, eventually making direct connections with spinal motoneurons (MNs) in higher primates. Despite its importance, our knowledge of the origin of the direct CS-MN connections is limited; in fact, there is controversy as to whether these connections occur in subprimate mammals, such as rodents. Here we studied the retrograde transsynaptic connection between cortical neurons and MNs in mice by labeling the cells with recombinant rabies virus. On postnatal day 14 (P14), we found that CS neurons make direct connections with cervical MNs innervating the forearm muscles. Direct connections were also detected electrophysiologically in whole cell recordings from identified MNs retrogradely-labeled from their target muscles and optogenetic CS stimulation. In contrast, few, if any, lumbar MNs innervating hindlimbs showed direct connections on P18. Moreover, the direct CS-MN connections observed on P14 were later eliminated. The transient CS-MN cells were distributed predominantly in the M1 and S1 areas. These findings provide insight into the ontogeny and phylogeny of the CS projection and appear to settle the controversy about direct CS-MN connections in subprimate mammals.
Assuntos
Channelrhodopsins/metabolismo , Neurônios Motores/fisiologia , Optogenética/métodos , Tratos Piramidais/fisiologia , Animais , Channelrhodopsins/genética , Desenvolvimento Embrionário , Feminino , Membro Anterior/crescimento & desenvolvimento , Membro Anterior/inervação , Vetores Genéticos/administração & dosagem , Membro Posterior/crescimento & desenvolvimento , Membro Posterior/inervação , Masculino , Camundongos , Técnicas de Patch-Clamp , Vírus da Raiva/fisiologiaRESUMO
Interest in chordate evolution has emphasized a need for a better understanding of the comparative neuroanatomy of invertebrate deuterostomes. However, molecular and genetic approaches to neurobiological studies in these groups are hampered by a lack of neuron-specific molecular markers. A monoclonal antibody, 1E11, is neuron specific and is useful in identification of neural structures in larvae and adults of echinoderms, hemichordates, and urochordates. To identify a neuron-specific gene product, we have characterized the antigen recognized by 1E11. In immunoblots and immunoprecipitations of neural tissue from adult Strongylocentrotus purpuratus, 1E11 recognizes a 57-kDa band. Tandem mass spectrometry of trypsin digests of the 57-kDa band permitted peptide mass mapping and sequencing of five peptides. All of the sequenced peptides, and 12 additional mass-mapped peptides, are found within the open reading frame of a cDNA encoding synaptotagmin B (Sp-SynB). In situ RNA hybridizations with synaptotagmin B probes with S. purpuratus larvae reveal a pattern of expression that is similar to that revealed by the antibody 1E11. Antibodies produced against a bacterially expressed Sp-SynB protein recognize a 57-kDa protein and colocalize with 1E11. When a full-length Sp-SynB cDNA is expressed in chicken embryonic cells, the cells become immunoreactive to 1E11. We conclude that synaptotagmin B is a gene expressed in neurons that has conserved epitopes in other invertebrate deuterostomes.
Assuntos
Expressão Gênica/fisiologia , Proteínas do Tecido Nervoso/metabolismo , Neurônios/fisiologia , Sinaptotagminas/metabolismo , Sequência de Aminoácidos , Animais , Anticorpos/metabolismo , Western Blotting/métodos , Embrião de Galinha , Drosophila , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Proteínas de Fluorescência Verde/metabolismo , Imuno-Histoquímica/métodos , Imunoprecipitação/métodos , Hibridização In Situ/métodos , Larva , Espectrometria de Massas/métodos , Peso Molecular , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/imunologia , Mapeamento de Peptídeos/métodos , Filogenia , RNA Mensageiro/biossíntese , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Ouriços-do-Mar , Sinaptotagminas/genéticaRESUMO
Neuronal plasticity is especially active in the young, during short windows of time termed critical periods, and loss of a critical period leads to functional limitations in the adults. The mechanism that governs the length of critical periods remains unknown. Here we show that levels of the NMDA receptor GluN2B subunit, which functions as a Ca2+ channel, declines in spinal cord synapses toward the end of the critical period for activity-dependent corticospinal synapse elimination. This period could be prolonged by blocking the decline of GluN2B, and after its termination the critical period could be reopened through upregulation of GluN2B. It is known that inhibitory neural activity increases with development in the CNS including the spinal cord. Suppression of the increasing inhibitory activity using low-dose strychnine also prolonged this critical period. During the strychnine-widened time window, Ca2+ influx through GluN2B channels returned to a level comparable to that seen during the critical period, though the level of GluN2B was slightly reduced. These findings indicate that loss of GluN2B subunits and the associated reduction in Ca2+ influx determines the end of the critical period in our in vitro CS system.
RESUMO
Self-sterility of solitary ascidians is a typical example of the allogeneic recognition, though its molecular mechanism remains an open question. In this paper we analyze the fertility between siblings from selfed and crossed eggs to understand the genetic basis of self-sterility in the ascidian, Ciona intestinalis. First, we show that the self-sterility is strict and stable, and the individuality expressed in gametes is highly diversified in the wild population that we used. Secondly, we show one-way cross-sterility and reciprocal cross-sterility within the siblings that are self-sterile but fertile with non-siblings. Thirdly, we show self-sterility and cross-sterility share some natures and both are closely related to the sperm capacity not to bind to the vitelline coat of the autologous eggs or the eggs sterile to the sperm concerned. In all, this paper shows that the self-sterility is genetically governed by a multiple-locus system, and that most probably individual-specific determinants are haploid expression in sperm and diploid expression in eggs, given they recognize self but not non-self.
Assuntos
Ciona intestinalis/genética , Ciona intestinalis/fisiologia , Fertilização/genética , Fertilização/fisiologia , Ácidos/farmacologia , Animais , Feminino , Fertilização/efeitos dos fármacos , Infertilidade/genética , Masculino , Interações Espermatozoide-Óvulo , Espermatozoides/metabolismo , Espermatozoides/fisiologia , Fatores de Tempo , Membrana Vitelina/efeitos dos fármacos , Membrana Vitelina/metabolismoRESUMO
Axonal regression is utilized to refine neuronal circuits during development, but the dynamic properties of such regression remain largely unknown. We used confocal time-lapse imaging to examine the regression of single enhanced yellow fluorescent protein-labeled axons in corticospinal slice cocultures. By acquiring images at long (1 day) and short (30-60 min) intervals on days 5-13 in vitro, we detected three types of regressive events: 1) retractions, 2) amputations (referred to as autoaxotomy), and 3) degeneration. Retractions proceeded at some constant rate for up to 3 hours and then paused or switched to another constant rate, apparently shifting stepwise among three retraction rates (6, 12, 17 microm/hours). Autoaxotomy was a previously unreported strategy for regression. It occurred spontaneously, either at a proximal branch neck or at a distal end. Axons also underwent a form of degeneration that had several novel characteristics. Degenerating axons showed bright bead-like spots arranged at 3-9-microm intervals. The gaps were much larger than the spot size, and there was no prior sign of damage (e.g., swelling). Each spot's fluorescence intensity often waxed and waned, with its position unchanged. Degeneration progressed without clear proximal-to-distal directionality and was complete within 3-4 hours. Quantitative analysis of daily branch regression showed that branches almost always regressed up to their branch point or stopped before it, thereby keeping the branch point stable. This branch-point stability was retained for all three regression strategies observed, suggesting that the fate of each branch is determined relatively independently during the development of axonal arborization.
Assuntos
Axônios/patologia , Córtex Cerebral/anatomia & histologia , Degeneração Neural/patologia , Neurônios/patologia , Tratos Piramidais/citologia , Medula Espinal/anatomia & histologia , Animais , Córtex Cerebral/citologia , Técnicas de Cocultura/métodos , Imunofluorescência , Microscopia Confocal , Neurônios/citologia , Tratos Piramidais/anatomia & histologia , Ratos , Medula Espinal/citologia , Fatores de TempoRESUMO
The nervous system of the brachiolaria larva of the starfish, Asterina pectinifera, was characterized using immunohistochemistry with the neuron-specific monoclonal antibodies 1E11 and 1F9 and an anti-serotonin antibody. The antigen recognized by 1F9 was determined by immunoprecipitation, peptide identification by mass spectrometry, and cDNA cloning as a novel START (steroidogenic acute regulatory protein [StAR]-related lipid transfer) domain-containing protein. Nerve cells are prominent in the brachiolar arms, ciliary bands, and adult rudiment. The brachiolar arms contain sensory-like nerve cells in the adhesive papillae, flask-shaped nerve cells in the adhesive disk, and bundles of fibers with branches interconnecting them. In the ciliary bands, nerve cells are interconnected with axon bundles along the ciliary bands and some neurons send fibers toward the oral and aboral epidermis. These neural components of the ciliary bands are regionally modified to form masses such as lateral and oral ganglia. The future aboral epidermis of the adult rudiment forms a nerve plexus with cell bodies enriched over spicules. Serotonergic nerve cell bodies are found throughout the nervous system except in the adhesive disk, the bipinnaria arms, and the adult rudiment. In addition, there are neural components in the esophagus and in the coelom where nerve fibers or bundles have distinct orientations with respect to the muscle fibers. The neuroanatomy of the brachiolaria suggests how it may function in controlling larval physiology and identifies intriguing problems on the origin of larval and adult nerves.
Assuntos
Asterina/anatomia & histologia , Gânglios dos Invertebrados/embriologia , Sistema Nervoso/embriologia , Animais , Western Blotting , Eletroforese em Gel de Poliacrilamida , Imuno-Histoquímica , Imunoprecipitação , Larva , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
It has been hypothesized by Barker that starfish brachiolaria larvae initiate metamorphosis by sensing of metamorphic inducing factor(s) with neural cells within the adhesive papillae on their brachiolar arms. We present evidence supporting Barker's hypothesis using brachiolaria larvae of the two species, Asterina pectinifera and Asterias amurensis. Brachiolaria larvae of these two species underwent metamorphosis in response to pebbles from aquaria in which adults were kept. Time-lapse analysis of A. pectinifera indicated that the pebbles were explored with adhesive papillae prior to establishment of a stable attachment for metamorphosis. Microsurgical dissections, which removed adhesive papillae, resulted in failure of the brachiolaria larvae to respond to the pebbles, but other organs such as the lateral ganglia, the oral ganglion, the adhesive disk or the adult rudiment were not required. Immunohistochemical analysis with a neuron-specific monoclonal antibody and transmission electron microscopy revealed that the adhesive papillae contained neural cells that project their processes towards the external surface of the adhesive papillae and they therefore qualify as sensory neural cells.
Assuntos
Asterias/crescimento & desenvolvimento , Asterina/crescimento & desenvolvimento , Metamorfose Biológica , Animais , Asterias/ultraestrutura , Asterina/ultraestrutura , Larva/crescimento & desenvolvimento , Larva/ultraestrutura , Microscopia Eletrônica de Transmissão , Microscopia de Fluorescência , Modelos BiológicosRESUMO
The nervous system development of the sea cucumber Stichopus japonicus was investigated to explore the development of the bilateral larval nervous system into the pentaradial adult form typical of echinoderms. The first nerve cells were detected in the apical region of epidermis in the late gastrula. In the auricularia larvae, nerve tracts were seen along the ciliary band. There was a pair of bilateral apical ganglia consisted of serotonergic nerve cells lined along the ciliary bands. During the transition to the doliolaria larvae, the nerve tracts rearranged together with the ciliary bands, but they were not segmented and remained continuous. The doliolaria larvae possessed nerves along the ciliary rings but strongly retained the features of auricularia larvae nerve pattern. The adult nervous system began to develop inside the doliolaria larvae before the larval nervous system disappears. None of the larval nervous system was observed to be incorporated into the adult nervous system with immunohistochemistry. Since S. japonicus are known to possess an ancestral mode of development for echinoderms, these results suggest that the larval nervous system and the adult nervous system were probably formed independently in the last common ancestor of echinoderms.
Assuntos
Proliferação de Células , Neurônios/citologia , Stichopus/embriologia , Animais , Diferenciação Celular/fisiologia , Imuno-Histoquímica , Larva/anatomia & histologia , Larva/citologia , Larva/crescimento & desenvolvimento , Sistema Nervoso/citologia , Sistema Nervoso/embriologia , Sistema Nervoso/crescimento & desenvolvimento , Stichopus/citologia , Stichopus/crescimento & desenvolvimentoRESUMO
By using a monoclonal antibody (4H11 Mab), we have investigated morphogenetic functions of a fibrous component of the blastocoelic extracellular matrix in relation to cellular activities during early development of the starfish Asterina pectinifera. The 4H11 fibers fill the blastocoele from the late-cleavage to late-gastrula stage and contain the 370-kDa proteinaceous molecule secreted only by the epithelial cells. When 4H11 Mab is introduced into the blastocoele of blastulae, the embryos reveal three distinct morphological abnormalities after the mid-gastrula stage: (1) Distribution of mesenchyme cells confined near the tip of the archenteron, (2) swelling of the posterior ectoderm, and (3) suppressed growth of the mouth, esophagus, and coelomic pouches. These abnormalities occur together with alterations in the distribution of the 4H11 fibers. In embryos recovering from the effect of 4H11 Mab, the mesenchyme cells rearrange the 4H11 fibers. We propose that 4H11 fibers play direct roles in the morphogenesis of starfish embryos by providing a dynamic scaffold not only for the mesenchyme cells but also for the epithelial cells. Moreover, 4H11 fibers have a resist force from within, in concert with the mesenchyme cells, to counter the bulging force intrinsic to the epithelia and hold the epithelia in specific positions, once the positions have been decided.