Biomedical subjects

D S Sakaguchi

Publications and source records attributed to D S Sakaguchi.

25 records · Page 2Linked to original sources

PubMed1989

Primary structure and developmental expression of a large cytoplasmic domain form of Xenopus laevis neural cell adhesion molecule (NCAM).

The neural cell adhesion molecule, (NCAM), is involved in cell-cell interactions during development of the vertebrate nervous system. NCAM exists in multiple protein forms and these are selectively expressed in different cells and at different times during development. Here we report the complete amino acid sequence of the large cytoplasmic form of Xenopus laevis NCAM, derived from a full-length cDNA clone. Using specific probes the expression of different NCAM transcripts during Xenopus embryogenesis has been examined. We find that transcripts encoding the large cytoplasmic domain form of NCAM exist in maternal RNA and that these are the only significant NCAM transcripts present until late gastrula when transcripts encoding the small cytoplasmic domain form of NCAM are first detected. No RNA encoding the small surface domain form of NCAM is detected during early development. These results indicate that the expression of NCAM sequences during early development of Xenopus differs from that described in other species.

Amino Acid Sequence↗

PubMed1989

The development of retinal ganglion cells deprived of their targets.

The influence of central targets on the morphological differentiation of retinal ganglion cells was investigated in Xenopus laevis. Since the ganglion cells mature into distinct morphological subtypes after their axons have reached their central targets, it is possible that the target tissues may influence or specify this aspect of neuronal cell development. To test this idea, Xenopus eyebuds were target-deprived by transplantation to the flank region of host embryos where they developed ectopically. The grafted eyes grew at normal rates, but could not make any projections into the central nervous system. To examine the morphological differentiation of the retinal ganglion cells their structures were revealed using an in vitro retinal preparation and intracellular injections of the dye Lucifer yellow. The elaboration and maturation of ganglion cell dendrites were found to be indistinguishable between control and transplanted eyes throughout development. Thus, the development of retinal ganglion cells into distinct morphological classes can occur even when their axons do not interact with the appropriate central targets.

Animals↗

PubMed1989

Growth cone interactions with a glial cell line from embryonic Xenopus retina.

We have isolated a nonneuronal cell line from Xenopus retinal neuroepithelium (XR1 cell line). On the basis of immunocytochemical characterization using monoclonal antibodies generated in our laboratory as well as several other glial-specific antibodies, we have established that the XR1 cells are derived from embryonic astroglia. A monolayer of XR1 cells serves as an excellent substrate upon which embryonic retinal explants attach and elaborate neurites. This neurite outgrowth promoting activity appears not to be secreted into the medium, as medium conditioned by XR1 cells is ineffective in promoting outgrowth. Cell-free substrates were prepared to examine whether outgrowth promoting activity is also associated with the XR1 extracellular matrix (ECM). Substrates derived from XR1 cells grown on collagen are still capable of promoting outgrowth following osmotic shock and chemical extraction. This activity does not appear to be associated with laminin or fibronectin. Scanning electron microscopy was used to examine growth cones of retinal axons on XR1 cells and other substrates that supported neurite outgrowth. Growth cones and neurites growing on a monolayer of XR1 cells, or on collagen conditioned by XR1 cells, closely resemble the growth cones of retinal ganglion cells in vivo. A polyclonal antiserum (NOB1) generated against XR1 cells effectively and specifically inhibits neurite outgrowth on XR1-conditioned collagen. We therefore propose that neurite outgrowth promoting factors produced by these cells are associated with the extracellular matrix and may be glial specific.

Animals↗

PubMed1988

A glial cell line promotes the outgrowth of neurites from embryonic Xenopus retina.

A glial cell line (XR1 cell line) derived from Xenopus retinal neuroepithelium was examined for neurite outgrowth promoting activity. A monolayer of the XR1 cells serves as an excellent substrate upon which embryonic retinal explants attach and freely elaborate neurites. The XR1 neurite outgrowth promoting activity is not secreted into the medium, but is laid down directly on the substrate where it remains active after lysing the cells by hypoosmotic shock. A polyclonal antiserum raised against membranes of the XR1 cells was effective in blocking neurite outgrowth on XR1 conditioned collagen. It is proposed that the neurite outgrowth promoting factors produced by the XR1 cells are associated with the extracellular matrix and possibly glial specific.

Animals↗

PubMed1985

Map formation in the developing Xenopus retinotectal system: an examination of ganglion cell terminal arborizations.

Single axonal arbors of retinal ganglion cells have been stained by injecting cobalt extracellularly into the retinae of Xenopus embryos and tadpoles. The axonal endings of the earliest retinal axons to arrive in the midbrain were usually simple in appearance, often ended in growth cones, and terminated in tectal regions appropriate to their location in the eye. Thus, a topographic projection exists very early in the development (stages 37 to 39) of the projection, before the elaboration of complex axonal arbors. Retinal axons began acquiring more mature features, exemplified by the elaboration of terminal arbors, by stage 39. The arbors of most ganglion cells were elongated in the rostral-to-caudal dimension during early larval life (stages 40 to 45) and covered a large portion of tectal neuropil. During mid-larval stages (stages 46 to 50), arbors covered a relatively smaller proportion of the tectal neuropil. A quantitative analysis of this change suggests that the apparent decrease in size of the arbors, with respect to the tectum, is due to rapid growth of tectal neuropil and not due to retraction of an initially diffuse arbor. Thus, the refinement in targeting of axonal arbors during development is a phenomenon distinct from that seen during regeneration.

Animals↗

PubMed1983

Anatomy and physiology of supernumerary cercal afferents in crickets: implications for pattern formation.

The afferent projection of supernumerary sensory neurons was examined in the cricket cercal sensory system. When a right cercus was exchanged for a left cercus the growth of supernumerary cerci was induced. The supernumerary cerci which formed tended to appear medial and/or lateral in a simple left leads to right exchange and were always right handed. Distal to the region where transplant and supernumerary meet, receptors on the supernumerary structure appear in a recognizable pattern typical of control cerci, and individual receptors homologous in position to control receptors could be identified. The supernumerary neurons associated with these identified receptors projected to the same area of neuropil as their homologs and thus uniquely identified neurons by all of the usual criteria were produced by the regeneration process. When the response properties of one postsynaptic neuron were examined it was shown that supernumerary afferents innervated it in a normal manner. The supernumerary neurons provide tests of various hypotheses for the assembly of ordered afferent projections. First, their axon trajectories are often atypical, but the terminal arbors grow into their proper areas in spite of this. Thus axon trajectory can be uncoupled from target area and is therefore unlikely to be a decisive factor in growth of the arbor. Second, supernumerary neurons are born later in development than their control homologs but their aroborizations are completely normal, adding to the existing evidence against a timing mechanism in the assembly of this afferent projection. Third, supernumerary neurons share target regions with their homologs, indicating a lack of competitive interactions. The most economical hypothesis to explain the precise mapping between the cercus and CNS holds that one step in the differentiation of insect sensory neurons is position dependent and that this step determines the choice of a target region within the CNS.

Afferent Pathways↗

PubMed1983

Transplantation of cricket sensory neurons to ectopic locations: arborizations and synaptic connections.

The cerci (abdominal sensory appendages) of crickets were transplanted to a leg stump after amputating the leg. Single identifiable cercal afferents were stained and found to regenerate into the host thoracic ganglia. A given neuron always arborizes in the same area of neuropil of the foreign ganglion and is distinctive in this property from other identified neurons. Taken as a whole, the results show that the afferents from the ectopic cercus are spatially ordered, the destination of a particular afferent within the ganglion being correlated with the location of its sensory cell body on the cercal surface. This is the case for the pro-, meso-, and metathoracic ganglion and the topography of these ectopic projections bears some resemblance to the normal projections found in the terminal ganglion. Thus the insect segmental ganglion seems to possess a set of markers which are interpretable by all afferent neurons, and this organization is repeated in each ganglion. The ectopic afferents make functional synaptic connections with intersegmental interneurons, one of which is described anatomically here. However, the ectopic afferents do not, as had previously been reported, make functional connections with the medial giant or lateral giant interneuron (the normal targets of cercal sensory neurons in the terminal ganglion).

Animals↗