Biomedical subjects

S L Zackson

Publications and source records attributed to S L Zackson.

12 recordsLinked to original sources

PubMed1997

Nerve-induced disruption and reformation of beta1-integrin aggregates during development of the neuromuscular junction.

The earliest biochemical change detected during synaptogenesis is a local elimination of muscle basal lamina proteins. To explore whether this provides signal(s) that regulate postsynaptic differentiation, we examined the effects of innervation on the distribution of beta1-integrins, which were initially present in scattered aggregates complexed with basal lamina ligands. These beta1-integrin aggregates disappear along paths of nerve contact as their basal lamina ligands are eliminated. New accumulations of these proteins then form during assembly of the postsynaptic apparatus. The new beta1-integrin aggregates at developing synapses form partly via a redistribution of mobile molecules on muscle surface. We thus consider whether (a) the removal of integrins' basal lamina ligands alters their cytoplasmic ligand-interactions, causing the dissociation of integrin clusters, and (b) this receptor modulation helps to transduce local changes in pericellular protease activity into cytoplasmic signals that control postsynaptic differentiation.

Animals↗

PubMed1996

Proteolytic disruption of laminin-integrin complexes on muscle cells during synapse formation.

To explore whether a neural modulation of muscle integrins' extracellular ligand interactions contributes to synapse induction, we compared the distributions of beta1-integrins and basal lamina proteins on Xenopus myotomal myocytes developing in culture. beta1-Integrins formed numerous organized aggregates scattered over the entire muscle surface, with particularly dense accumulations at specialized sites resembling myotendinous and neuromuscular junctions. Integrin aggregates on muscle cells differed from those on surrounding fibroblasts and epithelial cells, both in their lack of response to cross-linking by multivalent ligands and in their consistent association with the cells' own extracellular matrices. Muscle integrin clusters were usually associated with congruent basal lamina accumulations containing laminin and a heparan sulfate proteoglycan (HSPG), sometimes including fibronectin and vitronectin acquired from the surrounding medium. Immediately prior to synaptic differentiation, any existing laminin and HSPG accumulations along the path of cell contact were eliminated, disrupting otherwise stable laminin-integrin complexes. This apparently proteolytic modulation of integrins' extracellular ligand interactions was soon followed by the accumulation of new congruent accumulations of laminin and HSPG in the developing synaptic basal lamina. Combining these results with earlier findings, we consider the possibility that postsynaptic differentiation is induced, at least in part, by the proteolytic disruption of integrin-ligand complexes at sites of nerve-muscle contact.

Animals↗

PubMed1995

Cell interactions in testis development: overexpression of c-mos in spermatocytes leads to increased germ cell proliferation.

Possible functions of the c-mos proto-oncogene during spermatogenesis were investigated through perturbations of its expression in transgenic mice. Two promoters, one from the pre-meiotic male germ cell-specific mouse phosphoglycerate kinase 2 gene, and the other from the post-meiotic male germ cell-specific rat RT7 gene were used to direct expression of c-mos. Northern blot analysis of testis RNA from transgenic PGK-c-mos mice indicated elevated levels of c-mos RNA in spermatocytes and spermatids compared to controls. No transgene expression was detected in any other tissue examined, suggesting that the mouse PGK2 promoter, like the previously used human PGK2 promoter, confers correct cell-specific expression onto c-mos. The promoter from a newly characterized rat gene, RT7, was shown to direct expression specific to post-meiotic spermatids. Transgenic mice carrying an RT7-lacZ construct displayed immunoreactive bacterial beta-galactosidase as well as enzyme activity in round spermatids. The cellular specificity for beta-galactosidase expression observed in RT7-lacZ transgenic animals was in agreement with endogenous RT7 transcript expression. Northern blot analysis of testis RNA of RT7-c-mos transgenic mice showed elevated levels of c-mos in spermatids, but not in other cells or tissues examined. Western blot analysis demonstrated elevated levels of p43c-mos in spermatids of both PGK-c-mos and RT7-c-mos transgenic animals, but only PGK-c-mos transgenics had increased p43c-mos levels in spermatocytes. Both RT7-c-mos and PGK-c-mos transgenic mice are fertile and show no tendency toward transformation. RT7-c-mos mice have no discernible phenotype associated with the c-mos overexpression in spermatids. However, PGK-c-mos transgenic males exhibited a significant increase in germ cell number, as determined by cell counts using total germ cells and germ cells fractionated by centrifugal elutriation. Because mitotic divisions of germ cells occur prior to PGK-c-mos transgene expression, our observations suggest that c-mos overexpression in spermatocytes causes an alteration in cell-cell interactions.

Animals↗

PubMed1995

Erratic deposition of agrin during the formation of Xenopus neuromuscular junctions in culture.

In order to disclose the mechanism that regulate synapse development we compared the distributions of agrin, acetylcholine receptors (AChR) and a basal lamina heparan sulfate proteoglycan (HSPG) in sections and cultures prepared from Xenopus laevis and Ambystoma mexicanum embryos. While agrin, AChR and HSPG may accumulate almost synchronously at synapses in vivo, agrin deposition usually lagged well behind the other synaptic markers during development in culture, and was not detectable at many differentiated junctions. Agrin deposition at nerve-muscle contacts in culture also appeared to require the presence of other synaptic components. A similarly variable deposition occurred on noninnervated myocytes, where agrin again collected near sites of HSPG and AChR accumulation on some cells. Profuse agrin accretion occurred consistently, however, within the extracellular matrices of surrounding epithelial cells derived from both myotomes and neural tubes. In cocultures of Ambystoma neurons and Xenopus myocytes Ambystoma agrin collected at some chimeric neuromuscular junctions, but also accumulated on noninnervated myocytes and in the extracellular matrices of salamander neuroendothelial cells. Based upon these observations we conclude that (a) focal agrin deposition is not required for synaptic differentiation on Xenopus myocytes and (b) agrin may be one of several muscle basal lamina components that stem mainly from the secreted products of nearby epithelial cells.

Agrin↗

PubMed1993

Detection of electrophoretic variants of Notch, PS integrin, and DROP-1 proteins in Drosophila following extraction in guanidine hydrochloride.

A method is presented for the rapid extraction of proteins from Drosophila tissues. This method involves lysis of embryos in high concentrations of guanidine hydrochloride, followed by ultracentrifugation in a guanidine hydrochloride step gradient. Several membrane-associated antigens, including Notch and the beta subunit of PS integrin are enriched in this preparation. The quantity of the proteoglycan, DROP-1, obtained from Drosophila eggs and testes was also greatly improved by the guanidine hydrochloride extraction method. This method should prove useful in the isolation and characterization of many Drosophila antigens, particularly those associated with cell membranes.

Animals↗

PubMed1989

Axolotl pronephric duct cell migration is sensitive to phosphatidylinositol-specific phospholipase C.

On the basis of its distribution pattern in embryos of the axolotl (Ambystoma mexicanum), we recently identified alkaline phosphatase as a molecule potentially involved in guiding the migration of the pronephric duct. Alkaline phosphatase is a cell surface protein anchored to cell membranes via a covalent linkage to a phosphatidylinositol glycan (PI-G). The enzyme phosphatidylinositol-specific phospholipase C (PIPLC) specifically releases from cell surfaces molecules anchored by the PI-G linkage. In order to test the possibility that a PI-G anchored protein is involved in directing pronephric duct cell migration, PIPLC was applied to axolotl embryos. The enzyme was introduced into embryos through the use of a novel slow-release bead material, hydrolysed polyacrylamide. PIPLC blocked pronephric duct cell migration without interfering with somite fissure formation, a concurrent, neighbouring morphogenetic cell rearrangement which occurs with little if any alkaline phosphatase present. In addition, alkaline phosphatase activity was markedly diminished in the vicinity of the implanted beads. These observations suggest that at least one protein anchored to the cell membrane by a PI-G linkage, possibly alkaline phosphatase, is involved in guiding or promoting pronephric duct cell migration.

Alkaline Phosphatase↗

PubMed1988

A molecular marker for cell guidance information in the axolotl embryo.

Previous studies from this laboratory suggested that the elongation of the pronephric duct (PND) in the axolotl Ambystoma mexicanum is directed by an adhesion gradient along the migrating cells' substratum. We have also shown that cranial neural crest (CNC) cells are able to follow the PND guidance information, for which these cells serve as useful probes (S.L. Zackson and M.S. Steinberg, (1986) Dev. Biol. 117, 342-353). These experiments allow the construction of a map of the cell guidance information. This map is presumed to reflect a molecular prepattern representing the distribution of a cell guidance associated molecule (CGAM) responsible for the ensuing pattern of cell migration. We refer to this proposal as the molecular prepattern hypothesis. In this paper we describe and identify a candidate CGAM displaying a localization pattern corresponding closely with our map of the PND/CNC guidance information on the embryonic flank. This candidate CGAM is also found to be abundant on the posterior neural tube, an embryonic region not previously explored for PND/CNC guidance information. The latter observation has provided the opportunity for an independent test of the correlation between the presence of this molecule in an embryonic region and the ability of that region to direct cell migration. We have found that grafted CNC cells do indeed migrate upon the strongly labeling posterior neural tube in preference to the neighboring poorly labeling presomitic mesoderm. We identify this candidate CGAM as the cell surface enzyme alkaline phosphatase. Possible roles for alkaline phosphatase in directing embryonic cell migrations are discussed.

Alkaline Phosphatase↗

PubMed1987

Chemotaxis or adhesion gradient? Pronephric duct elongation does not depend on distant sources of guidance information.

Previously published experimental studies have led to conflicting interpretations concerning the mechanism guiding pronephric duct elongation in the urodele embryo. Although most studies have led to the conclusion that duct migration is directed by an adhesion gradient (haptotaxis), one set of experiments has been interpreted as supporting chemotactic guidance. We have resolved this conflict by conducting grafting experiments in Ambystoma embryos which distinguish between these two possible mechanisms of cell guidance. Our results provide an alternative explanation for the observations originally interpreted as supporting chemotaxis and add further evidence for adhesive guidance.

Ambystoma↗

PubMed1986

Cranial neural crest cells exhibit directed migration on the pronephric duct pathway: further evidence for an in vivo adhesion gradient.

Previous studies on the elongation of the Ambystoma pronephric duct provided evidence that this morphogenetic movement is adhesion directed. Through the use of a simple and rapid grafting technique that enables genetically marked donor and host cells to be distinguished in transplantation experiments, we demonstrate that cranial neural crest cells, which normally migrate concurrently with, but at a distance from, pronephric duct cells, are able to follow the pronephric duct guidance information. Utilizing neural crest cells as probes for adhesive properties of the lateral plate mesoderm, we extend our previous model of the formal properties of the pronephric duct guidance information. We propose that cells of the cranial neural crest, the pronephric duct primordium and the lateral plate mesoderm all exhibit molecular components of at least one shared cell adhesion system.

Age Factors↗

PubMed1984

Cell lineage, cell-cell interaction, and segment formation in the ectoderm of a glossiphoniid leech embryo.

Cell division patterns and cell-cell interactions in the germinal bands of the glossiphoniid leech Helobdella triserialis were studied with the aid of a cell lineage tracer dye. Each germinal band of the Helobdella embryo consists of five columns, or bandlets, of primary blast cells, designated as the mesodermal m bandlet and ectodermal n, o, p, and q bandlets. Primary blast cells of each ectodermal bandlet appear to undergo stereotyped, lineage-specific cell divisions. The metameric segmentation pattern of the leech thus appears to arise through a series of segmentally iterated, stereotyped cell divisions of serially homologous primary blast cell clones. Cell-cell interactions were studied by means of cell ablations. With one exception, blast cells underwent their stereotyped divisions without regard to the presence or absence of their normal neighbors. In the one exceptional case, o blast cells underwent divisions normally characteristic of p blast cells when their normal neighboring p bandlet was deleted. However, both o and p blast cells underwent their normal stereotyped divisions when their neighboring m, n, and q bandlets were deleted. It is proposed that the differential choice of pathway by the o and p blast cells depends upon their relative position with respect to each other and to a polarity cue external to the germinal band.

Animals↗

PubMed1982

Cell clones and segmentation in leech development.

Cell lineage tracer dyes rhodamine-D-peptide and fluorescein-D-peptide were used to study the development of segmentation in embryos of the leech Helobdella triserialis. The earliest overt manifestation of segmentation is in the mesodermal cell layer of the germinal bands, where a repeating pattern of nearly isomorphic mesoblast clusters is seen at an early stage of development. With joint use of both lineage tracers, it is shown that each mesoblast cluster is a clone derived from a single primary mesoblast, as well as being the precursor to an adult mesodermal hemisegment. Not all of the primary mesoblasts give rise to hemisegments, however. Cell clones derived from the first primary mesoblasts produced contribute to the nonmetameric prostomial region, whereas the last primary mesoblasts produced appear to be supernumerary.

Animals↗

PubMed1980

Cell lineage analysis by intracellular injection of fluorescent tracers.

Cell lineages during development of the leech are revealed by injection of a fluorescent peptide, rhodamine-D-peptide, into identified embryonic cells. Use of this peptide together with a nuclear stain showed a stereotypic cleavage pattern of stem cells and their progeny. Combined injection of rhodamine-D-peptide and pronase demonstrated the arrest of stem cell production in the pronase-injected teloblast.

Benzimidazoles↗