Radiosensitivity and differentiation of ganglion cells within fetal mouse retinal explants in vitro

Characterization of a novel set of membrane antigens associated with axonal growth. I. Biochemical and functional studies

Cranin, a prominent 120 kDa laminin-binding protein of cell membranes, was originally identified and characterized by virtue of its ability to bind laminin directly in ligand-blotting assays. We have now raised polyclonal ('3070') and monoclonal antibodies (MAbs 4 and 199) against a partially purified preparation of cranin, and have characterized the properties and expression of the corresponding antigens in further detail. In immunoblots of E14 chick brain membranes, these antibodies all recognized a single major band migrating at approximately 125 kDa, with minor bands at 115 kDa and 170/180 kDa. The major 125 kDa antigen bound to laminin affinity beads in a divalent cation- and conformation-dependent manner. The 125 and 115 kDa bands were also the most prominent HNK-1 positive proteins detected overall within E14 chick brain membranes. MAbs 4 and 199 specifically inhibited the attachment of NG108-15 cells to low, but not high amounts of substratum-bound laminin. While the relation of 3070/MAb 4 antigens to cranin requires further elucidation, these data, together with evidence presented in the companion papers and elsewhere, suggest that the antigens are important in neural development by mediating at least some of the responses of neural cells to laminin--for example, by acting as a laminin receptor guiding axonal outgrowth and neuronal migration, or by involvement in the transport and binding of laminin to the surface of neurons and reactive glial cells that synthesize laminin.

Cell commitment and differentiation in explants of embryonic rat neural retina. Comparison with the developmental potential of dissociated retina

The differentiation of presumptive neural retina following its isolation from rat embryos and growth in explant and monolayer culture has been studied to obtain information regarding the extent to which factors extrinsic and intrinsic to the retina participate in determining molecular and cytological differentiation. Explanted retinal epithelium retained the capacity for mitosis, as shown by [3H]thymidine incorporation, and from the undifferentiated neuroepithelium, retinal cell-types emerged and acquired a laminar organization resembling that in vivo. Characterization of rod photoreceptor cells at both the light and electron microscopic level showed that these cells exhibit differentiated structural features including inner segments, connecting cilia and membranous expansions suggestive of forming outer segments. Immunofluorescent labeling with an antibody to a synaptic vesicle protein, and electron microscopic identification of synaptic elements showed formation of synapses by the photoreceptor cells within the explant. Neurites extending from the explants exhibited growth on laminin, fibronectin and collagen substrates. Since the neurites immunolabeled with antibodies to the 140 kDa subunit of neurofilament and with antibodies to Thy-1, they could be identified as axons of ganglion cells. Antibodies to a variety of cell-type specific antigens showed that the cells expressed molecules associated with the fully differentiated cell. Furthermore, since our approach has been to explant embryonic retina at an age when the antigens are not yet expressed in vivo, the appearance of the antigens in culture represented de novo expression. In contrast, neural retinal cells in dissociated cultures did not exhibit de novo expression of differentiated molecular properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic analysis of 'rapid onset' neurite formation in NG108-15 cells reveals a dual role for substratum-bound laminin

Undifferentiated neural hybrid NG108-15 cells plated on laminin-coated, polylysine-treated plastic Petri dishes in minimal serum-free media formed long neurites within 1-4 h post-plating. Morphologic features and pharmacologic responses of these 'rapid onset' neurites were strikingly similar to those of neuronal growth cones. Cycloheximide (1-10 micrograms/ml) and forskolin (10(-7) to 10(-6) M) accelerated the initial formation of laminin-stimulated neurites, but did not cause rapid onset neurites to emerge upon Petri dishes coated with polylysine alone. Quantitative study of the substratum-dependent effect of cycloheximide showed that it was additive even with maximally effective amounts of laminin, independent of the magnitude of the laminin-stimulated baseline rate and not limited by an inherent ceiling in the rate at which neurites could form. The methylation inhibitor 5'-deoxy-5'-methyl thioadenosine (MTA) (3 X 10(-4) to 3 X 10(-3) M) did stimulate neurites to form on polylysine. MTA- and laminin-stimulated neurites were similar in their susceptibility to calmodulin antagonists and the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA). However, formation of MTA-stimulated neurites was not accelerated by cycloheximide. A simple two-compartment kinetic model of 'rapid onset' neurite formation is proposed: compartment A is common to both laminin- and MTA-stimulated neurites. Compartment B is affected by cycloheximide, and its access to the neurite formation machinery contained in compartment A is gated according to the nature of the substratum. In addition to its direct effects, laminin controls the relative dominance of the two kinetic compartments via modulating the effectiveness of other signals acting upon an endogenously active compartment B.