Ultrastructure of a model basement membrane lacking type IV collagen

VP23R of infectious spleen and kidney necrosis virus mediates formation of virus-mock basement membrane to provide attaching sites for lymphatic endothelial cells

Putative open reading frames (ORFs) encoding laminin-like proteins are found in all members of the genus Megalocytivirus, family Iridoviridae. This is the first study that identified the VP23R protein encoded by ORF23R of the infectious spleen and kidney necrosis virus (ISKNV), a member of these genes of megalocytiviruses. The VP23R mRNA covering the ISKNV genomic coordinates 19547 to 22273 was transcribed ahead of the major capsid protein. Immunofluorescence analysis demonstrated that VP23R was expressed on the plasma membrane of the ISKNV-infected cells and could not be a viral envelope protein. Residues 292 to 576 of VP23R are homologous to the laminin γ1III2-6 fragment, which covers the nidogen-binding site. An immunoprecipitation assay showed that VP23R could interact with nidogen-1, and immunohistochemistry showed that nidogen-1 was localized on the outer membrane of the infected cells. Electron microscopy showed that a virus-mock basement membrane (VMBM) was formed on the surface of the infected cells and a layer of endothelial cells (ECs) was attached to the VMBM. The VMBM contained VP23R and nidogen-1 but not collagen IV. The attached ECs were identified as lymphatic endothelial cells (LECs), which have unique feature of overlapping intercellular junctions and can be stained by immunohistochemistry using an antibody against a specific lymphatic marker, Prox-1. Such infection signs have never been described in viruses. Elucidating the functions of LECs attached to the surface of the infected cells may be useful for studies on the pathogenic mechanisms of megalocytiviruses and may also be important for studies on lymphangiogenesis and basement membrane functions.

Type IV collagen alpha chains of the basement membrane in the rat bronchioalveolar transitional segment

In the present study, we have analyzed the alpha(IV) chain distribution in the subepithelial basement membrane (BM) of the rat pulmonary airway from the bronchi to alveoli. We have furthermore analyzed the alpha(IV) chain distribution in the subepithelial BM of the bronchioalveolar duct junction (BADJ) using alpha(IV) chain specific monoclonal antibodies. Our results show that the BM of the bronchial and bronchiolar epithelium contains [alpha1(IV)]2alpha2(IV) and [alpha5(IV)]2alpha6(IV) molecules and confirmed that the alveolar BM consists of [alpha1(IV)]2alpha2(IV) and alpha3(IV) alpha4(IV)alpha5(IV) molecules. There are also small regions in BADJ consisting of only [alpha1(IV)]2alpha2(IV) molecules without alpha3(IV)alpha4(IV)alpha5(IV) and [alpha5(IV)]2alpha6(IV) molecules. Moreover, the bronchioalveolar stem cells (BASCs)-primordial cells for bronchiolar Clara cells and alveolar type II (AT2) cells - lie adjacent to such small regions. These findings suggest that [alpha1(IV)]2 alpha2(IV) may be important for the BASCs to self-renew or to self-maintain themselves and that microenvironments produced by alpha(IV) chains may be important for cell differentiation.

Collagen IV is essential for basement membrane stability but dispensable for initiation of its assembly during early development

Basement membranes are specialized extracellular matrices consisting of tissue-specific organizations of multiple matrix molecules and serve as structural barriers as well as substrates for cellular interactions. The network of collagen IV is thought to define the scaffold integrating other components such as, laminins, nidogens or perlecan, into highly organized supramolecular architectures. To analyze the functional roles of the major collagen IV isoform alpha1(IV)(2)alpha2(IV) for basement membrane assembly and embryonic development, we generated a null allele of the Col4a1/2 locus in mice, thereby ablating both alpha-chains. Unexpectedly, embryos developed up to E9.5 at the expected Mendelian ratio and showed a variable degree of growth retardation. Basement membrane proteins were deposited and assembled at expected sites in mutant embryos, indicating that this isoform is dispensable for matrix deposition and assembly during early development. However, lethality occurred between E10.5-E11.5, because of structural deficiencies in the basement membranes and finally by failure of the integrity of Reichert's membrane. These data demonstrate for the first time that collagen IV is fundamental for the maintenance of integrity and function of basement membranes under conditions of increasing mechanical demands, but dispensable for deposition and initial assembly of components. Taken together with other basement membrane protein knockouts, these data suggest that laminin is sufficient for basement membrane-like matrices during early development, but at later stages the specific composition of components including collagen IV defines integrity, stability and functionality.

An ultrastructural study of connective tissue in mollusc integument III. Cephalopoda

We studied structure and ultrastructure of the subepidermal connective tissue (SEC) of the integument of three cephalopods (Sepia officinalis, Octopus vulgaris and Loligo pealii). In all species, three distinct regions of the SEC were recognised: (a) an outer zone (OZ) that included the dermal-epidermal junction, and consisted of a thin layer of connective tissue containing muscles, (b) an extensive middle zone (MZ) containing a compact network of collagen fibres and numerous cells, (c) an inner zone (IZ) of loose connective tissue that merged with muscular fascia. This arrangement differs from that in bivalves and gastropods and recalls vertebrate integument. The dermal-epidermal junction of cephalopods differed from that of bivalves, gastropods and mammals in that the epidermal cells did not possess hemidesmosomes, and their intermediate filaments terminated directly in the plasmamembrane. The thick (120-500 nm) basal membrane (BM) had a superficial zone containing a regular array of granules; a lamina densa composed of a compact network of small filaments and granules; and an IZ distinguished by expansions of granular material protruding into underlying structures. Collagen fibres contained fibroblast-derived cytoplasmic thread, running through their centres and were surrounded by granular material that joins them to adjacent fibres. The collagen fibrils were of medium diameter (30-80 nm) had the typical ultrastructure of fibrillar collagens, and were surrounded by abundant interfibrillar material. The hypodermis was loose, with a network of small bundles of collagen fibrils. Cephalopod integument appears to represent a major evolutionary step distinguishing this class of molluscs.

Transcriptional state and chromatin structure of the murine entactin and laminin gamma1 genes

The positions of nucleosomes in the proximal 5' regions of the coordinately regulated murine entactin/nidogen and laminin gamma1 genes have been identified in four different transcriptional states--constitutively off, basal, induced, and constitutively induced. In the entactin gene a 450 base pair (bp) region of open chromatin is present between three positioned nucleosomes and the transcriptional start site in the basal, induced, and constitutively induced states. Additionally there is a 200 bp open chromatin region at approximately -2.1 kbp that is only present in the induced and constitutively induced states. In the laminin gamma1 gene, a 650 bp region of nucleosome-free chromatin is present between nucleosomes positioned at approximately -750 and +120 in all transcriptionally active states. These results suggest that basal co-expression of these genes requires sites present in these near upstream regions. The induction to high levels appears to involve additional sites and possibly the production of new and/or the modification of existing trans-acting factors.

An ultrastructural study of connective tissue in mollusc integument: I. Bivalvia

The ultrastructure of the subepidermal connective tissue (SEC) in different areas of the integument of the bivalves Callista chione, Pecten jacobaeus, Mytilus galloprovincialis and Ostrea edulis was studied by transmission electron microscopy. The main organisation of the SEC was broadly similar in all species: the SEC was connected to the epidermis by a basement membrane and merged directly with the deeper connective tissue surrounding muscles. The SEC was not differentiated into layers like the papillary and reticular dermis of mammals, however, the architecture, thickness and shape of the basement membrane varied from species to species, as well as within species (in the foot, central or marginal zones of the mantle). The ultrastructure of the lamina densa was broadly similar to that in mammals: although basotubules and double pegs were absent, proteoglycans and rod-like units homologous to 'double tracks' were always abundant. A zone similar to the lamina lucida was irregularly present and was shot thorough with small protrusions of the lamina densa that connected with the epithelial hemidesmosomes or focal adhesions. Nevertheless zones were observed where the lamina densa fuse directly to the epithelial plasmamembrane. This variability of connection may be related to the various types of epidermal cell. A lamina fibroreticularis was not recognized since anchoring fibrils and microfibrils were not present; lamina densa protrusions into the extracellular matrix (ECM) of SEC characterize the connection between basement membrane and SEC. Collagen fibrils were small and of constant diameter and were never organised into fibres. Anchoring devices - similar to the anchoring plaques of mammalian dermis - were abundant and scattered between SEC collagen fibrils. The orange-pink pigmentation of C. chione seems due to electron-dense granules embedded within the connective ECM.

Distribution of type IV collagen during avian limb bud development

Normal limb development is dependent on an epithelial-mesenchymal interaction between the overlying apical ectodermal ridge (AER) and the underlying mesenchyme. The basement membrane between the epithelium and the mesenchyme has been proposed to play an important role in regulating epithelial-mesenchymal interactions during development. To explore the role basement membrane type IV collagen may play during limb development we investigated the distribution of type IV collagen by immunolocalization. Developing avian leg buds were examined at 2 developmental stages: stage 23, when the AER is inductively active, and stage 28, when the AER is regressing. The proximal basement membrane in stage 23 limb buds stained much more intensely than the distal basement membrane. This proximal-distal immunostaining difference was less in stage 28 limb buds. We used the monoclonal antibody IIB12, which recognizes an epitope adjacent to the initial collagenase cleavage site on the type IV collagen molecule, to explore whether this proximal-distal difference in basement membrane staining could result from the loss of type IV collagen. The distal basement membrane of stage 23 limb buds demonstrated little immunostaining with the IIB12 antibody, suggesting enhanced collagenase-associated degradation. The immunostaining was increased in stage 28 limb buds. Consistent with a loss of type IV collagen, we also found that unfixed stage 23 leg bud cryostat sections stored at 4 degrees C lost their immunostaining for type IV collagen, in contrast to stored stage 28 limb bud cryostat sections. These results demonstrate that type IV collagen is distributed in a proximal-distal pattern in the basement membrane of the developing chick limb bud and suggest that this pattern may be the result of a selective degradation of type IV collagen in the basement membrane underlying the active AER. These results are consistent with the hypothesis that the basement membrane plays a role in regulating the epithelial-mesenchymal interaction responsible for induction of limb outgrowth.

Absence of basement membranes after targeting the LAMC1 gene results in embryonic lethality due to failure of endoderm differentiation

The LAMC1 gene coding for the laminin gamma1 subunit was targeted by homologous recombination in mouse embryonic stem cells. Mice heterozygous for the mutation had a normal phenotype and were fertile, whereas homozygous mutant embryos did not survive beyond day 5.5 post coitum. These embryos lacked basement membranes and although the blastocysts had expanded, primitive endoderm cells remained in the inner cell mass, and the parietal yolk sac did not develop. Cultured embryonic stem cells appeared normal after targeting both LAMC1 genes, but the embryoid bodies derived from them also lacked basement membranes, having disorganized extracellular deposits of the basement membrane proteins collagen IV and perlecan, and the cells failed to differentiate into stable myotubes. Secretion of the linking protein nidogen and a truncated laminin alpha1 subunit did occur, but these were not deposited in the extracellular matrix. These results show that the laminin gamma1 subunit is necessary for laminin assembly and that laminin is in turn essential for the organization of other basement membrane components in vivo and in vitro. Surprisingly, basement membranes are not necessary for the formation of the first epithelium to develop during embryogenesis, but first become required for extra embryonic endoderm differentiation.

Distribution of the alpha1 to alpha6 chains of type IV collagen in bovine follicles

During follicular development the proliferative and differentiated state of the epithelioid granulosa cells changes, and the movement of fluid across the follicular basal lamina enables the formation of an antrum. Type IV collagen is an important component of many basal laminae. Each molecule is composed of three alpha chains; however, six different type IV collagen chains have been identified. It is not known which of these chains are present in the follicular basal lamina and whether the type IV collagen composition of the basal lamina changes during follicular development. Therefore, we immunolocalized each of the six chains in bovine ovaries using antibodies directed to the nonconserved non-collagenous (NC) domains. Additionally, dissected follicles were digested with collagenase to release the NC domains, and the NC1 domains were then detected by standard Western immunoblot methods. The follicular basal lamina of almost all primordial and preantral follicles was positive for all type IV collagen alpha chains. Colocalization of type IV collagen and factor VIII-related antigen allowed for discrimination between the follicular and endothelial basal laminae. Type IV collagen alpha1, alpha2, alpha3, alpha4, and alpha5 chains were present within the follicular basal lamina of only a proportion of antral follicles (17 of 22, 20 of 21, 15 of 18, 14 of 28, and 12 of 23, respectively), and staining was less intense than in the preantral follicles. Staining for the alpha1 and alpha2 chains was diffusely distributed throughout the theca in regions not associated with recognized basal laminae. The specificity of this immunostaining for alpha1 and alpha2 chains of type IV collagen was confirmed by Western immunoblots. As well as being detected in the basal lamina of approximately half of the antral follicles examined, type IV collagen alpha4 also colocalized with 3beta-hydroxysteroid dehydrogenase-immunopositive cells in the theca interna. Type IV collagen alpha6 was detected in the basal lamina of only one of the 16 antral follicles examined. Thus, the follicular basal lamina changes in composition during follicular development, with immunostaining levels being reduced for all type IV collagen chains and immunoreactivity for type IV collagen alpha6 being lost as follicle size increases. Additionally, immunoreactivity for alpha1 and alpha2 appears in the extracellular matrix of the theca as it develops.

Type IV collagen is detectable in most, but not all, basement membranes of Caenorhabditis elegans and assembles on tissues that do not express it

Type IV collagen in Caenorhabditis elegans is produced by two essential genes, emb-9 and let-2, which encode alpha1- and alpha2-like chains, respectively. The distribution of EMB-9 and LET-2 chains has been characterized using chain-specific antisera. The chains colocalize, suggesting that they may function in a single heterotrimeric collagen molecule. Type IV collagen is detected in all basement membranes except those on the pseudocoelomic face of body wall muscle and on the regions of the hypodermis between body wall muscle quadrants, indicating that there are major structural differences between some basement membranes in C. elegans. Using lacZ/green fluorescent protein (GFP) reporter constructs, both type IV collagen genes were shown to be expressed in the same cells, primarily body wall muscles, and some somatic cells of the gonad. Although the pharynx and intestine are covered with basement membranes that contain type IV collagen, these tissues do not express either type IV collagen gene. Using an epitope-tagged emb-9 construct, we show that type IV collagen made in body wall muscle cells can assemble into the pharyngeal, intestinal, and gonadal basement membranes. Additionally, we show that expression of functional type IV collagen only in body wall muscle cells is sufficient for C. elegans to complete development and be partially fertile. Since type IV collagen secreted from muscle cells only assembles into some of the basement membranes that it has access to, there must be a mechanism regulating its assembly. We propose that interaction with a cell surface-associated molecule(s) is required to facilitate type IV collagen assembly.

Morphology of the basement membrane

The aim of this contribution is to summarize our knowledge of the morphology of the basement membrane (BM). The first step in this direction is the attempt to define this term. The BM is composed of the Lamina lucida, densa, and fibroreticularis. Subsequently, the historical development of this term is discussed. Our main interest is, of course, focused on the description of the BM-structure up to the macromolecular level and the special forms of this structure. This is supplemented by discussing its chemical composition and establishing a relationship between morphology and biochemistry. The obtained findings yielded some indications as to the molecular composition of the BM which may serve for the construction of "models." The composition of the Lamina lucida (L.l.) and the Lamina or Pars fibroreticularis (L.f.) must be discussed separately, since, if present, they show a different and strongly varying structure (L.f.). An important aspect is the function of this extracellular layer which comprises mechanical tasks up to inductive effects. Finally, the concepts of the formation of the BM, especially of the Lamina densa (L.d.), are summarized. It obviously consists of a sequence of individual steps which starts with expression and secretion of the L.d.-components and is followed by an induction of integrin expression.

A line of rat ovarian surface epithelium provides a continuous source of complex extracellular matrix

A spontaneously immortalized, yet non-tumorigenic rat ovarian surface epithelial (ROSE 199) cell line, deposits large amounts of extracellular matrix (ECM) in response to crowding. The characteristics and components of ROSE 199-derived cell-free ECM were compared after three different preparative techniques: treatment with 20 mM ammonium hydroxide, with 1% sodium deoxycholate, or by repeated freeze-thaws. The ECMs were analyzed by histochemistry, immunofluorescence, electron microscopy, and Western immunoblotting. Components of ROSE 199 ECM included laminin, fibronectin, and collagen types I and III. Even though ROSE 199 is an epithelial cell line, striated collagen fibers formed a major part of its matrix. Thus, ROSE 199 matrix consists of both basement membrane and stromal matrix components. This matrix supported the adhesion, spreading, and growth of several cell types without altering their morphology or growth pattern, and enhanced the attachment of some cell types that spread on plastic only with difficulty. Immunofluorescence, electron microscopy, and dry weight determinations indicated that a greater proportion of matrix was retained in preparations obtained by ammonium hydroxide or freeze thaw techniques than after sodium deoxycholate treatment. Ammonium hydroxide and freeze-thaw treated matrices were also superior to sodium deoxycholate preparations as evidenced by enhanced initial cellular adhesion and spreading compared to cells plated on plastic. Residual nuclear material did not seem to affect the biological activity of this matrix. ROSE 199 extracellular matrix provides a novel, complex substratum for cell culture and for studies of matrix functions and synthesis.

Perlecan gene expression precedes laminin gene expression during differentiation of F9 embryonal carcinoma cells

F9 embryonal cells can be induced to differentiate and synthesize basement membrane proteins. Perlecan and laminin are two basement membrane constituents that have extensive regions of homology. Expression of perlecan and laminin B1 genes was followed during differentiation of F9 cells by measurements of transcription rate and mRNA abundance using nuclear run on assays and Northern hybridizations, respectively. The rate of precursor protein synthesis was determined by immunoprecipitation from lysates of pulse-labeled F9 cells. The results showed that perlecan gene expression responds more rapidly after induction than does laminin B1 gene expression but is ultimately expressed at a substantially lower level than laminin. Thus, the perlecan and laminin genes appear to be regulated by different mechanisms and their gene products are not made in stoichiometric amounts.

Ultrastructural localization of lectin-binding sites in different basement membranes

In the present work we localized binding sites for the lectins WGA, RCA I, con A and SBA at the ultrastructural levels in morphologically different basement membranes. These different basement membranes included (a) thin ones, for example, tubular basement membrane of the mouse kidney which separates epithelial cell layers from mesenchymal cells and glomerular basement membrane which separates epithelial cells from other epithelial cells, (b) thick multilayered ones, for example. Reichert's membrane which is built up during the embryonic development of rodents and as an example of a pathologically thickened basement membrane, the basement membrane of the Engelbreth-Holm-Swarm (EHS) sarcoma. We were able to show that, in contrast to the thick multilayered basement membranes, the thin ones showed a strong positive SBA-binding pattern. Thick basement membranes otherwise revealed very strong labelling with the lectins WGA and RCA I. Our findings lead us to conclude that thin and thick basement membranes differ markedly in the quality and quantity of the carbohydrates which they contain.

Biological functions of entactin

Entactin is a sulfated multidomain glycoprotein component of basement membranes. The molecule consists of 1217 amino acids which are organized into two terminal globular domains linked by a rod-like structure largely composed of four EGF- and one thyroglobulin-like cysteine-rich homology repeats. Entactin binds to laminin, collagen IV, fibrinogen, and fibronectin. In the parietal endoderm M1536-B3 cell line, the laminin-entactin complex is formed intracellularly and transported in membrane enclosed vesicles to the extracellular compartment. Transfection of human choriocarcinoma JAR cells, which do not synthesize entactin, with entactin cDNA results in the synthesis and insertion of entactin into the extracellular matrix where it becomes associated with laminin and collagen IV. Indirect immunofluorescent staining also reveals that entactin co-localizes with fibronectin in the extracellular matrix of the embryonal carcinoma-derived 4CQ cell line. These observations suggest that entactin plays an important role in the assembly and properties of diverse extracellular matrices. In addition, entactin binds to immobilized fibrinogen, and more specifically, to the A alpha and B beta chains. The binding of radiolabeled entactin to immobilized fibrinogen is not dependent on metal ions, and is inhibited by antibodies against either fibrinogen or entactin, soluble fibrinogen, and unlabeled entactin. This interaction combined with the chemotactic and phagocytic promoting activities of entactin may be important in hemostasis and would healing.

Reversible inhibition of albumin production by rat hepatocytes maintained on a laminin-rich gel (Engelbreth-Holm-Swarm) in response to secretory products of Kupffer cells and cytokines

Decreased albumin synthesis by hepatocytes in liver injury is thought to occur in response to Kupffer cell-derived acute-phase cytokines. In this study we used hepatocytes maintained in a differentiated phenotype, by culture on a laminin-rich gel substratum (Engelbreth-Holm-Swarm matrix), to investigate the effects of Kupffer cell-conditioned medium and purified cytokines (interleukin-1, interleukin-6 and tumor necrosis factor-alpha) on albumin synthesis. Kupffer cell-conditioned medium caused a reversible decrease in albumin synthesis to 64.7% of control (p less than 0.01, Wilcoxon's rank sum test, n = 11) on day 2. Repeated doses caused further dose-dependent reversible responses. The same result was obtained when protease inhibitors (alpha 1-antitrypsin and alpha 2-macroglobulin) were added to Kupffer cell-conditioned medium (n = 3), thus eliminating the potential effect of matrix degradation. Pure interleukin-1, interleukin-6 and tumor necrosis factor-alpha also inhibited albumin synthesis (p less than 0.05, Wilcoxon's rank sum test, n = 5), interleukin-6 having the greatest effect. After exposure to interleukin-1 (30 U.ml-1) and tumor necrosis factor-alpha (300 U.ml-1), decreased albumin synthesis was followed by a rebound increase (n = 3). Our results support the hypothesis that reduced albumin synthesis in the acute-phase response is modulated by cytokines released from Kupffer cells. Moreover, our results suggest that hepatocytes may exhibit a compensatory increase in albumin synthesis after cytokine withdrawal. These findings may be of physiological importance in the recovery from injury and the acute-phase response in vivo.

Laminin forms an independent network in basement membranes

Laminin self-assembles in vitro into a polymer by a reversible, entropy-driven and calcium-facilitated process dependent upon the participation of the short arm globular domains. We now find that this polymer is required for the structural integrity of the collagen-free basement membrane of cultured embryonal carcinoma cells (ECC) and for the supramolecular organization and anchorage of laminin in the collagen-rich basement membrane of the Engelbreth-Holm-Swarm tumor (EHS). First, low temperature and EDTA induced the dissolution of ECC basement membranes and released approximately 80% of total laminin from the EHS basement membrane. Second, laminin elastase fragments (E4 and E1') possessing the short arm globules of the B1, B2, and A chains selectively acted as competitive ligands that dissolved ECC basement membranes and displaced laminin from the EHS basement membrane into solution. The fraction of laminin released increased as a function of ligand concentration, approaching the level of the EDTA-reversible pool. The smaller (approximately 20%) residual pool of EHS laminin, in contrast, could only be effectively displaced by E1' and E4 if the collagenous network was first degraded with bacterial collagenase. The supramolecular architecture of freeze-etched and platinum/carbon replicated reconstituted laminin gel polymer, ECC, and collagenase-treated EHS basement membranes were compared and found to be similar, further supporting the biochemical data. We conclude that laminin forms a network independent of that of type IV collagen in basement membranes. Furthermore, in the EHS basement membrane four-fifths of laminin is anchored strictly through noncovalent bonds between laminin monomers while one-fifth is anchored through a combination of these bonds and laminin-collagen bridges.

Electron-immunocytochemistry of laminin and type-IV collagen in the junctional epithelium of rat molar gingiva

The present study was carried out to examine the ultrastructural localization of laminin and type-IV collagen in the junctional epithelium of rat molar gingiva by means of the indirect immunoperoxidase method. Intense laminin reaction occurred in both the internal and the external basal laminae. Laminin reaction products were observed within the cisternae of the rough endoplasmic reticulum of junctional epithelium cells and in concavities formed at the distal plasma membranes adjacent to the basal lamina. Small spherical bodies occurring in the concavities also reacted positively to laminin. Type-IV collagen reaction was intense in the external basal lamina. The internal basal lamina, however, showed no reaction for type-IV collagen. These results indicate that the internal basal lamina contains laminin but no type-IV collagen and that junctional epithelium cells seem very likely to be involved in the production of laminin.

Terminal short arm domains of basement membrane laminin are critical for its self-assembly

Laminin self-assembles into large polymers by a cooperative two-step calcium-dependent mechanism (Yurchenco, P. D., E. C. Tsilibary, A. S. Charonis, and H. Furthmayr. 1985. J. Biol. Chem. 260:7636-7644). The domain specificity of this process was investigated using defined proteolytically generated fragments corresponding to the NH2-terminal globule and adjacent stem of the short arm of the B1 chain (E4), a complex of the two short arms of the A and B2 chains attached to the proximal stem of a third short arm (E1'), a similar complex lacking the globular domains (P1'), and the distal half of the long arm attached to the adjacent portion of the large globule (E8). Polymerization, followed by an increase of turbidity at 360 nm in neutral isotonic TBS containing CaCl2 at 35 degrees C, was quantitatively inhibited in a concentration-dependent manner with laminin fragments E4 and E1' but not with fragments E8 and P1'. Affinity retardation chromatography was used for further characterization of the binding of laminin domains. The migration of fragment E4, but not of fragments E8 and P1', was retarded in a temperature- and calcium-dependent fashion on a laminin affinity column but not on a similar BSA column. These data are evidence that laminin fragments E4 and E1' possess essential terminal binding domains for the self-aggregation of laminin, while fragments E8 and P1' do not. Furthermore, the individual domain-specific interactions that contribute to assembly are calcium dependent and of low affinity.