The pattern of cytokeratin synthesis is a marker of type 2 cell differentiation in adult and maturing fetal lung alveolar cells

During the last stages of fetal life, the immature epithelial cells of the rat lung alveolus develop the properties of mature type 2 cells. Adult type 2 cells rapidly lose these same properties when isolated and maintained in cell culture. We have examined the synthesis of cytokeratin proteins by adult type 2 cells as they lose their differentiated characteristics during 1 week in culture, and of immature fetal alveolar epithelial cells as they differentiate either in utero or when cultured on an extracellular matrix. Freshly isolated adult type 2 cells synthesize four cytokeratins which by electrophoretic mobilities and Western blot analysis correspond to human cytokeratins Nos. 7, 8, 18, and 19. During 7 days in culture synthesis of cytokeratin No. 19 is dramatically decreased and cytokeratin No. 18 becomes the predominant acidic cytokeratin produced. Fetal lung epithelial cells at 18 days gestation lack most characteristics of mature type 2 cells. When freshly isolated, these cells synthesize cytokeratins Nos. 7, 8, and 18 but make only minimal amounts of cytokeratin No. 19. When these cells are allowed to mature either in utero or in culture on a whole basement membrane extract, they develop both the morphological characteristics and the pattern of cytokeratin synthesis of fully developed type 2 cells, with cytokeratins No. 19 being the major acidic cytokeratin produced.

Immature neural elements in immature teratomas. An immunohistochemical and ultrastructural study

Immature neural tissue pathobiology in teratomas may have important implications for clinical prognosis, nervous system embryology, and neurological oncology. However, immunohistochemical and ultrastructural examinations of these neoplasms have been scarce. The authors examined immunohistochemically the immature neural elements in nine immature teratomas. Using modified peroxidase-antiperoxidase (PAP) immunoperoxidase (IP) techniques, they evaluated the immunoreactivity to glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), neurofilament (NF), chromogranin (CG), and vimentin (VM). All nine teratomas were immunoreactive for both GFAP and NSE, one was reactive for NF, and five (56%) were immunoreactive for vimentin. All cases were nonreactive for chromogranin. In addition, ultrastructural examination (electron microscopic [EM]) was performed on eight of these tumors. By EM examination, both astrocytes and oligodendroglia were identified in varying stages of development. Astrocytes often displayed abundant intermediate filaments. However, primitive undifferentiated cells were also found. Neuronal differentiation included long cell processes with tubules and filaments, vesicles, rare dense-core granules, and synapses. Ependymal differentiation (cilia, microvilli, prominent junctions) was observed in two cases. Pigmented retinal epithelium was seen in one tumor. No ambiguous (hybrid) cells were identified. Cellular interactions usually resembled the relationships found in normal adult brain tissue.

Radiosensitivity related to neuroendocrine and endodermal differentiation in lung carcinoma lines

A panel of human lung carcinoma lines was studied with respect to hormone production and intermediate filament expression to distinguish between endodermal and neuroendocrine differentiation. An index of the degree of neuroendocrine differentiation of each line was derived from the presence or absence of hormone production, cytokeratins, neurofilaments and an embryonic endodermal cell marker, which allowed identification of three groups showing high, intermediate or low neuroendocrine expression. This grouping correlated well with the in vitro radiosensitivity of the lines, those expressing pure neuroendocrine features being significantly more radiosensitive than those with an endodermal phenotype, with the intermediate group having intermediate sensitivity. Use of such an index might predict those patients likely to benefit from the use of radiotherapy in their management.

Immunofluorescent localization of cytokeratin intermediate filaments as a means of defining the presence of recurrent basal cell carcinoma

Intermediate filament subunits are reliable markers of cytogenetic origin for both normal and neoplastic cells. Immunohistochemical localization of cytokeratin filaments offers a sensitive and specific means of identifying basal or reserve cells when studying histologic sections of skin biopsy specimens. We have applied this technique on eighteen cases in which unequivocal diagnosis or recurrent basal cell carcinoma could not be rendered by conventional histologic techniques. In three of the cases studied, microscopic islands of basal cell carcinoma could be demonstrated by positive staining with cytokeratin antibodies. In the remaining fifteen cases, the possibility of recurrent basal cell carcinoma could be conclusively eliminated on the basis of negative staining with this antibody. Immunolabeling with tissue specific cytokeratin antibodies by indirect immunofluorescent examination may thus constitute a reliable and relatively simple technique that may serve to establish a definitive diagnosis in equivocal cases of suspected recurrent basal cell carcinoma.

Does amyloid precede paired helical filaments in the senile plaque? A study of 15 cases with graded intellectual status in aging and Alzheimer disease

The density of senile plaques in 15 women over 75 years of age was higher when evaluated by thioflavine S than by immunocytochemistry with a polyclonal antibody against paired helical filaments. Mental status had been prospectively assessed in this cohort by the test score of Blessed et al. A difference between the two methods was found whatever the degree of mental impairment. Senile plaques were exceptionally immunolabeled in the least affected cases. This could not be explained only by differences in sensitivity of the stains and suggests that the amyloid is surrounded by anti-PHF positive neurites only in the latest stages of the senile plaque.

The distribution of intermediate filament proteins, actin and desmoplakins in human placental tissue as revealed by polyclonal and monoclonal antibodies

The distribution of intermediate filament proteins (cytokeratin, vimentin, desmin), actin, and desmoplakins in various placental compartments was studied by immunofluorescence microscopy using polyclonal and monoclonal antibodies. Trophoblast cells (cytotrophoblast, syncytiotrophoblast, isolated trophoblast cells, trophoblastic giant cells) were strongly stained by all types of cytokeratin antibodies. Antibodies to desmoplakins revealed the presence of desmosomes at all membranes, except the basal membrane of cytotrophoblast cells, and at the basal as well as the lumen-oriented membrane of the syncytiotrophoblast. After disappearance of the cytotrophoblast cell layer the distribution of desmosomes in the syncytiotrophoblast was unaltered. Isolated trophoblast cells contained desmosomes around their entire circumference. Amnion epithelial cells were heterogeneous with respect to cytokeratin composition as revealed, for example, by polyclonal antibodies with a broad range of cytokeratin reactivity and by monoclonal antibodies to cytokeratin No. 18. With the latter, a heterogeneous staining of amnion epithelial cells was achieved. Desmosomes (spots reactive with desmoplakin antibodies) were present at the lateral membranes of the amnion epithelial cells. In addition, vimentin filaments were coexpressed in these cells. Large vessels of the chorionic plate and stem villi showed thick walls consisting of vimentin-, desmin- and actin-positive cells. They were surrounded by mantles rich in vimentin-, desmin- and actin-positive cells, resembling myofibroblasts. This indicates that these cells may play a role in villous contractility and modulation of the intervillous space with effect on both maternal and fetal placental circulation.

Organization of desmosomal plaque proteins in cells growing at low calcium concentrations

Desmosomes are not formed in epithelial cell cultures growing in media with low (less than or equal to 0.1 mM) concentrations of Ca2+ (LCM) but appear rapidly upon shift to media of normal calcium concentrations (NCM). Previous authors using immunolocalization of desmoplakin, a marker protein for the desmosomal plaque, in LCM-grown cells have interpreted positively stained, dense, cytoplasmic aggregates on intermediate filaments (IF) bundles as preformed plaque units which upon NCM shift would move to the plasma membrane and contribute to desmosome formation. Studying various cell cultures, including primary mouse keratinocytes and human A-431 cells, we show that most, probably all, desmoplakin-positive aggregates in LCM-grown cells are associated with membranous structures, mostly vesicles, and also contain other desmosomal markers, including desmoglein, a transmembrane glycoprotein. We interpret such vesicles as residual desmosome-derived domains endocytosed upon cell dissociation. Only keratinocytes grown for long times (2-4 wk) in LCM are practically free from such vesicles. In addition, we demonstrate that certain cells such as A-431 cells, when passaged in LCM and in the absence of stable junctions, are able to continually assemble "half-desmosomes" on the plasma membrane which in turn can be endocytosed as plaque-bearing vesicles. We also show that in LCM the synthesis of several desmosomal proteins (desmoplakins I and II, plakoglobin, desmoglein, "band 6 protein") continues and that most of the plaque protein, desmoplakin, is diffusely spread over the cytoplasm, apparently in a soluble monodisperse form of approximately 9S. From our results we propose that the plaque proteins occur in small, discrete, diffusible entities in the cytoplasm, in concentrations that are relatively high in LCM and low in NCM, from which they assemble directly, i.e., without intermediate precursor aggregates on IFs in the cytoplasm, on certain plasma membrane domains in a Ca2+ dependent process.

Primary cerebral neuroectodermal tumors: neuroblastoma, differentiated neuroblastoma, and composite neuroectodermal tumor

Seven cases of primary cerebral neuroectodermal tumors with predominant neuroblastic features were studied ultrastructurally and five were evaluated immunohistochemically. The fine structural features were indicative of neuroblastic differentiation by the presence of elongated cytoplasmic processes, electron-dense neurosecretory granules, and neurotubules. Five of the seven cases had the morphologic findings of classic cerebral neuroblastoma, and the sixth case, originally diagnosed as an oligodendroglioma, had the features of a differentiated neuroblastoma. Desmoplastic and/or stromal foci were intermingled with neuronal-ganglionic cells and neuroblasts in the seventh case. In addition to strong immunoreactivity for S-100 protein and glial fibrillary acidic protein in the desmoplastic areas, the spindle cells had fibroblastic and Schwannian features by electron microscopy in the latter case. The neuroblastic cells and fibrillary network were immunoreactive for neuron-specific enolase and neurofilament in the five study cases. It is concluded that cerebral neuroectodermal tumors may express an range of phenotypic features from the exclusive neuroblastic stage to a neuronal and stromogenic phase analogous to the classic neuroblastoma of the sympathetic nervous system.

The large neurofilament subunit (NF-H) of the rat: cDNA cloning and in situ detection

A lambda gt11 expression library was screened with a polyclonal antiserum directed against Wla Wolfgram protein which corresponds to the 2',3'-cyclic nucleotide 3'-phosphohydrolase. This antiserum also recognizes epitopes of the high protein subunit of neurofilaments (NF-H). An NF-H cDNA clone (pNF-H1: 1.7 kb) was isolated and characterized. Using pNF-H1 as a probe, a second cDNA clone (pNF-H2: 3 kb) was isolated from the lambda gt11 library. The two clones were sequenced and pNF-H2 was found to encode 80% of rat NF-H protein (coil-2 and C-terminal region). The C-terminal region contains an unusual sequence with stretches of repeats of Lys-Ser-Pro which represent possible phosphorylation sites. Specific localization in neurons of the corresponding mRNA was demonstrated by in situ hybridization using the pNF-H1 as a probe.

Cytoskeleton in preimplantation mouse development

This paper reviews the constituents of the cytoskeleton in the cells of the preimplantation mouse embryo and how they change as the development proceeds. The cytoskeleton can be divided into two distinct groups, that in the cytosplasm and that associated with the membrane. The first and better-known group contains microfilaments, microtubules and intermediate filaments, the second such components of the cell and nuclear membrane as spectrin-like protein and nuclear lamin. The filamentous components of the cytoplasmic cytoskeleton adhere to the nuclear and cell membrane at attachment points where specific proteins such as vinculin may mediate the interaction. Each cell of the early embryo has all of these components, but their morphological organization and molecular constitution alter as the embryo develops. These modifications are especially pronounced when the cleavage-stage embryo compacts and when the blastocysts forms and differentiates. These events represent the most critical stages of morphogenesis and cytodifferentiation in the preimplantation embryo. The cytoskeleton may thus have an important role in the control of the early mammalian development.

Functional significance of intermediate filament meshwork in annelid helical muscles

A desmin-like protein of mol wt 54 kDa was identified in the body wall muscles of some Polychaeta, Oligochaeta, and Hirudinea utilizing SDS-PAGE followed by blot and screening with a vertebrate anti-desmin antibody. The pattern in immunofluorescence is compared to electron micrographs where several bundles of filamentous structures are clearly identifiable. These bundles are unevenly arranged in round or flattened circomyarian fibers and sometimes clearly connect Z elements with hemidesmosomes. The mechanism of intermediate filaments as a functional integration in muscle fibers is analyzed and a possible role as a block to superelongation typical of helical muscles is discussed.

Expression of intermediate filaments and desmoplakin in vertebrate olfactory mucosa

The expression of intermediate filaments (IF) and desmoplakin was investigated in frog, bovine, and human (fetal) olfactory mucosa. IF are tissue-specific molecular cytoskeletal markers; desmoplakin is the major desmosomal protein. Positive immunoreactivity was observed in the epithelium and in the subepithelial Bowman's glands to keratin and to desmoplakin, indicating the epithelial nature of this tissue. Desmin, neurofilaments, and glial fibrillary acidic protein (GFAP) were not detected in the mucosa. The absence of neurofilaments and GFAP in the tissue containing sensory neurons and glia-like supporting cells is a unique feature and may be related to the fact that the chemosensory neurons are situated in a bonafide epithelium and are known to undergo continuous turnover. In view of the controversy regarding the expression of vimentin in the olfactory neurons, three independently derived antibodies to vimentin were used; weak or no labeling was found in the epithelium, whereas mesenchymal cells in the lamina propia were labeled with all three antibodies. Olfactory nerve fascicles in the lamina propia were heterogenously labeled: VIM 13.2 gave very weak labeling; aVimAS showed mild labeling and SBV-21 showed intensive labeling in the nerve fascicle. This heterogenous labeling pattern may suggest that olfactory vimentin is distinct in reacting only with some of the antivimentin antibodies.

Vimentin expression in oocytes, eggs and early embryos of Xenopus laevis

Immunocytochemical studies using a monoclonal anti-porcine vimentin antibody reveal a well-organized pattern of staining in Xenopus laevis oocytes, eggs and early embryos. The positions of Xenopus vimentin and desmin in two-dimensional (2D) polyacrylamide gels were first established by immunoblotting of muscle Triton extracts with anti-intermediate filament antibodies (anti-IFA), which cross-react with all intermediate filament proteins (IFPs). The anti-porcine vimentin reacts with vimentin and desmin in muscle 2D immunoblots, but only reacts with one polypeptide in oocyte blots in the position predicted for vimentin (Mr 55 × 10(3), pI 5.6). Using an anti-sense probe derived from a Xenopus vimentin genomic clone in RNase protection assays, we show that expression of vimentin begins in previtellogenic oocytes. The level of expression remains constant throughout oogenesis and in unfertilized eggs. These data suggest that vimentin is expressed in oocytes and eggs. Most interestingly, the immunocytochemical results also show that vimentin is present in the germ plasma of oocytes, eggs and early embryos. It is therefore possible that vimentin has an important role in the formation or behaviour of early germ line cells.

Neurofilament phosphorylation in axons and perikarya: immunofluorescence study of the rat spinal cord and dorsal root ganglia with monoclonal antibodies

Rat dorsal root ganglia and spinal cord were stained with 12 monoclonal antibodies reacting with phosphorylated epitopes of two neurofilament proteins (NF 150K and NF 200K). Three monoclonal antibodies were axon-specific in both locations; neuronal perikarya were not stained. Nine monoclonal antibodies stained a subpopulation of neurofilament-positive sensory neurons, as indicated by double labeling experiments with polyclonal antibodies reacting with phosphorylated and dephosphorylated forms of the neurofilament protein triplet. Of these nine antibodies, two stained motor neuron perikarya in the spinal cord, while the remaining seven antibodies were axon-specific in this location. Subpopulations of stained and unstained motor neurons were not observed. With all 12 antibodies, the staining pattern in the lumbar dorsal root ganglia and spinal cord remained unchanged following sciatic nerve crush and ligature. The findings suggest that, in the neurofilament, some phosphorylated epitopes are axon specific, while other phosphorylated epitopes are present in both axons and perikarya. Furthermore, they suggest that differences exist between neuronal populations as to the presence of phosphorylated epitopes in perikaryal neurofilaments. It remains to be seen whether phosphorylation events in perikarya and axons have similar or different effects on neurofilament structure and function.

Immunocytochemical analysis of intermediate filaments in human ependymal tumors

The peroxidase anti-peroxidase technique was used for localization of glial fibrillary acidic protein (GFAP) and vimentin (VM) in 19 ependymal tumors in order to determine if a unique pattern of intermediate filament (IF) expression could be demonstrated. Cytokeratin (CK) immunoreactivity was examined in a subgroup of 7 tumors with papillary pattern. Nineteen non-ependymal neuroectodermal tumors were used as controls. Ependymomas, subependymomas and astrocytomas were positive for both IF. Oligodendrogliomas, oligodendroglial portions of mixed gliomas and the majority of medulloblastomas were negative for GFAP and VM. Areas of poor differentiation in all tumors demonstrated little expression of any IF. A composite ependymoma/choroid plexus papilloma showed the presence of GFAP, VM and CK in the papillomatous portion only. Four papillary ependymomas were negative for CK. This study emphasizes the parallel distribution of GFAP and VM in well differentiated ependymomas and other glial tumors and casts doubt upon the concept of VM as a marker for de-differentiation in neuroectodermal neoplasia.

Ameloblastic fibroma: growth potentiality of odontogenic epithelium and coexpression of intermediate filament proteins in fibromatous cells

Four cases of ameloblastic fibroma are described immunohistochemically in terms of intermediate-sized proteins in both epithelial and mesodermal components. Keratin proteins were demonstrated by polyclonal anti-keratin antiserum (TK: detecting 41-65 kDa keratins) and 2 monoclonal antibodies to keratin (KL1: 55-57 kDa, PKK1: 44, 46, 52 and 54 kDa), and monoclonal antibodies to vimentin and desmin. Two types of odontogenic epithelial tumour cells were discriminated: undifferentiated odontogenic cells and common ameloblastoma cells. Keratin expression was found to be stronger in undifferentiated cells than in the ameloblastoma cells. Undifferentiated cells were PAS-positive, while ameloblastoma cells were negative. Fibroma cells were strongly positive for vimentin, and negative for desmin. Keratin proteins were also expressed slightly. Thus, coexpression of keratin and vimentin was seen in fibroma cells. Histogenesis is discussed from the standpoint of the distribution patterns of keratin and vimentin, as well as with respect to the histopathology.

Immunohistochemical staining for vimentin filaments and S-100 protein in myxoma of the jaws

Two jaw myxomas have been analyzed by a panel of antibodies to characterize this tumour type. Vimentin, but not keratin, neuron-specific enolase (NSE), glial fibrillary acidic protein (GFAP), neurofilament (NF), desmin and Factor VIII-related antigen (FVIII-AG), demonstrated positivity in the cytoplasm of the neoplastic cells. Moreover, an antibody against S-100 protein also showed a strong positive reaction in the cytoplasm of the tumour cells examined. Thus directly indicating a mesenchymal derivation for odontogenic myxoma, and is the first demonstration of S-100 protein within the cells of this tumour type.

Cytoskeleton-associated plectin: in situ localization, in vitro reconstitution, and binding to immobilized intermediate filament proteins

The association and interaction of plectin (Mr 300,000) with intermediate filaments and filament subunit proteins were studied. Immunoelectron microscopy of whole mount cytoskeletons from various cultured cell lines (rat glioma C6, mouse BALB/c 3T3, and Chinese hamster ovary) and quick-frozen, deep-etched replicas of Triton X-100-extracted rat embryo fibroblast cells revealed that plectin was primarily located at junction sites and branching points of intermediate filaments. These results were corroborated by in vitro recombination studies using vimentin and plectin purified from C6 cells. Filaments assembled from mixtures of both proteins were extensively crosslinked by oligomeric plectin structures, as demonstrated by electron microscopy of negatively stained and rotary-shadowed specimens as well as by immunoelectron microscopy; the binding of plectin structures on the surface of filaments and cross-link formation occurred without apparent periodicity. Plectin's cross-linking of reconstituted filaments was also shown by ultracentrifugation experiments. As revealed by the rotary-shadowing technique, filament-bound plectin structures were oligomeric and predominantly consisted of a central globular core region of 30-50 nm with extending filaments or filamentous loops. Solid-phase binding to proteolytically degraded vimentin fragments suggested that plectin interacts with the helical rod domain of vimentin, a highly conserved structural element of all intermediate filament proteins. Accordingly, plectin was found to bind to the glial fibrillar acidic protein, the three neurofilament polypeptides, and skin keratins. These results suggest that plectin is a cross-linker of vimentin filaments and possibly also of other intermediate filament types.

Modulation of desmin intermediate filament assembly by a monoclonal antibody

We have used a monoclonal antibody against desmin to examine the assembly of intermediate filaments (IF) from their building blocks, the tetrameric protofilaments. The antibody, designated D76, does not cross react with any other IF proteins (Danto, S.I., and D.A. Fischman. 1984. J. Cell Biol. 98:2179-2191). It binds to a region amino-terminal to cys-324 of avian desmin that is resistant to chymotrypsin and trypsin digestion, and in the electron microscope appears to bind to the ends of tetrameric protofilaments. In combination, these findings suggest that the epitope of the antibody resides at the amino-terminal end of the alpha-helical rod domain. Preincubation of desmin protofilaments with an excess of D76 antibodies blocks their subsequent assembly into IF. In the presence of sub-stoichiometric amounts of antibodies, IF are assembled from protofilaments but they are morphologically aberrant in that (a) they are capped by IgG molecules at one or both ends; (b) they are unraveled to varying degree, revealing a characteristic right-handed helical arrangement of sub-filamentous strands of different diameters. The antibody binds only to the ends but not along the length of desmin IF. The most straightforward explanation for this is that the epitope resides in a part of the desmin molecule that becomes buried within the core of the filament upon polymerization and is therefore inaccessible to the antibody.

Biological characterization and oncogene expression in human colorectal carcinoma cell lines

To establish well-characterized cellular reagents for the study of colon carcinoma, we have examined 19 human colorectal carcinoma cell lines with regard to morphology, ultrastructure, expression of tumor-associated antigens, proliferative capacity in vitro, anchorage-independent growth, oncogene expression, tumorigenicity and malignant potential. Cell lines examined were cultured under identical conditions, and in vitro and in vivo analyses were performed in parallel on replicate cultures. Three classes of colorectal cell lines were defined according to their tumorigenicity in nude mice. Class-1 lines formed rapidly progressing tumors in nearly all mice at an inoculum of 10(6) cells. Cell lines belonging to class-2 were less tumorigenic, producing tumors later and at a slower growth rate. Class-3 lines were non-tumorigenic under all experimental conditions tested. By Northern analysis, the oncogenes c-myc, H-ras, K-ras, N-ras, myb, fos and p53 were expressed in nearly all cell lines examined. In contrast, transcripts for abl, src and ros were not detected. The best in vitro predictor of tumorigenicity was colony formation in soft agar. There was no detectable correlation between tumorigenicity and metastatic potential, doubling time in vitro, production of tumor-associated markers, xenograft histology or expression of specific oncogenes.

Filamentous cross-bridges link intermediate filaments to the nuclear pore complexes

Intermediate filament-nuclear matrix interactions were studied in cultured rat ventral prostate cells and isolated rat uterine epithelial cells. Cytokeratin filaments were identified by immunoelectron microscopy. In addition to conventional thin section of Triton X-100 treated cells, subcellular residues composed of intermediate filaments and nuclear matrix were critical-point dried and platinum-carbon replicated. The results demonstrate the presence of a previously unrecognized type of filamentous cross-bridges that link intermediate filaments to the nuclear pore complexes.

Nuclear matrix-intermediate filament system and its alteration in adenovirus infected HeLa cell

The nuclear matrix-intermediate filament (NM-IF) of normal and adenovirus infected HeLa cells were investigated by means of both electron microscopy and two-dimensional gel electrophoresis. After infection there were some changes in NM-IF, and the viral factory was suspended in nuclear matrix. Two new polypeptides appeared in 2-D gel of NM-IF after infection. They are probably not viral proteins but cellular polypeptides. During viral replication, all of vimentin were degraded and phosphorylated keratin 18 increased. These facts suggest that NM-IF plays a certain role in adenovirus replication.

Immunoreactivity for laminin in the developing ventral longitudinal pathway of the brain

The first long tract to form in the brain of a vertebrate embryo is the ventral longitudinal pathway. In order to investigate what chemical cues may guide nerve growth cones along this pathway, affinity-purified antibodies to laminin and collagen type IV were used to stain sections of mouse embryos from Embryonic Days 8 through 17. A monoclonal anti-neurofilament antibody was used to show the development of the ventral longitudinal pathway in relationship to immunoreactivity for laminin and collagen type IV. At Day 8 fluorescent immunoreactivity for laminin is bright in the external limiting membrane of the neural tube, but the neuroepithelium does not show bright laminin or neurofilament immunoreactivity. At E9 the ventral longitudinal pathway is forming and punctate immunoreactivity for laminin is present on the surfaces of neuroepithelial cells in the marginal zone, through which axons of the ventral pathway extend. Punctate immunofluorescence for laminin remains concentrated in the marginal zone on Days E10 through E14, but on E16 punctate immunofluorescence was much reduced, although immunoreactivity for laminin remained bright in the maturing pial and arachnoid membranes and on blood vessels in the brain. Immunoreactivity for collagen type IV was strong in the external limiting membrane and on blood vessels, but never showed concentrated punctate immunofluorescence in the marginal zone. These results indicate that laminin may be available on cell surfaces and in extracellular spaces as an adhesive ligand for growth cones during the formation of the ventral longitudinal pathway.

Maturation of hagfish gland thread cells: composition and characterization of intermediate filament polypeptides

Previous studies with the hagfish, a primitive vertebrate, have shown that the gland thread cells (GTCs) each contain a single thread (approximately 60 cm long in average-sized cells) in the form of a concisely coiled cytoskeletal entity destined for export by holocrine secretion. The thread in relatively immature GTCs consists almost entirely of intermediate filaments (IFs) bundled in parallel alignment with far fewer microtubules (MTs). The three thread polypeptides described earlier (alpha, basic; beta, acidic; gamma, most acidic; each with a Mr of 63-64 kD) are now further evaluated with respect to in vitro assembly, cross-reactivity with IF polypeptides from higher vertebrates, and peptide sequence homology with known IF polypeptides. The overall results mainly suggest that the hagfish polypeptides are keratinlike substances but lamins or a new type of IF is not ruled out. However, cross-reactivity is weak with mammalian keratins; the 8-11-nm filaments formed from mixtures of alpha and gamma in vitro are generally linear rather than the curvilinear structures usually formed by keratin and nonkeratin IFs; and mixtures of alpha and beta tend to yield 9-12-nm granules or granular strings. Polypeptide analyses on GTCs segregated on the basis of maturational stage show a progressive increase in beta/gamma values which correlates with cell maturation, but the alpha/(beta + gamma) ratios remain near 1. Inasmuch as beta and gamma have many similar properties, the documented increase in the amount of the beta component in aging GTCs might in part be the result of a failure in a posttranslational modification system and may contribute to the ultrastructural changes that accompany thread maturation in preparation for holocrine secretion and subsequent modulation of the viscoelastic properties of mucus.