A domain-specific marker for the hepatocyte plasma membrane. II. Ultrastructural localization of leucine aminopeptidase to the bile canalicular domain of isolated rat liver plasma membranes

Leucine aminopeptidase (LAP) is an integral membrane glycoprotein localized to the apical membrane domain of intestinal and kidney epithelial cells. By indirect immunofluorescence, we have shown that antibodies raised against rat intestinal LAP recognized a similar protein concentrated in the bile canalicular (BC) domain of the hepatocyte in situ (Roman, L.M., and A.L. Hubbard, 1983, J. Cell Biol., 96:1548-1558). We have extended this localization to the ultrastructural level. When a saponin-permeabilized, agarose-embedded plasma membrane (PM) fraction was incubated with affinity-purified anti-LAP, 85% of the protein A-gold particles associated with the three recognizable PM domains were present in the BC. The levels of labeling on the other two domains (sinusoidal and lateral) did not exceed that observed with nonimmune controls. The concentration of LAP in the BC domain in isolated PM sheets prompted us to use this antigen for the affinity isolation of BC membrane (Roman, L.M., and A.L. Hubbard, 1984, J. Cell Biol., 98:1497-1504, companion paper).     

ACTIVITY OF MARGINAL AND PLATE MERISTEMS DURING LEAF DEVELOPMENT OF XANTHIUM PENNSYLVANICUM

The mitotic and biosynthetic activities of the marginal and plate meristems were studied during the entire course of leaf development of Xanthium pennsylvanicum. In contrast to statements in the literature, marginal meristem activity is long in duration, as assayed by the mitotic counts and H³-thymidine incorporation. This me istem is active 23 days. The plate meristem is active for an additional 3 days after cessation of cell division in the marginal meristem, but the total duration of its mitotic activity is also approximately 23 days. Numerous periclinal cell divisions of the plate meristem form additional cell layers and contribute to the growth of the lamina in thickness. Incorporation of H³-thymidine increased during the course of leaf development. Cells between plastochronic ages 0 and 2.0 incorporated more of the radioisotopic precursor than those of younger leaf primordia. The uptake and incorporation of H³-thymidine into nuclear DNA was more sluggish during the early stages of development than in the more expanded leaves. No DNA synthesis was demonstrated after cessation of cell division in the leaf lamina. Metabolic or endomitotic DNA synthesis after leaf plastochron index (LPI) 3.0 seems improbable. No significant differences in the incorporation of H³-thymidine could be demonstrated between the marginal and plate meristems. This would indicate no distinct biosynthetic differences between the two meristems. The definitions of the marginal and plate meristems of Xanthium leaves were formulated in view of the above findings.     

Growth Curve and Distribution of Rous Sarcoma Virus (Bryan) in Japanese Quail

On primary infection with the Bryan strain of Rous sarcoma virus (RSV), the growth curve of the virus in the brain of Japanese quail was similar to that observed in chicks and turkey poults. Infectious virus disappeared from the brain after inoculation. After an eclipse period during which no virus was detectable, infectious virus began to appear at 2 days and reached maximal titers in the brain samples at 7 days after inoculation. When Japanese quail were infected intracerebrally with RSV, relatively high titers of virus were recovered from brain tissue but not from liver, lung, kidney, or blood of moribund birds. Only tumors produced in the wing web of quail infected subcutaneously yielded high titers of virus. Other tissues yielded no virus, even though wing web tumors appeared as early as in chicks similarly infected. RSV could be propagated in the wing web of quail for at least 14 passages without any loss of infectivity. On the other hand, serial passage in quail brain resulted in a progressive loss of infectivity until virus was completely lost.     

On the formation of adipocere from fats

Summary The formation of adipocere is a process occurring under virtually anaerobic conditions in which human fat is converted into a complex of saturated fatty acids by a great variety of bacterial species occurring in and on the decomposing body.     

The fibronectin receptor is organized by extracellular matrix fibronectin: implications for oncogenic transformation and for cell recognition of fibronectin matrices

Cells interact with extracellular fibronectin (FN) via adhesive fibronectin receptors (FNRs) that are members of the very late antigens (VLAs) subgroup of the integrin family. In stationary fibroblasts, the FNR is highly organized and distributed identically to extracellular FN fibrils. However, in highly migratory neural crest cells and embryonic somatic fibroblasts, this organization is lost and the FNR appears diffuse. Similarly, oncogenic transformation typically leads to disorganization of the FN receptor and loss of matrix FN. Two models can account for these observations. First, the FN matrix may organize the FN receptor at extracellular matrix contacts on the cell surface. Motile cells not depositing FN matrices thus lack organized receptors. Alternatively, as the FNR is required for optimal FN matrix assembly, (McDonald, J. A., B. J. Quade, T. J. Broekelmann, R. LaChance, K. Forseman, K. Hasegawa, and S. Akiyama. 1987. J. Biol. Chem. 272:2957-2967; Roman, J. R. M. LaChance, T. J. Broekelmann, C. J. R. Kennedy, E. A. Wayner, W. G. Carter, J. A. McDonald. 1989. J. Cell Biol. 108:2529-2543) and has putative cytoskeletal links, it could be organized from within the cell helping to position newly forming FN fibrils. To study this question, we developed peptide antibodies specifically recognizing the alpha 5 subunit of the FNR. Using these antibodies, we examined the organization of FN and of the FNR in normal, matrix assembly inhibited, and SV40-transformed human fibroblasts. On FN-coated substrates, the FNR is found in focal contacts rather than diffusely on the basal cell surface, suggesting FNR interaction with intracellular components. However, when FN fibrils are deposited, the FNR is co-distributed with these fibrils. Preventing FN matrix assembly prevents organization of the FNR. Moreover, when fibroblasts with well established FN matrices and co-distributed FNR are incubated briefly with monoclonal antibodies that block FNR binding to FN, the FNR is no longer co-distributed with the FN matrix. Thus, the FN receptor is organized in fibrils on the cell surface in response to extracellular FN. Because exogenous FN restores a FN matrix and receptor organization to SV40-transformed cells, the diffuse FN receptor phenotype appears to be related to loss of the FN matrix rather than to impaired FNR function. These results explain diffusely distributed FNRs in migratory neural crest and embryonic fibroblasts lacking well organized FN matrices and emphasize the existence of separate but related systems controlling FN deposition and recognition by receptor-armed cells.