The Effects of Mutant Gene hairless in Chimeric Mice

The autosomal recessive gene hairless (hr) is responsible for the complete hairlessness in mice homozygous for this gene. Hair shedding that begins at the age of 10 days is caused by an abnormal cycle of hair follicle development disturbed at the catagen stage. This results in enhanced programmed cell death (apoptosis) and ultimately leads to the complete hair follicle destruction and shedding of all hairs by the age of three weeks. To study the phenotypic expression of the hr gene in a chimeric organism, we have obtained 12 chimeric mice hr/hr +/+ by means of aggregation of early embryos hr/hr and +/+. In chimeric mice, the hair shedding has begun two days later than in the hr/hr mice. By day 23 of postnatal development, hairless areas were present on the coat of chimeric mice or the latter were completely hairless depending on the percentage of the hr/hr mutant component. In four chimeras with high content of the mutant component (68–76%), the hair shedding process was similar to that in the hr/hr mice, though it was accomplished two days later. In three chimeras with 48–51% of the mutant component, alternating hairless and hair-covered bands were observed. These data suggest that the hr gene acts in epidermal cells of a hair follicle, because epidermal cell clones in embryonic skin migrate in the lateral–ventral direction coherently and without mixing. However, some chimeras displayed a pattern which was not so clear-cut: the band borders were illegible and hairs partly covered the hairless areas. In some chimeras, the uniform thinning of the coat was observed. Analysis of the effects of the hr mutant gene in chimeric mice differing in the ratio between mutant (hr/hr) and normal (+/+) components in tissues suggests that the hrgene acts in the epidermal cells of the hair follicle. The interactions between cells have an essential effect on the mode and degree of the hr gene expression, which leads to distortion of the ectodermal coat pattern in chimeras.     

Heart and the peritoneal cover of the gut sinus in the polychaete Arenicola marina: an ultrastructural and autoradiographic study

To elucidate the cellular mechanism underlying the growth of the peritoneal cover of the gut sinus and the heart in the polychaete Arenicola marina, cellular organization of these structures and proliferative potential of their cells were investigated using electron microscopy and electron microscopic autoradiography. Arenicola has a pair of dorsolaterally situated hearts connected to the gut sinus via a short duct and composed of two muscular layers separated by a layer of the extracellular matrix (ECM). The peritoneal cover of the gut sinus and the outer muscular layer of the heart present a myoepithelial layer resting on the ECM. The inner muscular layer of the heart is composed of myofibril-containing cells lacking well-defined polarity in arrangement of organelles. However, their persistent connection to branches of the ECM and the adherens-like intercellular junctions allow for considering the inner layer a modified myoepithelium. In the peritoneal cover of the gut sinus and in both myoepithelial layers of the heart, noncontractile epithelial cells have been observed. As determined by thymidine labeling, these epithelial cells are capable of DNA synthesis, while myoepithelial cells are not. Some suggestions are made about the myogenic nature of the epithelial cells in the investigated structures of A. marina.     

Effects of the Mutant Gene wellhaarig in the Chimeric Mice

The mutant genewellhaarig(we) controls the formation of the waved coat in mice, which is most pronounced in homozygotes at 10 to 21 days of postnatal development. Abnormal hair growth and structure in the we/we mutant mice results from defective cell differentiation in the inner root sheath of a hair follicle. To localize the site of the we gene action, we obtained ten chimeric mice by aggregation of the early C57BL/6-2we/we and BALB/c embryos. The chimera coat was waved, shaggy, or almost normal depending on the percentage of the mutant component. In the we/we +/+ chimeric animals of the first generation (G1) aged 21 days, both mutant and normal hair phenotypes were observed, which was especially discernible in zigzag hair. Note that none of the chimeras exhibited the alternating patterns of transversely oriented stripes or patches of either mutant or normal hair; i.e., they had a mixed parental hair phenotype. We also did not observe the animals with an intermediate phenotype, which suggests a discontinuous hair formation in chimeras according to the all or nothing principle. The data obtained indicate that the dermal papilla cells of a hair follicle are the sites for the we gene action. During the embryonic development, dermal cells are strongly mixed, which accounts for the lack of the clear-cut transverse stripes of either mutant or normal hair. The mutant genewe is probably responsible for a disrupted induction signal from the dermal papilla towards ectodermal cells of a hair follicle.     

Nuclear envelope-limited chromatin sheets are part of mitotic death

Nuclear envelope-limited chromatin sheets (ELCS) are enigmatic membranous structures of uncertain function. This study describes the induction of ELCS in p53 mutated Burkitt's lymphoma cell lines after treatment with irradiation or the microtubule inhibitor, SK&F 96365. Both treatments evoked similar mitotic death, involving metaphase arrest followed by extensive endopolyploidisation and delayed apoptosis, although the kinetics were different. We found that induction of ELCS and nuclear segmentation correlated with the amount and kinetics of M-phase arrest, mitosis restitution and delayed apoptosis of endopolyploid cells. In metaphases undergoing restitution, ELCS are seen participating in the restoration of the nuclear envelope, mediating the attachment of peripheral chromatin to it. In interphase cells, ELCS join nuclear segments, ectopically linking and fusing with heterochromatin regions. In cells with segmented nuclei, continued DNA replication was observed, along with activation and redistribution of Ku70, suggestive of non-homologous DNA end-joining. Induction of ELCS also parallels the induction of cytoplasmic stacked membrane structures, such as confronting cisternae and annulate lamellae, which participate in the turnover and degeneration of ELCS. The results suggest that arrest at a spindle checkpoint and the uncoupling of mitosis from DNA replication lead to the emergence of ELCS in the resulting endopolyploid cells.     

Atrial natriuretic peptide in the granular cells of the snail heart

Cardiomyocytes of vertebrates combine contractile and endocrine functions. They synthesize and secrete atrial natriuretic peptide (ANP), which is localized in their specific granules. The presence of ANP has been shown in some tissues of invertebrates, including the heart of molluscs. We have studied localization of ANP in cells of the snail heart. METHOD: The atrial and ventricular tissues of the snail Helix pomatia were studied by electron microscope immunocytochemistry, using anti-ANP antibodies. ANP-immunoreactivity has been detected in granules of granular cells located on the luminal surface of the snail myocardium. These cells are abundant in the atrium being very rare in the ventricle. Granular cells at different stages of maturation were revealed. Immature granular cells have light granules of moderate size with homogeneous tight content, while mature granular cells are huge in size and all their granules are fused together. The material of these granules loosens up and almost completely fills up the cytoplasm. No ANP-immunoreactivity was observed in muscle cells or nerve fibers. A possible origin of granular cells from the cardiac endothelial cells is discussed. The molluscan heart, similar to that of vertebrates, is a bifunctional organ. However, contrary to the heart of vertebrates, in the molluscan heart contractile and endocrine functions are separated between different types of cells.     

The ultrastructure of myotomal muscles of the golomianka, Cormephorus baikalensis Pallas

An ultrastructural study of the myotomal muscles in the golomianka, Comephorus baikalensis Pallas, revealed two main and distinct muscle regions: superficial and white. They were distinguished on the basis of histological and ultrastructural organization. Only the superficial fibre region shows homogeneous organization. The principal new finding is the unique ultrastructural organization of the superficial muscle fibres. Their myofibrils occur in the form of ribbons surrounded by large mitochondria.     

Interaction of trypsin with multilamellar vesicles of soybean lipids

The pH dependence of complex formation of trypsin with multilamellar vesicles (MLV) of soybean lipids has been investigated. The lipids were characterized by the same phospholipid composition, but the content of other lipids differed. Decrease of pH or introduction of negatively charged components into the lipid samples increased trypsin content in the protein-lipid complexes. This suggests electrostatic interaction between the protein and soybean lipids. The dependence of trypsin activity in the complexes with MLV on their concentration and on the presence of an ionic detergent was studied. Trypsin-MLV interaction did not result in complete inactivation of the protein molecules. Moreover, the effects of dilution and addition of ionic detergent on trypsin activity were additive. Using a fluorescence technique, complex formation with MLV was found to stabilize trypsin molecules, preventing their autolysis.     

Identification of the optochin-resistant Streptococcus pneumoniae strains

So far the prevalent method of the identification of pneumococci in the routine diagnostic practice has included three tests: sensitivity to optoxin, solubility in biliary salts and reaction with omniserum. At present optoxin-resistant pneumococcal strains, as well as those giving dual reaction to solubility in biliary salts, occur sufficiently often thatconsiderably complicates the identification of this infective agent. We have summarized experience in the isolation of S. pneumoniae strains, resistant to optoxin and not soluble in biliary salts; in addition, the prospects of introducing the complex approach to the identification of a given culture with the use of molecular diagnostic methods into daily practice are evaluated.     

The cytoskeletal protein zyxin—A universal regulator of cell adhesion and gene expression

The attachment of a cell to the extracellular matrix or the surface of another cells affects not only the cell motility, but also gene expression. In view of this, an important problem is to establish the molecular mechanisms of signal transduction from the receptors of cell adhesion to the nucleus, in particular, to identify and investigate the protein transducers of these signals. One of these transducers, the LIM domain protein zyxin, is predominantly localized at the sites of cell adhesion, where it participates in the assembly of actin filaments. Owing to its location near the inner surface of the membrane, zyxin can interact with the transmembrane receptors of some signaling cascades and affect the signal transduction from the extracellular ligands of these receptors. Furthermore, under certain conditions, zyxin moves from the sites of cell contacts to the nucleus, where it directly participates in the regulation of gene expression. Of particular interest is the function of zyxin as a possible coordinator of gene expression and morphogenetic movements in embryogenesis. The published data discussed in the present review indicate the important role of zyxin in transmitting information from the regions of cell contacts to the genetic apparatus of the cell.     

Emergent Self-Organized Criticality in Gene Expression Dynamics: Temporal Development of Global Phase Transition Revealed in a Cancer Cell Line

Background

The underlying mechanism of dynamic control of the genome-wide expression is a fundamental issue in bioscience. We addressed it in terms of phase transition by a systemic approach based on both density analysis and characteristics of temporal fluctuation for the time-course mRNA expression in differentiating MCF-7 breast cancer cells.

Methodology

In a recent work, we suggested criticality as an essential aspect of dynamic control of genome-wide gene expression. Criticality was evident by a unimodal-bimodal transition through flattened unimodal expression profile. The flatness on the transition suggests the existence of a critical transition at which up- and down-regulated expression is balanced. Mean field (averaging) behavior of mRNAs based on the temporal expression changes reveals a sandpile type of transition in the flattened profile. Furthermore, around the transition, a self-similar unimodal-bimodal transition of the whole expression occurs in the density profile of an ensemble of mRNA expression. These singular and scaling behaviors identify the transition as the expression phase transition driven by self-organized criticality (SOC).

Principal Findings

Emergent properties of SOC through a mean field approach are revealed: i) SOC, as a form of genomic phase transition, consolidates distinct critical states of expression, ii) Coupling of coherent stochastic oscillations between critical states on different time-scales gives rise to SOC, and iii) Specific gene clusters (barcode genes) ranging in size from kbp to Mbp reveal similar SOC to genome-wide mRNA expression and ON-OFF synchronization to critical states. This suggests that the cooperative gene regulation of topological genome sub-units is mediated by the coherent phase transitions of megadomain-scaled conformations between compact and swollen chromatin states.

Conclusion and Significance

In summary, our study provides not only a systemic method to demonstrate SOC in whole-genome expression, but also introduces novel, physically grounded concepts for a breakthrough in the study of biological regulation.