Ultrastructure of the human toenail

Summary The nail cells produced in the ventral, apical and dorsal portions of the proximal matrix moved in axiodistal direction to meat together at theproximal point of keratinization. The proximal nail plate from this point on was added continuously by the cells from ventral matrix and nail bed. Dorsal matrix soon ceased to produce nail cells and further distally transformed into the posterior nail fold. With Zeiss-Nomarski differential interference contrast equipment, the proximal nail plate could be divided into the ventral and dorsal halves. Near the lunula the nail bed produced one more distinct layer beneath the proximal ventral layer. Electron miscroscopically all nail cells regardless of their origins were seen keratinizing by accretion of tonofibrils without formation of keratohyaline granules. Membrane-coating granules (MGG's) were produced in abundance. They were discharged and provided the intercellular cement. The discharged material widened some of the gap junctions while it tightened nonspeccific junctions to produce 150–180 Å intercellular spaces, i.e. thenarrow junctions. The narrow junctions were the most common type of intercellular junction connecting the keratinized nail cells. The thick cellular envelope of the keratinized cells, i.e. themarginal band, was formed by a precipitation of dense material on the cytoplasmic side of the plasma membranes and not by discharged MCG's.

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Zusammenfassung Die Nagelzellen, die von den ventralen, apikalen und dorsalen Anteilen der proximalen Matrix gebildet wurden, rückten in axial-distaler Richtung vorwärts, bis sie amproximalen Verhornungspunkte zusammentrafen. Von diesem Punkte an wurden der proximalen Nagelplatte ununterbrochen Zellen von der ventralen und dorsalen Matrix und vom Nagelbett zugefügt. Bald hörte die dorsale Matrix auf, Nagelzellen zu entwickeln und wurde weiter distal in den hinteren Nagelfalz umgewandelt. Mit der differentialen Phasenkontrast-Apparatur von Zeiss-Nomarski konnte man die Teilung der proximalen Nagelplatte in eine ventrale und dorsale Hälfte erkennen. Nächst der Lunula entwickelte das Nagelbett noch eine weitere deutliche Schicht unter der proximalen ventralen Schicht. Elektronmikroskopisch zeigten alle Nagelzellen, ohne Rücksicht auf ihren Ursprung, Verhornung durch Anhäufung von Fibrillen ohne Bildung von Keratohyalinkörnern. Membrane-coating granules (MCG) entstanden in reichlicher Menge. Sie wurden abgestoßen und bildeten die intercellulßre Kittsubstanz. Das abgestoßene Material erweiterte einige der engen Membranspalten, während es gewöhnliche, klaffende (nicht-spezifische) Zellgrenzen verengte und dadurch 150–180 Å weite intercelluläre Zwischenräume bildete, nämlich dieengen Zellverkittungen. Die engen Zellverkittungen stellten den häufigsten Typ der intercellulären Anlagerung dar, wodurch die verhornten Nagelzellen zusammengehalten wurden. Die dicke Zellhülle der verhornten Zellen, nämlich dasGrenzband, wurde durch Niederschlag von dichtem Material an der protoplasmatischen Seite der Zellmembran gebildet und nicht durch die membrane-coating granules.

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This work was partially supported by Part I Designated Research Grant and Medical Investigatior sward of the Veterans Administration.     

Post-mitotic human dermal fibroblasts efficiently support the growth of human follicular keratinocytes

For growth at low seeding densities, keratinocytes isolated from human tissues like epidermis or hair follicles are dependent on mesenchyme-derived feeder cells such as the 3T3-cell employed so far. As an alternative method, the present study describes the use of post-mitotic human dermal fibroblasts sublethally irradiated or mitomycin C-treated. Special emphasis was put on efficient growth of primary keratinocyte cultures plated at very low seeding densities. Thus, outer root sheath cells isolated from two anagen human hair follicles and plated in a 35-mm culture dish (3 - 6 X 10(2) attached cells) grew to confluence within 3 weeks (6 - 8 X 10(5) cells). Similar results were obtained for interfollicular keratinocytes. A crucial point for the function of these fibroblast feeder cells is plating at appropriate densities, considering their tremendous increase in cell size at the post-mitotic state. Plating densities of 4 - 5 X 10(3/cm2 allow full spreading of the feeder cells and do not impede the settling and expansion of the keratinocytes. Major advantages of this system include easier handling and better reproducibility than using 3T3-cells. Moreover, homologous fibroblast feeders mimic more closely the physiologic situation and therefore might provide a valuable tool for studying interactions between human mesenchymal and epithelial cells. Finally, potential hazards of using transformed feeder cells from a different species in keratinocyte cultures raised for wound covering in humans could be thus avoided.     

Ultrastructure of the human stratum corneum

The ultrastructural study of the intercellular spaces of the human stratum corneum was based on transmission electron microscopy of thin vertical sections and freeze-fracture replicas, field emission scanning electron microscopy and immunofluorescence confocal laser scanning microscopy. The maturation of the corneosomes and their enzymatic degradation could be depicted at strategic interfaces. These sharp and rapid metamorphoses are now relatively well understood from a morphological point of view. But morphology raises a lot of unsolved physiological problems.     

Organization of the human immune system

During the past decade, our knowledge concerning immunologic development and function has expanded rapidly as a result of the interplay between fundamental studies of antigen receptors and lymphokine molecules and the genes encoding them and studies of patients with leukemias, autoimmune disorders, and immunodeficiency diseases. The latter have been particularly valuable in defining the critical stages in the differentiation of stem cells into mature lymphoid effector cells and the roles played by different subpopulations of cells in regulating immune responses. Several categories of defects in these cellular maturation and cellular interaction events lead to immunodeficiency diseases, including intrinsic defects in the lymphoid cells; abnormalities in the microenvironments necessary for the generation of the differentiation signals essential for the maturation of lymphoid cells; disorders of regulatory cells that normally control humoral and cellular immune responses; and, finally, disorders in which the production of lymphoid cells and immunoglobulins is normal but in which host environment abnormalities lead to excessive endogenous catabolism or excessive loss of immune elements. A second area of major advance has been in defining the arrangement of immunoglobulin and T-cell receptor genes. These genes in their germline form are organized as discontinuous DNA elements that are joined by recombinations during lymphocyte development. The analysis of immunoglobulin gene structure and arrangement has contributed to the study of human lymphoid neoplasms. In addition, the analysis of rearranged immunoglobulin and T-cell receptor genes has been valuable in defining the lineage (T or B cell) of neoplasms whose origins were previously unknown; in determining the clonality of abnormal lymphocyte proliferation; in diagnosing and monitoring the therapy of lymphoid malignancies; in determining the state of maturation and the causes for failure of maturation of cells of the B-cell series; and in providing insights into the causes of malignant transformation of B and T lymphoid cells. It is apparent that the application of this molecular genetic approach has great potential for complementing conventional marker analysis, cytogenetics, and histopathology, thus broadening the scientific basis for the classification, diagnosis, and monitoring of the therapy of lymphoid neoplasia. A final area of dramatic advance has been in defining an array of lymphokine molecules that regulate T-cell and B-cell growth and differentiation. One of the best studied of these lymphokine systems is that of IL-2 and its receptor. Antigen-induced activation of resting T cells induces the synthesis of IL-2 as well as the expression of specific cell surface high-affinity receptors for this lymphokine.(ABSTRACT TRUNCATED AT 400 WORDS)     

Primer on the human genome

The study of the expression patterns of many genes, or even the entire genome, is now routinely possible. Such powerful tools have enabled hypothesis-generating research at a scale never before possible. Moreover, spatially or temporally linked gene and protein expression, implying co-regulation and functional relatedness, has led to the identification of particular clusters of genes important for fundamental biologic processes, such as development and cancer. Not only is this expected to yield further mechanistic insights into disease processes, but perhaps most exciting, it will likely establish the foundation of predictive medicine, in which understanding of individual genomic signatures leads to the use of appropriately targeted therapy. LEARNING OBJECTIVE: At the conclusion of this learning activity, participants should be able to understand the fundamental tenets of molecular biology as they relate to the field of genomics.