Discovery of a novel murine keratin 6 (K6) isoform explains the absence of hair and nail defects in mice deficient for K6a and K6b

The murine genome is known to have two keratin 6 (K6) genes, mouse K6 (MK6)a and MK6b. These genes display a complex expression pattern with constitutive expression in the epithelia of oral mucosa, hair follicles, and nail beds. We generated mice deficient for both genes through embryonic stem cell technology. The majority of MK6a/b−/− mice die of starvation within the first two weeks of life. This is due to a localized disintegration of the dorsal tongue epithelium, which results in the build up of a plaque of cell debris that severely impairs feeding. However, ∼25% of MK6a/b−/− mice survive to adulthood. Remarkably, the surviving MK6a/b−/− mice have normal hair and nails. To our surprise, we discovered MK6 staining both in the hair follicle and the nail bed of MK6a/b−/− mice, indicating the presence of a third MK6 gene. We cloned this previously unknown murine keratin gene and found it to be highly homologous to human K6hf, which is expressed in hair follicles. We therefore termed this gene MK6 hair follicle (MK6hf). The presence of MK6hf in the MK6a/b−/− follicles and nails offers an explanation for the absence of hair and nail defects in MK6a/b−/− animals

p63 is the molecular switch for initiation of an epithelial stratification program

Development of stratified epithelia, such as the epidermis, requires p63 expression. The p63 gene encodes isoforms that contain (TA) or lack (DeltaN) a transactivation domain. We demonstrate that TAp63 isoforms are the first to be expressed during embryogenesis and are required for initiation of epithelial stratification. In addition, TAp63 isoforms inhibit terminal differentiation, suggesting that TAp63 isoforms must be counterbalanced by DeltaNp63 isoforms to allow cells to respond to signals required for maturation of embryonic epidermis. Our data demonstrate that p63 plays a dual role: initiating epithelial stratification during development and maintaining proliferative potential of basal keratino-cytes in mature epidermis

Transgenic models of skin diseases

Background: Transgenic animals have greatly enhanced our understanding of the contribution of various structural and regulatory components to epidermal biology. The expression of mutant versions of these components in the epidermis of transgenic mice has generated animal models of specific human skin diseases

A mutational hot spot in keratin 10 (KRT 10) in patients with epidermolytic hyperkeratosis

Epidermolytic hyperkeratosis (EHK), (bullous congenital ichthyosiform erythroderma), is an autosomal dominant human skin disorder. Recently, we and others have described mutations in keratins 1 and 10 (K1 and K10) in patients with this disease. Structure-function models predict that these mutations would impair normal filament assembly and function. We have extended our earlier studies to include 8 more incidences of EHK. In half of these families, we were unable to locate a mutation within the rod domains of either K1 or K10. However, polymorphic restriction site and sequence analysis of the other families revealed a mutational hot spot within the 1A alpha-helical segment of K10. These involve Arginine to Histidine, Arginine to Cysteine and Arginine to Leucine substitutions at residue 10 of the rod domain. Interestingly, mutations in the corresponding Arginine residue in keratin K14 have been identified in patients with epidermolysis bullosa simplex. The large number of mutations found at this position in both keratins K10 and K14 suggests that other epithelia cell disorders will be discovered that are caused by the corresponding mutation in related type I keratin gene

Isolation and Characterization of Squamous Cell Carcinoma-Derived Stem-like Cells: Role in Tumor Formation

In human epidermis, keratinocyte stem cells (KSC) are characterized by high levels of β1-integrin, resulting in the rapid adhesion to type IV collagen. Since epithelial tumors originate from KSC, we evaluated the features of rapidly adhering (RAD) keratinocytes derived from primary human squamous cell carcinoma of the skin (cSCC). RAD cells expressed higher levels of survivin, a KSC marker, as compared to non-rapidly adhering (NRAD) cells. Moreover, RAD cells proliferated to a greater extent and were more efficient in forming colonies than NRAD cells. RAD cells also migrated significantly better than NRAD cells. When seeded in a silicone chamber and grafted onto the back skin of NOD SCID mice, RAD cells formed tumors 2–4 fold bigger than those derived from NRAD cells. In tumors derived from RAD cells, the mitotic index was significantly higher than in those derived from NRAD cells, while Ki-67 and survivin expression were more pronounced in RAD tumors. This study suggests that SCC RAD stem cells play a critical role in the formation and development of epithelial tumors

RecA and RadA Proteins of Brucella abortus Do Not Perform Overlapping Protective DNA Repair Functions following Oxidative Burst

Very little is known about the role of DNA repair networks in Brucella abortus and its role in pathogenesis. We investigated the roles of RecA protein, DNA repair, and SOS regulation in B. abortus. While recA mutants in most bacterial species are hypersensitive to UV damage, surprisingly a B. abortus recA null mutant conferred only modest sensitivity. We considered the presence of a second RecA protein to account for this modest UV sensitivity. Analyses of the Brucella spp. genomes and our molecular studies documented the presence of only one recA gene, suggesting a RecA-independent repair process. Searches of the available Brucella genomes revealed some homology between RecA and RadA, a protein implicated in E. coli DNA repair. We considered the possibility that B. abortus RadA might be compensating for the loss of RecA by promoting similar repair activities. We present functional analyses that demonstrated that B. abortus RadA complements a radA defect in E. coli but could not act in place of the B. abortus RecA. We show that RecA but not RadA was required for survival in macrophages. We also discovered that recA was expressed at high constitutive levels, due to constitutive LexA cleavage by RecA, with little induction following DNA damage. Higher basal levels of RecA and its SOS-regulated gene products might protect against DNA damage experienced following the oxidative burst within macrophages. Originally published Journal of Bacteriology, Vol. 188, No. 14, July 200

Energy security in the post-Cold War era: Identifying future courses for crises

This paper addresses US energy security in the post-Cold War era for a conference on energy security jointly sponsored by the Department of Energy and the National Defense University. It examines the evolving nature of energy security based on analysis of past crisis-inducing events and-discusses potentially important geopolitical, environmental, regulatory, and economic developments during the next twenty-five years. The paper steps beyond the traditional economic focus of energy security issues to examine the interplay between fundamental economic and technical drivers on the one hand, and political, environmental, and perceptual phenomena, on the other hand, that can combine to create crises where none were expected. The paper expands on the premise that the recent demise of the Soviet Union and other changing world conditions have created a new set of energy dynamics, and that it is imperative that the United States revise its energy security perspective accordingly. It proceeds by reviewing key factors that comprise the concepts of ``energy security`` and ``energy crisis`` and how they may fit into the new world energy security equation. The study also presents a series of crisis scenarios that could develop during the next twenty-five years, paying particular attention to mechanisms and linked crisis causes and responses. It concludes with a discussion of factors that may serve to warn analysts and decision makers of impending future crises conditions. The crisis scenarios contained in this report should be viewed only as a representative sample of the types of situations that could occur. They serve to illustrate the variety of factors that can coalesce to produce a ``crisis.`