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R M Lavker

Publications and source records attributed to R M Lavker.

At least 55 records · Page 3Linked to original sources
PubMed1994

Lineage-specific and differentiation-dependent expression of K12 keratin in rabbit corneal/limbal epithelial cells: cDNA cloning and northern blot analysis.

Corneal epithelial cells synthesize an acidic (55 kDa) K12 and a basic (64 kDa) K3 keratin as their major differentiation products during an advanced stage of differentiation. In this paper, we describe the cDNA cloning of rabbit K12 keratin. We used a 36 base pairs (bp) oligonucleotide corresponding to a consensus sequence of many known acidic keratins as a probe to screen a cDNA library of normal rabbit corneal epithelium. Several partial cDNA clones were isolated. Hybrid-selection showed that the 3'keratin chain-specific portion of the cDNA hybridizes with K12 mRNA. A rabbit antiserum raised against the C-terminus of the cDNA-deduced amino acid sequence recognizes, in immunoblotting, the K12 keratin. In situ hybridization showed that K12 mRNA is present in all cell layers of central corneal epithelium, but in only the suprabasal cells of limbal epithelium indicating a parallel expression pattern between K12 and K3. Cultured rabbit corneal epithelial cells initially synthesize K14/K5 keratins, but later when the cells become heavily stratified they synthesize large quantities of K12 and K3 mRNAs, as detected by Northern blotting. Cultured esophageal epithelial cells do not make K12 mRNA confirming the tissue-specificity of K12 expression. Although it has been suggested that conjunctival epithelial cells can trans-differentiate into a bona fide corneal epithelium, we showed here that cultured conjunctival cells do not synthesize significant amounts of K12/K3 mRNAs. These results strongly suggest that conjunctival epithelial cells, whose differentiation can be modulated significantly by the extracellular matrix, form a lineage intrinsically distinct from the corneal/limbal epithelial lineage.

Amino Acid Sequence↗
PubMed1994

Cells in the bulge of the mouse telogen follicle give rise to the lower anagen follicle.

The slow-cycling cells in the bulge of the outer root sheath may represent stem cells for the hair follicle. With each new anagen (growing) phase bulge cells would give rise to a population of transient-amplifying cells which differentiate into outer root sheath and matrix keratinocytes. The lowermost part of the telogen (resting) follicle is composed of bulge cells lying in close proximity to the dermal papilla. In the mouse the first hair follicle growth is characterized by rapid follicular neogenesis, but the second and third growth cycles follow the normal follicular growth pattern. We have examined activity of cells in the bulge at the onset of anagen (growing phase) in the third hair cycle in Sencar mice, by treating animals at the end of the second telogen with colchicine to localize mitotic activity in the hair follicle. Mitoses were only seen in bulge cells during early anagen. This confirms that they proliferate transiently, solely at the onset of anagen and strongly supports the suggestion that bulge cells are the origin of the whole lower follicle in anagen.

Animals↗
PubMed1993

Effects of topical tretinoin on non-sun-exposed protected skin of the elderly.

BACKGROUND: Topical tretinoin can alter some cutaneous structural alterations induced by excessive exposure to sunlight. Most human studies have focused on photodamaged or photoaged skin. Little, if any, information is available on the effects of tretinoin on chronologically or "intrinsically" aged human skin. OBJECTIVE: Our purpose was to characterize the clinical and structural changes in non-sun-exposed skin after long-term topical treatment with tretinoin. METHODS: Six white women, 68 to 79 years of age, applied 0.025% tretinoin cream to the inner aspect of one thigh and vehicle cream to the opposite side, once daily for 9 months. Biopsy specimens were processed for histochemistry by light microscopy and for ultrastructural analysis by transmission electron microscopy. RESULTS: Tretinoin treatment produced a marked increase in the viable epidermal thickness and resulted in a more undulating dermoepidermal junction with prominent rete ridges. Return to a more uniform size and electron density of the basal and spinous keratinocytes was also noted. Dermal changes included increases in glycosaminoglycan deposition, elastic fibers, and new blood vessel formation. CONCLUSION: Tretinoin substantially altered the involutional structural changes in intrinsically aged protected skin. The magnitude of the changes may be even greater than those described for photodamaged skin.

Administration, Cutaneous↗
PubMed1993

Mouse skin is particularly susceptible to tumor initiation during early anagen of the hair cycle: possible involvement of hair follicle stem cells.

Stem cells are believed to be a necessary target of chemical carcinogens. Based on autoradiographic, ultrastructural, and biologic criteria, we have recently proposed that hair follicle stem cells reside not in the bulb, but in the upper outer root sheath in an area called the bulge. Proliferating cells have been shown to be more susceptible to tumor initiation, and we have recently demonstrated that cells in the bulge undergo transient proliferation during early anagen. Therefore, we theorized that mouse skin should be particularly susceptible to carcinogen application during early anagen phase. In this paper, we show that early anagen Swiss and Sencar mouse skin is indeed particularly susceptible to one- and two-stage chemical carcinogenesis, resulting in tumor yields one to five times those obtained with telogen-timed carcinogen application. Our findings implicate a possible involvement of the bulge cells as precursors to some of the skin cancers, and support the concept that these are stem cells. These observations also raise important questions about the cellular origins and biologic behavior of chemically induced murine skin tumors.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1993

Upper human hair follicle contains a subpopulation of keratinocytes with superior in vitro proliferative potential.

We and others have shown previously that corneal keratinocyte stem cells can proliferate in vitro better than their progeny cells. In this paper, we applied this approach to the identification of hair follicular stem cells. When human scalp hair follicles were placed in explant culture, the bulge area yielded best outgrowths. In another experiment, we isolated different subpopulations of human follicular keratinocytes by micro-dissection, dispersed them by trypsin/EDTA into single cells, and grew them in the presence of 3T3 feeder cells. The keratinocytes were then subcultured under identical conditions to compare their in vitro life span. Our results indicate that the life span of keratinocytes of the upper follicle (containing mainly the isthmus area) > sebaceous gland > lower follicle (between the bulge and bulb) > bulb (containing the matrix cells). The cultured upper follicular keratinocytes tend to be small and relatively uniform in size. The poor in vitro growth of matrix cells may reflect their non-stem cell nature and/or special growth requirement(s) satisfied in vivo by the neighboring dermal papilla cells. Unexpectedly, we found that the upper follicular keratinocytes grow even better than epidermal keratinocytes. The existence of a subpopulation of keratinocytes with an in vitro growth potential superior than other known keratinocytes of the skin supports the hypothesis that follicular stem cells reside in the upper follicle. Our data also raise the possibility that putative follicular stem cells are involved not only in forming the follicle, but also in the long-term maintenance of the epidermis. Finally, we discuss the possibility that keratinocyte stem cells, as defined by their in vivo slow-cycling nature, are absent in culture.

Cell Division↗
PubMed1993

In vitro growth and differentiation of rabbit bulbar, fornix, and palpebral conjunctival epithelia. Implications on conjunctival epithelial transdifferentiation and stem cells.

PURPOSE: The anterior surface of the eye is covered by several physically contiguous but histologically distinguishable epithelial overlying the cornea, limbus, bulbar conjunctiva, fornix conjunctiva, and palpebral conjunctiva. It is important to determine whether the different phenotypes of these epithelia are the result of intrinsic divergence, extrinsic modulation, or a combination of both. Based on keratin expression and cell kinetic criteria, the authors previously suggested that corneal epithelial stem cells may actually reside in the limbal basal layer. METHODS: In this article, the relationship between the corneal-limbal epithelial cells and conjunctival epithelial cells was analyzed by comparing their growth and differentiation properties in an identical cell culture environment. RESULTS: Using Dispase instead of trypsin to dissociate the cells, the authors were able to grow all five rabbit ocular surface epithelia in the presence of 3T3 feeder cells. They found that corneal and limbal cells synthesize identical keratins, including large amounts of the K3 and K12 markers of corneal-type differentiation. By contrast, all three conjunctival epithelia shared another keratin pattern, with large amounts of simple epithelial keratins but only minute amounts of K3/K12 keratins. CONCLUSIONS: This observation, coupled with previous findings that the "transdifferentiation" of conjunctival epithelial cells to corneal epithelium appears to be both incomplete and reversible, provides strong evidence that (1) the limbal-corneal epithelial cells form a lineage distinct from the conjunctival lineage and (2) conjunctival transdifferentiation actually represents a process of environmental modulation. In addition, of the three types of conjunctival epithelial cells, fornix cells were found to have a much greater proliferative potential than bulbar and palpebral cells. This observation, coupled with recent finding that fornix is enriched in slow-cycling (label-retaining) cells, raises the possibility that conjunctival epithelial stem cells may preferentially reside in the fornix.

Animals↗
PubMed1992

Effects of topical ammonium lactate on cutaneous atrophy from a potent topical corticosteroid.

BACKGROUND: Topical corticosteroids produce atrophic changes in skin, including thinning of the epidermis and decrease in dermal ground substance. We observed that 12% ammonium lactate produced an increase in the thickness of epidermis and increased amounts of dermal glycosaminoglycans. OBJECTIVE: Our purpose was to determine whether 12% ammonium lactate could minimize cutaneous atrophy produced by a potent topical corticosteroid. METHODS: Clobetasol propionate, 12% ammonium lactate, and both agents were repetitively applied under occlusive patches as well as in open patches on the forearms of human volunteers for 3 to 4 weeks. Biopsy specimens were analyzed for thickness of the epidermis and dermal glycosaminoglycans by image analysis. RESULTS: Twelve percent ammonium lactate produced a significant sparing of atrophy in both the epidermis and dermis without any influence on the bioavailability or antiinflammatory properties of the corticosteroid. CONCLUSION: Twelve percent ammonium lactate may be useful in mitigating the adverse effects of corticosteroid on skin.

Administration, Topical↗
PubMed1991

Ultrastructure of the human vomeronasal organ.

Virtually all vertebrates have a vomeronasal system whose involvement in pheromone detection plays a crucial role in reproduction. In humans, the vomeronasal organ has been assumed to be vestigial or absent and without functional significance. In the present study involving over 400 subjects, vomeronasal pits were observed in all individuals except those with pathological conditions affecting the septum. Electron microscopy of the adult human vomeronasal organ indicates the presence of two potential receptor elements in the pseudostratified epithelial lining: microvillar cells, and unmyelinated, intraepithelial axons. In addition, unmyelinated axons are common in the lamina propria surrounding the organ. They appear to constitute the components essential for a functional chemosensory system, and may thus provide the basis for a pheromone detection system as in other animals.

Adult↗
PubMed1991

The human skin: fragrances and pheromones.

Non-human mammalian pheromones are commonly used as perfumery ingredients. The actual purpose for using these compounds is as a fixative or carrier for the odor effects of the other ingredients as well as a contributor, in part, to the over-all scent of the perfume. Although such materials are used for their fixative and odor qualities rather than their pheromonal effects, perfumes are generally marketed as having the ability to enhance sexual attractiveness. While providing a scent may elicit a positive pleasant response, this should not be confused with a pheromone response. The attractive effect of perfumes is principally related to the effect of the pleasant scent. A more logical approach would be to use human pheromones which, for humans, are both more natural and more effective as true sensual attractants. It seems likely that implementation of this approach will constitute an important paradigm in the perfume industry as perfumery moves from the realm of art to that of science.

Administration, Cutaneous↗
PubMed1991

Extracellular localization of human connective tissue mast cell granule contents.

In early phases of cutaneous inflammation, connective tissue mast cell degranulation is associated with apparent secretion and externalization of immunoreactive chymotryptic serine proteinase. To determine whether this event is associated with structural evidence of granule externalization, we studied the sequential evolution of IgE-mediated hypersensitivity in vivo, as well as mast cell degranulation provoked by a variety of stimuli in cultured explants of human skin. By 1 min after intradermal antigen challenge with ragweed extract, mast cell degranulation was associated with apparent extrusion of intragranule constituents into the pericellular connective tissue. Similar features typified cultured skin explants exposed for 45 min to anti-IgE and other mast cell secretagogues (morphine sulfate, calcium ionophore A23187, compound 48/80, and substance P). Once externalized, granule constituents could be identified within the dermal matrix by their rounded contour and structural similarity to solubilized granule matrices remaining within actively secreting cells. These data indicate that externalization of connective tissue mast cell granule contents occurs early after secretagogue exposure, potentially accounting for infrequent documentation of this event in naturally occurring dermatoses. The ability to recognize externalized granule products at a morphologic level should facilitate the understanding of interactions between mast cell-derived mediators and target structures of the dermal microvasculature.

Adult↗
PubMed1991

Cytotoxic folliculitis in GvHD. Evidence of follicular stem cell injury and recovery.

Recent observations indicate that stem cells of the murine hair follicle exist exclusively as a subpopulation of relatively undifferentiated outer root sheath cells located in the bulge region at the mid-portion of the follicle. Because it has been hypothesized that stem cells of interfollicular epidermis may represent targets of cytotoxic responses in acute graft-versus-host disease (AGVHD), we studied murine AGVHD and observed sequential skin biopsies for the presence and evolutionary pattern of follicular injury. Highly purified subsets of donor T cells were used to produce AGVHD to multiple minor histocompatibility (H) antigens in two strain combinations of mice matched for the major histocompatibility complex (MHC). In the C3H.SW- greater than B6 strain combination, only CD8+ effector cells produced histologic evidence in skin of AGVHD, which peaked three weeks post-transplant. In the B10.D2- greater than DBA/2 strain combination, CD4+ effector cells, and to a lesser extent, CD8+ cells, mediated disease, which peaked during the fourth week post-transplant. Analysis of skin from both strain/effector cell combinations revealed follicular infiltrates preferentially involving follicular stem cell (FSC) regions (bulge) of anagen follicles between the second and third weeks post-transplant. These infiltrates often preceded infiltration of adjacent interfollicular epidermis and were associated with follicular involution to telogen (resting) phase. By the fourth week post-transplant, greater than 50% of follicles were in telogen phase and residual inflammation was minimal. This provided a unique opportunity to observe follicular recovery from telogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗