Vitamin A in epithelial differentiation and skin carcinogenesis.
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Animals↗
Biomedical subjects
N Darwiche
Publications and source records attributed to N Darwiche.
Specificity of retinoid receptor gene expression in mouse cervical epithelia.
Retinoids are powerful regulators of epithelial differentiation and are essential for its maintenance. Because retinoids are necessary for cervical epithelial differentiation, they have been used as chemopreventive agents of cervical dysplasia and neoplasia. We were interested in determining whether different cervical epithelial phenotypes express specific retinoid receptors. The cervical epithelium contains the two phenotypes, stratified squamous and simple columnar, which join at the squamocolumnar junction. In addition, the simple columnar epithelium undergoes squamous metaplasia in response to vitamin A deficiency. Therefore, the cervical epithelium is suitable to study the expression pattern of the retinoid receptors in the three phenotypes, simple columnar, stratified squamous, and squamous metaplastic, simultaneously. The distribution pattern of the major retinoic acid receptor (RAR) isoforms (alpha 1, alpha 2, beta 2, beta 3, gamma 1, and gamma 2) and retinoid-X receptors (RXR alpha, -beta, and -gamma) was studied by in situ hybridization. At the tissue level, RAR alpha (1 and 2) and RXR (alpha and beta) transcripts and, to a lesser extent, RAR gamma (1 and 2) transcripts were associated with the cervical stratified squamous subjunctional epithelium. The simple columnar epithelium, which is highly responsive to vitamin A status, expressed high levels of RAR alpha (1 and 2), RAR beta (2 and 3), and RXR (alpha and beta) transcripts. Only RAR beta (2 and 3) and RXR (alpha and beta) transcripts were down-modulated by the condition of vitamin A deficiency and expressed less in squamous metaplastic foci than the simple columnar epithelium. RXR gamma was undetectable in all three cervical epithelia. At the cellular level, basal and suprabasal expression was found for RARs, and preferential localization of RXRs was seen in basal cells. RXRs are auxiliary proteins for a variety of other nuclear receptors with which they form heterodimers, including RARs. The fact that RXRs are mainly localized in basal and columnar cells of the cervix suggests the need for the regulation and diversity generated by potential heterodimeric interactions in these rapidly proliferating cells in vivo. The unique pattern of expression and localization of the RARs and RXRs in different cervical epithelial tissues and cell types supports the hypothesis that they perform specific functions in cervical epithelial differentiation. This is in contrast to the major isoforms of each RAR, which have similar patterns of expression in the different cervical epithelial phenotypes and cell types, suggesting a redundancy in function.
Animals↗
Retinoid status controls the appearance of reserve cells and keratin expression in mouse cervical epithelium.
We describe an animal model to induce the histogenesis of squamous metaplasia of the cervical columnar epithelium, a condition usually preceding cervical neoplasia. This model is based on dietary retinoid depletion in female mice. Control sibling mice fed the same diet but with all-trans-retinoic acid (at 3 micrograms/g diet) showed the normal endocervical epithelial and glandular columnar morphology, typical of a simple epithelium without subcolumnar reserve cells. The stratified squamous ectocervical epithelium of these mice fed all-trans retinoic acid showed intense immunohistochemical staining in basal and suprabasal cells with mono-specific antibodies against keratins K5, K14, K6, K13, and, suprabasally, with antibodies specific for K1 and K10. At the squamocolumnar junction, the adjacent columnar epithelium (termed "suprajunctional") did not show staining for K5, K14, K6, K13, K1, and K10 but specifically stained for keratin K8, typical of simple epithelia and absent from the adjacent ectocervical squamous stratified lining (termed "subjunctional"), in striking contrast. Sections of the squamocolumnar junction from mice kept on the vitamin A-deficient diet for 10 weeks showed suprajunctional isolated patches of reserve cells, proximal and distal to the junction. These cells were detected prior to any symptoms of vitamin A deficiency, such as loss of body weight or respiratory discomfort. The subcolumnar reserve cells induced by vitamin A deficiency displayed positive staining for K5 and K14. As deficiency became severe, the reserve cells occupied the entirety of the suprajunctional basement membrane. This epithelium eventually became stratified and squamous metaplastic, the squamocolumnar junction was no longer discernible, and the entire endocervical epithelium and the endometrial glands lost K8 positivity, while acquiring K5, K14, K6, K13, K1, and K10 keratins typical of the ectocervix under normal conditions of vitamin A nutriture. Vitamin A deficiency also altered keratin expression and localization in squamous subjunctional epithelium. In situ hybridization studies for K1 and K5 mRNA showed their major site of expression at the basal (K5) and immediately suprabasal (K1) cell layers. The localization of both K5 and K1 proteins in these same cell layers, and above, is consistent with transcriptional regulation of these keratins. Early vitamin A deficiency caused the appearance of single subcolumnar reserve cells expressing K5 mRNA. After these cells grew into a squamous focus, K1 mRNA became expressed suprabasally. We conclude that retinoid status plays a key role in maintaining differentiative characteristics of the cervical and glandular epithelia and, as such, may be a modulating factor in the development of cervical cancer.
Animals↗
Expression of cornifin in squamous differentiating epithelial tissues, including psoriatic and retinoic acid-treated skin.
The expression of cornifin, a putative cross-linked envelope precursor, was investigated in several squamous differentiating tissues by in situ hybridization and immunohistochemical analysis. Cornifin mRNA and protein, which are absent in the normal mucociliary tracheal epithelium, are induced in the suprabasal layers of the squamous metaplastic tracheal epithelium of vitamin A-deficient hamsters. Similar to the induction of squamous metaplasia in vivo, culture of rabbit tracheal cells in the absence of retinoids results in squamous differentiation and expression of cornifin. This induction of cornifin expression is suppressed by retinoic acid and several of its analogs. Cornifin mRNA and protein are also detected in the suprabasal layers of the squamous epithelium of rabbit esophagus and tongue. The distribution of cornifin in human epidermis was compared with that of two other crosslinked envelope precursor proteins, involucrin and loricrin. The localization of cornifin and involucrin is very similar. Both are induced in the spinous layer and appear at an earlier stage during epidermal differentiation than loricrin. The expression of cornifin is greatly increased in psoriatic skin. Cornifin mRNA is barely detectable in normal epidermis, whereas it is present at relatively high levels in the suprabasal layers of psoriatic epidermis. Topical treatment with RA results in thickening of the skin and increases the level of cornifin mRNA and protein in the upper spinous layers of mouse skin. Cornifin expression correlates generally with squamous differentiation in a variety of tissues and is abnormally regulated in psoriatic skin and in skin treated topically with retinoic acid.
Administration, Topical↗
Retinoid status and the control of keratin expression and adhesion during the histogenesis of squamous metaplasia of tracheal epithelium.
We induced vitamin A depletion to define early and late changes during the histogenesis of squamous metaplasia of hamster tracheal epithelium. An early change is the "minimal morphological change" (MMC), in which the mucociliary epithelium is separated from the basement membrane by a continuous layer of basal cells. Immunohistochemistry showed an exclusive localization of the keratins K5 and K14 in basal cells of normal and MMC epithelia. At the MMC stage no staining was observed above the basal layer with antibodies to K5, but upon progression of the lesion to a squamous focus all cells from basal to terminally differentiated were positive for K5 and K14. In contrast, when we used antibodies to the keratins K6 or K13 all cells were negative in the normal epithelium and in the MMC epithelium. Successive layers of suprabasal squamous cells found in squamous metaplasia failed to express normal epidermal differentiation marker keratins K1 and K10 but expressed the proliferation marker keratin K6 and the internal stratified epithelium keratin K13, not normally found in the epidermis or in the trachea. Hamster tracheal epithelial cells could be maintained in culture in serum-free medium for at least 4 weeks in the presence of retinoic acid (RA). In non-RA-containing medium, cells from vitamin A-deficient hamsters showed markedly reduced growth and an increase in the expression of keratins K5, K6, K13, and K14. Since our previous work had implicated retinoids in the control of cell adhesiveness, we were interested to find out whether changes in cell adhesion occur in vitamin A-deficient hamster tracheal epithelial cells, compared to normal cells. Functional assays demonstrated that hamster tracheal epithelial cells, obtained from non-RA-treated tracheas or maintained in culture, displayed reduced attachment to laminin, compared to RA-treated cells. Immunofluorescence studies did not show a decrease either in the alpha 6 integrin subunit, which was localized in the basal aspect of basal cells, or in basement membrane laminin. However, the expression of laminin-binding protein 37 decreased as the epithelium changed from pseudostratified to stratified. Therefore, a coordinated pattern of changes in keratin gene expression, as well as in the expression of laminin-binding protein 37, the precursor to the cell surface laminin receptor 67LR, and in adhesive properties takes place in tracheal epithelium when its phenotype changes from mucociliary to the preneoplastic stage of squamous metaplasia.
Amino Acid Sequence↗
Karyotype of amniotic fluid cells at the AUB-MC results on 2000 cases.
We report results on 2000 cases of amniotic fluid referred for karyotype analysis. Referrals were advanced maternal age in 64% of cases and abnormal ultrasound in 12% of cases. The frequency of chromosome aneuploidy was 2.4% in the first category and that of chromosome abnormalities 8% in the second. The incidence of marker chromosomes was 0.25%, that of mosaicism 0.3%, and maternal cell contamination was observed in 0.6% of cases. The overall culture failure rate was 0.9%. Our results are mostly in accordance with figures from larger surveys, published in the literature and differences might be due to the smaller number of samples in this series and variation in referral and/or sampling protocols.
Academic Medical Centers↗
Constitutional chromosome abnormalities among patients referred for blood karyotype analysis: a 5-year study at the AUBMC.
We report results on 2010 cases of blood referred for constitutional karyotype analysis. Referrals were grouped into 16 different categories, of which reproductive failure represented the highest percentage (33%), followed by structural congenital abnormalities (14.17%), developmental delay (11.34%), Down syndrome (9.65%), and abnormal sexual development (8.16%), while other categories represented smaller percentages. The total rate of abnormality was 16%, and the highest abnormality rates were among the clinically-recognizable chromosomal syndromes, while lower percentages were detected among less specific referrals. However, abnormality rates were generally different from the typical reported rates, probably due to the inclusion of cases not requiring chromosome analysis or the failure to recognize specific chromosomal syndromes. Other identified problems included lack of proper phenotypic description and difficulty in obtaining familial follow-up for proper diagnosis and genetic counseling.
Chromosome Aberrations↗