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Biomedical subjects

Bogi Andersen

Publications and source records attributed to Bogi Andersen.

8 recordsLinked to original sources
PubMed2006

The Grainyhead-like epithelial transactivator Get-1/Grhl3 regulates epidermal terminal differentiation and interacts functionally with LMO4.

Defective permeability barrier is an important feature of many skin diseases and causes mortality in premature infants. To investigate the control of barrier formation, we characterized the epidermally expressed Grainyhead-like epithelial transactivator (Get-1)/Grhl3, a conserved mammalian homologue of Grainyhead, which plays important roles in cuticle development in Drosophila. Get-1 interacts with the LIM-only protein LMO4, which is co-expressed in the developing mammalian epidermis. The epidermis of Get-1(-/-) mice showed a severe barrier function defect associated with impaired differentiation of the epidermis, including defects of the stratum corneum, extracellular lipid composition and cell adhesion in the granular layer. The Get-1 mutation affects multiple genes linked to terminal differentiation and barrier function, including most genes of the epidermal differentiation complex. Get-1 therefore directly or indirectly regulates a broad array of epidermal differentiation genes encoding structural proteins, lipid metabolizing enzymes and cell adhesion molecules. Although deletion of the LMO4 gene had no overt consequences for epidermal development, the epidermal terminal differentiation defect in mice deleted for both Get-1 and LMO4 is much more severe than in Get-1(-/-) mice with striking impairment of stratum corneum formation. These findings indicate that the Get-1 and LMO4 genes interact functionally to regulate epidermal terminal differentiation.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Identification of hair cycle-associated genes from time-course gene expression profile data by using replicate variance.

The hair-growth cycle is an example of a cyclic process that is well characterized morphologically but understood incompletely at the molecular level. As an initial step in discovering regulators in hair-follicle morphogenesis and cycling, we used DNA microarrays to profile mRNA expression in mouse back skin from eight representative time points. We developed a statistical algorithm to identify the set of genes expressed within skin that are associated specifically with the hair-growth cycle. The methodology takes advantage of higher replicate variance during asynchronous hair cycles in comparison with synchronous cycles. More than one-third of genes with detectable skin expression showed hair-cycle-related changes in expression, suggesting that many more genes may be associated with the hair-growth cycle than have been identified in the literature. By using a probabilistic clustering algorithm for replicated measurements, these genes were grouped into 30 time-course profile clusters, which fall into four major classes. Distinct genetic pathways were characteristic for the different time-course profile clusters, providing insights into the regulation of hair-follicle cycling and suggesting that this approach is useful for identifying hair follicle regulators. In addition to revealing known hair-related genes, we identified genes that were not previously known to be hair cycle-associated and confirmed their temporal and spatial expression patterns during the hair-growth cycle by quantitative real-time PCR and in situ hybridization. The same computational approach should be generally useful for identifying genes associated with cyclic processes from complex tissues.

Algorithms↗
PubMed2004

Expression of an engrailed-LMO4 fusion protein in mammary epithelial cells inhibits mammary gland development in mice.

LIM domain factors and associated cofactors are important developmental regulators in pattern formation and organogenesis. In addition, overexpression of two LIM-only factors (LMOs) causes acute lymphocytic leukemia. The more recently discovered LMO factor LMO4 is highly expressed in proliferating epithelial cells, and frequently overexpressed in breast carcinoma. Here we show that while LMO4 is expressed throughout mammary gland development, it is dramatically upregulated in mammary epithelial cells during midpregnancy. The LMO coactivator Clim2/Ldb1/NLI showed a similar expression pattern, consistent with the idea that LMO4 and Clim2 act as a complex in mammary epithelial cells. In MCF-7 cells, LMO4 transcripts were upregulated by heregulin, an activator of ErbB receptors that are known to be important in mammary gland development and breast cancer. To test the hypothesis that LMO4 plays roles in mammary gland development, we created an engrailed-LMO4 fusion protein. This fusion protein maintains the ability to interact with Clim2, but acts as a dominant repressor of both basal and activated transcription when recruited to a DNA-regulatory region. When the engrailed-LMO4 fusion protein was expressed under control of the MMTV promoter in transgenic mice, both ductular development in virgin mice and alveolar development in pregnant mice were inhibited. These results suggest that LMO4 plays a role in promoting mammary gland development.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Use of RT-PCR and DNA microarrays to characterize RNA recovered by non-invasive tape harvesting of normal and inflamed skin.

We describe a non-invasive approach for recovering RNA from the surface of skin via a simple tape stripping procedure that permits a direct quantitative and qualitative assessment of pathologic and physiologic biomarkers. Using semi-quantitative RT-PCR we show that tape-harvested RNA is comparable in quality and utility to RNA recovered by biopsy. It is likely that tape-harvested RNA is derived from epidermal cells residing close to the surface and includes adnexal structures and present data showing that tape and biopsy likely recover different cell populations. We report the successful amplification of tape-harvested RNA for hybridization to DNA microarrays. These experiments showed no significant gene expression level differences between replicate sites on a subject and minimal differences between a male and female subject. We also compared the array generated RNA profiles between normal and 24 h 1% SLS-occluded skin and observed that SLS treatment resulted in statistically significant changes in the expression levels of more than 1,700 genes. These data establish the utility of tape harvesting as a non-invasive method for capturing RNA from human skin and support the hypothesis that tape harvesting is an efficient method for sampling the epidermis and identifying select differentially regulated epidermal biomarkers.

Actins↗
PubMed2003

Xenopus Xlmo4 is a GATA cofactor during ventral mesoderm formation and regulates Ldb1 availability at the dorsal mesoderm and the neural plate.

We have identified and functionally characterized the Xenopus Xlmo4 gene, which encodes a member of the LIM-domain-only protein family. Xlmo4 is activated at gastrula stages in the mesodermal marginal zone probably in response to BMP4 signaling. Soon after, Xlmo4 is downregulated in the dorsal region of the mesoderm. This repression seems to be mediated by organizer-expressed repressors, such as Gsc. Xlmo4 downregulation is necessary for the proper formation of this territory. Increasing Xlmo4 function in this region downregulates Spemman Organizer genes and suppresses dorsal-anterior structures. By binding to Ldb1, Xlmo4 may restrict the availability of this cofactor for transcription factors expressed at the Spemman Organizer. In the ventral mesoderm, Xlmo4 is required to establish the identity of this territory by acting as a positive cofactor of GATA factors. In the neural ectoderm, Xlmo4 expression depends on Xiro homeoprotein activity. In this region, Xlmo4 suppresses differentiation of primary neurons and interferes with gene expression at the Isthmic Organizer, most likely by displacing Ldb1 from active transcription factor complexes required for these processes. Together, our data suggest that Xlmo4 uses distinct mechanisms to participate in different processes during development.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Identification and characterization of Grainyhead-like epithelial transactivator (GET-1), a novel mammalian Grainyhead-like factor.

LMO-4 is an LIM-only factor that is highly expressed in many epithelial cells, including those of the epidermis and hair follicles. Because LMOs may function by interacting with DNA-binding proteins, we have used the yeast two-hybrid system to screen mouse skin libraries for LMO-4-interacting DNA-binding proteins. In this screen, we isolated a novel LMO-4-interacting factor highly related to the Drosophila gene Grainyhead. Grainyhead is epidermally expressed and carries out important functions in cuticular formation in the fly embryo. With the identification of this novel mammalian Grainyhead-like gene, referred to as Grainyhead-like epithelial transactivator 1 (GET-1), the known members of the mammalian Grainyhead-like gene family are extended to six, falling into two classes based on sequence homology. Of interest, the expression pattern of GET-1 is similar to that of Drosophila Grainyhead with highest expression in the somatic ectoderm/epidermis, but GET-1 is additionally expressed in epithelial cells of gastrointestinal, genitourinary, and respiratory tracks. The GET-1 protein localizes to the nucleus and binds to at least one Grainyhead DNA-binding site. The GET-1 DNA-binding domain maps to a region containing homology to the Drosophila Grainyhead DNA-binding domain. GET-1 homodimerizes in solution by means of a short C-terminally located domain that is homologous to other Grainyhead-like genes. A short domain located between amino acids 100 and 190, which bears no homology to known transactivation domains, is sufficient to confer transactivation to the heterologous GAL4 DNA-binding domain. In addition, GET-1 appears to contain repression domains consistent with the observation that Grainyhead and other mammalian Grainyhead-like genes can act both as activators and repressors. These data suggest that GET-1 is a transcriptional regulator that may perform important functions in epithelial tissues of mammals.

Adaptor Proteins, Signal Transducing↗
PubMedDate not supplied

Imaging corneal pathology in a transgenic mouse model using nonlinear microscopy.

A transgenic mouse model with a Clim [co-factor of LIM (a combination of first letters of Lin-11 (C. elegans), ISL1 (rat), and Mec-3 (C. elegans) gene names) domain proteins] gene partially blocked in the epithelial compartment of its tissues is used to establish the sensitivity of intrinsic reflectance nonlinear optical microscopy (NLOM) to stromal and cellular perturbations in the cornea. Our results indicate dysplasia in the squamous epithelium, irregular collagen arrays in the stroma, and a compromised posterior endothelium in the corneas of these mice. As suggested by biochemical data, the collagen alterations are likely due to collagen III synthesis and deposition during healing and remodeling of transgenic mice corneal stromas. All of the topographic features seen in NLOM images of normal and aberrant corneas are confirmed by coregistration with histological sections. In this work, we also use ratiometric redox fluorometry based on two-photon excited cellular fluorescence from reduced nicotinamide adenine dinucleotide (NAD)(P)H and oxidized flavin adenine dinucleotide (FAD) to study mitochondrial energy metabolism. Employing this method, we detect higher metabolic activity in the endothelial layer of cornea compared to an epithelial layer located further away from the metabolites. The combination of two-photon excited fluorescence (TPF) with second harmonic generation (SHG) signals allows imaging to aid in understanding the relationship between alternation of specific genes and structural changes in cells and extracellular matrix.

Animals↗