Overexpression of Galectin-7 in Mouse Epidermis Leads to Loss of Cell Junctions and Defective Skin Repair

Background

The proteins of the galectin family are implicated in many cellular processes, including cell interactions, polarity, intracellular trafficking, and signal transduction. In human and mouse, galectin-7 is almost exclusively expressed in stratified epithelia, notably in the epidermis. Galectin-7 expression is also altered in several human tumors of epithelial origin. This study aimed at dissecting the consequences of galectin-7 overexpression on epidermis structure and functions in vivo.

Methods

We established transgenic mice specifically overexpressing galectin-7 in the basal epidermal keratinocytes and analyzed the consequences on untreated skin and after UVB irradiation or mechanical injury.

Results

The intercellular cohesion of the epidermis is impaired in transgenic animals, with gaps developing between adjacent keratinocytes, associated with loss of adherens junctions. The epidermal architecture is aberrant with perturbations in the multilayered cellular organisation of the tissue, and structural defects in the basement membrane. These transgenic animals displayed a reduced re-epithelialisation potential following superficial wound, due to a defective collective migration of keratinocytes. Finally, a single mild dose of UVB induced an abnormal apoptotic response in the transgenic epidermis.

Conclusion

These results indicate that an excess of galectin-7 leads to a destabilisation of adherens junctions associated with defects in epidermal repair. As this phenotype shares similarities with that of galectin-7 null mutant mice, we conclude that a critical level of this protein is required for maintaining proper epidermal homeostasis. This study brings new insight into the mode of action of galectins in normal and pathological situations.     

Structural and functional analysis of SGT1 reveals that its interaction with HSP90 is required for the accumulation of Rx, an R protein involved in plant immunity

SGT1 (for suppressor of G2 allele of skp1) and RAR1 (for required for Mla12 resistance) are highly conserved eukaryotic proteins that interact with the molecular chaperone HSP90 (for heat shock protein90). In plants, SGT1, RAR1, and HSP90 are essential for disease resistance triggered by a number of resistance (R) proteins. Here, we present structural and functional characterization of plant SGT1 proteins. Random mutagenesis of Arabidopsis thaliana SGT1b revealed that its CS (for CHORD-SGT1) and SGS (for SGT1 specific) domains are essential for disease resistance. NMR-based interaction surface mapping and mutational analyses of the CS domain showed that the CHORD II domain of RAR1 and the N-terminal domain of HSP90 interact with opposite sides of the CS domain. Functional analysis of the CS mutations indicated that the interaction between SGT1 and HSP90 is required for the accumulation of Rx, a potato (Solanum tuberosum) R protein. Biochemical reconstitution experiments suggest that RAR1 may function to enhance the SGT1-HSP90 interaction by promoting ternary complex formation.     

Structure of the histone chaperone ASF1 bound to the histone H3 C-terminal helix and functional insights

Asf1 is a histone chaperone that favors histone H3/H4 assembly and disassembly. We solved the structure of the conserved domain of human ASF1A in complex with the C-terminal helix of histone H3 using nuclear magnetic resonance spectroscopy. This structure is fully compatible with an association of ASF1 with the heterodimeric form of histones H3/H4. In our model, ASF1 substitutes for the second H3/H4 heterodimer that is normally found in heterotetrameric H3/H4 complexes. This result constitutes an essential step in the fundamental understanding of the mechanisms of nucleosome assembly by histone chaperones. Point mutations that perturb the Asf1/histone interface were designed from the structure. The decreased binding affinity of the Asf1-H3/H4 complex correlates with decreased levels of H3-K56 acetylation and phenotypic defects in vivo.     

Direct evidence for the secretion of lactoferrin and its binding to sperm in the porcine epididymis

Lactoferrin has been for the first time purified from the porcine cauda epididymal fluid as a 70 kDa protein. Both Western and Northern blot analyses show that lactoferrin is synthesized in the regions from the distal caput to the cauda epididymis and secreted into the luminal fluid. Lactoferrin is first secreted as a 75 kDa glycoprotein and its carbohydrate moieties are gradually digested to form 70 kDa protein in the cauda epididymis. Lactoferrin has already bound to the surface of the epididymal sperm because the anti-lactoferrin antiserum induces the mature sperm tail-to-tail agglutination. These results strongly suggest new physiological functions of lactoferrin on the sperm maturation in the epididymis. Mol. Reprod. Dev. 47:490–496, 1997. © 1997 Wiley-Liss, Inc.     

Flavodoxin accumulation contributes to enhanced cyclic electron flow around photosystem I in salt-stressed cells of Synechocystis sp. strain PCC 6803

The salt-regulated accumulation of flavodoxin encoded by the isiB gene and its possible function were investigated in the cyanobacterium Synechocystis sp. strain PCC 6803. In Northern blot experiments, a slight increase of the isiB -specific mRNA was observed in salt-shocked and salt-acclimated cells. High levels of flavodoxin protein were detected in cells acclimated to 342 m M NaCl. In order to analyze the function of flavodoxin in cyanobacterial salt acclimation, an insertion null mutant of isiB was constructed. It was possible to adapt this mutant to raised salt concentrations and, as expected, to low iron contents. Salt-acclimated cells of wild type (WT) Synechocystis display increased activity of photosystem I (PSI), primarily used for increased cyclic electron transport capacity (Jeanjean et al. 1993, Plant Cell Physiol 34: 1073–1079). In salt-acclimated cells of the flavodoxin null mutant, the level of cyclic electron flow was lower than in wild type cells. It was concluded that flavodoxin plays a role as an alternative electron carrier, used for cyclic electron flow in salt-treated Synechocystis cells.     

Quantification of Bias Related to the Extraction of DNA Directly from Soils

In recent years, several protocols based on the extraction of nucleic acids directly from the soil matrix after lysis treatment have been developed for the detection of microorganisms in soil. Extraction efficiency has often been evaluated based on the recovery of a specific gene sequence from an organism inoculated into the soil. The aim of the present investigation was to improve the extraction, purification, and quantification of DNA derived from as large a portion of the soil microbial community as possible, with special emphasis placed on obtaining DNA from gram-positive bacteria, which form structures that are difficult to disrupt. Furthermore, we wanted to identify and minimize the biases related to each step in the procedure. Six soils, covering a range of pHs, clay contents, and organic matter contents, were studied. Lysis was carried out by soil grinding, sonication, thermal shocks, and chemical treatments. DNA was extracted from the indigenous microflora as well as from inoculated bacterial cells, spores, and hyphae, and the quality and quantity of the DNA were determined by gel electrophoresis and dot blot hybridization. Lysis efficiency was also estimated by microscopy and viable cell counts. Grinding increased the extracellular DNA yield compared with the yield obtained without any lysis treatment, but none of the subsequent treatments clearly increased the DNA yield. Phage λ DNA was inoculated into the soils to mimic the fate of extracellular DNA. No more than 6% of this DNA could be recovered from the different soils. The clay content strongly influenced the recovery of DNA. The adsorption of DNA to clay particles decreased when the soil was pretreated with RNA in order to saturate the adsorption sites. We also investigated different purification techniques and optimized the PCR methods in order to develop a protocol based on hybridization of the PCR products and quantification by phosphorimaging.     

Galectin-3, a Novel Centrosome-associated Protein,Required for Epithelial Morphogenesis

Galectin-3 is a β-galactoside–binding protein widely expressed in all epithelia where it is involved in tissue homeostasis and cancer progression. We recently reported unique abnormalities in the identity of membrane domains in galectin-3 null mutant mice, suggesting that galectin-3 may participate in epithelial polarity program. We investigated the potential role of galectin-3 on early events in polarization of epithelial renal cells, using three-dimensional cultures of MDCK cells and also galectin-3 null mutant mouse kidneys. We show that depletion in galectin-3 systematically leads to severe perturbations of microtubular network associated with defects in membrane compartimentation, both in vitro and in vivo. Moreover, the absence of galectin-3 impinges on the morphology of the primary cilium, which is three times longer and unusually shaped. By immunological and biochemical approaches, we could demonstrate that endogenous galectin-3 is normally associated with basal bodies and centrosomes, where it closely interacts with core proteins, such as centrin-2. However, this association transiently occurs during the process of epithelial polarization. Interestingly, galectin-3–depleted cells contain numerous centrosome-like structures, demonstrating an unexpected function of this protein in the formation and/or stability of the centrosomes. Collectively, these data establish galectin-3 as a key determinant in epithelial morphogenesis via its effect on centrosome biology.     

Fatal multiple pterygium syndrome and nuchal hygroma

A turkish family with three sibs (including twins) affected by the lethal multiple syndrome is reported.