Developmental change of distribution of beta-galactoside alpha 2,6-sialyltransferase mRNA in rat retina

Lycopersicon esculentum lectin is a marker of transient amplifying cells in in vitro cultures of isolated limbal stem cells

The maintenance of a healthy corneal epithelium under both normal and wound healing conditions is achieved by a population of stem cells (SCs) located in the basal epithelium at the corneoscleral limbus. In the light of the development of strategies for reconstruction of the ocular surface in patients with limbal stem cell deficiency, a major challenge in corneal SCs biology remains the ability to identify stem cells in situ and in vitro. To date, not so much markers exist for the identification of different phenotypes. CESCs (corneal epithelial stem cells) isolated from limbal biopsies were maintained in primary culture for 14 days and stained with Hoechst and a panel of FITC-conjugated lectins. All lectins, with the exception of Lycopersicon esculentum, labelled CESCs irrespective of the degree of differentiation. Lycopersicon esculentum, that binds N-acetylglucosamine oligomers, labelled intensely only the surface of TACs (single corneal epithelial stem cells better than colonial cells). These results suggest that Lycopersicon esculentum lectin is a useful and easy-to-use marker for the in vitro identification of TACs (transient amplifying cells) in cultures of isolated CESCs.

Regional glycoprotein expression in the chicken lens

PURPOSE

Several previous studies have shown that glycoconjugates of extracellular matrix, cell membrane and nucleus play an important role in the mediation of cell proliferation, migration and differentiation. Lens epithelial cells and lens fiber cells show regional differences with regard to these parameters. If glycoconjugates participate in the regulation of these patterns in the lens, there should be regional differences in the expression of glycoconjugates. The investigation was focused on the anterior pole, equator and nuclear bow regions, which differ extensively in lens cell proliferation and differentiation.

METHODS

To check this hypothesis, the regional binding pattern of twelve different FITC-conjugated lectins was studied glycohistochemically, using paraffin embedded material. The investigation was focused on the anterior pole, equator and nuclear bow regions.

RESULTS

Regional differences in lectin binding patterns were identified in the lens capsule, epithelium and the nuclear bow regions. The lens capsule was fluorescently labeled with GS-I, UEA-I, LPA, MAA, SNA only at the anterior pole and with CON-A, WGA, DBA, SBA only at the equator. Staining of the entire anterior surface of the lens capsule was observed with LFA. Cell membranes of the lens epithelium showed binding of MAA and LFA only at the equator. LFA, LPA, MAA and SNA only stained the nuclei of fiber cells at the nuclear bow region but not of lens epithelial cells. WGA strongly labeled the nuclei of equatorial epithelial cells and fiber cells at the bow region.

CONCLUSIONS

It is assumed that the observed regional variations in glycoprotein expression in the extracellular matrix and lens cells contribute to the regulation of cell behavior in different areas of the lens.

The interphotoreceptor matrix, a space in sight

The interphotoreceptor matrix (IPM) has in recent years been receiving much attention due to its delicate localization between the photoreceptors and the retinal pigment epithelium (RPE). The IPM is a resilient, structure forming and hydrophilic matrix composed of large glycoproteins and proteoglycans, which occupies the subretinal space between the photoreceptors. The IPM is most likely assembled with components synthesized by all the surrounding cell types: the photoreceptor cells, the RPE cells, and the Müller cells. It has been implied to be involved in the development and maintenance of photoreceptors, and as a major factor in retinal adhesion. Therefore, it has been thoroughly studied also in several models of photoreceptor degeneration. Comparative studies have revealed some remarkably consistent features between different species, such as the presence of the rod and cone specific matrix domains. Studies made in the IPM of several species have measured large fluctuations in ion concentrations as a result of changes in illumination. In some species, these ionic fluctuations coincide with the intriguing dynamic redistributions of IPM constituents that can be visualized with histochemical techniques. It can be hypothesized that because of the intensive biochemical activity and the frequent changes in metabolic states of rods and cones the IPM may act as a kind of "buffer." These studies have brought a new extracellular aspect to photoreceptor studies and a new perspective to photoreceptor-RPE research.

Specific stimulation of alpha 2-6 sialyltransferase activity by a novel cytosolic factor from rat colon

A factor present in the 100,000 g supernatant from the homogenate of rat colon stimulated the activity of purified Gal beta 1-4GLcNAc alpha 2,6 sialyltransferase [alpha 2-6ST(N)] from rat liver and alpha 2-6ST(N) from either liver microsomes or Golgi membrane. The stimulation of alpha 2-6ST(N) activity by the colon factor using protein acceptors was about four-fold and highly reproducible when the reaction product of the alpha 2-6ST(N) was assayed by either precipitation or affinity chromatography. In contrast, the colon factor did not stimulate the Gal beta 1-4GlcNAc alpha 2,3 sialyltransferase [alpha 2-3ST (N)], from rat jejunum microsomes or purified Gal beta 1-3GalNAc alpha 2,4 sialyltransferase [alpha 2-3ST (O)] from porcine liver, of purified beta 1,4 galactosyltransferase (GT) from bovine milk. In addition to rat colon, the 100,00 g supernatant from the homogenates of rat brain and kidney also stimulated the alpha 2-6ST(N) activity. The stimulation of alpha 2-6ST(N) by the colon factor resulted in a decrease in the Km (by about two-fold) and an increase in Vmax (about 2- to 3-fold) for desialylated alpha 1 acid glycoprotein and CMP-[14C]N-acetylneuraminic acid. The stimulation of alpha 2-6ST(N) activity by the colon factor was temperature dependent, protease sensitive and was inhibited by CTP, but did not need the presence of either metal ions or detergent. The cytosolic factor was partially purified by ion-exchange chromatography with the retention of the activator activity in the peaks containing low molecular weight proteins, but the activity was lost on attempts to further purification. A specific marked stimulation of the alpha 2-6ST(N) activity by cytosolic factors in certain tissues might suggest a physiological role for these factors in the regulation of alpha 2-5ST(N) activity.

Identification and expression of six family genes in mouse retina

We identified five cDNA clones of the Six gene family which are expressed in retina. They are Six2, Six3 alpha and Six3 beta (which are derived from alternative splicing forms), Six5, and AREC3/Six4. All of these Six family genes possess extensive sequence similarity among each other in the so-homologous region (Six domain and homeodomain) but differ greatly in structure in some other regions. The amino acid sequence similarity of the so-homologous region to the previously identified AREC3/Six4 is 70.1% for Six2, 57.3% for Six3 alpha and Six3 beta, and 70.3% for Six5. The expression of these genes was observed in inner and outer nuclear layer, ganglion cell layer, and pigment epithelium of mouse retina by in situ hybridization. The so-homologous region of each Six family protein has specific DNA binding activity. Six5 and Six2 bind to the same sequence as does AREC3/Six4, while Six3 does not. These observations suggest that some of the Six family genes can regulate the same target genes.

The control of sialyltransferase activity in tumor-cell lines derived from different tissues in multifactorial

The activities of the sialyltransferase enzymes and the resulting expression of sialoglycoproteins were examined in tumor cells derived from different tissues in order to gain a greater understanding of the factors controlling the cell glycosylation state. Cell-cell contact, which is dependent on cell confluency state, was shown to influence glycosylation in the neurally-derived mouse neuro-2A neuroblastoma and the C6 glioma cell lines. Both showed a relatively high level of cell sialyltransferase activity under sub-confluent conditions with activity decreasing upon the formation of cell-cell contacts associated with confluency. A parallel decrease in the expression of sialoglycoproteins, as determined by lectin blot analysis, was observed under these conditions. In contrast, the H411e hepatoma cell line showed an increase in enzyme activity with confluency with the susceptibility of the enzyme in this cell line to glucocorticoid induction only being detected in sub-confluent cell cultures. The number of trypsinisation cycles of the cells was also shown to affect the enzyme activity of the neuro-2A and C6 cells with an increase in enzyme activity coincident with passage number being observed in the neuro-2A cells, and a decrease in the C6 glioma cell line. Trypsinisation had no effect on enzyme activity in the H411e cells. These results demonstrate that the control of sialyltransferase activity in tumor cells is multifactorial with the tissue of origin playing a key role.