Erdal Balcan

Regressing amphibian tail as a model for the cadherin/β-catenin complex disruption and glycosylation alteration during epithelial apoptosis

Epidermis is one of the many tissues that are resorbed during metamorphosis in the regressing tail of amphibian tadpoles. Apoptotic mechanisms play an important role in this process. In this study, loss of intercellular contacts and alterations in plasma membrane glycosylation were observed during apoptosis. The cadherin/beta-catenin complex represents one of the major adhesive systems in multiple epithelial tissues. Here, we analysed the fate of cadherin/beta-catenin complex and alterations of plasma membrane glycoconjugate compositions in apoptotic epithelial cells. Our results showed that the cadherin molecules were cleaved into extracellular and beta-catenin associated cytosolic domains by an intracellular mechanism. However, the extracellular domains were probably removed completely by matrix metalloproteinases. Lectin histochemistry studies suggested that mannose and alpha(2-->6) linked (but not alpha(2-->3) linked) sialic acids were major sugar motifs in plasma membranes of apoptotic tadpole epithelial cells. Although previous studies indicated reduced levels of sialic acid residues during apoptosis, elevated Sambucus nigra agglutinin (SNA) reactivity might be due to the degradation of high molecular weight glycoproteins (probably including cadherin) that masked the SNA-binding residues of the plasma membrane prior to apoptosis.

Quantitative approach to lectin-based glycoprofiling of thymic tissues in the control- and the dexamethasone-treated mice.

Dexamethasone (DEX) is the most commonly used synthetic glucocorticoid in treatment of various inflammatory conditions. Here we focused on evaluating the effect of DEX on apoptosis and glycan profile in the mouse thymic tissues. Histological examinations revealed that the DEX treatment cause severe alterations in thymus, such as disruption of thymic capsule, impaired epithelial cell-thymocyte contacts, cellular loss and increased apoptosis. The identification of thymic glycans in the control- and the DEX-treated mice was carried out by using a panel of five plant lectins, Maackia amurensis agglutinin (MAA), peanut agglutinin (PNA), Sambucus nigra agglutinin (SNA), Concanavalin A (ConA) and wheat germ agglutinin (WGA). Lectin histochemistry results showed that glycosylation pattern of thymus changes upon DEX treatment. For further detailed quantitative analyses of the binding intensities for each lectin, histochemical data were scored as high positive (HP), mild positive (MP) and low positive (LP) and differences among signaling densities were investigated. The staining patterns of thymic regions observed with lectin histochemistry suggest that DEX can affect the thymic glycan profile as well as thymocyte apoptosis. These results are consistent with the opinion that not only sialic acid, but also other sugar motifs may be responsible for thymocyte development.

Glycoconjugate histochemistry of mucous glands in the skin of metamorphosing Bufo viridis

Mucins are the major glycoprotein secretions of mucous glands and display important functions in amphibian skin such as regulation of water homeostasis and mechanical and chemical protection. In the present study, we evaluated the glycoconjugate contents of developing mucous glands on dorsal regions of metamorphosing Bufo viridis (Amphibia: Anura) tadpoles using an alcian blue-PAS panel and lectin histochemistry. All the conical cells of mucous glands showed weak positivity for alcian blue in 0.025 M MgCl2 at pH 5.7 but only a few cells were positive for 0.3 M MgCl2 at the same pH. In addition, all the conical cells of mucous glands were negative for alcian blue at pH 2.5. In lectin histochemistry, conical cells reacted strongly with Galanthus nivalis agglutinin (GNA), Datura stramonium agglutinin (DSA) and peanut agglutinin (PNA), weakly with Maackia amurensis leucoagglutinin (MAL). These results suggest that they express predominantly mannose, galactose and partially α(2→3)-linked sialic acid containing glycoconjugates. We concluded that dorsal mucous glands of metamorphosing Bufo viridis tadpoles contain at least two different conical cell types and glycoconjugate heterogeneity of mucous glands may be related with different functions of mucins.

Prion Proteinlerinin Biyolojisi / Biology of Prion Proteins

Alzheimer, Parkinson, Huntington ve prion hastaliklari gibi norodejeneratif bozukluklarda ortak ozellik, yanlis katlanma gosteren spesifik proteinlerin kumelenmesi ve genis amiloid fibril ya da plaklarin olusumudur. Son bulgular kucuk soluble oligomerlerin noronal yetersizlikten oncelikli olarak sorumlu oldugunu gostermistir. Glikozilfosfatidilinozitol (GPI) capali h ucresel bir glikoprotein olan prion proteini i nsan ve hayvanlarda prion hastaliklari olarak bilinen transmissible spongiform ensefalopatilerin (TSE) patogenezinde onemli bir rol oynamaktadir. Prion hastaliklarinda bu proteininin normal hucresel formu (PrP C ) hastalik etkeni izoforma (PrP Sc ) donusebilir. Prion proteinlerinin bu yapisal donusum sirasinda kullandigi molekuler stratejiler henuz tam olarak anlasilamamis olmasina karsin bu proteinin norodejeneratif hastaliklarin etyolojisinde ve patolojisinde merkezi bir rol oynadigi ve prion proteinlerini kodlayan genlerin ( Prnp ) mutasyonlari ve polimorfizmlerinin hastaliga duyarlik acisindan onemli etkilerinin oldugu bilinmektedir. Ote yandan, cok sayidaki calismaya karsin prion proteininin patolojik ve fizyolojik kosullardaki rolleri tam olarak belirlenememistir. Bu derlemede, prion proteinlerinin yapisal ozellikleri, hucre ici trafigi, olasi fizyolojik rolleri ve apoptozis ile iliskisi ozetlenmistir.

Do prion protein gene polymorphisms induce apoptosis in non-mammals?

Genetic variations such as single nucleotide polymorphisms (SNPs) in prion protein coding gene, Prnp, greatly affect susceptibility to prion diseases in mammals. Here, the coding region of Prnp was screened for polymorphisms in red-eared turtle, Trachemys scripta. Four polymorphisms, L203V, N205I, V225A and M237V, were common in 15 out of 30 turtles; in one sample, three SNPs, L203V, N205I and M237V, and in the remaining 14 samples, only L203V and N205I polymorphisms, were investigated. Besides, C658T, C664T, C670A and C823A SNPs were silent mutations. To elucidate the relationship between the SNPs and apoptosis, TUNEL assays and active caspase-3 immunodetection techniques in brain sections of the polymorphic samples were performed. The results revealed that TUNEL-positive cells and active caspase-3-positive cells in the turtles with four polymorphisms were significantly increased compared with those of the turtles with two polymorphisms (P<0.01 and P<0.05, respectively). In conclusion, this study provides preliminary information about the possible relationship between SNPs within the Prnp locus and apoptosis in a non-mammalian species, Trachemys scripta, in which prion disease has never been reported.

Histological structure of the skin of the Southern Crested Newt, Triturus karelinii (Salamandridae: Urodela)

Abstract The histological structure of the skin of the Southern Crested Newt, Triturus karelinii, from the active aquatic period has been studied by different staining methods. The species has two main layers: epidermis and dermis. The epidermal layer contains stratum germinativum and stratum corneum; the dermal layer stratum spongiosum and stratum compactum. The dermis has a connective tissue structure and contains large amounts of chromatophores and secretory glands. While the stratum compactum of the dermis contains collagen fibres, the basal laminae of the epidermal stratum germinativum cells, apical facies of the stratum corneum cells and the dermal ground substances contain glycosaminoglycan structures. By using computerized image processing software, the thickness of the epidermis and dermis has been measured and the amount of collagen fibres in terms of chosen point determined. We conclude that the extracellular matrix of the T. karelinii skin is largely comprised of two structurally distinct molecular components: collagen and glycosaminoglycans, but the amount of these components may be different in the water and land periods, depending upon the activity of these amphibians.