Abstract
The aim of this study was to characterize the nature and regional distribution of the glycoconjugates secreted by epidermal mucous cells in Eisenia foetida (Annelida). Specimens were divided into six regions from anterior to posterior. The histochemistry was carried out by using standard histochemical methods. Histochemical staining properties of glycoconjugates in epidermal mucous cells were determined regionally. The epidermis of all regions contained strong to stronger PAS (+) cells in various degrees. The epidermis of the first, fourth, fifth, and sixth regions had strong to stronger AB pH 2.5 (+) cells. On the contrary, all regions contained weak to moderate AB pH 0.5 and AB pH 1.0 (+) cells. Most of mucous cells in epidermis of the first region contained both PAS (+) and AB (+) mucosubstances. All regions included weaker to weak AF (+) cells. All regions featured KOH/PAS (+) cells, with a slight reduction in reaction intensity in the epidermis of the last three regions. In this context, the different staining patterns observed in epidermal mucous cells hinted at their functional roles with respect to production of mucus with different physical properties. This study provided comprehensive information about the regional distribution patterns of the glycoconjugates and an opportunity to compare their distributional patterns in other annelids.
Highlights
Histological, histochemical, and ultrastructural studies have unveiled the existence of a variable and complex structure of the epidermis in annelids [1,2,3]
Histological and histochemical methods revealed that the epidermis covered by cuticle consists of a monostratified epithelium, which contains many glandular mucous cells that have a variable morphology, and that the vast majority of cells in the epidermis are composed of these glandular mucous cells
We noticed many types of secretory cells that cannot be discriminated especially due to various morphological appearances in the epidermis of Eisenia foetida (Annelida, Oligochaeta)
Summary
Histological, histochemical, and ultrastructural studies have unveiled the existence of a variable and complex structure of the epidermis in annelids [1,2,3]. The glandular cells in the surface epithelia secrete mucus that is rich in glycans, glycoproteins, and sialic acid residues [5,6,7]. In the annelids, this mucous secretion plays a fundamental role in the formation of the ground substance of tubes, protection from dehydration, absorption of metabolites, and protection against parasites [4]. In some epithelial cells, which morphologically and functionally polarize in relation to different behaviours in ion transport [9], it is likely that a functional specialization of the glycoconjugates is observed on the basolateral surface. In addition to the aforementioned, acidic polysaccharides— sulfated glycosaminoglycans— whose presence has been shown by using electrophoretic and chromatographic methods in Eisenia andrei [13] fulfil important biological functions
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