title: Ultrastructural and cytochemical investigations on the formation of chorion in oocyte of Ascidia malaca.
abstract: In the present work are reported investigations on the formation and chemical nature of the chorion of Ascidia malaca oocytes. The ultrastructural observations have shown that both follicle cells and test cells play a key role on chorion formation. At the beginning of vitellogenesis (stage I), chorion is formed by a single fibrogranular layer. During vitellogenesis (stage II), the chorion becomes, at first, bi-layered and successively presents three layers. The outer layer (ofl) is composed of a thin and irregular network of short fibrils. The central layer (cdl) is also made by a fibrillar component which is very compact to form an electron-dense layer. The inner layer (ifl) has a larger size compared to that of outer and central layer and it is composed by a matrix containing little and scattered globular electron-dense granules and several fibrils oriented in all directions. At the end of vitellogenesis beneath the three-layered chorion a large perivitelline space will be formed. In this space are found the test cells. Cytochemical investigations performed at light microscopy (toluidine blue) and electron microscopy (PA-TCH-SP) have shown in Ascidia malaca chorion the presence of substances with a polysaccharidic nature that are probably conjugated as glycoprotein and/or proteoglycans.
authors.affiliation: Department of Biopathology and Biomedical Methodologies, University of Palermo, Italy. dolcemas@unipa.it
authors.forename: G
authors.initials: G
authors.lastname: Dolcemascolo
authors.forename: R
authors.initials: R
authors.lastname: Alessandro
authors.forename: M
authors.initials: M
authors.lastname: Gianguzza
mesh_terms: D000818:Animals; D002823:Chorion / Q000737:chemistry / Q000648:ultrastructure*; D004396:Coloring Agents; D005260:Female; D006651:Histocytochemistry; D006834:Hydrazines; D008854:Microscopy, Electron; D009865:Oocytes / Q000737:chemistry / Q000648:ultrastructure*; D010504:Periodic Acid; D011134:Polysaccharides / Q000032:analysis; D012836:Silver Proteins; D014561:Urochordata / Q000502:physiology* / Q000648:ultrastructure; D014818:Vitellogenesis / Q000502:physiology
chemical_list: D004396:Coloring Agents; D006834:Hydrazines; D011134:Polysaccharides; D012836:Silver Proteins; C055835:periodic acid-thiocarbohydrazide-silver proteinate; D010504:Periodic Acid