Early stages of test formation in larva of Ascidia malaca (Tunicata, Ascidiacea: ultrastructural and cytochemical investigations

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    Abstract

    The swimming larvae of ascidians are entirely covered by a hyalin coat called tunic, or test. This covering consists of two cuticular layers,C1 and C2, which surround an inner compartment composed of an amorphous hyalin matrix with numerous fibrils dispersed inside. Data fromthe literature agree on the key role played by the cells of the larval ectodermic layer in the synthesis and secretion of larval test components.In the present article are reported ultrastructural and cytochemical investigations made during test formation in the swimming larva ofAscidia malaca. Besides confirming the role played by ectodermic cells during the early stages of test formation, the investigations highlightthe way in which the fibrillar component of the test is synthetized and secreted. At the ultrastructural level it has been evidenced that the C1and C2 cuticular layers originate from the tight packing of fibrils. Based on the data reported in the present study, it is hypothesized that whilea relevant part of the fibrils, once secreted, remains dispersed inside the matrix of the inner compartment of the test, quite likely in order toincrease its consistency, packing of the remaining fibrils leads to the formation of the C1 and C2 cuticular layers. Packing of the fibrils in C1and C2 could be favoured by their chemically adhesive nature. This hypothesis is strongly supported by the herewith reported results of thecytochemical investigations carried out on the test of the swimming larva of A. malaca. The cytochemical PA–TCH–SP reaction has in factevidenced that both fibril types, i.e. those dispersed inside the inner compartment and those packed in the C1 and C2 cuticular layers, areconstituted by glycoproteins and/or proteoglycans substances whose adhesive properties are well documented in the literature.
    Lingua originaleEnglish
    pagine (da-a)261-271
    RivistaMicron
    Volume35
    Stato di pubblicazionePublished - 2004

    All Science Journal Classification (ASJC) codes

    • Structural Biology
    • Materials Science(all)
    • Physics and Astronomy(all)
    • Cell Biology

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