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

Dolcemascolo, G; Gianguzza, M

doi:10.1016/j.micron.2003.11.012

Cited by 5 publications

(4 citation statements)

References 24 publications

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“…However, in ultrastructural appearance the extracellular covering of early developmental stages of appendicularians is also layered consisting of at least an inner electron-light, nearly homogenous layer and a thin, electron-dense outermost layer. Such an electron-dense outermost layer can be recognized in all tunicate larvae examined (e. g., Burighel and Cloney 1997;Gianguzza and Dolcemascolo 2004;present paper). These similarities warrant the hypothesis that the two structures might be homologous and the extracellular material in appendicularian larvae is therefore called tunic as well in the present paper.…”

Section: Homology Assessmentmentioning

confidence: 86%

Ontogeny of the appendicularian Oikopleura dioica (Tunicata, Chordata) reveals characters similar to ascidian larvae with sessile adults

Stach

2007

Zoomorphology

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Appendicularians have always occupied a central role in considerations of tunicate and chordate evolution. Two hypotheses have been proposed -one holds that appendicularia represents the sister taxon to the remaining tunicates, the other suggests that appendicularians were derived from an ascidian-like ancestor. In the present study I report results from electron microscopic investigation of larval tunicates including the Wrst electron microscopic investigation of the tail of the early ontogenetic appendicularian "Streckform" and discuss their phylogenetic implications. The early "Streckform" of Oikopleura dioica Fol, 1872 is invested with an extracellular covering that consists of an inner electron-light layer and an electron-dense outermost layer. In addition, the extracellular covering forms Wn blades. Because these traits are shown to be similar to the tunic of diVerent ascidian larvae, the extracellular covering in early appendicularian embryos is suggested to be homologous to the larval tunic of ascidian larvae. Overall, the tail of early developmental stages of appendicularians consists of a mosaic of apomorphic and plesiomorphic features. The straight, continuous endodermal strand was inherited from a common chordate ancestor whereas the Wnlets of larvae, consisting of extracellular material, were inherited from a common tunicate ancestor. The horizontal orientation of the tail as a whole was inherited from the last common ancestor of appendicularians and aplousobranch ascidians, and the discovered Xoating extension at the posterior tip of the tail is unique to the holoplanktonic Oikopleura dioica. These Wndings support the hypothesis that Appendicularia is derived from a sessile, ascidian-like ancestor.

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Section: Homology Assessmentmentioning

confidence: 86%

Ontogeny of the appendicularian Oikopleura dioica (Tunicata, Chordata) reveals characters similar to ascidian larvae with sessile adults

Stach

2007

Zoomorphology

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“…While the tunic is rather thin around the trunk and the flanks of the tail, it is massively expanded along the dorsal and ventral tail midlines to form a large median fin with essential hydrodynamic properties for swimming [ 54 ]. The tunic is a cellulose-based extracellular matrix secreted by the epidermal cells [ 56 , 57 ], but very little is know about the genetic and biochemical pathways that control its secretion. To our knowledge, the only gene expressed in the epidermis and having a function in tunic synthesis is the gene coding for cellulose synthase [ 58 – 60 ].…”

Section: Discussionmentioning

confidence: 99%

Formation of the Ascidian Epidermal Sensory Neurons: Insights into the Origin of the Chordate Peripheral Nervous System

et al. 2006

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The vertebrate peripheral nervous system (PNS) originates from neural crest and placodes. While its developmental origin is the object of intense studies, little is known concerning its evolutionary history. To address this question, we analyzed the formation of the larval tail PNS in the ascidian Ciona intestinalis. The tail PNS of Ciona is made of sensory neurons located within the epidermis midlines and extending processes in the overlying tunic median fin. We show that each midline corresponds to a single longitudinal row of epidermal cells and neurons sharing common progenitors. This simple organization is observed throughout the tail epidermis, which is made of only eight single-cell rows, each expressing a specific genetic program. We next demonstrate that the epidermal neurons are specified in two consecutive steps. During cleavage and gastrula stages, the dorsal and ventral midlines are independently induced by FGF9/16/20 and the BMP ligand ADMP, respectively. Subsequently, Delta/Notch–mediated lateral inhibition controls the number of neurons formed within these neurogenic regions. These results provide a comprehensive overview of PNS formation in ascidian and uncover surprising similarities between the fate maps and embryological mechanisms underlying formation of ascidian neurogenic epidermis midlines and the vertebrate median fin.

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“…During the study of GAGs distribution in ascidian tissues we found a Hep-containing cell that resides in the tissue -the oocyte test cell [22], which is believed to originate from blood cells [33]. The function of the test cells remains an open question, although some authors believe these cells secrete factors important for the oocyte development, while others associate test cells with the release of substances that provide hydrophilic properties to the tunic [34]. Lastly, there is also the hypothesis that links them to processes of formation of the larval tunic [35,36].…”

Section: Intracellular Hepmentioning

confidence: 99%

Biological function of unique sulfated glycosaminoglycans in primitive chordates

et al. 2016

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Glycosaminoglycans with unique sulfation patterns have been identified in different species of ascidians (sea squirts), a group of marine invertebrates of the Phylum Chordata, sub-phylum Tunicata (or Urochordata). Oversulfated dermatan sulfate composed of [4-α-L-IdoA-(2-O-SO) → 3-β-D-GalNAc(4-OSO)] repeating disaccharide units is found in the extracellular matrix of several organs, where it seems to interact with collagen fibers. This dermatan sulfate co-localizes with a decorin-like protein, as indicated by immunohistochemical analysis. Low sulfated heparin/heparan sulfate-like glycans composed mainly of [4-α-L-IdoA-(2-OSO) → 4-α-D-GlcN(SO) (6-O-SO)] and [4-α-L-IdoA-(2-O-SO) → 4-α-D-GlcN(SO)] have also been described in ascidians. These heparin-like glycans occur in intracellular granules of oocyte assessory cells, named test cells, in circulating basophil-like cells in the hemolymph, and at the basement membrane of different ascidian organs. In this review, we present an overview of the structure, distribution, extracellular and intracellular localization of the sulfated glycosaminoglycans in different species and tissues of ascidians. Considering the phylogenetic position of the subphylum Tunicata in the phylum Chordata, a careful analysis of these data can reveal important information about how these glycans evolved from invertebrate to vertebrate animals.

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

Cited by 5 publications

References 24 publications

Ontogeny of the appendicularian Oikopleura dioica (Tunicata, Chordata) reveals characters similar to ascidian larvae with sessile adults

Ontogeny of the appendicularian Oikopleura dioica (Tunicata, Chordata) reveals characters similar to ascidian larvae with sessile adults

Formation of the Ascidian Epidermal Sensory Neurons: Insights into the Origin of the Chordate Peripheral Nervous System

Biological function of unique sulfated glycosaminoglycans in primitive chordates

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