The organization and cell-lineage of the ascidian egg / by Edwin G. Conklin.

Conklin, Edwin G.

doi:10.5962/bhl.title.4801

Cited by 293 publications

(455 citation statements)

References 4 publications

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“…S3). The second cleavage is traditionally thought to establish the anterior-posterior axis in tunicates (18)(19)(20)(21). Our results, however, demonstrate that what traditionally was labeled ''anterior'' coincides with the prospective nervous system in early stages in O. dioica (Figs.…”

Section: Resultscontrasting

confidence: 54%

“…It remains unclear where the two remaining cells needed to complete juvenile cell number originate. The cell lineage and fate map of O. dioica share similarities with those of ascidians, such as rapid and precise determinative cleavage, general bilateral symmetry of cleavage pattern, and the derivation of nervous system and musculature from both vegetal and animal lineages (18)(19)(20). However, closer inspection reveals also major differences between larvaceans and ascidians.…”

Section: Resultsmentioning

confidence: 96%

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Embryology of a planktonic tunicate reveals traces of sessility

Stach

Winter

Bouquet³

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

100

102

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A key problem in understanding deuterostome evolution has been the origin of the chordate body plan. A biphasic life cycle with a sessile adult and a free-swimming larva is traditionally considered ancestral in chordates with subsequent neotenic loss of the sessile adult stage. Molecular phylogenies challenged this view, suggesting that the primitive life cycle in chordates was entirely free-living as in modern day larvaceans. Here, we report the precise cell lineage and fate map in the normal embryo of the larvacean Oikopleura dioica , using 4D microscopy technique and transmission electron microscopy. We document the extraordinary rapidity of cleavage and morphogenetic events until hatching and demonstrate that—compared with ascidians—fate restriction occurs considerably earlier in O. dioica and that clonal organization of the cell lineage is more tightly coupled to tissue fate. We show that epidermal cells in the trunk migrate through 90°, reminiscent of events in ascidian metamorphosis and that the axis of bilateral symmetry in the tail rotates in relation to the trunk. We argue that part of the tail muscle cells are ectomesodermal, because they are more closely associated with prospective epidermis than with other tissues in the cell lineage. Cladistic comparison with other deuterostomes suggests that these traits are derived within tunicates strengthening the hypothesis that the last common ancestor of tunicates had a sessile adult and thus support traditional morphology-derived scenarios. Our results allow hypothesizing that molecular developmental mechanisms known from ascidian models are restricted to fewer, yet identifiable, cells in O. dioica .

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Section: Resultscontrasting

confidence: 54%

Section: Resultsmentioning

confidence: 96%

Embryology of a planktonic tunicate reveals traces of sessility

Stach

Winter

Bouquet³

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

100

102

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“…In ascidians, including Ciona intestinalis, C. savignyi and Halocynthia roretzi, the notochord comprises exactly 40 cells, and their lineage has been completely described (Conklin, 1905;Nishida, 1987). The 32 anterior notochord cells are derived from the A4.1 pair (A-line) of the bilaterally symmetrical 8-cell embryo and the eight posterior cells are derived from the B4.1 pair (B-line) (Fig.…”

Section: Introductionmentioning

confidence: 99%

A zinc finger transcription factor, ZicL, is a direct activator ofBrachyuryin the notochord specification ofCiona intestinalis

2004

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“…It is now clear that vertebrate TRPs are more closely related to vertebrate tyrosinase than to tyrosinase characterized from protostomes or from other kingdoms, which implies that the evolution of TRPs occurred after the protostome-deuterostome divergence. Therefore, if 1) multiplication of the tyrosinase family responsible for elaboration of the melanin synthetic pathway and 2) the genetic as well as cellular requirements for the expression of tyrosinase family genes are to be elucidated, animals closer to the ancestral stock of chordates, in particular, ascidians (Urochordata, Ascidiacea), which have well-characterized pigment cells (Conklin, 1905;Whittaker, 1966;Whittaker, 1973;Nishida, 1987;Nishida and Satoh, 1989;Nishida, 1991), are obvious and feasible first targets.…”

Section: Introductionmentioning

confidence: 99%

Structure and developmental expression of the ascidian TRP gene: Insights into the evolution of pigment cell–specific gene expression

Satō¹,

Toyoda²,

Katsuyama³

et al. 1999

Dev. Dyn.

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The tyrosinase family in vertebrates consists of three related melanogenic enzymes: tyrosinase, tyrosinase-related protein-1 (TRP-1), and TRP-2. These proteins control melanin production in pigment cells and play a crucial role in determining vertebrate coloration. We have isolated a gene from the ascidian Halocynthia roretzi which encodes a tyrosinase-related protein (HrTRP) with 45-49% identity with vertebrate TRP-1 and TRP-2. The expression of the HrTRP gene in pigment lineage a8.25 cells starts at the early-mid gastrula stage, which coincides with the stage when these cells are determined as pigment precursor cells; therefore, it provides the earliest pigment lineage-specific marker, which enables us to trace the complete cell lineage leading to two pigment cells in the larval brain. In addition, the expression pattern of the HrTRP gene appears to share similar characteristics with the mouse TRP-2 gene although structurally the HrTRP gene is more closely related to mammalian TRP-1 genes. Based on these observations and on results from molecular phylogenetic and hybridization analyses, we suggest that triplication of the tyrosinase family occurred during the early radiation of chordates. Initially, duplication of an ancestral tyrosinase gene produced a single TRP gene before the urochordate and cephalochordate-vertebrate divergence, and a subsequent duplication of the ancestral TRP gene in the vertebrate lineage gave rise to two TRP genes before the emergence of teleost fishes. Evolution of the melanin synthetic pathway and possible phylogenetic relationships among chordate pigment cells that accommodate the metabolic process are discussed. Dev Dyn 1999;215:225-237.1999 Wiley-Liss, Inc.

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The organization and cell-lineage of the ascidian egg / by Edwin G. Conklin.

Cited by 293 publications

References 4 publications

Embryology of a planktonic tunicate reveals traces of sessility

Embryology of a planktonic tunicate reveals traces of sessility

A zinc finger transcription factor, ZicL, is a direct activator ofBrachyuryin the notochord specification ofCiona intestinalis

Structure and developmental expression of the ascidian TRP gene: Insights into the evolution of pigment cell–specific gene expression

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