Time course for tail regression during metamorphosis of the ascidian Ciona intestinalis

Abstract

In most ascidians, the tadpole-like swimming larvae dramatically change their body-plans during metamorphosis and develop into sessile adults. The mechanisms of ascidian metamorphosis have been researched and debated for many years. Until now information on the detailed time course of the initiation and completion of each metamorphic event has not been described. One dramatic and important event in ascidian metamorphosis is tail regression, in which ascidian larvae lose their tails to adjust themselves to sessile life. In the present study, we measured the time associated with tail regression in the ascidian Ciona intestinalis. Larvae are thought to acquire competency for each metamorphic event in certain developmental periods. We show that the timing with which the competence for tail regression is acquired is determined by the time since hatching, and this timing is not affected by the timing of post-hatching events such as adhesion. Because larvae need to adhere to substrates with their papillae to induce tail regression, we measured the duration for which larvae need to remain adhered in order to initiate tail regression and the time needed for the tail to regress. Larvae acquire the ability to adhere to substrates before they acquire tail regression competence. We found that when larvae adhered before they acquired tail regression competence, they were able to remember the experience of adhesion until they acquired the ability to undergo tail regression. The time course of the events associated with tail regression provides a valuable reference, upon which the cellular and molecular mechanisms of ascidian metamorphosis can be elucidated.

The ontology of the anatomy and development of the solitary ascidian Ciona: the swimming larva and its metamorphosis

“…2 The duration of larval swimming differs among individuals. Matsunobu et al (2015) showed that the hatched larva requires at least three or four hours to get competence to commence metamorphosis. So the time after fertilization during Larva Period was broad.…”

“…It should be noted that, in annotating the progressive organ appearance and degeneration, we could also describe in detail the metamorphosis process, whose general reports for ascidians are dated, not so accurate and timed, and limited to a few species (see for review: 29,41 ). Only some specific processes occurring during metamorphoses, such as tail regression 39,42 or papillae retraction 42 , have been described in detail in C. robusta.…”

Neuronal map reveals the highly regionalized pattern of the juvenile central nervous system of the ascidian Ciona intestinalis

“…When the larvae started adhesion, the seawater of the petri dishes was exchanged several times to remove any unsettled larvae. This treatment was done to synchronize the timing of metamorphosis (Matsunobu and Sasakura, 2015).…”

The ontology of the anatomy and development of the solitary ascidianCiona

“…It should be noted that, in annotating the progressive organ appearance and degeneration, we could also describe in detail the metamorphosis process, whose general reports for ascidians are dated, not so accurate and timed, and limited to a few species (see for review: 29,41 ). Only some specific processes occurring during metamorphoses, such as tail regression 39,42 or papillae retraction 42 , have been described in detail in C. robusta (C. intestinalis type A).…”