Direct evidence for the role of pigment cells in the brain of ascidian larvae by laser ablation

Abstract

SUMMARY The anterior sensory vesicle of ascidian larvae contains a single large vesicle in which lie two distinct types of pigment cells, anterior and posterior. The ultrastructure of these pigment cells suggests that the anterior pigment cell is an otolith, presumably used for gravity detection,and the posterior pigment cell is an ocellus, used for photoreception. However, there is no direct experimental evidence for this assignment of function. Upward swimming behaviour occurring during the initial period of larval life was examined before and after laser ablation of the anterior pigment and posterior pigment cells. Posterior pigment cell-ablated larvae retained the upward swimming behaviour, but anterior pigment cell-ablated larvae lost it. These results suggest that the anterior pigment acts as a gravity sensor. The negatively phototactic swimming during the latter part of larval life was also examined before and after laser ablation of the anterior pigment or posterior pigment cells. Anterior pigment cell-ablated larvae retained the phototactic response, but posterior pigment cell-ablated larvae lost it. These results suggest that the posterior pigment of the sensory vesicle is involved in the negatively phototactic, downward swimming behavior. The effect of pressure on swimming behaviour was studied, and a putative pressure-detection organ was found not to be involved in the larval swimming behaviour. These are the first published experimental results that permit a functional role in ascidian larval behavior to be assigned to the sensory organs.

Ciona intestinalis: Chordate development made simple

“…During this free-swimming period, the larva displays a characteristic pattern of behavior, initially swimming upward (toward more illuminated surface waters), before swimming downward (away from illuminated surface waters; Svane and Young, 1989). In C. intestinalis, morpholino knockdown of Ci-opsin1 translation is sufficient to inhibit the photosensitivity responsible for downward swimming behavior (Inada et al, 2003;Tsuda et al, 2003).…”

FGF/MAPK/Ets signaling renders pigment cell precursors competent to respond to Wnt signal by directly controllingCi-Tcftranscription

“…In the C. intestinalis larval anterior sensory vesicle, there are two pigment cell sensory organs: the anterior geotactic otolith and the posterior photoreceptive ocellus (Dilly, 1969;Eakin and Kuda, 1971;Torrence, 1986;Ohtsuki, 1991;Tsuda et al, 2003), which directs larval swimming behavior before metamorphosis (Svane, 1989;Tsuda et al, 2003). The otolith is a single cell, containing a melanin granule and is connected by a narrow stalk to the sensory vesicle ventral floor (Dilly, 1962).…”

Neuronal subtype specification in the spinal cord of a protovertebrate

“…These neurons are thought to receive inputs from the sensory vesicle, as well as from the peripheral nervous system (Horie et al, 2008a;Takamura, 1998). It has been shown that swimming behavior is modulated by light and gravity (Horie et al, 2008b;Jiang et al, 2005;Tsuda et al, 2003), and that the response of the larvae to these stimuli can change over time (Kajiwara and Yoshida, 1985). Thus, the CNS of the ascidian larva can be seen as a central pattern generator for swimming, modulated by photo-and geotropic sensory systems (Goulding, 2009).…”