Whole Nervous System Expression of Glutamate Receptors Reveals Distinct Receptor Roles in Sensorimotor Circuits.

The goal of connectomics is to reveal the links between neural circuits and behavior. Larvae of the primitive chordate are well-suited to make contributions in this area. In addition to having a described connectome, larvae have a range of readily quantified behaviors.

Deep homologies in chordate caudal central nervous systems.

Invertebrate chordates, such as the tunicate , can offer insight into the evolution of the chordate phylum. Anatomical features that are shared between invertebrate chordates and vertebrates may be taken as evidence of their presence in a common chordate ancestor. The central nervous systems of larvae and vertebrates share a similar anatomy despite the CNS having ~180 neurons.

A single oscillating proto-hypothalamic neuron gates taxis behavior in the primitive chordate Ciona.

Ciona larvae display a number of behaviors, including negative phototaxis. In negative phototaxis, the larvae first perform short spontaneous rhythmic casting swims. As larvae are cast in a light field, their photoreceptors are directionally shaded by an associated pigment cell, providing a phototactic cue.

A single oscillating proto-hypothalamic neuron gates taxis behavior in the primitive chordate .

larvae display a number of behaviors, including negative phototaxis. In negative phototaxis, the larvae first perform short spontaneous rhythmic casting swims. As larvae cast in a light field, their photoreceptors are directionally shaded by an associated pigment cell, providing a phototactic cue.

Fold Change Detection in Visual Processing.

Visual processing transforms the complexities of the visual world into useful information. , an invertebrate chordate and close relative of the vertebrates, has one of the simplest nervous systems known, yet has a range of visuomotor behaviors. This simplicity has facilitated studies linking behavior and neural circuitry.

Disruption of left-right axis specification in Ciona induces molecular, cellular, and functional defects in asymmetric brain structures.

Background: Left-right asymmetries are a common feature of metazoans and can be found in a number of organs including the nervous system. These asymmetries are particularly pronounced in the simple central nervous system (CNS) of the swimming tadpole larva of the tunicate Ciona, which displays a chordate ground plan. While common pathway elements for specifying the left/right axis are found among chordates, particularly a requirement for Nodal signaling, Ciona differs temporally from its vertebrate cousins by specifying its axis at the neurula stage, rather than at gastrula.

Antagonistic Inhibitory Circuits Integrate Visual and Gravitactic Behaviors.

Larvae of the tunicate Ciona intestinalis possess a central nervous system of 177 neurons. This simplicity has facilitated the generation of a complete synaptic connectome. As chordates and the closest relatives of vertebrates, tunicates promise insight into the organization and evolution of vertebrate nervous systems.

Parallel visual circuitry in a basal chordate.

A common CNS architecture is observed in all chordates, from vertebrates to basal chordates like the ascidian stands apart among chordates in having a complete larval connectome. Starting with visuomotor circuits predicted by the connectome, we used expression maps of neurotransmitter use with behavioral assays to identify two parallel visuomotor circuits that are responsive to different components of visual stimuli. The first circuit is characterized by glutamatergic photoreceptors and responds to the direction of light.

Photoreceptor specialization and the visuomotor repertoire of the primitive chordate .

The swimming tadpole larva of has one of the simplest central nervous systems (CNSs) known, with only 177 neurons. Despite its simplicity, the CNS has a common structure with the CNS of its close chordate relatives, the vertebrates. The recent completion of a larval CNS connectome creates enormous potential for detailed understanding of chordate CNS function, yet our understanding of larval behavior is incomplete.

Reciprocal and dynamic polarization of planar cell polarity core components and myosin.

The Ciona notochord displays planar cell polarity (PCP), with anterior localization of Prickle (Pk) and Strabismus (Stbm). We report that a myosin is polarized anteriorly in these cells and strongly colocalizes with Stbm. Disruption of the actin/myosin machinery with cytochalasin or blebbistatin disrupts polarization of Pk and Stbm, but not of myosin complexes, suggesting a PCP-independent aspect of myosin localization.

An organismal perspective on C. intestinalis development, origins and diversification.

The ascidian Ciona intestinalis, commonly known as a 'sea squirt', has become an important model for embryological studies, offering a simple blueprint for chordate development. As a model organism, it offers the following: a small, compact genome; a free swimming larva with only about 2600 cells; and an embryogenesis that unfolds according to a predictable program of cell division. Moreover, recent phylogenies reveal that C.

A one-dimensional model of PCP signaling: polarized cell behavior in the notochord of the ascidian Ciona.

Despite its importance in development and physiology the planar cell polarity (PCP) pathway remains one of the most enigmatic signaling mechanisms. The notochord of the ascidian Ciona provides a unique model for investigating the PCP pathway. Interestingly, the notochord appears to be the only embryonic structure in Ciona activating the PCP pathway.

Key steps in the morphogenesis of a cranial placode in an invertebrate chordate, the tunicate Ciona savignyi.

Tunicates and vertebrates share a common ancestor that possessed cranial neurogenic placodes, thickenings in embryonic head epidermis giving rise to sensory structures. Though orthology assignments between vertebrate and tunicate placodes are not entirely resolved, vertebrate otic placodes and tunicate atrial siphon primordia are thought to be homologous based on morphology and position, gene expression, and a common signaling requirement during induction. Here, we probe key points in the morphogenesis of the tunicate atrial siphon.

A conserved role for FGF signaling in chordate otic/atrial placode formation.

The widely held view that neurogenic placodes are vertebrate novelties has been challenged by morphological and molecular data from tunicates suggesting that placodes predate the vertebrate divergence. Here, we examine requirements for the development of the tunicate atrial siphon primordium, thought to share homology with the vertebrate otic placode. In vertebrates, FGF signaling is required for otic placode induction and for later events following placode invagination, including elaboration and patterning of the inner ear.

Did the first chordates organize without the organizer?

Models of vertebrate development frequently portray the organizer as acting on a largely unpatterned embryo to induce major components of the body plan, such as the neural plate and somites. Recent experiments examining the molecular and genetic basis of major inductive events of vertebrate embryogenesis force a re-examination of this view. These newer observations, along with a proposed revised fate map for the frog Xenopus laevis, suggest a possible reconciliation between the seemingly disparate mechanisms present in the ontogeny of the common chordate body plan of vertebrate and invertebrate chordates.

T-box gene tbx5 is essential for formation of the pectoral limb bud.

The T-box genes Tbx4 and Tbx5 have been shown to have key functions in the specification of the identity of the vertebrate forelimb (Tbx5) and hindlimb (Tbx4). Here we show that in zebrafish, Tbx5 has an additional early function that precedes the formation of the limb bud itself. Functional knockdown of zebrafish tbx5 through the use of an antisense oligonucleotide resulted in a failure to initiate fin bud formation, leading to the complete loss of pectoral fins.