12-P010 Role of LIM homedomain transcription factors LHX7 and ISL1 in the specification of mouse basal forebrain cholinergic neurons

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MECHANISMS OF DEVELOPMENT

1 2 6 (2 0 0 9) S1 8 9–S 19 4

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onds after the embryos were flashed with a bright light. To try

Role of LIM homedomain transcription factors LHX7 and ISL1 in

to establish a relation between the observed phenotype and neu-

the specification of mouse basal forebrain cholinergic neurons

ron activity, a high-throughput chemical screen was made. This

Rita

Lopes1, Angela Tye1, Sylvia Evans2, Robin Lovell-Badge1,

consisted in flashing wild type embryos treated with a small

Vassilis Pachnis1

chemical molecule that supposedly affects the neural system.

1

NIMR, MRC, London, United Kingdom

We could conclude that after treating the embryos with different

2

University of California San Diego, La Jolla, CA, United States The forebrain cholinergic system consists of the cholinergic

interneurons of the striatum and projection neurons that are distributed in loosely defined groups along the basal forebrain. Forebrain cholinergic neurons (FCNs) are born between E11 and E15, begin to express cholinergic markers at late embryonic stages, invade their projection target areas postnatally and continue to mature for weeks after birth. Little is known about the cell-intrin-

compounds they still looked normal with regular light, but behaved differently after being flashed. The phenotypes were divided in six categories: healthy sedatives, excitatory extenders, latency extenders, general stimulants, magnitude stimulants and refractory period stimulants. Our preliminary results have the potential to make this assay an easy, fast and essential method to test new drugs implicated with neurological diseases – presently we are screening for new agonists and suppressors of known drugs used to treat well-known neurological disorders.

sic factors that regulate this process. FCNs derive from NKX2.1 precursors that upon exiting the cell

doi:10.1016/j.mod.2009.06.465

cycle express the LIM homeodomain proteins LHX7 and ISL1. Our group and others have shown that deletion of Lhx7 leads to a reduction of 80% in the number of FCNs. In particular, studies

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from our group have demonstrated that in the striatum of Lhx7

A bioinformatic and in situ screen for novel axon guidance

null mice the missing cholinergic interneurons are respecified

molecules

as GABAergic interneurons (Fragkouli et al., submitted). Similarly,

Samantha

deletion of Isl1 results in a dramatic reduction in the number of

Tear

Alsbury1, Tatsuya Okafuji2, Kevin J. Mitchell2, Guy

1

FCNs . To gain further insight into the role of LHX7 and ISL1 in the development and maintenance of the FCNs we have generated and analyzed an Lhx7 conditional knockout. Here we describe

1

MRC Centre for Developmental Neurobiology, Kings College London,

London, United Kingdom 2

Smurfit Institute of Genetics, Trinity College London, Dublin, Ireland

the effect of deleting Lhx7 at embryonic and postnatal stages using the Nkx2.1-Cre and Isl1-Cre lines and an inducible Cre line.

Previous screens for axon guidance molecules have identified

We also report on studies addressing the role of Isl1 in the devel-

that many of the molecular cues and their axonal receptors fall

opment of FCNs. We discuss the role of LIM HD transcription fac-

into a few major classes that are conserved from invertebrates

tors in the development of FCNs and in the plasticity of

to vertebrates. While it has been speculated that the majority of

cholinergic phenotype at different pre and postnatal stages.

axon guidance molecules have already been discovered it seems likely that many such molecules would have been missed due

doi:10.1016/j.mod.2009.06.464

to experimental biases in the genetic or biochemical methods used to identify them. Additionally it seems unlikely that sufficient molecules have been identified to encode the complete wiring of the embryonic nervous system. In order to identify further

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axon guidance molecules we have taken a systematic bioinfor-

Understanding neurons through light: A novel behavioral assay

matic approach to identify novel transmembrane proteins that

Rita Mateus, David Kokel, Randall Peterson

contain any of a number of motifs previously found in known

Cardiovascular Research Center, Massachusetts General Hospital, Charlestown, Massachusetts, United States

axon guidance molecules. These axon guidance motifs include, for example, immunoglobulin (Ig) motifs, fibronectin-type III (FN3) motifs, leucine-rich repeats (LRR) and epidermal growth factor (EGF) repeats amongst others. This screen has identified 162

The ability of neurons to sense is a remarkable capacity pres-

genes in Drosophila that fulfil these criteria and their expression

ent throughout the animal world, supplying both survival and

patterns were subsequently determined by in situ hybridization.

developmental skills to the organism. The zebrafish are no excep-

This study yielded 41 candidate axon guidance molecules that

tion and, during development, neural activity is necessary to help

show neural expression in the embryo during the period of axon

target motorneuron axons to their peripheral destinations – this

extension. These include 9 genes that appear to have orthologues

property has been linked to the activity of the Rohon-Beard

in vertebrates including the CG32635/Neto and Ten/Odz families.

mechanosensory neurons and it is seen by the regular movement

We are now carrying out functional analyses to assess the

of the embryo tail after 18 h post fertilization (hpf).

involvement of these genes in axon guidance in the embryo.

We report a novel light-associated behavior present in wild type zebrafish embryos aged between 28 and 35 hpf. This consists in an abrupt reaction by trembling and shivering for some sec-

doi:10.1016/j.mod.2009.06.466