15-P041 Early Neurogenesis in the red flour beetle Tribolium castaneum

MECHANISMS OF DEVELOPMENT

S259

1 2 6 ( 2 0 0 9 ) S 2 4 7 –S 2 6 1

demonstrate that the floral symmetry gene CYC can enhance

that the formation of the CNS via neural stem cells – so-called

flower diversity allowing pollinators to co-evolve with the flow-

neuroblasts – is similar in insects and higher crustaceans (Mala-

ering plants.

costraca) whereas neuroblasts are missing in myriapods and chelicerates; rather groups of neural precursors that directly differentiate into neural cells segregate from the neuroectoderm.

doi:10.1016/j.mod.2009.06.681

However, crustaceans are a very diverse group and it is not clear whether neuroblasts are present in major crustacean groups other than malacostracans. Therefore, we are analysing early 15-P038

neurogenesis in the water flea Daphnia magna (Branchiopoda)

Stra6.2: A novel member of the STRA6 gene family

by histological (semithin sectioning, nucleic specific stainings,

Niki

Wyatt1, Chris Ponting2, Julia Dorin1, David Fitzpatrick1,

phalloidin

staining)

and

immunohistochemical

(antibodies

Robert Hill1

against acetylated alpha tubulin and HRP) methods. Furthermore,

1

as until now moleculargenetic analyses of neurogenesis in crus-

2

taceans are largely missing, we are investigating the process of

MRC HGU, Edinburgh, United Kingdom MRC FGU, Oxford, United Kingdom

neural precursor formation in D. magna at the molecular level.

Retinoids are vital for normal embryonic development and are necessary during postnatal development and adulthood for the maintenance of the reproductive and nervous system and for visual pigment synthesis. STRA6 (Stimulated by retinoic acid 6) is the cell surface receptor for retinol binding protein (RBP4), which facilitates the cellular uptake of retinol. Mutations in Stra6 are responsible for some cases of a birth defect syndrome known as PDAC (Pulmonary hypoplasia,

Diaphragmatic

hernia,

Anopthalmia,

Cardiac

defects). The developmental disruption in this syndrome occurs

We have identified genes which are known to be involved in recruitment and specification of neural precursor cells in arthropods, e.g. proneural (ASH) and neurogenic (Notch, Delta) genes by computational analyses using the Daphnia pulex genome. We have cloned these genes in D. magna and are studying their expression patterns by in-situ hybridisations. We are comparing our results to neurogenesis in the remaining arthropod groups to develop an evolutionary scenario of how the developmental mechanisms have been modified in the individual arthropod groups.

in those systems that are affected in animal models of vitamin A deficiency (VAD) indicating the importance of STRA6 in provid-

doi:10.1016/j.mod.2009.06.683

ing cellular retinol during development. A bioinformatics approach identified a paralogue of STRA6, which has 18% identity at the protein level in mouse (STRA6.2) and also conserves many of the residues mutated in PDAC cases. Stra6.2 was found to have orthologues in diverse species,

15-P040 – Withdrawn

including Trichoplax adhaerens. Stra6.2 is well conserved amongst mammals, however, the gene has been split across the chromosome in great apes resulting in a functional C-terminus and a pseudogenised N-terminus with an associated break in synteny. Expression analysis in humans, however, confirms that mRNA from this truncated gene is expressed in tissues from the adult, foetus and in cell lines. In zebrafish, expression analysis indicates that both Stra6 and Stra6.2 transcripts are present and

15-P041 Early Neurogenesis in the red flour beetle Tribolium castaneum Lucia Biffar, Angelika Stollewerk Queen Mary University, London, United Kingdom

deposited maternally into the egg. Morpholino knockdown of the Stra6.2 transcript in zebrafish embryos is underway to

The ground pattern of neurogenesis in insects, malacostracan

determine if it has a similar role in development to that of

crustaceans, chelicerates and myriapods seems to be the forma-

STRA6.

tion of about 30 neuroblasts/groups of neural precursors that are arranged in 7 rows in each hemisegment. This raises the

doi:10.1016/j.mod.2009.06.682

question if individual neuroblasts/neural precursor groups that occupy similar positions can be considered as homologous. In order to address this question we are comparing neurogenesis

15-P039 Neurogenesis in the water flea Daphnia magna (Crustacea, Branchiopoda) Petra Ungerer, Angelika Stollewerk

in two distantly related insects, Drosophila melanogaster and Tribolium castaneum. It has been shown recently that the mechanisms of neuroblast specification by proneural genes are similar in Tribolium and Drosophila. However, there are neither data available on the precise number of neuroblasts per hemisegment

Queen Mary University of London, School of Biological and Chemical

nor their order of formation and segmental arrangement. We are

Sciences, London, United Kingdom

establishing a map of all trunk neuroblasts including the sequence of neuroblast formation. In addition to the stereotyped

Remarkably, despite arthropods share a characteristic ladder-

position, each Drosophila neuroblast can be identified by its

like central nervous system (CNS), the mode of formation is not

unique gene expression profile. In Tribolium the temporal expres-

the same in the major groups. Only recently it has been shown

sion patterns of some of the genes which are expressed in

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MECHANISMS OF DEVELOPMENT

1 2 6 (2 0 0 9) S2 4 7–S 26 1

conserved domains in the neuroectoderm (e.g. dorso-ventral pat-

Branches are produced from groups of ‘stem cells’ at the join

terning genes) differ as compared to Drosophila (Wheeler etal.,

between leaf and stem, called axillary meristems, which either

2005). We assume that temporal changes in spatial cues might

remain dormant or grow out. This decision is affected by several

influence neuroblast identity. This mechanism might have con-

hormones, either repressing or promoting outgrowth.

tributed to evolutionary changes in arthropod neurogenesis. We

Strigolactones, originally identified as germination stimulants

are therefore analysing the expression pattern of homologues of

for parasitic plants, and more recently as signals in the formation

the Drosophila neuroblast identity genes (e.g. segment polarity

of mycorrhizal symbioses, have now been shown to repress

genes, dorso-ventral patterning genes) during the whole course

branching in rice, pea and Arabidopsis. MAX1 in Arabidopsis

of neurogenesis in Tribolium.

encodes a cytochrome P450 family member, which is required for the synthesis of the strigolactone-related signal, and forms

doi:10.1016/j.mod.2009.06.685

part of a biosynthetic and signal transduction pathway containing at least three other genes in Arabidopsis. While other known components of the strigolactone-signalling pathway are conserved throughout the land plants, genes

15-P042

closely related to MAX1 are present in all plant genomes pub-

Specification of neural precursor identity in the chelicerate

lished except the ‘basal’ land plant, moss. These findings suggest

Cupiennius salei and the myriapod Glomeris marginata

that MAX1 is an evolutionarily later addition to pathway. We aim

Carola Doeffinger, Angelika Stollewerk School of Biological and Chemical Sciences, London, United Kingdom

to test this hypothesis by investigating the ability of homologues from a range of species to complement Arabidopsis max1 mutants. We also investigate whether the loss of mycorrhizal symbiosis in Arabidopsis has freed strigolactone signalling from

Although the genetic network that is involved in the recruit-

coevolutionary constraint imposed by the fungal partner, and

ment of neural precursors is conserved in all four arthropod

allowed diversification of the endogenous signal in this species,

groups, the formation of neural precursors is different in chelicer-

by analysing the complementation of max1 with homologues of

ates and myriapods as compared to insects and crustaceans.

the putative strigolactone receptor MAX2 from other species.

Groups of neural precursors are specified in chelicerates and myriapods, while single neural precursors (neuroblasts) arise in the

doi:10.1016/j.mod.2009.06.687

ventral neuroectoderm of the remaining arthropods. However, the number and the arrangement of neuroblasts/neural precursor groups are similar in all arthropods. This raises the question

15-P044

whether these are ancestral features and crustacean and insect

Comparative analysis of midline guidance and axonal path

neuroblast lineages can be homologised with the neural precur-

finding in the chelicerates Cupiennius salei and Achaearanea

sor groups of chelicerates and myriapods. We are therefore ana-

tepidariorum

lysing the establishment of neural precursor identity in

Viktoria Linne, Angelika Stollewerk

chelicerates and myriapods and compare our data to the wellstudied Drosophila melanogaster system. In Drosophila 30 neuroblasts per hemisegment aquire their identities by positional information mediated by the expression of dorso-ventral and anteriorposterior patterning genes in the neuroectoderm. We have named each neural precursor group in Cupiennius and Glomeris according to the neuroblast nomenclature of Drosophila and we analysed the expression patterns of several dorso-ventral and anterior– posterior patterning genes that are known to be involved in neuroblast identity in Drosophila. Furthermore, we are studying the function of these genes by RNA interference in order to uncover evolutionary modifications and conserved mechanisms in the generation of neural precursor identity in arthropods. doi:10.1016/j.mod.2009.06.686

School of Biological and Chemical Sciences, London, United Kingdom Axonal path finding is a crucial process in the development of the central nervous system (CNS) in bilateral symmetrical organisms. To find their appropriate targets and connect both sides of an animal, axon growth cones are guided by specific attractive and/or repulsive cues provided by the surrounding environment. Recent studies on the ventral midline of Drosophila melanogaster and vertebrates on the genetic and biochemical level have uncovered a conserved system of ligands and receptors that guide pioneer axons at the midline such as Netrin and Slit. In addition, primary axonal tracts are marked by adhesion molecules such as fasciclins and cadherins, which in turn function as guide posts for follower axons. We are analysing axonal path finding in the spiders Cupiennius salei and Achaearanea tepidariorum by cloning genes that have a known conserved function in this process and compare our data to the remaining arthropod groups. We

15-P043 The evolution of a plant branching hormone Joanna Hepworth, Ce´line Mouchel, Ottoline Leyser University of York, York, United Kingdom The pattern of branch outgrowth is a key determinant of the flexible plant body plan, and varies among and within species.

assume that differences in axonal path finding correlate with changes in the expression of guidance cues or axonal markers. We expect that our data will uncover conserved features and evolutionary modifications in axonal path finding within the arthropods and contribute to the resolution of arthropod phylogeny. doi:10.1016/j.mod.2009.06.688