13-P008 Sonic hedgehog-dependent control of basement membrane assembly in the myotome

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5

MECHANISMS OF DEVELOPMENT

Telethon Institute of Genetics and Medicine (Tigem), Via Pietro

1 2 6 (2 0 0 9) S1 9 5–S 23 8

13-P007

Castellino 111, Napoli, Italy

Midline and groucho interact to regulate wg in the embryonic

6

ectoderm

Department of Craniofacial Development, King’s College London, Floor

27, Guy’s Tower, London, United Kingdom Elucidating the gene regulatory networks that govern pharyn-

Ann Formaz-Preston, Jae-Ryeon Ryu, William Brook University of Calgary, Calgary, Alta., Canada

geal arch artery (PAA) development is an important goal, as such knowledge can help identify new genes implicated in the manifestation of cardiovascular disease. The transcription factor Tbx1 plays a vital role in PAA development and is a major contributor to cardiovascular disease associated with DiGeorge syndrome. In this report, we used various genetic approaches to reveal part of a signalling network by which Tbx1 controls PAA development. We investigated the critical role played by the homeobox-containing transcription factor Gbx2 downstream of Tbx1. We found that PAA formation requires the pharyngeal surface ectoderm (PSE) as a key signalling centre from where Gbx2, in response to Tbx1, triggers essential directional cues to adjacent cardiac neural crest cells (cNCCs) en route to caudal PAAs. Abrogation of this signal generates cNCC patterning defects leading to PAA abnormalities. Finally, we showed that the Slit/Robo signalling pathway is activated during cNCC migration and found that components of that pathway are affected in Gbx2 and Tbx1 mutant embryos at the time of PAA development. We propose that the spatio-temporal control of this tightly orchestrated network of genes participates in crucial aspects of PAA development. doi:10.1016/j.mod.2009.06.478

T-box genes play a variety of roles in vertebrate and invertebrate development. In the fly Drosophila melanogaster, midline and H15 are paralogous and partially redundant T-box genes that act in segmentation, neurogenesis, dorsal vessel development and imaginal disc patterning. In the embryonic ectoderm where mid H15 are part of the segmentation cascade they are responsible for inhibiting bidirectional activation of wg by Hh signaling. We find that Mid represses wg directly and have found 4 predicted T-box binding sites within a 1 kB wg regulatory region. Mutation of all 4 sites mimics the effects of mid loss of function on enhancer expression pattern. We also find that wg repression by Mid is dependent on the Mid eh1 motif, a domain required for direct binding of the co-repressor Groucho (Gro) in other transcription factorsa. Gro, homologous with mouse Grg or human TLE, is broadly expressed in the embryonic ectoderm during segmentation and is believed to link transcription factors to the histone deacetylase machinery. We show that Mid binds Gro and that a mutation of Mid’s eh1 domain causes both a reduction in Gro binding and in Mid’s ability to repress wg. Mutation of the eh1 domain does not however limit Mid’s ability to repress another of its targets in the ectoderm Serrate (Ser) suggesting that Mid has multiple roles in the embryonic ectoderm. doi:10.1016/j.mod.2009.06.480

13-P006 Neural crest derived signals pattern the cranial sensory nervous system by repressing lens potential Tim Grocott, Andrea Streit

13-P008 Sonic hedgehog-dependent control of basement membrane assembly in the myotome

King’s College London, Department of Craniofacial Development,

Claire Anderson1, Solveig Thorsteinsdottir2,

London, United Kingdom

Anne-Gae¨lle Borycki1

The sensory nervous system in the vertebrate head comprises the paired sense organs and cranial sensory ganglia. It largely arises from specialised neurogenic ectoderm, the cranial placodes that form at distinct positions along the developing brain. Despite the structural and functional diversity of placode derivatives in the adult, placode precursors arise form a pool of multipotent progenitors, which initially share a common developmental programme. Irrespective of their later fate they are specified as lens and undergo lens differentiation when cultured in isolation suggesting that during normal development lens potential must be repressed in non-lens tissue. We have uncovered a novel role for neural crest cells in patterning the sensory nervous system as potent lens suppressors. Here, we provide evidence that both TGF-beta and Wnt signalling pathways mediate the lens repression and thus provide a molecular mechanism to restrict lens formation to its normal position next to the future retina. doi:10.1016/j.mod.2009.06.479

1

University of Sheffield, Sheffield, United Kingdom

2

Universidade de Lisboa, Lisboa, Portugal Skeletal muscles originate mostly from transient embryonic

structures called somites. During their development, somites produce morphologically distinct compartments, including the myotome, a transient somitic structure where primary myogenesis takes place. The myotome forms when Myf5-positive muscle progenitor cells (MPCs) delaminate from the dorso-medial lip of the dermomyotome, and translocate underneath it to form the epaxial myotome. As development proceeds, additional MPCs sequentially populate the myotome from the caudal, rostral and lateral edges of the dermomyotome and participate in the formation of the central and hypaxial myotomes, respectively. As MPCs populate the myotome, they interact with the extra-cellular matrix to form a myotomal basement membrane that separate the myotome from the sclerotome and plays essential role in the growth and differentiation of the myotome. Here, we report that in the absence of Sonic hedgehog (Shh) signalling, the myotome is abnormally patterned. We demonstrate that this defect is due to a failure to assemble a continuous basement

MECHANISMS OF DEVELOPMENT

1 2 6 ( 2 0 0 9 ) S 1 9 5 –S 2 3 8

membrane. Our genetic and embryological analyses further indi-

1

UMR7139 CNRS-UPMC Station Biologique, Roscoff, France

cate that Shh signalling controls Laminin gene expression, a crit-

2

Dpt. Forest Genetics & Plant Physiology, Umea, Sweden

ical step in the formation of the myotomal basement membrane,

3

FR2424 CNRS Station Biologique, Roscoff, France

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and that Laminin-111 has specific and essential role in myotomal basement membrane assembly. Together, our data reveal a

The development of the filamentous brown alga Ectocarpus sil-

novel role for Shh signalling in the control of basement mem-

iculosus is under the control of intrinsic mechanisms (Le Bail et al.,

brane assembly and provide a framework for understanding

J. Phycol., 2008). Modelling showed that local positional informa-

the complex interactions between extra-cellular matrix and

tion is determining for the proper development of the very early

intercellular signalling.

sporophyte, and that an additional mechanism is further required to ensure a correct organisation of the branching pattern (Billoud et al., Funct. Plant Biol., 2008).

doi:10.1016/j.mod.2009.06.481

Here, we show that the auxin phytohormone Indole-3 Acetic Acid is present in E. siliculosus mainly at the apices of the filaments. Several auxin compounds are able to interfere with both 13-P009

the cell differentiation and the branching pattern in this filamen-

Characterization of dorsal neuron subtypes and their axonal

tous alga. Genome-wide survey displays a partial conservation of

trajectories in the chick hindbrain

the auxin biosynthesis pathways and the identification of an

Ayelet Kol, Dalit Sela-Dnenfeld, Avihu Klar

auxin hypersensitive mutant supports the existence of a signal-

The Hebrew University, Rehovot, Israel

ling pathway. Transcriptional microarray experiments allowed the identifi-

The hindbrain represents the key relay hub of the central nervous system, linking the bilaterally symmetric half-sides of its lower and upper centers via an extensive network of sensory circuits. The early hindbrain is transiently subdivided into repetitive rhombomeres along its anterior–posterior (AP) axis, that underlies segmental formation of motor nerves and ganglia. It is less clear whether this AP segmentation also contributes to the formation of dorsal interneurons, in addition to dorso-ventral (DV) cues that are known to pattern spinal cord sensory neurons. The aim of this study is to determine the spatial/temporal formation of 3 dorsal interneuron populations (dI1–3) in the chick hindbrain and to delineate their axonal projections during development. In order to characterize dI1–3 distribution along the hindbrain,

immunohistochemistry

analysis

was

performed

at

subsequent stages using antibodies against several Lim-homeodomain proteins (Lhx2/9, Lim1, Islet1). This analysis showed a

cation of an auxin inducible gene, EsGRP1, which codes for a secreted chimeric protein containing both a glycin-rich region involved in land plant cell wall extension, and a von Willebrand A domain specific for animal extracellular matrix proteins. Specific antibodies were raised against the EsGRP1 protein in order to confirm its localisation in the extracellular matrix. Real-time RT-PCR experiments showed that EsGRP1 is induced 30 min upon addition of auxin Naphthalene Acetic Acid, and that its expression is altered in a series of morphogenetic Ectocarpus mutants. Altogether, these data suggest that auxins control the cell differentiation and the branching pattern in Ectocarpus sporophytes, by potentially involving the extracellular vWA-glycin-rich protein EsGRP1. doi:10.1016/j.mod.2009.06.483

dynamic DV/AP distribution of these cell subtypes along the hindbrain. Next, we applied a Cre/loxP-based dual-expression system for studying the axonal-trajectories of dI1–2 neurons using

13-P011

mapped enhancer determinants. For dI1 neurons, detected by

Restriction of EMT within the primitive streak and correct pat-

math1/pouf3 elements, 2 main distinct axonal projections were

terning of the mesoderm requires Pofut2

found, both crossing the ventral midline and turning caudally

Jianguang Du, Christina L. Leonhard-Melief, Hideyuki Takeuchi,

toward the spinal cord. DI2 axons, mapped with Foxd3 element,

Kenneth R. Shroyer, Malgosia Dlugosz, Robert S. Haltiwanger,

showed one main contra-lateral pattern after crossing the floor

Bernadette C. Holdener

plate. In addition, both subtypes revealed also ipsilateral routes. Taken together, this study enabled us to construct a comprehen-

Stony Brook University, Stony Brook, NY, United States

sive map of the developmental programming of dI1–3 together with discovering novel trajectories of their axons in the hindbrain.

Thrombospondin type 1 repeat (TSR) superfamily members regulate diverse biological activities ranging from cell motility to

doi:10.1016/j.mod.2009.06.482

inhibition of angiogenesis. Here we demonstrate that mouse protein O-fucosyltransferase-2 (POFUT2) specifically adds O-fucose to TSRs, and is essential for restricting epithelial to mesenchymal transition in the primitive streak and correct patterning of meso-

13-P010

derm. Pofut2 mutant embryos establish anterior/posterior polar-

Auxin in the control of the development of the brown alga Ecto-

ity. However, abnormalities at mid-gastrulation are reminiscent

carpus siliculosus

of the ventralizing effects of overexpression of BMP or inhibition

Aude Le Bail1, Nathalie Kowalczyk1, Marius Kowalczyk2,

of Activin on Xenopus embryos. Mutant embryos undergo exces-

Bernard Billoud1, Sophie Le Panse3, Sarah Stewart1,

sive epithelial to mesenchymal transition, resulting in the loss

Morgane Gicquel1, Karin Ljung2, Be´ne´dicte Charrier1

of pluripotency markers Sox2 and Oct4 and overexpression of