of ltk and melanoblast or xanthoblast markers can be found in

the embryo, consistent with a shared origin of these cell-types.

We also present evidence that iridophore precursors are likely

to also have glial potential. Finally, we engineered constitutively

active form of ltk gene by analogy with oncogenic gene nucleo-

phosmin-anaplastic lymphoma kinase, and examine the results

from experiments asking what happens to NCCs with constitu-

tively active Ltk signaling.

doi:10.1016/j.mod.2009.06.154

03-P102

Expression and regulation of the claudin family of tight junction

proteins during gastrulation

Michelle Collins, Aimee Ryan

McGill University, Montreal, Quebec, Canada

Research Institute of the Montreal Children’s Hospital, Montreal, Quebec,

Canada

During gastrulation epiblast cells undergo epithelial to mesen-

chymal transition (EMT) as they delaminate and ingress through

the primitive streak to form the definitive endoderm and meso-

derm. The dissociation of junctional complexes is essential for

EMT to occur. We are examining the expression and regulation

of the claudin family of integral tight junction proteins during

chick gastrulation. Tight junctions are localized to the apical pole

of epithelial cells and the claudin component of the tight junction

is responsible for determining the ion and size selectivity of the

junction. We hypothesize that claudin expression must be

repressed in the epiblast cells that ingress through the primitive

streak. More than 20 members of the Claudin family have been

identified in vertebrates. We found that Claudins -1, -3, -10, -11,

-12, -22 and -24 showed distinct expression patterns during gas-

trulation and we are now determining how these expression pat-

terns are regulated. For example, Claudin-1 is highly expressed in

the epiblast layer reduced in the cells that delaminate and ingress

through the primitive streak and absent from the nascent meso-

derm. The Claudin-1 promoter contains an evolutionarily con-

served E-box regulatory element that is recognized by members

of the Snail family of zinc-finger transcriptional repressors that

play a key role in EMT. We showed that the chick Claudin-1 pro-

moter is repressed by Snail2 in vitro, and that this interaction

occurs through binding to the E-box element. We are currently

investigating the role of Snail-2 in regulating Claudin-1 expression

in vivo.

doi:10.1016/j.mod.2009.06.155

03-P103

Morphogenesis and cellular mechanisms in mice molar root

development

Min-A. Choi1, Wern-Joo Sohn2, Hye-In Jung3, Hong-In Shin1,

Sang Gyu Lee2, Han-Sung Jung4, Jae-Young Kim3

1 Department of Oral Pathology and Regenerative Medicine, School of

Dentistry, IHBR, Kyungpook National University, Daegu, Republic of

Korea2 School of Life Science and Biotechnology, Kyungpook National Univer-

sity, Daegu, Republic of Korea3 Department of Biochemistry, School of Dentistry, IHBR, Kyungpook

National University, Daegu, Republic of Korea4 Division in Anatomy and Developmental Biology, Department of Oral

Biology, Research Center for Orofacial Hard Tissue Regeneration, Brain

Korea 21 project, Oral Science Research Center, College of Dentistry, Yo,

Seoul, Republic of Korea

Most of studies in tooth development have been focused on

the early development with crown formation. In root formation,

known as a following event after the completion of crown forma-

tion, developmental mechanisms and cellular events were not

elucidated properly. In this study, morphogenesis and cellular

mechanisms such as cytoskeletal formation, cell proliferation

and apoptosis have been examined with three dimensional

approaches during mouse root development. Specific localization

and expression patterns of cellular markers and signalling mole-

cules in the root forming region would suggest that differential

cellular mechanisms would be involved in the formation of root

and diaphragm regions in multi-rooted tooth development. Espe-

cially, cell proliferation and actinfilament formation, examined by

Ki67 immunostaining and phalloidin staining, showed the signif-

icant differences of localization patterns in root forming and dia-

phragm forming regions. In order to evaluate the precise cellular

mechanisms in root formation, we treated Cytochalasin D and

Nocodazole, well known inhibitors for actinfilament and microtu-

bule formations, during in vitro organ culture. Based on these

results, we could conclude that differential roles of cytoskeletal

formation and proliferation between root and diaphragm forming

region would play important roles in multi-rooted tooth

morphogenesis.

doi:10.1016/j.mod.2009.06.156

03-P104

Transient innervation of retinal axons to the deeper laminae

prior to establishment of the lamina-specific projection in chick

optic tectum

Minoru Omi1, Hidekiyo Harada2, Harukazu Nakamura1,2

1 Graduate School Life Science, Tohoku University, Sendai, Japan2 IDAC, Tohoku University, Sendai, Japan

The visual center of the lower vertebrates is the optic tectum.

Retinal fibers invade the tectum from the rostral, run through the

superficial layer of the tectum, make a right turn near the termi-

nal, and make terminal arborizations in the specific retinorecipi-

ent laminae. Previous studies have shown that the terminals

arborize only in upper laminae (above lamina g in SGFS) and it

has been accepted that retinal axons never enter deeper laminae.

We re-examined the projection pattern of retinal axons in the tec-

tum laminae of developing chick embryos utilizing high sensitive

tracing system in which gene of fluorescent protein marker is

integrated in the genome by transposon mediated system

S97M E C H A N I S M S O F D E V E L O P M E N T 1 2 6 ( 2 0 0 9 ) S 6 7 – S 1 0 6