03-P092 Morphogenetic cell movements and rearrangement during the early eye development in zebrafish

S94

M 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

retinal pigment epithelial cells. In future experiments we are

from the pharyngeal mesoderm is accompanied by downregula-

going to focus on the interplay between photoreceptors and RPE

tion of the cell adhesion molecules Alcam and N-cadherin in the

during development. We hypothesise that transport efficiency is

anterior part of the embryonic heart. Tbx2 misexpression also

crucial for maintaining structure and functionality of vertebrate

results in downregulation of Tbx20 within the OFT, indicating that

eyes.

complex and region-specific transcriptional cross-regulation between the two T-box genes is essential for normal deployment

doi:10.1016/j.mod.2009.06.144

of the SHF at the arterial pole of the developing heart. doi:10.1016/j.mod.2009.06.146

03-P092 Morphogenetic cell movements and rearrangement during the early eye development in zebrafish

03-P094

Kenzo Ivanovitch, Florencia Cavodeassi, Stephen Wilson

Does the lizard, Calotes versicolor, exhibit a new pattern (FMFM) of

University College London, London, United Kingdom In vertebrates, retinal progenitor cells (RPCs) are specified at the end of the gastrulation within the anterior neural plate

TSD? Laxmi S. Inamdar1, V. Vani1, Polani B. Seshagiri2 1

Karnatak University, Dharwad, India

2

Indian Institute of Science, Bangalore, India

(ANP) as a single domain called the eye field. From that single domain, positioned medially within the ANP, the RPCs give rise

Among squamate reptiles, lizards exhibit an impressive array of

to two optic vesicles, positioned more laterally. How this dra-

sex determining modes viz., Genotypic sex determination (GSD),

matic morphogenetic remodelling occurs is not well understood.

Temperature-dependent sex determination (TSD), co-occurrence

We will show that soon after their specification, RPCs do not

of both these and those that reproduce parthenogenetically.

present a classical neuroepithelial appearance, with apical and

The oviparous lizard, Calotes versicolor lacks heteromorphic sex

basal sides; instead, RPCs seem to be randomly oriented and

chromosomes. Earlier studies on this species presented little evi-

present a more mesenchymal morphology. Less than an hour

dence to the sex determining mechanism. Here we provide evi-

later, the RPCs have organised into a neuroepithelium with all

dences, based on the data collected over 15 years that

their apical sides oriented towards the lumen of the eye field.

incubation temperature has a significant effect (p < 0.01) on gona-

This reorganisation is followed by the splitting of the eye field

dal sex and sex ratio. The eggs of C. versicolor were incubated at 14

and the evagination of the optic vesicles. We will discuss the

different incubation temperatures. Interestingly, 100% males were

potential role of the Wnt/PCP pathway and the transcription fac-

produced at low (25.5 ± 0.5 °C) as well as at high (34 ± 0.5 °C) incu-

tor Rx3 in these cellular rearrangements as well as the role of

bation temperatures and 100% females were produced at low

the morphogenetic movements of surrounding tissues (prospec-

(23.5 ± 0.5 °C) and at high (31.5 ± 0.5 °C) temperatures; indicating

tive telencephalon and hypothalamus) in the splitting of the eye

clearly the occurrence of TSD in C. versicolor. The temperature shift

field.

experiments revealed the occurrence of the thermosensitive period (TSP) during the embryonic stages 31, 32, and 33 coinciding

doi:10.1016/j.mod.2009.06.145

with early stages of gonadal sex differentiation. Two pivotal temperatures operate producing 1:1 sex ratio. Histology of gonad and accessory reproductive structures, expression of estrogen receptors, plasma steroid and maternal

03-P093

yolk steroid levels provide additional evidence for TSD in this spe-

Tbx2 modulates proliferation and elongation of the mouse

cies. The unique sex determining pattern, observed for the first

embryonic heart tube

time in this species, that neither compares to Pattern I [Ia-(MF)

Laurent Dupays, Surendra Kotecha, Timothy Mohun

and Ib-(FM)] nor to Pattern II (FMF), is being referred to as FMFM

National Institute for Medical Research, London, United Kingdom

pattern of TSD. This pattern of sex ratio exhibited by C. versicolor has an adaptive significance in maintaining its sex ratio.

Tbx2 is a member of the T-box family of transcription factors that play important roles during heart development. In the embry-

doi:10.1016/j.mod.2009.06.147

onic heart tube, Tbx2 is expressed in non-chamber myocardium (outflow tract and interventricular canal) and has been shown to block chamber formation. We have developed a genetic system to conditionally misexpress Tbx2 in the embryonic mouse heart at early stages of development. We show that Tbx2 expression throughout the myocardium of the heart tube both represses proliferation and impairs secondary heart field (SHF) progenitor cell deployment into the outflow tract (OFT). Repression of proliferation is accompanied by the upregulation of Ndrg2 and downregu-

03-P095 Fate and molecular mapping of the telencephalic domain in the chick neural plate Luisa Sanchez Arrones1, Jose Luis Ferran1, Lucia Rodriguez Gallardo2, Luis Puelles1 1

Department of Human Anatomy and Psychobiology, University of

lation of Ndrg4 expression, both genes believed to be involved in

Murcia, School of Medicine, and CIBER en Enfermedades Raras U736,

cell growth and proliferation. Impaired deployment of SHF cells

Murcia, Spain