Page 75 - Mouse Molecular Genetics

Full Abstracts
Program number is above title. Author in bold is the presenter.
The inner ear and cochleovestibular ganglion (CVG) derive from a specialized region of head ectoderm termed the otic
placode. During embryogenesis, the otic placode invaginates into the head to form the otic vesicle (OV), the primordium of the
inner ear and CVG. To date, it is widely accepted that the otic placode ectoderm is the only source for the inner ear labyrinth and
neurons of the CVG. Using
mice to label and fate map cranial neuroepithelial cells (NECs),
including neural crest cells (NCCs), we show that their cellular derivatives contribute directly to the OV from the neural tube.
NEC derivatives constitute a significant population of the OV and moreover are regionalized specifically to proneurosensory
domains. Descendents of
labeled cells are localized within sensory epithelia of the saccule, utricle, and
cochlea throughout development and into adulthood where they differentiate into hair cells and supporting cells. Some NEC
derivatives give rise to neuroblasts in the OV and CVG in addition to their known contribution to glial cells. This finding defines
a dual cellular origin of the inner ear from sensory placode ectoderm and NECs and changes the current paradigm of inner ear
neurosensory development. Our current goals are to identify signaling pathways that regulate the contribution and localization of
NEC derivatives in the inner ear. We also seek to understand the functional significance of this dual embryonic origin. To further
investigate, we are performing FACS and comparative gene expression analysis of NEC- versus placode-derived populations. We
are also utilizing the putkflox allele to induce conditional cellular ablation of NEC derivatives in a manner that we hope will
bypass the requirement for non-autonomous cell signaling from the hindbrain to the OV.
Identification of novel mouse testis-determining genes in the MAP3K4 pathway.
Nick Warr, Gwenn Carre, Pam Siggers,
Rachel Brixey, Madeleine Pope, Sara Wells,
Andy Greenfield
Mammalian Genetics Unit, Harwell, Oxfordshire, United
The mammalian testis develops from an initially bipotential primordium when the Y-linked SRY gene is activated in gonadal
somatic cells during a critical period. The MAPK signalling cascade functions in human testis determination (1) and we have
previously reported male-to-female gonadal sex reversal in mice lacking the kinase MAP3K4 (2). Map3k4-deficient mutant
gonads are characterised by dramatic loss of the key testis-determining gene Sox9, caused by reduced Sry expression. However,
the widespread expression of MAP3K4 meant that determining the stage- and cell-type dependency of MAP3K4 function in the
developing gonad was difficult. In an attempt to identify novel regulators of MAPK signalling in testis development, and thereby
shed light on the spatiotemporal specificity of this pathway, we screened genes encoding MAP3K4-interacting proteins for
expression in the developing mouse gonad. One of these genes, encoding a protein associated with the cellular stress response,
exhibited strong expression in the gonadal soma in a spatiotemporal profile reminiscent of Sry itself. We show that knockout
mice lacking this gene exhibit fully penetrant XY gonadal sex reversal on a C57BL/6J genetic background. We will describe the
molecular genetic analysis of this novel sex-reversing mutant, including genetic interaction with Map3k4 and biochemical data
suggesting that the disrupted gene acts to regulate MAPK signalling required for normal Sry expression in the developing XY
gonad. In addition, we will present novel genetic data identifying a MAP3K4 target protein required for testis determination. (1)
Pearlman et al (2010) Am.J.Hum.Genet. 87:898-904 (2) Bogani et al (2009) PLoS Biology e1000196.
Core mesodermal functions of Tbx1 in branchiomeric muscle formation.
Ping Kong
Stephania Macchiarulo
Tingwei Guo
Silvia Racedo
Steven Ola
Vimla Aggarwal
Deyou Zheng
Bernice Morrow
. 1)
Einstein College of Medicine, 1301 Morris Park Avenue, Bronx, NY 10461, USA; 2) Department of Surgery, Montefiore
Medical Center, 111 East 210th Street, Bronx, NY 10467, USA; 3) Department of Neurology and Neuroscience, Albert Einstein
College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
Haploinsufficiency of TBX1, a T-box transcription factor, is believed to be responsible for most of the physical defects in
patients with Velo-cardio-facial syndrome/DiGeorge syndrome/22q11.2 deletion syndrome (22q11DS), including craniofacial,
which is of interest to us in this project. These craniofacial anomalies include velo-pharyngeal insufficiency, facial muscle
hypotonia and feeding difficulties, in part due to hypoplasia of branchiomeric muscles. Inactivation of both alleles of mouse Tbx1
results in overt cleft palate and reduction or loss of branchiomeric muscles, suggesting loss of tissue at some point during
embryogenesis. To determine the precise developmental stage when Tbx1 is required and this tissue is lost, we performed lineage
tracing using both pan-mesodermal drivers, Mesp1-Cre and T-Cre, in combination. We found that the core mesoderm cluster
within MdPA1, which is present at E9.5, is missing by E10.5 in Tbx1-/- embryos, suggesting that cells are lost earlier than
previously thought. Additionally, we performed gene profiling in Tbx1+/+ and Tbx1-/- mouse embryos and identified genes that
function downstream of Tbx1 in MdPA1 at these two critical time points, including Lhx2, Chrdl1 and Lrrn1, which were all
downregulated in null mutants. Based upon these results, we also sought to answer whether Tbx1 was required tissue-specifically
within the core mesoderm for branchiomeric muscle formation. To do this we inactivated Tbx1 with Mesp1-Cre and T-Cre
together because neither one alone resulted in complete Tbx1 inactivation. We found that Tbx1 is in fact required in the core
mesoderm for proper branchiomeric muscle development.
Additional sex com-like 1 is essential for normal alveolar development in mice. Seung-Tae Moon
Myengmo Kang, Soo-
Jong Um. Department of Bioscience & Biotechnology, Institute of Bioscience, BK21 Graduate Program, Sejong university,
Seoul, South Korea.
Retinoic acid (RA) plays a pivotal role in during mouse development and organ morphogenesis. Additional sex com-like 1