Page 52 - Mouse Molecular Genetics

Full Abstracts
Program number is above title. Author in bold is the presenter.
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50
Gadd45 functions in male sex determination by promoting p38 signaling and
Sry
expression. Wolfram H. Gruhn
1,2
,
Mathias S. Gierl
1
,
Annika von Seggern
1
,
Nicole Maltry
3
,
Christof Niehrs
1,2
. 1)
Institute of Molecular Biology, 55128 Mainz,
Germany; 2) DKFZ-ZMBH Alliance, Division of Molecular Embryology, DKFZ, 69120 Heidelberg, Germany; 3) Division of
Cellular Immunology, DKFZ, 69120 Heidelberg, Germany.
Sex determination in mammals is tightly controlled by a complex gene regulatory network. In most mammals, male sex
development is induced in embryogenesis by the transcription factor Sex-determining region Y protein (Sry). Mice that do not
induce
Sry
expression within a critical time window during gonadogenesis develop into phenotypic females. Despite its pivotal
role in male sex determination, regulatory events mediating
Sry
transcriptional activation are poorly understood. In this study, we
show that male mice mutant for the stress-response gene
Gadd45
display complete male-to-female sex-reversal. In order to shed
light on the molecular mechanism of
Sry
transactivation and Gadd45 function in male sex determination, we employed gene
expression analysis, MAPK signaling activity investigation, bisulfite sequencing and chromatin immunoprecipitation (ChIP) on
the
Sry
promoter.
Gadd45
and
Sry
have a strikingly similar expression pattern in the genital ridge and they are co-expressed in
gonadal somatic cells. Notably,
Gadd45
expression is induced in gonadal cells shortly before
Sry
is expressed. In
Gadd45
mutant
embryos
Sry
expression is reduced and delayed while other factors known to regulate
Sry
are expressed normally.
Although
Gadd45
genes are implicated in active DNA demethylation, the
Sry
promoter undergoes normal DNA demethylation
in
Gadd45
mutant embryos. Instead, p38 MAPK signaling is reduced in
Gadd45
mutant gonads. Inhibition of p38 MAPK
signaling in gonadal cells strongly decreases
Sry
expression whereas pharmacological induction of p38 MAPK signaling
rescues
Sry
expression in
Gadd45
mutant gonads. Furthermore, the transcription factor Gata4, which is required
for
Sry
expression, binds to the
Sry
promoter
in vivo
in a p38 MAPK-dependent manner. Based on these findings, we suggest that
Gadd45 is a novel regulator of male sex determination in mice, which promotes
Sry
expression by inducing p38 MAPK-
dependent Gata4 binding to the
Sry
promoter.
51
Tbx20
and
Tbx3
act independently of each other in the developing heart. Virginia E Papaioannou
1
,
Svetlana Gavrilov
1,2
. 1)
Genetics and Development, Columbia University, New York, NY; 2) Developmental Biology Program, Sloan-Kettering Institute,
New York, NY.
Tbx20
and
Tbx3
,
members of the T-box gene family, play important roles in the developing embryo and are critical for proper
heart development. Individually
Tbx20
and
Tbx3
genes, when mutated, cause distinct congenital heart abnormalities, but their
overlapping expression in the developing heart raises the question of whether they act independently or through transcriptional
regulation of common target genes.
Tbx20
gene expression is induced ectopically in the
Tbx3
mutant heart but the potential
genetic interaction between these two genes has not been investigated. In this study, we investigated the genetic interaction
of
Tbx20
and
Tbx3
in the developing heart. Mice heterozygous for both
Tbx20
-
and
Tbx3
-
locus were intercrossed to generate
compound heterozygotes (
Tbx20
+/-
;
Tbx3
+/-
).
Compound heterozygotes were viable and fertile, present at expected Mendelian
ratios at weaning. No apparent abnormalities were observed. Double null embryos were recovered at expected frequency from
compound heterozygote matings and there were no significant deviations from expected Mendelian ratios.
Tbx20
-/-
;
Tbx3
-/-
double null mice are embryonic lethal by midgestation. They display looping defects similar to
Tbx20
-/-
embryos, with small
hypoplastic hearts and disturbed chamber morphology. Cardiac marker analysis for
Tbx2
,
Tbx5
,
Nppa
and
Pitx2
confirmed
this
Tbx20
-/-
like phenotype in double nulls mutants. In addition, we observed overall developmental delay in double null
mutants. An embryo was considered delayed if its somite number was lower than the mean somite number for the litter. In order
to compare developmental delay between litters we have calculated the ratio for each embryo (number of somites in an
embryo/mean number of somites in the litter) and used notched box plots to compare double null embryos to wild type and single
mutants. Using statistical analysis we determined that overall developmental delay in double null mutants is similar to
developmental delay in
Tbx3
-/-
mutants. In conclusion, there is no evidence for genetic interaction between
Tbx20
and
Tbx3
and
the effects of
Tbx20
are epistatic to
Tbx3
.
52
Genetic pathways required for maintenance of vascular smooth muscle phenotype. Sylvia M Evans
1
,
Nuno Guimaraes-
Camboa
1,2
,
Chase Bolt
3
,
Lisa Stubbs
3
. 1)
Skaggs School of Pharmacy, Department of Medicine, University of California San
Diego, La Jolla, CA; 2) Biomedical Sciences Institute Abel de Salazar, Graduate Program in Areas of Basic and Applied
Biology, University of Porto, Portugal; 3) Institute for Genomic Biology, Department of Cell and Developmental Biology,
University of Illinois, Urbana, IL.
Our lab has been interested in studying genetic pathways required for epicardial cell development. One of the cell lineages
derived from epicardium is vascular smooth muscle of the coronary arteries. Vascular smooth muscle plays an important role in
coronary vascular disease and is also important for maintaining integrity of the aorta. We have performed gene ablation studies in
mouse which have identified a novel pathway required for maintenance and function of vascular smooth muscle. This genetic
pathway intersects with pathways affected in human patients with vascular smooth muscle disorders. Results of these studies will
be discussed.