Abstracts - Society for Developmental Biology

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Congenital renal malformations are common birth defects affecting approximately 1% of the infants and often arising from
the defects in ureteric bud (UB) development. Glial cell line-derived neurotrophic factor (GDNF) signaling through the
RET receptor tyrosine kinase is essential for ureteric bud outgrowth but the events that occur downstream of RET to
promote ureter morphogenesis remain largely obscure. In addition, the cellular mechanisms by which GDNF/RET
signaling promotes kidney growth through branching morphogenesis remain to be discovered. We have focused our studies
on the function of mitogen activated protein kinase (MAPK) pathway in the ureteric bud (UB) lineages. Mice lacking
MAPK activity specifically in the UB initiate renal morphogenesis normally and are capable of undergoing nephrogenesis,
but fail to form complex UB patterns. The analysis of Hoxb7CreGFP; Mek1F/F; Mek 2kidney phenotype revealed that
only a fraction of previously identified GDNF target genes are regulated through this pathway. The results also suggest
specific role for MAPK pathway in branch point determination potentially through the maintenance of epithelial integrity.
Program/Abstract # 131
Calcium/NFAT signaling is essential for mesenchymal-epithelial transition during nephron formation
Tanigawa, Shunsuke; Sharma, Nirmala; Tarasova, Nadya; Yamaguchi, Terry; Perantoni, Alan, National Cancer Institute,
Frederick, United States
During kidney development, a subpopulation of stem cells in the metanephric mesenchyme (MM) undergoes
mesenchymal-epithelial transition (MET) to form the tubular segments of the nephron. To elucidate the mechanism of
MET, we developed a culture system for the maintenance and propagation of MM progenitor cells and have demonstrated
that WNT4 induces MET by a non-canonical Wnt/calcium pathway and not by a canonical Wnt/β-catenin pathway as
previously believed. WNT4 stimulated calcium influx and phospholylation of CaMKII in MM cells, and Ionomycin, a
calcium ionophore, induced MET in MM, indicating that activation of the calcium signaling pathway is sufficient for MET
induction. Leukemia inhibitory factor (LIF) also induced MET in MM and similarly activated calcium signaling and
induced phosphorylation of CaMKII. Reporter activity for the transcription factor, Nuclear Factor Activated T-cells
(NFAT), which has been implicated in calcium signaling, was greatly elevated in MM cells treated with WNT4 or LIF, and
expression of a constitutively active form of NFAT in MM cells up regulated MET markers, consistent with a possible role
for NFAT in this morphogenesis. GSK3β normally blocks the nuclear accumulation of NFAT by phosphorylation, and
GSK3β inhibitor CHIR99021 causes NFAT dephosphorylation, allowing its translocation to the nucleus for transcription.
In our system, CHIR99021 activated an NFAT reporter and induced MET in MM cells. Finally, induction of MET by
WNT4, LIF or CHIR99021 was blocked by the NFAT inhibitor cyclosporin A, but not a β-catenin peptide inhibitor,
suggesting that NFAT is required for MET and that these very different signaling molecules share a common calciumdependent
process for MET. These results demonstrate that the calcium/NFAT pathway is essential for morphogenesis of
nephronic stem cells and provide insight into key signaling mechanisms involved in kidney development.
Program/Abstract # 132
Incidence of vesicoureteric reflux and other urinary tract abnormalities in OSR1 deficient mice
Watt, Christine; El Andalousi, Jasmine; Fillion, Marie-Lyne; Gupta, Indra, McGill, Montreal, Canada
Congenital abnormalities of the kidney and urinary tract (CAKUT) are a cause of chronic kidney disease and encompass a
spectrum of phenotypes including vesicoureteric reflux (VUR), the retrograde movement of urine from the bladder to the
kidney, duplex systems and/or urinary tract (UT) obstruction. This broad range of phenotypes is attributed to aberrations at
different key developmental time points. The kidney and UT arise from the ureteric bud (UB), an epithelial structure
derived from reciprocal signaling between the nephric duct and surrounding metanephric mesenchyme. The distal portion
of the UB will branch and form the kidney, while the proximal portion will elongate to form the ureter. Initially, the ureter
is connected to the nephric duct via the common nephric duct and subsequently separates, moving to its final insertion
point in the bladder. We have identified the C3H mouse as a model of fully penetrant VUR and identified a 22Mb
susceptibility locus on proximal chromosome12, the Vurm1 locus that contains many candidate genes including, Odd
Skipped Related 1 (Osr1), a gene encoding a zinc finger protein, that has been implicated in kidney and UT development.
Osr1 is expressed in intermediate and undifferentiated metanephric mesenchyme and homozygous null mice are anephric.
Analysis of B6.129S1-Osr1tm1Jian/J+/-(Osr1+/-) mice has shown an increased incidence of VUR:35% in Osr1+/- (5/14)
compared to 3% in wild-type littermates (1/26). Other UT abnormalities in addition to VUR are also observed, including
duplex kidneys, bifidureters, and urinary tract obstruction. This data suggests that haploinsufficiency of OSR1 has a critical
impact on urinary tract development.
Program/Abstract # 133
Three-dimensional modeling of the zebrafish liver network reveals regulators of biliary morphogenesis.
Justin M.Nussbaum; Hasan, Ayesha; Sakaguchi, Takuya (Lerner Research Institute).