Abstracts - Society for Developmental Biology

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transcription factor associated with a GABAergic phenotype. More broadly, we are examining the different patterns of
calcium activity displayed by developing retinal cellsand the relationship to phenotype.
Program/Abstract # 304
Lineage commitment and differentiation of renal progenitor cells
Sharma, Richa; Bouchard, Maxime, Goodman Cancer Centre, McGill University, Montreal, Canada
Maintenance and differentiation of stem cell/progenitor state are central concept in cancer and embryo development.
Pax2/8 genes are found to be necessary and sufficient in lineage commitment and cell differentiation in different stages of
kidney development. Previous studies from our lab clearly establish that embryos deficient for Pax2 and its paralog Pax8
fail to specify the first renal cells in the embryo. Conversely, ectopic expression of Pax2 in mesodermal progenitor cells
was sufficient to induce mesodermal-epithelial transition, tubulogenesis and specify the renal fate (Bouchard et al., Genes
Dev, 2002). Hence, we hypothesize that Pax2 acts as a master control gene regulating the transition from stem cell/
progenitors to a more differentiated state by integrating upstream signals and establishing a lineage-restricted
transcriptional program. Although the crucial importanceof Pax2/8 in renal lineage commitment from progenitor cells is
well established the molecular and cellular mechanisms responsible for this transition are poorly understood. The aim of
this project is to study the molecular signals that activate Pax2/8 expression to initiate cell lineage specification from
progenitor cells. To examine it we recently developed a primary culture system in which we purifyrenal primordium cells
expressing a Pax2-GFP transgene from E9.25 embryos.These cells in culture gradually turn off GFP expression, acquiring
a progenitor-like state. We then tried to follow renal lineage specification from these progenitors by reactivation of GFP
through addition of candidate Pax2 inducing factors. We were able to identify some of the early regulators of nephric
lineage activation. Our long-term goal is to shed some light on the exact mechanisms of cellular transition from a stem
cell/progenitorstate to a lineage-restricted committed state. This will impact our understanding of cellular mechanisms that
have direct consequences not only for the renal developmental diseases but also for the study of embryogenesis.
Program/Abstract # 305
Kruppel-like factor 5 is required for villus morphogenesis and terminal differentiation of the intestinal epithelium
Bell, Sheila; Zhang, Liqian; Xu, Yan; Whitsett, Jeffrey, Cincinnati Children's Hospital Medical Center, Cincinnati, United
States
Kruppel-like factor 5 (Klf5) is a transcription factor demonstrated to regulate cell proliferation, migration, and
differentiation in a variety of cell types. We created a Klf5 floxed allele and crossed it into mice harboring Crerecombinase
under control of the Shh promoter resulting in embryos deficient in Klf5 throughout the gut endoderm. KLF5
immunohistochemistry confirmed that the Klf5 alleles were efficiently floxed. At E14.5, the forming intestine of Klf5Δ/Δ
embryos was morphologically indistinguishable from controls, epithelial cells were proliferating, and expressed the early
endoderm markers SOX9 and FOXA1. Between E15.5-E16.5 formation of the crypt-villus axis begins and the first signs of
malformation were observed in Klf5Δ/Δ embryos. In mutants, villi failed to form and expression of SOX9 and FOXA1
persisted throughout most of the intestinal epithelium. At later developmental stages, a marked paucity of normal
cytodifferentiation was observed. The microvilli comprising the brush border were disorganized and there was a dramatic
reduction in the number of goblet and enteroendocrine cells. Microarray analysis and qPCR of fetal intestines revealed
misregulation of transcription factors known to drive intestine epithelial terminal differentiation including Elf3, Ascl2, and
Atoh1. Notably, reductions in the expression of signaling molecules associated with villus morphogenes is were not
detected: PdgfA, Shh, Ptc1, Bmp2, andBmp4. In contrast, the intestinal mesenchyme of embryos with Klf5 deficient
epithelia differentiated normally. These observations indicate that KLF5 plays a critical role in the signaling cascade
leading to crypt-villus axis formation that precedes epithelial differentiation.
Program/Abstract # 306
KIF17 controls the ciliary localization of GLI2 and GLI3
Carpenter, Brandon S.; Blasius, Teresa; Verhey, Kristen; Allen, Benjamin, University of Michigan Cell and
Developmental Biology, Ann Arbor, United States
Primary cilia are essential for Hedgehog (HH) signal transduction during vertebrate embryogenesis. The HH
transcriptional effectors GLI2 and GLI3 traffic through primary cilia, and these cellular organelles are required for proper
processing of GLI proteins. However, the mechanisms that control ciliary trafficking of the GLI proteins are largely
unknown. Kinesin-2 motorproteins, namely KIF3A, KIF3B, and KIF17, mediate anterograde trafficking of proteins
through primary cilia, making them presumptive candidates for regulating anterograde transport of GLI2 and GLI3.
However, since KIF3A and KIF3B function in both anterograde cilia transport, as well as cilia formation, teasing out a
HH-specific function is difficult. Unlike KIF3Aand KIF3B, KIF17 function appears to be restricted to anterograde