Jennifer Plank, a current student in Cell and Developmental Biology, received the award in the graduate student category. Working with Patricia Labosky, Ph.D., Jennifer studies regulators of pancreatic beta cell mass expansion. She has identified important roles for the neural crest and for the transcription factor Foxd3 in the beta cell. The findings from both of her projects can be applied to the generation of beta cells to treat patients with diabetes.
Susan Wente, Associate Vice Chancellor for Research, Senior Associate Dean for Biomedical Sciences, and Professor, Cell and Developmental Biology, Vanderbilt University School of Medicine, was named by the ASCB’s Women in Cell Biology (WICB) Committee to receive the 2011 WICB Senior Award. Wente is a world-recognized leader and has made seminal advances in three key areas: mechanism of translocation across the nuclear pore; assembly of the nuclear pore complex; and inositol phosphate signaling. She has published almost 80 papers since she began her career, and has recently received a MERIT award to continue her studies on nuclear pore complexes. In a field of comparably exceptional scientists, Wente further stood out in the strength of her mentorship both individually
and institutionally. Within her own research group, she has been an outstanding mentor. Many of her trainees have gone on to active careers in research either in academia or industry, or have found success in alternative careers such as journal editing or patent law. And she is well known for celebrating the growth and successes of each lab member, demonstrating the importance of each individual’s accomplishment. Wente has successfully taken on significant leadership responsibilities as well. When she was recruited from Washington University to Vanderbilt to chair the Department of Cell and Developmental Biology, she joined the few women who chair similar departments at major research universities. By extensive recruiting and mentoring, she has built a truly impressive faculty. (She has also served as a member of the ASCB Council.) As a result of her successes at the departmental level, she was recently promoted to Associate Vice Chancellor for Research and Senior Associate Dean for Biomedical Sciences at Vanderbilt, with new challenges for her mentoring and leadership skills. As of this writing, Wente is spending a week rafting the Colorado River with her husband and two daughters. An extraordinary scientist, mentor, leader, and person, Wente exemplifies everything the WICB Senior Award is about.
- Vivian Siegel for the Women in Cell Biology Committee
Jennifer L. Plank, Audrey Y. Frist, Alison W. LeGrone, Mark A. Magnuson and Patricia A. Labosky
- Author Affiliations
Department of Cell and Developmental Biology (J.L.P., A.Y.F., A.W.L., M.A.M., P.A.L.), Center for Stem Cell Biology (J.L.P., A.Y.F., A.W.L., M.A.M., P.A.L.), Program in Developmental Biology (J.L.P., A.Y.F., A.W.L., M.A.M., P.A.L.), Department of Molecular Physiology and Biophysics (M.A.M.), and Department of Pharmacology (P.A.L.), Vanderbilt University Medical Center, Nashville, Tennessee 37232-0494
Address all correspondence and requests for reprints to: Patricia A. Labosky, 9415D MRBIV, 2213 Garland Avenue, Nashville, Tennessee 37232-0494. E-mail: trish.labosky@vanderbilt.edu.
A complete molecular understanding of β-cell mass expansion will be useful for the improvement of therapies to treat diabetic patients. During normal periods of metabolic challenges, such as pregnancy, β-cells proliferate, or self-renew, to meet the new physiological demands. The transcription factor Forkhead box D3 (Foxd3) is required for maintenance and self-renewal of several diverse progenitor cell lineages, and Foxd3 is expressed in the pancreatic primordium beginning at 10.5 d postcoitum, becoming localized predominantly to β-cells after birth. Here, we show that mice carrying a pancreas-specific deletion of Foxd3 have impaired glucose tolerance, decreased β-cell mass, decreased β-cell proliferation, and decreased β-cell size during pregnancy. In addition, several genes known to regulate proliferation, Foxm1, Skp2, Ezh2, Akt2, and Cdkn1a, are misregulated in islets isolated from these Foxd3 mutant mice. Together, these data place Foxd3 upstream of several pathways critical for β-cell mass expansion in vivo.
Notch signaling and hepatocyte nuclear factor-6 (HNF-6) are two genetic factors known to affect lineage commitment in the bipotential hepatoblast progenitor cell (BHPC) population. A genetic interaction involving Notch signaling and HNF-6 in mice has been inferred through separate experiments showing that both affect BHPC specification and bile duct morphogenesis. To define the genetic interaction between HNF-6 and Notch signaling in an in vivo mouse model, we examined the effects of BHPC-specific loss of HNF-6 alone and within the background of BHPC-specific loss of RBP-J, the common DNA-binding partner of all Notch receptors. Isolated loss of HNF-6 in this mouse model fails to demonstrate a phenotypic variance in bile duct development compared to control. However, when HNF-6 loss is combined with RBP-J loss, a phenotype consisting of cholestasis, hepatic necrosis, and fibrosis is observed that is more severe than the phenotype seen with Notch signaling loss alone. This phenotype is associated with significant intrahepatic biliary system abnormalities, including an early decrease in biliary epithelial cells evolving to ductular proliferation and a decrease in the density of communicating peripheral bile duct branches. In this in vivo model, simultaneous loss of both HNF-6 and RBP-J results in down-regulation of both HNF-1β (hepatocyte nuclear factor-1β) and Sox9 (SRY-related HMG box transcription factor 9).
HNF-6 and Notch signaling interact in vivo to control expression of downstream mediators essential to the normal development of the intrahepatic biliary system. This study provides a model to investigate genetic interactions of factors important to intrahepatic bile duct development and their effect on cholestatic liver disease phenotypes. (HEPATOLOGY 2011.)
Jason Stumpff2, 4, Yaqing Du1, 4, Chauca A. English1, Zoltan Maliga3, Michael Wagenbach2, Charles L. Asbury2, Linda Wordeman2, 4, , and Ryoma Ohi1, 4,
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Mechanisms Underlying the Dual-Mode Regulation of Microtubule Dynamics by Kip3/Kinesin-8 Molecular Cell, Volume 43, Issue 5, 2 September 2011, Pages 751-763, Xiaolei Su, Weihong Qiu, Mohan L. Gupta Jr., José B. Pereira-Leal, Samara L. Reck-Peterson, David Pellman |
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| Referred to by: |
Mechanisms Underlying the Dual-Mode Regulation of Microtubule Dynamics by Kip3/Kinesin-8 Molecular Cell, Volume 43, Issue 5, 2 September 2011, Pages 751-763, Xiaolei Su, Weihong Qiu, Mohan L. Gupta Jr., José B. Pereira-Leal, Samara L. Reck-Peterson, David Pellman |
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Metaphase chromosome positioning depends on Kif18A, a kinesin-8 that accumulates at and suppresses the dynamics of K-MT plus ends. By engineering Kif18A mutants that suppress MT dynamics but fail to concentrate at K-MT plus ends, we identify a mechanism that allows Kif18A to accumulate at K-MT plus ends to a level required to suppress chromosome movements. Enrichment of Kif18A at K-MT plus ends depends on its C-terminal tail domain, while the ability of Kif18A to suppress MT growth is conferred by the N-terminal motor domain. The Kif18A tail contains a second MT-binding domain that diffuses along the MT lattice, suggesting that it tethers the motor to the MT track. Consistently, the tail enhances Kif18A processivity and is crucial for it to accumulate at K-MT plus ends. The heightened processivity of Kif18A, conferred by its tail domain, thus promotes concentration of Kif18A at K-MT plus ends, where it suppresses their dynamics to control chromosome movements.
Using single transcription factors to reprogram cells could produce important insights into the epigenetic mechanisms that direct normal differentiation, or counter inappropriate plasticity, or even provide new ways of manipulating normal ontogeny in vitro to control lineage diversification and differentiation. We enforced Pdx1 expression from the Neurogenin-3-expressing endocrine commitment point onward and found during the embryonic period a minor increased β-cell allocation with accompanying reduced α-cell numbers. More surprisingly, almost all remaining Pdx1-containing glucagon/Arx-producing cells underwent a fairly rapid conversion at postnatal stages, through glucagon–insulin double positivity, to a state indistinguishable from normal β cells, resulting in complete α-cell absence. This α-to-β conversion was not caused by activating Pdx1 in the later glucagon-expressing state. Our findings reveal that Pdx1 can work single-handedly as a potent context-dependent autonomous reprogramming agent, and suggest a postnatal differentiation evaluation stage involved in normal endocrine maturation.
A major hurdle for cell replacement-based diabetes therapy is the difficulty of supplying vast numbers of functioning insulin-producing β cells. One method could be through the reprogramming of alternative cell types. While this process might be easier with closely lineage-related cells, even substantially different cells may be susceptible (e.g., Zhou et al. 2008).
Recent studies reveal significant plasticity between pancreatic α and β cells under certain induced conditions, implying a potential route to β cells through α cells. In a near-total β-cell destruction and regeneration model in adult mice, a proportion of new β cells were produced from α cells via a bihormonal glucagon+insulin+ (Gcg+Ins+) transitional state (Thorel et al. 2010). The interconversion presumably occurs in response to a combination of the physiological need to replenish β cells and regeneration-induced stress, raising questions as to the local or systemic signals triggered by such lesions. Direct superimposition of a pro-β-lineage condition was reported when Pax4 expression was forced in pancreatic or endocrine progenitors or in embryonic α cells to redirect endocrine differentiation or coax pre-existing α cells into β cells. The converted cells seemed similar to normal β cells and temporarily improved glycemia under induced diabetes, although the effect was superseded by uncontrolled α-cell neogenesis and fatality caused by extreme hyperglycemia (Collombat et al. 2009). These studies on the ability of a single lineage-allocating transcription factor to sustain complete cell fate conversion suggest that similar analyses for other transcription factors could be insightful. Determining which factors induce specific types of lineage reprogramming, as well as the repertoire of cellular competence states amenable to fate switching, could lead to pharmacological intervention to activate such factors in vivo, or to improved differentiation of embryonic stem cells to β cells.
Clues to the fate-instructing capacity of Pdx1 as a β-cell selector are inferred from its enriched expression in embryonic and mature β cells. Ectopic Pdx1 alone can induce incomplete reprogramming of liver or pancreatic acinar cells (e.g., Ferber et al. 2000; Heller et al. 2001). A synergistic effect between Pdx1, Neurog3, and MafA was observed when acinar cells were converted into β-like cells (Zhou et al. 2008), which inefficiently ameliorated hyperglycemia caused by loss of endogenous β cells, perhaps because the reprogrammed cells did not assemble into islet-like clusters. Rather than triggering a redirection into endocrine cells, forced Pdx1 expression in Ptf1a-expressing cells caused late stage acinar-to-ductal hyperplasia (Miyatsuka et al. 2006). While these studies suggest that Pdx1 alone is contextually sufficient to induce partial trans-differentiation or trans-determination, little is known about how different competence states affect the response to this single factor.
Here, we report on the previously unknown sufficiency for Pdx1 as a potent regulator of endocrine lineage allocation and maintenance of the mature state. With Pdx1 expression enforced from the Neurog3+ endocrine progenitor state onward, two periods of dominant lineage redirection occurred: (1) during early organogenesis, a minor reproducible reduction in cells directed to the α fate, and (2) a surprising peri/postnatal redirection of Pdx1-expressing α cells, with rapid reprogramming into Ins+ cells that are indistinguishable from normal β cells. The delayed conversion occurred despite α cells having expressed exogenous Pdx1 from their endocrine commitment point onward, suggesting the possibility of a cryptic chromatin-priming effect. In contrast, exogenous Pdx1 in Gcg+ embryonic or adult α cells suppressed Gcg expression but did not induce α/β fate switching. Our findings reveal differential α-to-β plasticity between endocrine progenitors and hormone-secreting cells in response to Pdx1. We speculate on the epigenetic ramifications of these differential lineage-switching findings.
Neural crest (NC) progenitors generate a wide array of cell types, yet molecules controlling NC multipotency and self-renewal and factors mediating cell-intrinsic distinctions between multipotent versus fate-restricted progenitors are poorly understood. Our earlier work demonstrated that Foxd3 is required for maintenance of NC progenitors in the embryo. Here, we show that Foxd3 mediates a fate restriction choice for multipotent NC progenitors with loss of Foxd3 biasing NC toward a mesenchymal fate. Neural derivatives of NC were lost in Foxd3 mutant mouse embryos, whereas abnormally fated NC-derived vascular smooth muscle cells were ectopically located in the aorta. Cranial NC defects were associated with precocious differentiation towards osteoblast and chondrocyte cell fates, and individual mutant NC from different anteroposterior regions underwent fate changes, losing neural and increasing myofibroblast potential. Our results demonstrate that neural potential can be separated from NC multipotency by the action of a single gene, and establish novel parallels between NC and other progenitor populations that depend on this functionally conserved stem cell protein to regulate self-renewal and multipotency.
EMBO J. 2011 Jan 19;30(2):341-54. Epub 2010 Dec 3.
Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, USA.
Proper cell division requires strict coordination between mitotic exit and cytokinesis. In the event of a mitotic error, cytokinesis must be inhibited to ensure equal partitioning of genetic material. In the fission yeast, Schizosaccharomyces pombe, the checkpoint protein and E3 ubiquitin ligase, Dma1, delays cytokinesis by inhibiting the septation initiation network (SIN) when chromosomes are not attached to the mitotic spindle. To elucidate the mechanism by which Dma1 inhibits the SIN, we screened all SIN components as potential Dma1 substrates and found that the SIN scaffold protein, Sid4, is ubiquitinated in vivo in a Dma1-dependent manner. To investigate the role of Sid4 ubiquitination in checkpoint function, a ubiquitination deficient sid4 allele was generated and our data indicate that Sid4 ubiquitination by Dma1 is required to prevent cytokinesis during a mitotic checkpoint arrest. Furthermore, Sid4 ubiquitination delays recruitment of the Polo-like kinase and SIN activator, Plo1, to spindle pole bodies (SPBs), while at the same time prolonging residence of the SIN inhibitor, Byr4, providing a mechanistic link between Dma1 activity and cytokinesis inhibition.
2/10/2011 - Vivien Casagrande, Ph.D., professor of Cell & Developmental Biology at Vanderbilt University, has been named a fellow of the American Association of Anatomists.
Vivien Casagrande, Ph.D.
The honor recognizes “excellence in science and in … overall contributions to the anatomical sciences.”
Casagrande, who also is a professor of Psychology and of Ophthalmology & Visual Sciences, is one of 11 fellows named by the association this year, and the first fellow from Vanderbilt University.
The 2011 fellows will be recognized during the association's annual awards banquet April 12 in Washington, D.C.
“Nobel laureate Francis Crick stressed the critical importance of neuroanatomical study to understanding how the brain works,” Casagrande said.
“I am truly honored to receive this award from the American Association of Anatomists, the most prestigious international society devoted to the study of anatomy.
“This society was the first scientific association to which I was nominated and became a member,” she said. “At the time I was thrilled to be accepted as a member and now I’m humbled to be included among its fellows.”
Casagrande has been a member of the Vanderbilt faculty since 1975, and is a Vanderbilt Kennedy Center investigator.
Her laboratory studies how visual information is processed by the brain, specifically within the visual cortex. She has mapped visual brain circuitry in a variety of primate species, and her studies have revealed clues to the evolution of the visual system.
The American Association of Anatomists previously honored Casagrande in 1981 with the Charles Judson Herrick Award for “meritorious contributions to comparative neurology.”
In 2006, she was elected as a fellow of the American Association for the Advancement of Science.
Received 30 June 2010;
Abstract
Interactions between cells from the ectoderm and mesoderm influence development of the endodermally-derived pancreas. While much is known about how mesoderm regulates pancreatic development, relatively little is understood about how and when the ectodermally-derived neural crest regulates pancreatic development and specifically, beta cell maturation. A previous study demonstrated that signals from the neural crest regulate beta cell proliferation and ultimately, beta cell mass. Here, we expand on that work to describe timing of neural crest arrival at the developing pancreatic bud and extend our knowledge of the non-cell autonomous role for neural crest derivatives in the process of beta cell maturation. We demonstrated that murine neural crest entered the pancreatic mesenchyme between the 26 and 27 somite stages (approximately 10.0 dpc) and became intermingled with pancreatic progenitors as the epithelium branched into the surrounding mesenchyme. Using a neural crest-specific deletion of the Forkhead transcription factor Foxd3, we ablated neural crest cells that migrate to the pancreatic primordium. Consistent with previous data, in the absence of Foxd3, and therefore the absence of neural crest cells, proliferation of insulin-expressing cells and insulin-positive area are increased. Analysis of endocrine cell gene expression in the absence of neural crest demonstrated that, although the number of insulin-expressing cells was increased, beta cell maturation was significantly impaired. Decreased MafA and Pdx1 expression illustrated the defect in beta cell maturation; we discovered that without neural crest, there was a reduction in the percentage of insulin-positive cells that co-expressed Glut2 and Pdx1 compared to controls. In addition, transmission electron microscopy analyses revealed decreased numbers of characteristic insulin granules and the presence of abnormal granules in insulin-expressing cells from mutant embryos. Together, these data demonstrate that the neural crest is a critical regulator of beta cell development on two levels: by negatively regulating beta cell proliferation and by promoting beta cell maturation.
► Neural crest cells first enter the pancreatic primordium at the 27 somite stage. ► Neural crest reaches the dorsal pancreas prior to the ventral pancreas.
► In the absence of neural crest, insulin-expressing area is increased.
► Neural crest is required for beta cell maturation.
► Neural crest derivatives directly contact beta and alpha cells by 15.5 dpc.