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Newsletter excerpt: Ninety-four incoming IGP, CPB and IMSD students joined Cell and Developmental Biology faculty and students on Thursday, August 27, 2009 for our annual departmental IGP Orientation.
The event kicked off with an introduction by Kathy Gould, the Director of CDB Graduate Studies. The CDB mission statement, the composition of the primary and secondary faculty, the diversity within department and how faculty research is integrated, were all presented. CDB classes and seminars that make our curriculum special and offer graduate students additional opportunities to interact with Vanderbilt faculty and invited speakers were emphasized. Importantly, many of the best the graduate student and postdoctoral achievements of the past year were announced, and illustrating the national and international meetings attended and publication successes.
This year we added three short presentations from CDB faculty, highlighting their lab’s research and use of different model organisms to investigate specific biological questions. The presentations featured Puck Ohi, Trish Labosky and David Miller..............

By Elaine Oakley Caine

Golgi-derived CLASP-dependent microtubules control Golgi organization and polarized trafficking in motile cells

 

Nature Cell Biology 11, 1069 - 1080 (2009)
Published online: 23 August 2009 | doi:10.1038/ncb1920

Paul M. Miller¹, Andrew W. Folkmann¹, Ana R. R. Maia^1,2, Nadia Efimova¹, Andrey Efimov^1,3 & Irina Kaverina¹

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Irina Kaverina and others, recognized with Chancellor’s Awards for Research, which recognizes excellence in research, scholarship or creative expression.

Chancellor's Awards Page

 

VUcast faculty assembly

Identifying a borealin component of the
yeast chromosome passenger complex..

 

MBC Online

 

Originally published as MBC in Press, 10.1091/mbc.E09-04-0289 on July 1, 2009

Vol. 20, Issue 16, 3646-3659, August 15, 2009

 

A Link between Aurora Kinase and Clp1/Cdc14 Regulation Uncovered by the Identification of a Fission Yeast Borealin-Like Protein

K. Adam Bohnert^*,, Jun-Song Chen^*,, Dawn M. Clifford^*,, Craig W. Vander Kooi, and Kathleen L. Gould^*

*Howard Hughes Medical Institute and Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232; and Department of Molecular and Cellular Biochemistry and Center for Structural Biology, University of Kentucky, Lexington, KY 40536

Submitted April 9, 2009; Revised June 18, 2009; Accepted June 19, 2009
Monitoring Editor: Daniel J. Lew

 

 

 

ABSTRACT

 
The chromosomal passenger complex (CPC) regulates various events in cell division. This complex is composed of a catalytic subunit, Aurora B kinase, and three nonenzymatic subunits, INCENP, Survivin, and Borealin. Together, these four subunits interdependently regulate CPC function, and they are highly conserved among eukaryotes. However, a Borealin homologue has never been characterized in the fission yeast, Schizosaccharomyces pombe. Here, we isolate a previously uncharacterized S. pombe protein through association with the Cdc14 phosphatase homologue, Clp1/Flp1, and identify it as a Borealin-like member of the CPC. Nbl1 (novel Borealin-like 1) physically associates with known CPC components, affects the kinase activity and stability of the S. pombe Aurora B homologue, Ark1, colocalizes with known CPC subunits during mitosis, and shows sequence similarity to human Borealin. Further analysis of the Clp1–Nbl1 interaction indicates that Clp1 requires CPC activity for proper accumulation at the contractile ring (CR). Consistent with this, we describe negative genetic interactions between mutant alleles of CPC and CR components. Thus, this study characterizes a fission yeast Borealin homologue and reveals a previously unrecognized connection between the CPC and the process of cytokinesis in S. pombe.

 

 

Sonic hedgehog signaling regulates a novel epithelial
progenitor domain of the hindbrain choroid plexus.

Huang X, Ketova T, Fleming JT, Wang H, Dey SK, Litingtung Y, Chiang C.

Development. 2009 Aug;136(15):2535-43. Epub 2009 Jul 1.

Note that VUMC reporter will do an aliquot report on this paper on August 14

2. Shh and Gli3 activities are required for timely generation of motor neuron progenitors.

 

Oh S, Huang X, Liu J, Litingtung Y, Chiang C.

Dev Biol. 2009 Jul 15;331(2):261-9. Epub 2009 May 9.

 

Microvilli give gut vesicles the brush-off

A surprising new function for intestinal cells in shaping their local environment. Every cell lining the small intestine bristles with thousands of tightly packed microvilli that project into the gut lumen, forming a brush border that absorbs nutrients and protects the body from intestinal bacteria. McConnell et al. now find that microvilli extend their functional reach even further using a molecular motor to send vesicles packed with gut enzymes out into the lumen to get a head start on breaking down their substrates

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Published online June 29, 2009
doi:10.1083/jcb.1857if
The Journal of Cell Biology, Vol. 185, No. 7, 1131-
The Rockefeller University Press, 0021-9525 $30.00
© 2009 Short

Microvilli give gut vesicles the brush-off

A surprising new function for intestinal cells in shaping their local environment.

Every cell lining the small intestine bristles with thousands of tightly packed microvilli that project into the gut lumen, forming a brush border that absorbs nutrients and protects the body from intestinal bacteria. McConnell et al. now find that microvilli extend their functional reach even further using a molecular motor to send vesicles packed with gut enzymes out into the lumen to get a head start on breaking down their substrates (1).

FOCAL POINT Intestinal cells release enzyme-laden vesicles into the gut lumen from the tips of their microvilli (red circles) through the action of the motor protein myosin-1a. Russell McConnell (left), Matthew Tyska (right) and colleagues think these lumenal vesicles function to process nutrients and protect against bacterial infection.

Microvilli have traditionally been viewed as passive scaffolds that increase the surface area of the gut wall. The apical plasma membrane tightly wraps around each protrusive bundle of actin, providing more space for nutrient processing and absorption. The motor protein myosin-1a (myo1a) maintains this structure by connecting the plasma membrane to the actin filaments. In myo1a's absence, the membrane detaches and blebs outwards (2).

In 2007, Matthew Tyska and colleagues found that myo1a functions in isolated brush borders to actively move membrane along the length of the microvilli, like a "membrane escalator" (3). To their surprise, at the top of these escalators—the tips of the microvilli—the membrane pinched off to form small vesicles that were released into the surrounding medium. According to Tyska, when they showed their data to gastroenterologists, they immediately asked "Why would brush borders do that? They're wasting perfectly good apical membrane!" Tyska therefore wanted to see if vesicle shedding was a bona fide physiological function for microvilli.

Sure enough, scanning electron micrographs of rat intestines showed protrusions at the tips of microvilli that looked similar to budding vesicles. And a look at the gut's contents revealed vesicles enriched in the brush border enzyme intestinal alkaline phosphatase (IAP). The researchers used this as a marker to purify the vesicles using a technique called fluorescence-activated vesicle sorting. "The starting material was a raw gut lumen wash. It's the dirtiest, most disgusting stuff you can find in biology!" says Tyska. "You have a lot of purifying to do."

Nevertheless, McConnell et al. used vesicle sorting to purify the lumenal vesicles enough to analyze their contents by mass spectrometry. The vesicles were packed with classical brush border membrane proteins such as aminopeptidases and sugar-processing enzymes, suggesting that the vesicles were derived from microvilli. The vesicles also contained several proteins such as annexin A13 that bend cell membranes and could form part of the vesicle budding machinery.

One protein definitely involved in vesicle formation is myo1a. Myo1a knockout mice still produce lumenal vesicles but they are irregularly sized and no longer enriched in specific proteins like IAP. Tyska thinks that these knockout vesicles are actually chunks of microvillar membrane that are nonspecifically shed when myo1a isn't present to keep them attached to the actin core. In wild-type brush borders, the membrane stays tightly curved around the actin bundles, which probably helps specific proteins and lipids sort to microvillar tips where they bud into vesicles.

Returning to the gastroenterologists' question: Why would brush borders do that? McConnell et al. showed that the packaged enzymes were exposed on the vesicles' outer surface and were catalytically active. Releasing the enzymes in vesicles might increase their mixing with substrates in the gut's contents. Tyska is particularly interested in IAP, which has recently been shown to detoxify the bacterial outer-membrane component lipopolysaccharide (4, 5). Releasing IAP in lumenal vesicles could be an important defense mechanism against intestinal pathogens.

Tyska admits that when he initially characterized the myo1a knockout mouse as a postdoc in Mark Mooseker's laboratory, he was disappointed that the entire actin-based structure of the brush border didn't collapse. "We could have given up," he says. "But the closer we get to the real physiological function, the more interesting it becomes."

References

1. McConnell, R.E., et al. 2009. J. Cell Biol. doi:10.1083/jcb.200902147.[Abstract/Free Full Text]
2. Tyska, M.J., et al. 2005. Mol. Biol. Cell. 16:2443–2457.[Abstract/Free Full Text]
3. McConnell, R.E., and M.J. Tyska. 2007. J. Cell Biol. 177:671–681.[Abstract/Free Full Text]
4. Bates, J.M., et al. 2007. Cell Host Microbe. 2:371–382.[Medline]
5. Beumer, C., et al. 2003. J. Pharmacol. Exp. Ther. 307:737–744.[Abstract/Free Full Text]

Ben Short

bshort@rockefeller.edu

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The enterocyte microvillus is a vesicle-generating organelle

Russell E. McConnell, James N. Higginbotham, David A. Shifrin, Jr., David L. Tabb, Robert J. Coffey, and Matthew J. Tyska
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"VCDB June 2009 Binary" Newsletter

Chemicals turn human embryonic stem cells towards beta cells

 

nature chemical biology 5, 195 - 196 (2009) doi:10.1038/nchembio0409-195

Yu-Ping Yang¹ & Chris Wright¹

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Defining elements in contractile ring assembly

 

 

Vanderbilt Reporter, Lords of the contractile ring

 

Cell division requires the formation of a contractile ring. While many protein components of this ring are known, how they interact with each other and with the plasma membrane remains unclear.

Rachel Roberts-Galbraith, Kathy Gould, Ph.D., and colleagues are studying these ring proteins in yeast. One such protein, Cdc15, has two “domains” that carry out different functions – the F-BAR domain, which binds and curves the plasma membrane, and the SH3 domain, which had not been characterized.

In the January Journal of Cell Biology, the researchers show that the SH3 domains of Cdc15 and of another member of the same protein family (Imp2) recruit other proteins (including a paxillin-like protein Pxl1 and a highly conserved C2-domain protein Fic1) to the contractile ring. Together, Pxl1 and Fic1 add structural integrity to the contractile ring and prevent it from fragmenting during cell division. The SH3 domains of Cdc15 and Imp2 overlap in function, and the authors suggest that this redundancy is essential for division of the cellular contents.

 

 

— Melissa Marino, Vanderbilt Reporter

 

 

 

See Also PubMed Article

 

Roberts-Galbraith, R.H., Chen, J.-S., Wang, J. and Gould, K.L. (2009) The SH3 domains of two PCH family members cooperate in construction of the Schizosaccharomyces pombe contractile ring. J. Cell Biol. 184:113-127.

 

Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA.

Schizosaccharomyces pombe cdc15 homology (PCH) family members participate in many cellular processes by bridging the plasma membrane and cytoskeleton. Their F-BAR domains bind and curve membranes, whereas other domains, typically SH3 domains, are expected to provide cytoskeletal links. We tested this prevailing model of functional division in the founding member of the family, Cdc15, which is essential for cytokinesis in S. pombe, and in the related PCH protein, Imp2. We find that the distinct functions of Imp2 and Cdc15 are SH3 domain independent. However, the Cdc15 and Imp2 SH3 domains share an essential role in recruiting proteins to the contractile ring, including Pxl1 and Fic1. Together, Pxl1 and Fic1, a previously uncharacterized C2 domain protein, add structural integrity to the contractile ring and prevent it from fragmenting during division. Our data indicate that the F-BAR proteins Cdc15 and Imp2 contribute to a single biological process with both distinct and overlapping functions.

 

 ER membrane–bending proteins are necessary for de novo nuclear pore formation

T. Renee Dawson¹, Michelle D. Lazarus¹, Martin W. Hetzer², and Susan R. Wente¹

¹ Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232
² Molecular and Cell Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037

Correspondence to Susan R. Wente: susan.wente@vanderbilt.edu

Nucleocytoplasmic transport occurs exclusively through nuclear pore complexes (NPCs) embedded in pores formed by inner and outer nuclear membrane fusion. The mechanism for de novo pore and NPC biogenesis remains unclear. Reticulons (RTNs) and Yop1/DP1 are conserved membrane protein families required to form and maintain the tubular endoplasmic reticulum (ER) and the postmitotic nuclear envelope. In this study, we report that members of the RTN and Yop1/DP1 families are required for nuclear pore formation. Analysis of Saccharomyces cerevisiae prp20-G282S and nup133 NPC assembly mutants revealed perturbations in Rtn1–green fluorescent protein (GFP) and Yop1-GFP ER distribution and colocalization to NPC clusters. Combined deletion of RTN1 and YOP1 resulted in NPC clustering, nuclear import defects, and synthetic lethality with the additional absence of Pom34, Pom152, and Nup84 subcomplex members. We tested for a direct role in NPC biogenesis using Xenopus laevis in vitro assays and found that anti-Rtn4a antibodies specifically inhibited de novo nuclear pore formation. We hypothesize that these ER membrane–bending proteins mediate early NPC assembly steps.