[Maize] UC Berkeley Postdoc position available

Lisa Harper via maize%40net.bio.net (by ligule from nature.berkeley.edu)
Mon Jun 18 18:01:20 EST 2007

Dear Colleagues: Please bring this postdoctoral opportunity to the 
attention of any graduate student you know who is searching for a 
position.  We are looking for one or two postdocs to work on the 
mechanism of  meiotic prophase and anther development in maize using 
molecular genetics, genomics and proteomics strategies as well 
advanced imaging techniques. The research is described in more detail 
	Regards Zac Cande

Postdoctoral positions are available to work on maize meiosis and 
commitment to meiosis during anther development. The candidate should 
have some experience working on the molecular biology or cell biology 
of plants.

Please send cv and references to: zcande from berkeley.edu

Zac Cande
341 LSA
Department of Molecular and Cell Biology
University of California
Berkeley, CA 94720-3200


Cande Lab Research Projects:
1. Meiosis and Anther development in maize

Meiosis cytogenetics: The superb cytology of the maize chromosome, 
its well developed genetic and genomic resources, the large meiotic 
mutant collection, and the ability to obtain large amounts of highly 
synchronized meiocytes make it an excellent organism for integrating 
cytological, molecular, genomics and proteomic approaches to answer 
key questions in meiosis. The ability to perform meiosis depends on a 
switch to the meiotic cell cycle, and the formation of unique 
leptotene chromosome architecture. We hypothesize that in maize this 
switch is mediated by the protein AMEIOTIC1 (AM1), and that the 
indicator of a successful switch is the formation of the leptotene 
chromosome. Secondly, changes in leptotene chromosome architecture 
regulate downstream meiotic processes. To test these hypotheses, we 
will elucidate the mechanism of AM1 function using an allelic series 
to define functional domains, proteomics to identify interacting 
proteins, and reverse genetics to resolve the functions of 
interacting proteins. To identify genes that are regulated by AM1, we 
will use microarrays   using meiotic RNA from wild type and am1 
mutants. To determine how leptotene chromosomes regulate downstream 
processes, we will analyze the architecture of the leptotene 
chromosome using ultra high resolution structured illumination (SI) 
light microscopy and relate structure to function. We will develop an 
integrated model of chromomere and axial element organization using 
SI and elucidate changes as chromosomes pair and synapse. We will use 
ChIP on tiling arrays to identify histone modifications and 
RAD21/REC8 binding  sites in a defined chromosome region. Mutants 
deficient in intragenic recombination or chromosome architecture will 
be used to determine how spatial constraints in chromomere 
architecture affect recombination. We will identify the defining 
features of the chromatin remodeling that occurs at the leptotene 
zygotene transition in wild type, and in am1-pra1 cells arrested at 
this stage, and determine whether small RNA metabolism is responsible 
for these changes.  Finally, we are  cloning and characterizing 
mutations in genes that have been identified in forward genetic 
screens as essential for pairing and synapsis. 

Cell Fate Acquisition in Pre-Meiotic Maize Anthers: this is a NSF 
Plant genomics collaborative proposal with Virginia Walbot,  Stanford 
-from the grant proposal:
	The regulation and required downstream functions resulting in 
cell fates in Angiosperms remain largely undefined.  In particular, 
the differentiation of meiotic cells is not well understood despite 
its central importance to plant breeding and reproduction.  To study 
how cells are fated to enter meiosis, the five cell types in anther 
locules will be analyzed.  The maize tassel is a very favorable organ 
for cell fate analysis, because sufficient carefully staged, 
synchronous anthers can be dissected and a collection of >350 
male-sterile mutants already exists.  Mutants will be classified 
cytologically and in a qRT-PCR survey using stage and cell-type 
markers.  Mutants defective in cell fate acquisition or maintenance 
will be subjected to transcriptome and proteomics profiling on 
anthers and dissected cell types.   Pilot RNA and protein profiling 
on staged msca1 (all anther cells switch fate), ms23 (no tapetum), 
and mac1 (excess meiotic cells) demonstrate the feasibility of the 
proposed approach.  Using reverse genetics, Mu knockout mutations in 
genes implicated as important in rice and Arabidopsis or from 
transcriptome or proteomics analysis in maize will be identified, and 
if male sterile, examined for cytological defects prior to meiosis to 
identify genes with non-redundant roles in pre-meiotic cell fate 
acquisition.  Discovery of a greatly enriched number of male sterile 
mutants among Mu-tagged, anther-expressed genes demonstrates the 
feasibility and potential power of this approach.  For important 
loci, directed Mu tagging will be conducted to clone and sequence key 
genes required in anther cell fate decisions.  Detailed genetic and 
molecular analysis will then help pinpoint the role of these key 
genes in setting cell fates prior to meiosis and for regulating the 
switch in the cell cycle from mitosis to meiosis.  Insights will be 
used to define the signals present late in anther development that 
specify cell fates.  Collectively these data will permit correlation 
of gene and protein expression with actual cellular processes such as 
entry into meiosis or acquisition of the tapetal cell fate, and will 
lead to testable hypotheses of meiotic cell fate acquisition.
Selected Publications:
Hamant, O., Golubovskaya, I., Meeley, R., Fiume, E., Timofejeva, L., 
Schleiffer, A., Nasmyth, K., and W. Z. Cande. 2005. A REC8 dependent 
plant Shugoshin is required for maintenance of centromeric cohesion 
during meiosis, and has no mitotic functions. Current Biology 
Chung-Ju R. W., Chen, ., C-C., Harper, L.,and W. Z.  Cande. 2006. 
Toward construction of an integrated cytogenetic map of maize 
chromosomes  by fluorescence in situ hybridization.  Plant Cell 
Hamant, O., Ma, H. and W. Z. Cande. 2006. Genetics of Meiotic 
Prophase I in Plants. Ann. Rev Plant Biology  57:267-302.
Golubovskaya, I. N., Hamant, O., Timofejeva, L., Wang, R.C. J. , 
Braun, D., Meeley, R., and Cande, W.Z. (2006) Alleles of AFD1 
uncouple axial element elongation and bouquet formation from RAD51 
distribution and homologous pairing. J. Cell Science, 119:3306-3315.
Li, J., Harper, L.C., Golubovskaya, I., C. Wang, R. Weber, D., 
Meeley, R.B., McElver, J., Bowen, B., Cande, W. Z. and P. S. 
Schnable. 2007.  Maize RAD51 is required for efficient chromosome 
pairing and proper chromosome segregation in meiosis and the repair 
of radiation-induced mitotic DSBs. Genetics in press

2. Other lab research projects:
Heterochromatin function in fission yeast: Fission yeast has only 
three chromosomes and their behavior during meiosis can be readily 
monitored using such tools as GFP-Swi6, a chromodomain protein that 
binds to telomeres and centromeres, and GFP-histone. We have 
developed a cytologically based screen to identify mutants defective 
in various aspects of meiosis including telomere clustering during 
meiotic prophase, and chromosome segregation during anaphase I and 
II. One mutant dot6/bqt2 is essential for telomere clustering during 
meiosis. Two mutants, dos1 and 2, are novel genes required for 
heterochromatin structure  and function and interact with the RNAi 
machinery. We have identified several proteins that interact with 
dos1 including a histone demethylase and a nuclear pore protein and 
we are studying their role in heterochromatin formation.

Evolution of the cytoskeleton, mitosis, meiosis in basal eukaryotes: 
To assess the molecular evolutionary conservation of spindle motors 
during eukaryotic evolution, we are studying mitosis in Giardia 
intestinalis, an intestinal parasite and diplomonad (with 
twonuclei/cell). Giardia is a member of the earliest diverging 
lineage of eukaryotes and thus provides a model to study the 
evolutionary history of cytoskeletal proteins and processes such as 
meiosis, mitosis, and cytokinesis. Giardia is easily grown in the 
laboratory, has a nearly sequenced genome; and is amenable to reverse 
genetic methodologies. It has a very complex microtubule 
cytoskeleton, with more more different classes of microtubule motors 
than plants, yeasts or metazoans, but its actin cytoskeleton is 
noncannonical (for example no myosins, arp2/3 etc). We have 
identified, cloned, and phylogenetically classified twenty-four 
kinesin like protein homologs (klps) from Giardia, roughly triple the 
number of klps as in yeasts. Many of these klps, although found in 
metazoans, are lacking in yeasts.  We are investigating their 
function in pathogenesis and mitosis. Novel kinesins may be prime 
targets for development of drugs for treating giardiasis. We have 
worked out a method of synchronizing cells and have described how 
mitosis works in cells that have two nuclei. We are studying 
microtubule, klp,  and chromosome behavior in living and fixed cells 
using state of the art light and electron microscopy and are studying 
phenotypes of dominant negative klp mutants strains. While 
investigating cytoskeletal behavior during encystment, we have shown 
that cyst nuclei undergo "automixis" (defined as the fusion of nuclei 
or cells derived from the same parent to yield homozygous offspring) 
and genes that have meiotic function are specifically expressed at 
this time.  In collaboration  with the Joint Genomics Institute we 
are sequencing Spironucleus,  another diplomonad, and Naegleria, a 
Valkhamphid that is the deepest amoebid cell that can be grown in 
culture. It can also form basal bodies and axonemes de novo and we 
developing this organism as an experimental system to study basal 
body formation.
Selected publications:
Jin Y., Mancuso J., Uzawa, S., Cromnebold, D. and W. Z. Cande. 2005. 
The fission yeast homolog of human transcription factor EAP30 blocks 
meiotic Spindle Pole Body amplification. Developmental Cell 9:63-73.
Li, F., Goto, D., Zaratiegui,  M., Tang, X., Martienssen, R., and W. 
Z. Cande. 2005. Two novel proteins, Dos1 and Dos2, interact with Rik1 
to regulate heterochromatic RNA interference and histone 
modification. Current Biology 15:1-10.
MacRae, I.J.,  Zhou, K., Li, F., Repic, A., Brooks, A.N., Cande, 
W.Z., Adams, P.  and J. Doudna. 2006.  Structural basis for 
double-stranded RNA processing by dicer. Science 311:195-198.
Tang X, Jin Y, Cande WZ. 2006.  Bqt2p is Essential for Initiating 
Telomere Clustering upon Pheromone Sensing in Fission Yeast. J. Cell 
Biol. 173:845-5.
Sagolla, M.S., Dawson, S.C., Mancuso, J.J. and W. Zacheus Cande. 
2006. Three dimensional analysis of mitosis and cytokinesis in the 
binucleate parasite Giardia intestinalis. J. Cell Sci. 119:4889-4900.


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