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
below.
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
http://mcb.berkeley.edu/labs/cande//
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
University
-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
15:948-954.
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
18:529-544.
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.
--
-Lisa
