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Richard
M. Schultz
Patricia Williams
Professor of Biology
Developmental
Biology Program
Address
204B Carolyln Lynch Labs
433 S. University Ave.
Philadelphia
. PA . 19104
Office tel.: 215 898-7869
Lab tel.: 215 898-7806
Fax: 215 898-7806
E-mail: rschultz@sas.upenn.edu
Link(s)
Richard Schultz at the Dept
of Biology
Education
Brandeis University, B.S. (Biology), 1971
Harvard University, Ph.D. (Biochemistry), 1975
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Research
Interests
- Egg activation and gene expression in mouse
embryos.
Key words: oocyte, egg activation,
preimplantation embryo, gene expression, RNAi.
Search PubMed for articles
Description
of Research
The role of calcium oscillations during
egg activation
It is well documented that changes in egg calcium homeostasis
following sperm-egg fusion initiate events that constitute
egg activation, e.g., cortical granule (CG) exocytosis, cell
cycle resumption. In mammals, the release of intracellular
calcium (Ca2+i) following fertilization is mediated by inositol-1,4,5-trisphosphate
(IP3) through the IP3receptor . Fertilization-induced changes
in Ca2+i are characterized by an initial rise that lasts for
several minutes, followed by a series of Ca2+i oscillations
of shorter duration. The initial Ca2+i rise, as well as the
subsequent oscillations, is due to the release of Ca2+i from
an IP3-sensitive pool followed by Ca2+ sequestration. The
ability of eggs to display this Ca2+oscillatory behavior is
acquired following oocyte maturation, and occurs only in the
1-cell embryo where it ceases following pronucleus formation.
While evidence suggests that these Ca2+ oscillations are critical
for successful development, little is known about the underlying
molecular mechanisms that link these oscillations to successful
development. We are pursuing
- the molecular mechanisms underlying the acquisition
during oocyte maturation of the Ca>2+ oscillatory behavior
observed following fertilization,
- the linkage between these Ca2+ oscillations
in the 1-cell embryo and changes in gene expression that
occur during preimplantation development, and
- the linkage between these changes in gene
expression and post-implantation development.
This work is done in collaboration with Carmen
Williams.
RNAi in mouse oocytes and preimplantation
embryos
Double-strand RNA (dsRNA) mediated post-transcriptional gene
silencing, also known as RNA interference (RNAi), is a powerful
tool to inhibit gene expression in several experimental model
systems including Arabidopsis, Caenorhabditis elegans, and
Drosophila, and we have shown that RNAi operates in mouse
oocytes and preimplantation embryos. We have developed a transgenic
RNAi approach that is suitable to study the function of any
gene during mouse oocyte development and early embryogenesis,
and are using this method to study the function several genes
that regulate chromatin structure in oocyte development.
In the initial step of RNAi, Dicer, a ribonuclease
first identified in Drosophila, processes dsRNA into 21-23
nucleotide dsRNA fragments called short interfering RNA (siRNA).
mDicer activity increases ~100-fold between the oocyte and
blastocyst stages. Both MuERV-L and IAP, two autonomous long
terminal repeat (LTR) retrotransposons, are activated during
genome activation, and both sense and antisense transcripts
are detected at the 2-cell stage. We noted that by reducing
the increase in dicer activity that there was a selective
increase in the expression of repetitive elements. These results
suggest that RNAi represses expression of repetitive parasitic
sequences in preimplantation embryos, thus providing a protective
mechanism to minimize retrotransposition, and thereby preserving
genomic integrity at stage of development when the organism
consists of only a few cells. We are pursuing these finding
by examining the role of RNAi in retrotransposition in the
preimplantation embryo.
Gene expression during oogenesis and
preimplantation development
The paucity of biological material has inhibited identifying
genes that are differentially expressed during mammalian oogenesis
and preimplantation development. We have developed a method
to amplify linearly mRNA from small numbers of mouse oocytes
and preimplantation embryos to generate amounts of sense RNA
that are sufficient for hybridizing to Affymetrix microarrays.
We have analyzed gene expression in oocytes derived from primordial
follicles to the blastocyst stage.
Results of these studies have yielded several
candidate genes involved in oogenesis and preimplantation
development. The function of genes involved in oocyte development
will be studied with our transgenic RNAi approach and in preimplantation
development by a convention RNAi approach.
Effect of culture on gene expression
and behavior
The use of assisted reproductive technologies (ART) to treat
human infertility is gaining widespread use, and it is estimated
that in the US that 1 out of 80 children born in 2002 will
have been conceived by ART. Disconcerting to many researchers
is that the clinical procedures used in ART are rapidly outpacing
the underlying science, an example of ART before science.
We have noted that culture conditions can perturb global patterns
of gene expression in preimplantation mouse embryos. In particular,
certain culture conditions result in biallelic expression
of the imprinted H19 gene in the blastocyst, and this biallelic
expression persists in extra-embryonic tissue following implantation.
Recent retrospective studies have unmasked an increased incidence
of certain syndromes that are the result of loss-of-imprinting,
highlighting the concern about the aggressive practice of
ART. The long-term developmental and behavioral consequences
of ART are unknown. To address this, we have developed a mouse
model to study the effects of embryo culture, which is an
integral part of every ART-conceived child, on behavior in
the offspring. We find that mice derived from cultured embryos
exhibit specific behavioral alterations in anxiety and spatial
memory, e.g., mice derived from cultured embryos display deficiencies
in spatial memory. We are pursuing these studies by
- examining the effect of different culture
conditions on the expression of a battery of imprinted genes,
as well as on global patterns of gene expression as determined
by microarray analysis,
- altering the culture conditions to minimize
or eliminate the behavioral consequences of culture, and
- mimicking clinical procedures known to produce
“low quality eggs” used in ART affect gene expression
in the embryos and behavior in the offspring in our mouse
model system.
Recent
Publications
Svoboda, P., Stein, S., Anger, M., Bernstein,
E., Hannon, G.J., and Schultz, R.M. (2004). RNAi and expression
of retrotransposons MuERV-L and IAP in preimplantation mouse
embryos. Dev. Biol. 269, 276-285.
Zeng, F., Baldwin, D.A., and Schultz, R.M. (2004). Transcript
profiling during preimplantation mouse development. Dev.
Biol. 272, 483-496.
Ecker, D.J., Stein, P., Xu, Z., Williams, C.J.,
Kopf, G.S., Bilker, W.B., Abel, T., and Schultz, R.M. (2004).
Long-term effects of culture of preimplantation mouse embryos
on behavior. Proc. Natl. Acad. Sci. USA. 101, 1595-1600.
Yu, J., Deng, M., Medvedev, S., Yang, J., Hecht, N.B., and
Schultz, R.M. (2004). Transgenic RNAi-mediated reduction of
MSY2 in mouse oocytes results in reduced fertility. Dev.
Biol. 268, 195-206.
Fedoriw, A.M., Stein, P., Svoboda, P.,Schultz,
R.M., and Bartolomei, M.S. (2004). Maternal CTCF requirement
for appropriate DNA methylation of the imprinted H19 gene.
Science 303, 238-240.
Lab
Rotation
Projects
Role of PAR3 and phospho-MARCKS in development
of egg polarity; role of calcium oscillations in regulating
gene expression in preimplantation embryo; analysis of gene
function during oocyte and preimplantation embryo development
by transgenic RNAi; role of RNAi in retrotransposition in
preimplantation embryo; effect of embyo culture on expression
of imprinted genes and global patterns of gene expression.
- Lab
personnel:
- Adam Doherty, Research Assistant
Jason Knott, post-doc
Jun Ma, post-doc
Pengpeng Ma, post-doc
Sergey Medvedev, post-doc
Hua Pan, research associate
Rocio Rivera, post-doc
Karen Schindler, post-doc
Josh Sommovilla, Research Assistant
Paula Stein, research associate
last updated 6/2005
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