Richard M Schultz

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Professor of Biology in Obstetrics and Gynecology
Department: Obstetrics and Gynecology

Contact information
223 Leidy Laboratory
3740 Hamilton Walk
Philadelphia, PA 19104
Office: 215-898-7869
Fax: 215 898-7806
B.S. (Biology)
Brandeis University, 1971.
Ph.D. (Biochemistry)
Harvard University, 1975.
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Description of Research Expertise

Research Interests
Egg activation and gene expression in mouse embryos.

Key words: oocyte, egg activation, preimplantation embryo, gene expression, RNAi.

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

1. the molecular mechanisms underlying the acquisition during oocyte maturation of the Ca>2+ oscillatory behavior observed following fertilization,
2. the linkage between these Ca2+ oscillations in the 1-cell embryo and changes in gene expression that occur during preimplantation development, and
3. 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
1. 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,
2. altering the culture conditions to minimize or eliminate the behavioral consequences of culture, and
3. 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.

Selected Publications

Svoboda, P., Stein, S., Anger, M., Bernstein, E., Hannon, G.J., and Schultz, R.M. : RNAi and expression of retrotransposons MuERV-L and IAP in preimplantation mouse embryos. Dev Biol 269: 276-85, 2004.

Mann, M.R.W., Lee, S.S., Doherty, A.S., Verona R.I., Nolen, L.D., Schultz, R.M. and Bartolomei, M.S. : Selective loss of imprinting in the lacenta following preimplantation development in culture. Development 131: 327-2735, 2004.

Zeng, F., Baldwin, D.A., and Schultz, R.M. : Transcript profiling during preimplantation mouse development. Dev Biol 2004 Notes: In Press.

Ecker, D.J., Stein, P., Xu, Z., Williams, C.J., Kopf, G.S., Bilker, W.B., Abel, T., and Schultz, R.M.: Long-term effects of culture of preimplantation mouse embryos on behavior. Proc. Natl. Acad. Sci. USA. 101: 1595-1600, 2004.

Yu, J., Deng, M., Medvedev, S., Yang, J., Hecht, N.B., and Schultz, R.M. : Transgenic RNAi-mediated reduction of MSY2 in mouse oocytes results in reduced fertility. Dev Biol 269: 195-206, 2004.

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Last updated: 08/25/2006
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