The egg-to-embryo transition entails transforming a highly differentiated oocyte into totipotent blastomeres, and represents one of the earliest obstacles that must be successfully hurdled for continued development. Degradation of maternal mRNAs (which initiates during oocyte maturation) and reprogramming gene expression (which is clearly evident in 2-cell embryos) lie at the heart of this transition. The overarching objective of the proposed studies is to use mouse as a model system to gain deeper insights into the molecular basis for each of these underlying events, i.e., degradation of maternal mRNA and reprogramming gene expression. An apparently universal feature of the egg-to-embryo transition is degradation of maternal mRNAs either during maturation or shortly after fertilization/genome activation. How mRNAs are degraded is gaining increased attention because mRNA degradation is highly regulated. Moreover, there is growing consensus that degradation of maternal mRNA is essential for the egg-to-embryo transition.
Specific Aim 1 will test the hypothesis that recruitment of maternal mRNAs encoding DCP1A &2 results in the 5'mRNA degradation pathway as the dominant pathway. The proposed studies will also define the role of the maturation-associated phosphorylation of DCP2 in mRNA degradation. Results of these studies will provide a detailed understanding of degradation of maternal mRNAs during the course of oocyte maturation. How reprogramming of gene expression occurs and uses a maternally inherited transcription apparatus remains enigmatic.
Specific Aim 2 will test the hypothesis that recruitment during oocyte maturation of mRNAs encoding chromatin remodelers and transcription factors is essential for reprogramming gene expression. Results of these studies will likely provide a simple and elegant solution to this problem. Post-transcriptional mechanisms are rapidly gaining attention as a major locus of regulation of gene expression, and in particular, the role of microRNAs (miRNA) in mRNA degradation. Although oocytes express a plethora of miRNAs, as well as mediators of their function, miRNA activity that leads to mRNA degradation functions poorly in oocytes and inhibiting miRNA biogenesis has no marked effect on oocyte and preimplantation development.
Specific Aim 3 will identify the molecular basis for failure of miRNAs to promote degradation of their target mRNAs in oocytes. Understanding the basis for this failure will shed further light on the role of small RNAs in oocyte development. Taken together, results of the proposed studies will generate a detailed understanding of two critical processes that underly the egg-to- embryo transition, i.e., maternal mRNA degradation and reprogramming gene expression.

Public Health Relevance

The proposed studies will provide new information regarding molecular mechanisms underlying the egg-to- embryo transition. The results of these studies will provide further insights into how eggs develop into early embryos, and thereby impact the treatment of human infertility and assisted reproduction technologies.

National Institute of Health (NIH)
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Research Project (R01)
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Cellular, Molecular and Integrative Reproduction Study Section (CMIR)
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Ravindranath, Neelakanta
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University of Pennsylvania
Schools of Arts and Sciences
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Balboula, Ahmed Z; Stein, Paula; Schultz, Richard M et al. (2014) Knockdown of RBBP7 unveils a requirement of histone deacetylation for CPC function in mouse oocytes. Cell Cycle 13:600-11
Liu, W; Stein, P; Cheng, X et al. (2014) BRD4 regulates Nanog expression in mouse embryonic stem cells and preimplantation embryos. Cell Death Differ 21:1950-60
Ihara, Motomasa; Meyer-Ficca, Mirella L; Leu, N Adrian et al. (2014) Paternal poly (ADP-ribose) metabolism modulates retention of inheritable sperm histones and early embryonic gene expression. PLoS Genet 10:e1004317
Ma, Jun; Flemr, Matyas; Strnad, Hynek et al. (2013) Maternally recruited DCP1A and DCP2 contribute to messenger RNA degradation during oocyte maturation and genome activation in mouse. Biol Reprod 88:11
Ma, Pengpeng; Schultz, Richard M (2013) Histone deacetylase 2 (HDAC2) regulates chromosome segregation and kinetochore function via H4K16 deacetylation during oocyte maturation in mouse. PLoS Genet 9:e1003377
Stein, Paula; Svoboda, Petr; Schultz, Richard M (2013) RNAi-based methods for gene silencing in mouse oocytes. Methods Mol Biol 957:135-51
Lin, Shu; Ferguson-Smith, Anne C; Schultz, Richard M et al. (2011) Nonallelic transcriptional roles of CTCF and cohesins at imprinted loci. Mol Cell Biol 31:3094-104
Stein, Paula; Schindler, Karen (2011) Mouse oocyte microinjection, maturation and ploidy assessment. J Vis Exp :
Medvedev, Sergey; Pan, Hua; Schultz, Richard M (2011) Absence of MSY2 in mouse oocytes perturbs oocyte growth and maturation, RNA stability, and the transcriptome. Biol Reprod 85:575-83
Pan, Hua; Schultz, Richard M (2011) Sox2 modulates reprogramming of gene expression in two-cell mouse embryos. Biol Reprod 85:409-16

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