B.A., Brandeis University, 1971
Ph.D., Harvard University, 1975
Post-doctoral Fellow, Harvard Medical School, 1975-1978
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, C. elegans, and Drosophila. We have shown that RNAi operates in mouse oocytes and preimplantation embryos and studies centered on the role of Dicer in oocyte development have revealed that oocytes deficient in Dicer do not undergo proper maturation and that degradation of many maternal mRNAs does not occur correctly. In contrast to somatic cells, endogenous miRNAs in fully-grown GV oocytes poorly repressed translation of mRNA reporters whereas their RNAi-like activity is much less affected. In addition, reporter mRNA carrying let-7-binding sites fails to localize to P-body-like structures in oocytes. These findings indicate that miRNA-mediated degradation of maternal mRNAs is not a robust pathway in oocytes and that the failure of Dicer-deficient oocytes to mature properly can be ascribed to failure to generate endo-siRNAs. Current studies are focused on deciphering the molecular mechanisms that why this pathway does not function robustly in oocytes and what pathways are involved in degradation of maternal mRNAs that initiates with the onset of oocyte maturation (see below).
Maternal age-associated increase in incidence of aneuploidy
A hallmark of animal development is an age-related decrease in fertility. In mammals, an increase in aneuploidy is the major underlying factor responsible for the increase in infertility with advancing age in human females. Aneuploidy is a leading cause of pregnancy loss, and when development goes to term, aneuploidy is an aggravating source of developmental disabilities and mental retardation, e.g., trisomy 21. The incidence of aneuploidy in eggs from women in their 20s’ is ~2%, but dramatically increases to 35% around 40 years-of-age. Spindle abnormalities and faulty chromosome congression on the metaphase plate are associated with advanced maternal age and likely contributes to the observed increased incidence of aneuploidy. Remarkably, little is known regarding the underlying molecular basis for the age-associated increase in aneuploidy.
Mice also exhibit an increase in the incidence of aneuploidy with increasing maternal age. Expression profiling global patterns of gene expression of oocytes obtained from young and old mice revealed mis-expression of many genes, including genes involved the Spindle Assembly Checkpoint (SAC), chromosome congression and attachment to kinetocore microtubules, and spindle assembly. In addition, the normal pattern of degradation of maternal mRNAs is not observed following maturation of old oocytes. We have found that old oocytes possess a highly functional SAC, i.e., a defective SAC is unlikely the primary cause of aneuploidy associated with maternal age. Rather, we find that ~90% of age-related aneuploidies are best explained by weakened centromere cohesion. Moreover, levels of the meiotic cohesin protein REC8 are severely reduced on chromosomes in oocytes from old mice. Together, these results demonstrate that the maternal age-associated increase in aneuploidy is primarily due to a failure to effectively replace cohesin proteins that are lost from chromosomes during aging. This work is done in collaboration with Michael Lampson.
Regulation of degradation of maternal mRNA
Degradation of maternal mRNA is thought to be essential to undergo the maternal-to-embryonic transition. Messenger RNA is extremely stable during oocyte growth in mouse and MSY2, an abundant germ cell-specific RNA-binding protein, likely serves as a mediator of global mRNA stability. Oocyte maturation, however, triggers an abrupt transition in which most mRNAs are degraded to different extents. We noted that CDK1-mediated phosphorylation of MSY2 triggers this transition. In addition, we have found that critical components of the RNA degradation machinery are maternal mRNAs that are recruited during oocyte maturation and are also critical for the transition from mRNA stability to instability. Current studies are focusing on dissecting out the contributions of the 5'-to-3' and 3'-to-5' degradation pathways and the effect of inhibiting degradation of maternal mRNAs on early development.
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 ~5 million children have been conceived using 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 , (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. The work on imprinted gene expression is done collaboration with Marisa Bartolomei and the work on behavior was done in collaboration with Ted Abel.
Medvedev, S., Stein, P., and Schultz, R.M. (2014). Specificity of calcium/ calmodulin-dependent protein kinases in mouse egg activation. Cell Cycle. 13, 1482-8.
Ihara, M., Meyer-Ficca, M.L., Leu, N.A., Rao, S., Li, F., Gregory, B.D., Zalenskaya, I.A., Schultz, R.M., and Meyer, R.G. (2014). Paternal poly(ADP-ribose) metabolism modulates retention of inheritable sperm histones and early embryonic gene expression. PLoS Genetics. 10(5):e1004317.
DeWaal, E., Mak, W., Calhoun, S., Stein, P. Ord, T., Krapp, C., Coutifaris, C., Schultz, R.M., and Bartolomei, M.S. (2013). In vitro culture increases the frequency of stochastic epigenetic errors at imprinted genes in placental tissues from mouse concepti produced through assisted reproductive technologies. Biol. Reprod. In Press.
Balboula, A.Z., Stein, P., Schultz, R.M., and Schindler, K. (2013). Knockdown of RBBP7 unveils a requirement for histone deacetylation for CPC function in mouse oocytes. Cell Cycle, 1, 600-11.
Davydenko, O, Schultz, R.M., and Lampson, M.A. (2013). Increased CDK1 activity determines the timing of kinetochore-microtubule attachments in meiosis I. J. Cell Biol. 202, 221-229.
Ma, P. and Schultz, R.M. (2013). Histone deacetylase 2 (HDAC2) regulates chromosome segregation and kinetochore function via H4K16 deacetylation during oocyte maturation in mouse. PLoS Gen. 9(e)1003377.
Oh, J.S., Susor, A., Schindler, K., Schultz, R.M., and Conti, M. (2013). Cdc25A activity is required for the metaphase II arrest in mouse oocytes. J. Cell Sci. 126, 1081-1085.
Ma, J., Flemr, M., Strnad, H., Svoboda, P., and Schultz, R.M. (2012). Maternally-recruited DCP1A and DCP2 1 contribute to mRNA degradation during oocyte maturation and genome activation in mouse. Biol. Reprod. 88, 1-12.
Duncan, F.E., Hornick, J.E., Lampson, M.A., Schultz, R.M., Shea, L.E., and Woodruff, T.K. (2012). Chromosome cohesion decreases in human eggs with advanced maternal age. Aging Cell. 11, 1121-1124.
Solc, P., Baran, V., Mayer, A., Bohmova, T., Panenkova-Havlova, G., Saskova, A., Schultz, R.M., and Motlik, J. (2012). Aurora Kinase A drives MTOC biogenesis but does not trigger resumption of meiosis in mouse oocytes matured in vivo. Biol. Reprod. 87, 1-12.
Schindler, K., Davydenko, O., Fram, Brianna, Lampson, M.A., and Schultz, R.M. (2012). Maternally-recruited Aurora C kinase is more stable than Aurora B to support mouse oocyte maturation and early development. Proc. Natl. Acad. Sci. USA. 109, E2215-2222.
Ma, P., Pan, H., Montgomery, R.L., Olson, E.N., and Schultz, R.M. (2011). Compensatory functions of HDAC1 and HDAC2 regulate transcription and apoptosis during mouse oocyte development. Proc. Natl. Acad. Sci. USA. 109, E481-489.
Banrezes, B., Sainte-Beuve, T., Canon, E., Schultz, R.M., Cancela, J., and Ozil, J.P. (2011). Adult body weight is programmed by a redox-regulated and energy-dependent process during the pronuclear stage in mouse. PLoS One. 6, e29388.
Chiang, T., Schultz, R.M., and Lampson, M.A. (2011). Age-dependent susceptibility of chromosome cohesion to premature separase activation in mouse oocytes. Biol. Reprod. 85, 1279-1283.
Medvedev, S., Pan H., and Schultz, R.M. (2011). Absence of MSY2 in mouse oocytes perturbs oocyte growth and maturation, RNA stability, and the transcriptome. Biol. Reprod. 85, 575-583.
Chiang, T., Duncan, F.E., Schindler, K., Schultz, R.M., and Lampson, M.A. (2010). Evidence that weakened centromere cohesion is a leading cause of age-related aneuploidy in oocytes. Curr. Biol. 14, 1522-1528.
Flemr, M., Ma, J., Schultz, R.M., and Svoboda, P. (2010). P-body loss is concomitant with formation of an mRNA storage domain in mouse oocytes. Biol. Reprod. 82, 1008-1017.
Ma, Jun, Flemr, M., Stein, P., Berninger, P., Malik, R., Zavolan, M., Svoboda, P., and Schultz, R.M. (2009). microRNA activity is suppressed in mouse oocytes. Curr. Biol. 9, 265-270.
Backs, J., Stein, P., Backs, T., Duncan, F.E., Grueter, C.E., McAnnally, J., Qi, X., Schultz, R.M., and Olson, E.N. (2009). The g isoform of CaM kinase II controls mouse egg activation by regulating cell cycle resumption. Proc. Natl. Acad. Sci. USA. 107, 81-86.
Duncan, F.E., Chiang, T., Schultz, R.M., and Lampson, M.A. (2009). Evidence that a defective spindle assembly checkpoint is not the primary cause of maternal age-associated aneuploidy in mouse eggs. Biol. Reprod. 81, 768-776.
Schindler, K. and Schultz, R.M. (2009). The CDC14A phosphatase regulates oocyte maturation in mouse. Cell Cycle. 8, 1090-1098.
Ma, P. and Schultz, R.M. (2008). Histone deacetylase 1 (HDAC1) regulates histone acetylation, development, and gene expression in preimplantation mouse embryos. Dev. Biol. 319, 110-120.
Tam, O.H., Aravin, A.A., Stein, P., Girard, A., Murchison, E.P., Cheloufi, S., Hodges, E., Anger, M., Sachidanandam, R., Schultz, R.M., and Hannon, G.J. (2008). Pseudogene-derived siRNAs regulate gene expression in mouse oocytes. Nature. 453, 534-538.
Pan, H., Ma, P., Zhu, W., and Schultz, R.M. (2008). Age-associated increase in aneuploidy and changes in gene expression in mouse eggs. Dev. Biol. 316, 397-407.
Rivera, R.M., Stein, P., Weaver, J.R., Mager, J., Schultz, R.M., and Bartolomei, M.S. (2008). Manipulations of mouse embryos prior to implantation result in aberrant expression of imprinted genes on day 9.5 of development. Hum. Mol. Genet. 17, 1-14.
Igarashi, H., Knott, J.G., Schultz, R.M., and Williams, C.J. (2007). Alterations in PLCb1 in mouse eggs change calcium oscillatory behavior following fertilization. Dev. Biol. 312, 321-330.
Murchison, E.P., Stein, P., Xuan, Z., Pan, H., Zhang, M.Q., Schultz, R.M., and Hannon, G.J. (2007). Critical roles for Dicer in the female germline. Genes and Development 21, 682-693.