Ovca1, a Candidate Gene of the Genetic Modifier of Tp53, Mop2, Affects Mouse Embryonic Lethality Min Liang, 1,2 Bernard Ayanga, 1,2 Shuhua Du, 2,3 Andrew K. Godwin, 4 Jennifer K. Hartsock, 1 and Susan C. Evans 1,2 * 1 Department of Chemistry and Biochemistry,Ohio University, Athens,OH 45701 2 Molecular and Cellular Biology Program,Ohio University, Athens,OH 45701 3 Department of Biological Sciences,Ohio University, Athens,OH 45701 4 Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, PA19111 In this study, we show genetic modifier genes of Tp53 that can exacerbate embryonic abnormalities. Using a mouse model in which CE/J mice were crossed with the Tp53-null 129/Sv (129-Trp53 tm1 Tyj ) mice, a subset of Tp531/2 and 2/2 male and female embryos died during gestation. Our hypothesis, based on the genotypes of survivors, is that two genetic modifiers and a Tp53 null allele lead to an increase in embryonic lethality. We previously identified a recessive modifier (Mop1) from CE/J mice on chromosome 11 centromeric to Tp53. We have uncovered a dominant modifier (Mop2) from 129/Sv mice telo- meric to Tp53. We discovered a polymorphic change (321P?321S) of Ovca1 within the Mop2 locus of CE/J mice. This poly- morphism increased both mRNA and protein levels of OVCA1 in various tissues. CE/J primary cells cultured from different tissues proliferated more rapidly than 129/Sv cells. In addition, CE/J cells cycled while 129/Sv cells had a higher arrest in the G1 phase. Transfection of Ovca1 containing the 321P polymorphism into CE/J cells caused a higher G1 arrest. The pattern of OVCA1 expression also changed from being diffuse throughout the cytoplasm in 129/Sv cells to being punctuate in the cyto- plasm of CE/J cells. Tp531/2 abnormal embryos had more proliferating cells than normal embryos, but no obvious difference in differentiated neuronal cells. Tp532/2 small embryos had less differentiated neuronal cells and proliferating cells than nor- mal embryos. Thus, a polymorphism of Ovca1, combined with Mop1, genetically modifies embryonic lethality in Tp53 deficient mice. V V C 2008 Wiley-Liss, Inc. INTRODUCTION Tp53 is a tumor suppressor gene which is a key player in regulating cell cycle, apoptosis, DNA repair, and angiogenesis (Lane, 1992; Burns and El-Deiry, 1999; Fisher, 2001). Other than suppress- ing tumor formation, p53’s function in cell cycle control and apoptosis are also important for embry- onic development (Eizenberg et al., 1996; Choi and Donehower, 1999). Additionally, it stimulates differentiation in various cell lines (Eizenberg et al., 1996; Almog and Rotter, 1997). Proper amount of p53 is required for the development of normal embryos. For example, 10–23% of the female Tp53-null mouse embryos die of exence- phaly depending on mouse strain (Armstrong et al., 1995; Sah and Attardi, 1995; Jacks, 1996). Tp53’s effect on embryonic development alters in the con- text of genetically deficient knock-out mice. The lack of Tp53 partially or completely rescues embry- onic lethality in mdm-2, Rad51, and Pax knock-out mice (Jones and Roe, 1995; Montes de Oca Luna et al., 1995; Lim and Hasty, 1996; Pani et al., 2002). In few cases, such as in NF1-null mice, Tp53’s deficiency enhances embryonic lethality (Vogel and Parada, 1998). Moreover, we discovered novel genetic modifiers of Tp53, that when com- bined together, can exacerbate embryonic lethality in Tp53 heterozygous or homozygous null mice (Evans et al., 2004). By crossing CE/J (hereafter CE) mice with the Tp53-null 129-Trp53 tm1 Tyj (hereafter 129) mice, we observe that in the F2 generation a subset of Tp53 heterozygous and homozygous male and female mice die (Evans et al., 2004). Previous results show mapping of a recessive genetic modi- fier of Tp53, Mop1, on mouse chromosome 11 cen- tromeric to Tp53. Modeling of the data suggests that a dominant modifier (Mop2), in addition to Mop1, when combined with a Tp53 null allele, The first two authors contributed equally to this work. Supported by: NIH, Grant numbers: R03CA112639 and K01CA79743; Ohio University SEA. *Correspondence to: Susan C. Evans, Ohio University, Edison Biotechnology Institute, The Ridges, Athens, Ohio 45701, USA. E-mail: evanss1@ohio.edu Received 6 August 2007; Accepted 27 November 2007 DOI 10.1002/gcc.20535 Published online 7 January 2008 in Wiley InterScience (www.interscience.wiley.com). V V C 2008 Wiley-Liss, Inc. GENES, CHROMOSOMES & CANCER 47:315–325 (2008)