Scaffold Attachment Factor B1 Functions in Development, Growth, and Reproduction

Abstract

Scaffold attachment factor B1 (SAFB1) is a multifunctional protein that can bind both DNA and RNA and is involved in RNA processing and stress response. In addition, SAFB1 contains a transcriptional repression domain and can bind certain hormone receptors and repress their activity. To assess the role of SAFB1 in vivo, we generated SAFB1 mutant mice through targeted deletion in embryonic stem cells. While viable homozygous mutant (SAFB1^−/−) mice were obtained, genotypic distribution indicated that homozygous deficiency resulted in both prenatal and neonatal lethality. Mice lacking SAFB1 exhibited dwarfism, as a result of in utero growth retardation, and had low serum insulin-like growth factor 1 (IGF1) levels. In agreement with the previous characterization of SAFB1 as a corepressor for hormone receptors, we found that SAFB1^−/− mice displayed dramatic defects in the development and function of the reproductive system. Male SAFB1 null mice were infertile, apparently because of low circulating levels of testosterone. SAFB1^−/− testes were small and showed progressive degeneration of the germinal epithelium, increased apoptosis of germ cells, and Leydig cell hyperplasia. SAFB^−/− female mice were subfertile and showed progressive infertility, in part because of defects in oviductal transport and reduced numbers of follicles. Immortalized SAFB1^−/− mouse embryonic fibroblasts showed cell-intrinsic defects including increased transcriptional estrogen receptor α activity and enhanced responsiveness to IGF1. Together, these in vivo findings establish a critical role for SAFB1 in development, growth regulation, and reproduction.

ACKNOWLEDGMENTS

This work was supported by NIH grants R01 CA92713 (S.O.) and R01 CA94118 (A.V.L.), NIH program project grant P01 CA030195 (principal investigator, C. K. Osborne; project leader, S.O.), a Chao award (S.O.), a Women in Endocrinology award (S.O.), and postdoctoral (M.I.) (DAMD 17-01-Q1-0136) and predoctoral (K.D.) (W81XWH 04-01-0355) fellowships from the Department of Defense.

We thank F. DeMayo (BCM) at the Transgenic Core for outstanding service and continuing support throughout the project; Earlene Schmitt (BCM) for helping with the ES cell work; G. C. Enders, University of Kansas Medical Center, for providing GCNA antibodies; Ora Britton (BCM) for outstanding technical support; A. I. Agoulnik (BCM) for help with the analysis of the male reproductive system; J. Richards (BCM) for help with the ovary analysis and critical reading of the manuscript; S. Mohsin and staff at the Breast Center Pathology Core (BCM) for outstanding service and helpful discussion; R. Behringer (M. D. Anderson Cancer Center, Houston, Tex.) for providing the pNTRLacZPGKneolox plasmid; M. Matzuk and G. Chamness (BCM) for critical review of the manuscript; and Heidi Weiss (BCM) at the Breast Center Biostatistical Core for the statistical analysis.