Developmental arrest induced in cleavage stage porcine embryos following microinjection of mRNA encoding Brahma (Smarca 2), a chromatin remodeling protein.

Smarca 2 (Brahma) and Smarca 4 (Brahma related gene 1, BRG1) alternatively occupy the catalytic site of SWI/SNF chromatin remodeling complexes. Mammalian embryos undergo a dramatic amount of epigenetic remodeling during cleavage development, which plays key roles in regulating both gene transcription and the developmental potential of the embryo. In order to understand how the epigenetic state of cleavage stage embryos is regulated, it is important to identify the factors that mediate epigenetic changes during cleavage development. In this study we hypothesized that altered expression of Smarca 2 would have profound effects on embryo development. The objectives of this study were to determine the expression pattern of Smarca 2 and determine the effects of Smarca 2 overexpression in cleavage stage parthenogenetic porcine embryos. Smarca 2 transcripts are most abundant in germinal vesicle (GV) stage oocytes and decline progressively during cleavage development. At the blastocyst stage, Smarca 2 transcripts are reduced by 18-fold (GV stage oocyte vs. blastocyst stage embryo, P < 0.05). Parthenogenetic porcine embryos injected with mRNA encoding wild type human Smarca 2 exhibited a dramatic developmental arrest as compared to noninjected embryos, embryos injected with GFP mRNA, or mRNA encoding a dominant negative version of human Smarca 2 (P < 0.01). This work demonstrates the importance of Smarca 2 containing SWI/SNF chromatin remodeling complexes in preimplantation porcine embryos and how perturbing the amount of Smarca 2 in porcine embryos disrupts cleavage development.

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