Novel key roles for structural maintenance of chromosome flexible domain containing 1 (Smchd1) during preimplantation mouse development

Abstract

Structural maintenance of chromosome flexible domain containing 1 (Smchd1) is a chromatin regulatory gene for which mutations are associated with facioscapulohumeral muscular dystrophy and arhinia. The contribution of oocyte- and zygote-expressed SMCHD1 to early development was examined in mice ( Mus musculus) using a small interfering RNA knockdown approach. Smchd1 knockdown compromised long-term embryo viability, with reduced embryo nuclear volumes at the morula stage, reduced blastocyst cell number, formation and hatching, and reduced viability to term. RNA sequencing analysis of Smchd1 knockdown morulae revealed aberrant increases in expression of a small number of trophectoderm (TE)-related genes and reduced expression of cell proliferation genes, including S-phase kinase-associated protein 2 ( Skp2). Smchd1 expression was elevated in embryos deficient for Caudal-type homeobox transcription factor 2 ( Cdx2, a key regulator of TE specification), indicating that Smchd1 is normally repressed by CDX2. These results indicate that Smchd1 plays an important role in the preimplantation embryo, regulating early gene expression and contributing to long-term embryo viability. These results extend the known functions of SMCHD1 to the preimplantation period and highlight important function for maternally expressed Smchd1 messenger RNA and protein.

Smchd1 is a maternal effect gene required for autosomal imprinting

“…1a). Contrary to previous reports where Smchd1 depletion by siRNA knockdown in preimplantation embryos resulted in reduced blastocyst formation, hatching and survival to term (37,38), we found no embryonic or preweaning lethality following maternal deletion of Smchd1 (Fig. S1a).…”

“…These data led to a model where Smchd1-mediated chromatin interactions insulate the genome against the action of other epigenetic regulators, such as Ctcf (26,28,35,36); however, it is not known whether this model holds true for all Smchd1 target genes. Based on Smchd1's known role at some imprinted clus-ters (26)(27)(28)(29) and its expression in the oocyte (37), we sought to test the role of oocyte-supplied maternal Sm-chd1 in regulating imprinted gene expression. Here we show that Smchd1 is a novel maternal effect gene, required for imprinted expression of at least 16 genes.…”

Listening to mother: Long‐term maternal effects in mammalian development

“…Small interfering RNA (siRNA) Smchd1 knockdown inhibits the termination of the first wave of embryonic gene transcription, revealing an important early maternal effect role for SMCHD1 (Ruebel, Vincent, Schall, Wang, & Latham, 2019; Schall, Ruebel, & Latham, 2019). But in addition, transient reduction of maternal plus early embryonic sources of this protein through the morula stage by siRNA knockdown leads to reduced blastocyst formation and hatching, reduced total cell number, reduced inner cell mass allocation, and disruptions in gene regulation, with increased expression of genes related to the trophectoderm lineage (Midic et al, 2018). Importantly, these modest preimplantation developmental effects are accompanied by a nearly 40% reduction in term development from the two‐cell stage (Midic et al, 2018).…”

“…But in addition, transient reduction of maternal plus early embryonic sources of this protein through the morula stage by siRNA knockdown leads to reduced blastocyst formation and hatching, reduced total cell number, reduced inner cell mass allocation, and disruptions in gene regulation, with increased expression of genes related to the trophectoderm lineage (Midic et al, 2018). Importantly, these modest preimplantation developmental effects are accompanied by a nearly 40% reduction in term development from the two‐cell stage (Midic et al, 2018). Smchd1 knockdown also reduced expression of the mRNA encoding the essential cell cycle driver, S‐phase kinase associated protein 2 (SKP2).…”

Probing lasting cryoinjuries to oocyte-embryo transcriptome

“…The first S-phase establishes the ability for gene transcription to occur, and the second S-phase allows a transcriptionally repressive state to be established; this constitutes the emergence of the fundamental ability of the embryo to regulate gene transcription [62,68]. Because early actions of oocyte-expressed transcription factors like SMCHD1 impact gene expression and developmental events during later cleavage stages [69] cryoinjuries to the oocyte can exert long-term effects on a variety of processes. The disruptions in the four-cell stage transcriptome profile observed with cryoinjury impact a number of essential processes that are regulated by the newly activated genome, as evidenced by effects on mitochondrial function, cellular dynamics and blebbing, cell division, protein metabolism, and diverse signaling pathways.…”