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Introduction
Although genomewide transcriptome studies are readily available for many tissues and cell types, functional annotation of the entire mammalian genome remains a daunting challenge. Several consortium-based genomewide knockout and mutagenesis projects are well underway, with the goal of generating mutant alleles for every gene in the mouse (Austin et al., 2004; Guan et al., 2010). While these resources are immensely valuable and continue to produce data through large-scale phenotype screening efforts, usually they will not functionally assess genes during development other than to document lethality when an essential gene is abrogated. We have undertaken an RNAi-based screen during mouse preimplantation, aimed at identification of genes involved in epigenetic and developmental events during the first cell lineage decisions in vivo. During the initial phase of this screen we have identified many genes required for blastocyst formation. In an effort towards functional genome annotation, here we characterize four genes that are each essential during the morula to blastocyst transition in the mouse. This report documents the preimplantation requirement of Splicing Factor 3b, subunit 1 (Sf3b1 also called SAP155 and Sf3B155); 0610009D07Rik (hereafter called by the human orthologue gene name, Sf3b14, but also called HSPC175, Ht006, P14, SAP14, Sf3b14a)); Ribosomal RNA Processing 7 homolog A ( S. cerevisiae, Rrp7a); and Ribosomal Protein L7-like 1 (Rpl7l1).
Sf3b1 has been shown in vitro to be an integral member of both the major and minor spliceosome and binds to both sides of the pre-mRNA branch site (Das et al., 1999; Gozani et al., 1998; Wang et al., 1998). Sf3b1 regulates ceramide Bcl-x alternative splicing through binding to ceramide-responsive RNA cis-element 1 in pre-mRNA, preventing splicing and resulting in exon inclusion (Massiello et al., 2006). Mice homozygous for a knockout allele of Sap155 die at the 16-32-cell stage and, interestingly, heterozygotes show homeotic transformations that are rescued in an Mll null background (Isono et al., 2005). U2snrp/Sf3b1 have been shown to interact with polycomb group genes ZFP144 and RNF2 (Isono et al., 2005), possibly explaining the homeotic transformations due to shifts in Hox gene expression boundaries. Although morula-stage lethality was noted by Isono et al. (2005) limited characterization of the preimplantation phenotype was...