Moreover, in mitosis, AURKs are also known to regulate correct microtubule-kinetochore attachment, chromosomal cohesion and cytokinesis (reviewed in Nguyen and Schindler, 2017). identified as an important mechanism of blastocyst lineage specification. Without listing all involved molecular players [see reviews (Hirate et al., 2015; Chazaud and Yamanaka, 2016; Sasaki, 2017)], polarity dependent Hippo-pathway suppression in outer cells enables formation of activating TEAD4 transcriptional complexes (involving nuclear localisation of specific co-factors, YAP and WWTR1/TAZ, collectively referred to here as Sema3e YAP) to potentiate TE specific gene expression, whereas activated Hippo-signaling in apolar inner cells inhibits this process (via activating LATS1/2 kinases to prevent YAP nuclear localisation in a phosphorylation dependent manner) (Nishioka et al., 2009). TEAD4-YAP complexes also simultaneously suppress pluripotent T863 gene expression (e.g., expression prior to the 16-cell stage (Frum et al., 2019). However, eventual EPI specification by the late blastocyst stage, actually requires ICM cell YAP redistribution to the nucleus (implying suppression of Hippo-signaling) in an inherently heterogeneous process that causes competitive apoptotic elimination of EPI progenitors of reduced na?ve pluripotency (Hashimoto and Sasaki, 2019). Collectively, these data illustrate the important and integral nature of Hippo-signaling in regulating key cell fate events in preimplantation mouse embryo development. We hypothesize they also indicate potential roles for other functionally upstream, uncharacterised and potentially novel factors (related to the core Hippo-pathway machinery) that may be functionally important during early mouse embryogenesis. The WW- and C2-domain containing (WWC-domain) gene is a positive regulator of Hippo-signaling, causing phosphorylation of the fly ortholog of mammalian LATS1/2 (warts/Wts) (Baumgartner et al., 2010; Genevet et al., 2010; Yu et al., 2010); a role confirmed in mammalian cell lines (Xiao et al., 2011a). Unlike and genome does not contain an equivalent gene due to an evolutionarily recent chromosomal deletion. The three paralogous human WWC-domain proteins are highly conserved, cable of homo- and hetero-dimerisation, can all activate Hippo-signaling (causing LATS1/2 and YAP phosphorylation) and result in the Hippo-related rough-eye phenotype, caused by reduced cell proliferation, when over-expressed in the developing fly eye (Wennmann et al., 2014). Despite T863 a T863 comparatively large and pan-model KIBRA-related literature, the roles of WWC2/3 are considerably understudied and restricted to limited prognostic reports consistent of tumor suppressor function in specific cancers [e.g., hepatocellular carcinoma (Zhang et al., 2017) and epithelial-mesenchymal lung cancers (Han et al., 2018)]. There are no reports of any functional roles for WWC-domain containing genes during mammalian preimplantation development. Mouse MII oocytes arise from the maturation of subpopulations of meiosis I (MI) prophase arrested primary oocytes, stimulated to re-enter meiosis by maternal reproductive hormones [reviewed (Sanders and Jones, 2018)]. Failed bivalent chromosome segregation, resulting in egg and/or zygotic aneuploidy, has usually terminal consequences for embryonic development and aneuploidy attributable to the human female germline is recorded as the leading single cause of spontaneously aborted pregnancy (Hassold and Hunt, 2001; Nagaoka et al., 2012). An extensive literature covering many aspects of the germane segregation of homologous chromosomes during MI exists [see comprehensive reviews (Bennabi et al., 2016; Mihajlovic and Fitzharris, 2018; Mogessie et al., 2018; Namgoong and Kim, 2018; Sanders and Jones, 2018)]. As in all mammals, and unlike most mitotic somatic cells, mouse meiotic spindle formation occurs in the absence of centrioles/centrosomes and is initiated around condensed chromosomes from coalescing microtubule organising centres (MTOCs) that are further stabilized by chromosome derived RAN-GTP gradients (Bennabi et al., 2016; Severson et al., 2016; Gruss, 2018; Mogessie et al., 2018; Namgoong and Kim, 2018). Transition from MTOC initiated spindle formation to centrosomal control in mice only occurs by the mid-blastocysts (E4.0) stage, when centrosomes appear (Courtois et al., 2012), and contrasts with other mammalian species in which the fertilizing sperm provides a founder centriole that duplicates and ensures the first mitotic spindle is assembled centrosomally (Sathananthan et al., 1991; Schatten and Sun, 2009). Amongst the known key regulators of meiotic/mitotic spindle dynamics are the conserved Aurora-kinase family (AURKA, AURKB, and AURKC, collectively referred.