A RHO Small GTPase Regulator ABR Secures Mitotic Fidelity in Human Embryonic Stem Cells.

Pluripotent stem cells can undergo repeated self-renewal while retaining genetic integrity, but they occasionally acquire aneuploidy during long-term culture, which is a practical obstacle for medical applications of human pluripotent stem cells. In this study, we explored the biological roles of ABR, a regulator of RHO family small GTPases, and found that it has pivotal roles during mitotic processes in human embryonic stem cells (hESCs). Although ABR has been shown to be involved in dissociation-induced hESC apoptosis, it does not appear to have direct effects on cell survival unless cell-cell contact is impaired. Instead, we found that it is important for faithful hESC division. Mechanistically, ABR depletion compromised centrosome dynamics and predisposed the cell to chromosome misalignment and missegregation, which raised the frequency of aneuploidy. These results provide insights into the mechanisms that support the genetic integrity of self-renewing hESCs.

Rho-Signaling-Directed YAP/TAZ Activity Underlies the Long-Term Survival and Expansion of Human Embryonic Stem Cells.

Human embryonic stem cells (hESCs) can survive and proliferate for an extended period of time in culture, but unlike that of tumor-derived cells, this form of cellular immortality does not depend on genomic aberrations. In this study, we sought to elucidate the molecular basis of this long-term growth property of hESCs. We found that the survival of hESCs depends on the small GTPase Rho and its activator AKAP-Lbc. We show that AKAP-Lbc/Rho signaling sustains the nuclear function of the transcriptional cofactors YAP and TAZ by modulating actin microfilament organization. By inducing reprogramming and differentiation, we found that dependency on this Rho signaling pathway is associated with the pluripotent state. Thus, our findings show that the capacity of hESCs to undergo long-term expansion in vitro is intrinsically coupled to their cellular identity through interconnected molecular circuits that link cell survival to pluripotency.

Self-formation of functional adenohypophysis in three-dimensional culture.

The adenohypophysis (anterior pituitary) is a major centre for systemic hormones. At present, no efficient stem-cell culture for its generation is available, partly because of insufficient knowledge about how the pituitary primordium (Rathke's pouch) is induced in the embryonic head ectoderm. Here we report efficient self-formation of three-dimensional adenohypophysis tissues in an aggregate culture of mouse embryonic stem (ES) cells. ES cells were stimulated to differentiate into non-neural head ectoderm and hypothalamic neuroectoderm in adjacent layers within the aggregate, and treated with hedgehog signalling. Self-organization of Rathke's-pouch-like three-dimensional structures occurred at the interface of these two epithelia, as seen in vivo, and various endocrine cells including corticotrophs and somatotrophs were subsequently produced. The corticotrophs efficiently secreted adrenocorticotropic hormone in response to corticotrophin releasing hormone and, when grafted in vivo, these cells rescued the systemic glucocorticoid level in hypopituitary mice. Thus, functional anterior pituitary tissue self-forms in ES cell culture, recapitulating local tissue interactions.

Construction of a high-density and high-resolution human chromosome X array for comparative genomic hybridization analysis.

The human chromosome X is closely associated with congenital disorders and mental retardation (MR), because it contains a significantly higher number of genes than estimated from the proportion in the human genome. We constructed a high-density and high-resolution human chromosome X array (X-tiling array) for comparative genomic hybridization (CGH). The array contains a total of 1,001 bacterial artificial chromosome (BACs) throughout chromosome X except pseudoautosomal regions and two BACs specific for Y. In four hybridizations using DNA samples from healthy males, the ratio of each spotted DNA was scattered between -3SD and 3SD, corresponding to a log(2) ratio of -0.35 and 0.35, respectively. Using DNA samples from patients with known congenital disorders, our X-tiling array was proven to discriminate one-copy losses and gains together with their physical sizes, and also to estimate the percentage of a mosaicism in a patient with mos 45,X[13]/46,X,r(X)[7]. Furthermore, array-CGH in a patient with atypical Schinzel-Giedion syndrome disclosed a 1.1-Mb duplication at Xq22.3 including a part of the IL1RAPL2 gene as a likely causative aberration. The results indicate our in-house X-tiling array to be useful for the identification of cryptic copy-number aberrations containing novel genes responsible for diseases such as congenital disorders and X-linked MR.