Dynamics of single human embryonic stem cells and their pairs: a quantitative analysis.

Numerous biological approaches are available to characterise the mechanisms which govern the formation of human embryonic stem cell (hESC) colonies. To understand how the kinematics of single and pairs of hESCs impact colony formation, we study their mobility characteristics using time-lapse imaging. We perform a detailed statistical analysis of their speed, survival, directionality, distance travelled and diffusivity. We confirm that single and pairs of cells migrate as a diffusive random walk for at least 7 hours of evolution. We show that the presence of Cell Tracer significantly reduces hESC mobility. Our results open the path to employ the theoretical framework of the diffusive random walk for the prognostic modelling and optimisation of the growth of hESC colonies. Indeed, we employ this random walk model to estimate the seeding density required to minimise the occurrence of hESC colonies arising from more than one founder cell and the minimal cell number needed for successful colony formation. Our prognostic model can be extended to investigate the kinematic behaviour of somatic cells emerging from hESC differentiation and to enable its wide application in phenotyping of pluripotent stem cells for large scale stem cell culture expansion and differentiation platforms.

Current trends in breast reduction.

Current trends in the development of breast reduction surgery include a few minor refinements in classic inverted-T scar methods but, more, the increased use of vertical-scar reduction mammaplasty. The benefits of the latter, which include reduced scar burden and improved long-term projection, are attractive, although the technique itself has proved to be somewhat intuitive and more difficult to master. These shortcomings can be minimized and the technique safely learned by initially applying it to patients with minor degrees of macromastia and ptosis. New modifications and alternative approaches have been introduced recently to address the problematic areas of the vertical-scar technique. A survey of members of the American Society of Plastic and Reconstructive Surgeons was undertaken at the 1998 annual meeting to review the current role of various techniques in breast reduction. The results revealed a slow acceptance of vertical-scar methods and the dominance of the inferior/central pedicle inverted-T scar method for a wide variety of macromastia types. Other issues were reviewed; they revealed the minimal role of both blood transfusion and liposuction and that more than half of breast reductions are still performed on an inpatient basis.