Mitotic activity of keratinocytes in regeneration and tissue homestasis

Despite decades of research, the exact regulation of epidermal development and homeostasis remains elusive. Proliferation in the epidermis is controversially discussed and knowledge is mostly derived from studies of mouse skin. However, it is well established that mouse and human skin differ regarding anatomy and likely also proliferative regulation. To address this question, mitoses were systematically assessed in a long-term human fibroblast-derived matrix-based skin equivalent (fdmSE). Keratinocytes in our fdmSE divided in 4 different ways: horizontal, oblique, or perpendicular to the basement membrane (BM) or suprabasally. The largest proportion of divisions occurred in horizontal orientation (< 80 %) at all time points. The second most common division type was oblique division (< 50 %). Perpendicular divisions were found at a low frequency (< 20 %) at intermediate time points only. They were absent at early and late time points. Thus, it appears that in the human interfollicular epidermis (IFE) all types of divisions are active. Importantly, we also observed suprabasal mitoses present at all analysed time points in the SE. Suprabasal division in epidermis has so far been restricted to embryogenesis, wound healing and diseased skin. We could confirm that it is also part of the normal human epidermis in situ thus suggesting that this spatial mitotic organisation is part of tissue homeostasis in human epidermis. These cells are in an early stage of differentiation as suggested by their expression of keratin 10 with a connection to the BM still detectable in some cases. Furthermore, we aimed at investigating asymmetric cell division in the IFE. To maintain the delicate interplay between self-renewal and differentiation, progenitor cells have to divide asymmetrically. Differential daughter cell fate can be established in two ways: oriented division which displaces one daughter cell from the stem cell niche, or asymmetric distribution of cell fate determinants to the daughter cells. Several components of oriented division have been proposed in invertebrate and vertebrate systems including the PAR-complex, or the adaptor proteins NuMA, Inscuteable and LGN. However, antibodies available for those proteins did not allow detecting these markers here. Instead, we identified the Notch inhibitor Numb as a possible marker for asymmetric keratinocyte division. Numb was segregated asymmetrically during some divisions of the human keratinocytes in 2D cultures. To determine its function, we established a protocol to stably knock down Numb in the human keratinocytes using CRISPR/Cas9. Notably, Numb deletion did not affect proliferation in short term culture (14 days), suggesting that it is not essential for mitosis per se. Instead, Numb may be important for the regulation of cell fate in epidermal regeneration, a question that needs to be addressed in future studies

Mitotic Diversity in Homeostatic Human Interfollicular Epidermis

Despite decades of skin research, regulation of proliferation and homeostasis in human epidermis is still insufficiently understood. To address the role of mitoses in tissue regulation, we utilized human long-term skin equivalents and systematically assessed mitoses during early epidermal development and long-term epidermal regeneration. We now demonstrate four different orientations: (1) horizontal, i.e., parallel to the basement membrane (BM) and suggestive of symmetric divisions; (2) oblique with an angle of 45°–70°; or (3) perpendicular, suggestive of asymmetric division. In addition, we demonstrate a fourth substantial fraction of suprabasal mitoses, many of which are committed to differentiation (Keratin K10-positive). As verified also for normal human skin, this spatial mitotic organization is part of the regulatory program of human epidermal tissue homeostasis. As a potential marker for asymmetric division, we investigated for Numb and found that it was evenly spread in almost all undifferentiated keratinocytes, but indeed asymmetrically distributed in some mitoses and particularly frequent under differentiation-repressing low-calcium conditions. Numb deletion (stable knockdown by CRISPR/Cas9), however, did not affect proliferation, neither in a three-day follow up study by life cell imaging nor during a 14-day culture period, suggesting that Numb is not essential for the general control of keratinocyte division

Meeting report: the road to science-based policy - ESOF through the eyes of young scientists

Communication and common understanding between politicians, scientists, and the society can lead to evidence-based science policy, a core principle that guides high caliber research and open innovation for a sustainable future

Mitotic diversity in homeostatic human interfollicular epidermis

Despite decades of skin research, regulation of proliferation and homeostasis in human epidermis is still insufficiently understood. To address the role of mitoses in tissue regulation, we utilized human long-term skin equivalents and systematically assessed mitoses during early epidermal development and long-term epidermal regeneration. We now demonstrate four different orientations: (1) horizontal, i.e., parallel to the basement membrane (BM) and suggestive of symmetric divisions; (2) oblique with an angle of 45°–70°; or (3) perpendicular, suggestive of asymmetric division. In addition, we demonstrate a fourth substantial fraction of suprabasal mitoses, many of which are committed to differentiation (Keratin K10-positive). As verified also for normal human skin, this spatial mitotic organization is part of the regulatory program of human epidermal tissue homeostasis. As a potential marker for asymmetric division, we investigated for Numb and found that it was evenly spread in almost all undifferentiated keratinocytes, but indeed asymmetrically distributed in some mitoses and particularly frequent under differentiation-repressing low-calcium conditions. Numb deletion (stable knockdown by CRISPR/Cas9), however, did not affect proliferation, neither in a three-day follow up study by life cell imaging nor during a 14-day culture period, suggesting that Numb is not essential for the general control of keratinocyte division

The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project

The PREDICTS project—Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)—has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity