Mitochondrially targeted redox probe reveals the variations in oxidative capacity of the haematopoietic cells.

Both oxidative stress and mitochondrial dysfunction play roles in a myriad of pathological conditions. There is therefore a need for tools that possess the ability to measure the dynamics of oxidative capacity within the mitochondria, particularly those that can measure reversible changes. Here, we report a mitochondrially-targeted fluorescent redox sensor NpFR2, which can reversibly measure changes in the mitochondrial redox environment. The probe has been used to report on variations in oxidative capacity of the haematopoietic cells in bone marrow, thymus and spleen.

Making Blood: The Haematopoietic Niche throughout Ontogeny.

Approximately one-quarter of all cells in the adult human body are blood cells. The haematopoietic system is therefore massive in scale and requires exquisite regulation to be maintained under homeostatic conditions. It must also be able to respond when needed, such as during infection or following blood loss, to produce more blood cells. Supporting cells serve to maintain haematopoietic stem and progenitor cells during homeostatic and pathological conditions. This coalition of supportive cell types, organised in specific tissues, is termed the haematopoietic niche. Haematopoietic stem and progenitor cells are generated in a number of distinct locations during mammalian embryogenesis. These stem and progenitor cells migrate to a variety of anatomical locations through the conceptus until finally homing to the bone marrow shortly before birth. Under stress, extramedullary haematopoiesis can take place in regions that are typically lacking in blood-producing activity. Our aim in this review is to examine blood production throughout the embryo and adult, under normal and pathological conditions, to identify commonalities and distinctions between each niche. A clearer understanding of the mechanism underlying each haematopoietic niche can be applied to improving ex vivo cultures of haematopoietic stem cells and potentially lead to new directions for transplantation medicine.

Gastrokine-2 is transiently expressed in the endodermal and endothelial cells of the maturing mouse yolk sac.

The yolk sac (YS) is a thin, bi-layered membrane encompassing the developing mammalian embryo in utero. The outer layer of the YS is composed of visceral endodermal cells derived from the primitive endoderm. The inner mesenchymal layer is highly vascularised and the first source of haematopoietic cells. YS haematopoiesis takes place from shortly after gastrulation (E7.5) until after midgestation (~E12.5) when the placenta and sites within the embryo proper predominate as sites of blood cell production. Here, we have assessed gene expression in the developing YS to determine what factors are associated with the end of haematopoietic cell production in this extra-embryonic tissue. We have observed that transcripts encoding gastrokine-2 (Gkn2) are up-regulated in the YS at E11.5, peak at E12.5 and are then reduced. Low levels of Gkn2 transcript were detected in purified YS endothelial cells. Gastrokine-2 protein was detected in the EpCAM-expressing visceral endodermal layer. Gastrokine-2 protein predominantly clustered at the basal side of the visceral endodermal cells facing the endothelial cell layer though did not appear to be strongly associated with secretory lysosomes. Gastrokine-1 protein binds F-actin. In contrast, gastrokine-2 in the YS is predominantly expressed at the basal side of the visceral endodermal cells, whereas F-actin in the YS is mostly found in the inner leaf of the luminal side of visceral endoderm. We have therefore identified expression of Gkn2 transcript and protein in the visceral endodermal layer and at lower levels in YS endothelial cells. This previously unreported expression of a "stomach-specific" secreted protein may be linked to the changes in the YS niche coinciding with the shift of haematopoiesis away from the YS into the embryo.