It is expected that use of adult multipotential mesenchymal stem cells (MSCs) for bone tissue engineering (TE) will lead to improvement of TE products. Prior to clinical application, biocompatibility of bone TE products need to be tested in vitro and in vivo. In orthopedic research, sheep are a well-accepted model due to similarities with humans and are assumed to be predictive of human outcomes. In this study we uncover differences between human and ovine bone marrow–derived MSCs (BMSCs) and adipose tissue–derived MSCs (ADSCs) in response to osteogenic media. Osteogenic differentiation of BMSCs and ADSCs was monitored by alkaline phosphatase (ALP) activity and calcium deposition. Mineralization of ovine BMSC was achieved in medium containing NaH2PO4 as a source of phosphate ions (Pi), but not in medium containing β-glycerophosphate (β-GP), which is most often used. In a detailed study we found no induction of ALP activity in ovine BMSCs and ADSCs upon osteogenic stimulation, which makes β-GP an unsuitable source of phosphate ions for ovine cells. Moreover, mineralization of human ADSCs was more efficient in osteogenic medium containing NaH2PO4. These results indicate major differences between ovine and human MSCs and suggest that standard in vitro osteogenic differentiation techniques may not be suitable for all types of cells used in cell-based therapies. Since mineralization is a widely accepted marker of the osteogenic differentiation and maturation of cells in culture, it may lead to potentially misleading results and should be taken into account at the stage of planning and interpreting preclinical observations performed in animal models. We also present a cell culture protocol for ovine ADSCs, which do not express ALP activity and do not mineralize under routine pro-osteogenic conditions in vitro. We plan to apply it in preclinical experiments of bone tissue–engineered products performed in an ovine model.

Abstract. We study category counterparts of the notion of a universal measure zero set of reals.We say that a set A ⊆ R is universally meager if every Borel isomorphic image of A is meager in R. We give various equivalent definitions emphasizing analogies with the universally null sets of reals.In particular, two problems emerging from an earlier work of Grzegorek are solved.

Let I ccc be the σ-ideal of subsets of the Cantor group 2 N generated by Borel sets which belong to every translation-invariant σ-ideal on 2 N satisfying the countable chain condition (ccc). We prove that I ccc strongly violates ccc. This generalizes a theorem of Balcerzak-Ros lanowski-Shelah stating the same for the σ-ideal on 2 N generated by Borel sets B ⊆ 2 N which have perfectly many pairwise disjoint translates. We show that the last condition does not follow from B ∈ I ccc even if B is assumed to be compact. Various other conditions which for a Borel set B imply that B ∈ I ccc are also studied. As a consequence we prove in particular that:• If A n are Borel sets, n ∈ N, and 2 N = n A n , then there is n 0 such that every perfect set P ⊆ 2 N has a perfect subset Q, a translate of which is contained in A n 0 . • CH is equivalent to the statement that 2 N can be partitioned into ℵ 1 many disjoint translates of a closed set.

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