Cell biology: tumour stem cells in bone

The distribution of chondromas: Why the hand?

Chondroma is a benign hyaline cartilage tumor and is a relatively common skeletal neoplasm. Uneven distribution of this tumor among the various bones and regions of the skeleton is known but no explanation of this phenomenon followed. The current research aimed to document the exact chondroma distribution in the body. We hypothesized that the cases of all subtypes of chondroma have to be investigated in complex and that obtaining combined data from a large cohort of cases may explain the logic of chondroma distribution and may answer the question of why the hand is the main target of the tumor. We retrospectively analyzed 1529 cases of various subtypes of chondroma. Enchondroma was the most frequent type (65.4%) and the hand was the main target location (49.8% of all cases). The right side of the body was affected in 900 cases (58.9%) and in 629 cases (41.1%) the left side was affected (p = 0.03). The general results for tumor distribution are as follows: head and extremities - 92.8%; head, hands, and feet - 71.8%; and hands and feet - 62.8%. In the hand and the feet, multiple chondromas were distributed along the same digital ray in all cases. The anatomical distribution of various subtypes of chondroma follows "the periphery of the being", the uneven lateral distribution, and the "same digital ray" patterns that permits to suggest that genetic mutations affecting the development of the body during the embryonic period are the main etiological component for this tumor.

The neural crest is a source of mesenchymal stem cells with specialized hematopoietic stem cell niche function

Mesenchymal stem cells (MSCs) and osteolineage cells contribute to the hematopoietic stem cell (HSC) niche in the bone marrow of long bones. However, their developmental relationships remain unclear. In this study, we demonstrate that different MSC populations in the developing marrow of long bones have distinct functions. Proliferative mesoderm-derived nestin⁻ MSCs participate in fetal skeletogenesis and lose MSC activity soon after birth. In contrast, quiescent neural crest-derived nestin⁺ cells preserve MSC activity, but do not generate fetal chondrocytes. Instead, they differentiate into HSC niche-forming MSCs, helping to establish the HSC niche by secreting Cxcl12. Perineural migration of these cells to the bone marrow requires the ErbB3 receptor. The neonatal Nestin-GFP⁺ Pdgfrα⁻ cell population also contains Schwann cell precursors, but does not comprise mature Schwann cells. Thus, in the developing bone marrow HSC niche-forming MSCs share a common origin with sympathetic peripheral neurons and glial cells, and ontogenically distinct MSCs have non-overlapping functions in endochondrogenesis and HSC niche formation.

DOI:http://dx.doi.org/10.7554/eLife.03696.001

During the earliest phases of development, the embryo is formed by groups of stem cells that can develop into all the different types of tissue in the body—from bones to brain tissue. Later in life, small stockpiles of adult stem cells are found in various tissues and provide a reservoir of new cells available for replacing old or damaged cells. The most important source of blood stem cells is the bone marrow, which produces and stores cells that are capable of developing into blood and immune system cells. These processes are assisted by different bone marrow cells called stromal cells, which create a specialized local environment or ‘niche’.

But are the stromal stem cells that form the skeleton the same ones that form this niche during development? Or do the various types of stromal stem cells develop from distinct groups of cells in the embryo? Furthermore, it is unclear which cells guide blood stem cells towards the forming bones.

Other types of cells, including some of the cells of the nervous system, can communicate with the stem cells in the adult marrow and influence their behavior. This led scientists to wonder whether the stem cells in the bone marrow niche and the cells that communicate with them developed from the same type of embryonic stem cell.

Isern et al. tracked down the developmental origins of different types of bone marrow stromal stem cells by examining the bone marrow from the long bones (for example, the bones in the leg) of unborn and infant mice. It turns out that not all stromal stem cells in the developing bone marrow are alike. In fact, one pool of stromal stem cells forms the skeleton and loses stem cell activity in the process. In contrast, a different population of stromal stem cells develops from the same group of embryonic cells that gives rise to the cells of the nervous system. The stromal stem cells in this second group function as a niche to recruit and store the incoming blood stem cells and retain their stem cell activity throughout life.

The findings of Isern et al. help to explain why the nervous system is able to communicate with stem cells in the adult marrow, and provide a model for understanding how stem cell niches in organs that contain nerve tissue are established.

DOI:http://dx.doi.org/10.7554/eLife.03696.002

Targeting cancer's weaknesses (not its strengths): Therapeutic strategies suggested by the atavistic model

In the atavistic model of cancer progression, tumor cell dedifferentiation is interpreted as a reversion to phylogenetically earlier capabilities. The more recently evolved capabilities are compromised first during cancer progression. This suggests a therapeutic strategy for targeting cancer: design challenges to cancer that can only be met by the recently evolved capabilities no longer functional in cancer cells. We describe several examples of this target-the-weakness strategy. Our most detailed example involves the immune system. The absence of adaptive immunity in immunosuppressed tumor environments is an irreversible weakness of cancer that can be exploited by creating a challenge that only the presence of adaptive immunity can meet. This leaves tumor cells more vulnerable than healthy tissue to pathogenic attack. Such a target-the-weakness therapeutic strategy has broad applications, and contrasts with current therapies that target the main strength of cancer: cell proliferation.