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Biomedical subjects

R Schofield

Publications and source records attributed to R Schofield.

At least 37 records · Page 2Linked to original sources
PubMed1986

Development of spleen CFU-S colonies from day 8 to day 11: relationship to self-renewal capacity.

To investigate the persistence of spleen colonies from day 8 to day 11 of their development, we injected low numbers of marrow cells in order to obtain single colonies on the spleens of irradiated mice. Colonies were isolated on either half of the spleen on the eighth day. The position of day-11 colonies, determined relative to the ligature, indicated where novel colonies appear between those times. The results showed no evidence of the persistence of colonies from day 8 to day 11. The self-reproduction capacity of CFU-S that survive various cytotoxic drugs depends on the specific subpopulations that are affected by the drug. Using cyclophosphamide, busulphan, or BCNU, the self-renewal capacity of surviving CFU-S was manipulated. The results show that after cytotoxic treatments, a high day-11-day-8 ratio is not necessarily a reflection of a high self-renewal capacity of the CFU-S population that forms the day-11 colonies.

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PubMed1986

An analysis of haemopoietic and microenvironmental populations of mouse bone marrow after treatment with busulphan.

The effects of the cytotoxin busulphan (myleran) have been investigated in order to ascertain the unique nature of the lesion which it induces. It is one of only few compounds which can cause marked residual marrow dysfunction and the only drug reported to induce a marrow lesion of such magnitude that after a prolonged interval mice may die of the effects of pancytopaenia resulting from hypoplastic marrow failure. We have found that busulphan has a major microenvironmental effect as assessed by the ability of the marrow to form a complete organ in an ectopic site, which confirms existing evidence from a range of putative stromal assays. The effects upon CFU-S are known to include a selective action against certain subpopulations. Our investigation of the dose relationship of busulphan effects have shown that induction of the prolonged marrow lesion is not dependent on the dose of drug administered, or the fractionation regime employed, and is not dependent therefore on the number of CFU-S removed by the drug. The unique action of busulphan probably rests therefore in its ability to damage the microenvironment and the most primitive stem cells which are closely associated with it, if not entirely dependent on it, for their existence.

Animals↗
PubMed1986

Radiosensitivity of murine hemopoietic colony-forming units assayed in situ in the rib and in other marrow sites.

The radiosensitivity of murine hemopoietic colony-forming cells, which produce colonies in situ and which were counted at Day 8 after irradiation in sections of the femur, humerus, sternum, and spleen, is characterized by a D0 value of 91 +/- 9 cGy. The radiosensitivity of such cells in the rib was assessed using a new technique measuring regeneration or ablation of marrow in transverse sections of ribs observed at Day 8 after irradiation. The mean D0 value over a range determined using several different criteria was 108 cGy. These results provide evidence for the common assumptions that radiosensitivity measured using conventional transplantation assays reflects radiosensitivity in situ, and that the radiosensitivity of stem cells in different medullary marrow sites is similar. The techniques could be used with other species where assays for stem cells are not available.

Animals↗
PubMed1985

Studies on the self-renewal ability of CFU-S which have been serially transferred in long-term culture or in vivo.

The progressive decline in the repopulating ability of bone marrow serially-transferred through a succession of recipients is well documented. A similar series of transfers onto successive long-term culture adherent layers has been carried out using as 'donor' cells both adherent layer cells and cells from the culture supernatant. For as long as the in vitro serial transfer regime can be maintained the decline in self-renewal ability ('quality') of the CFU-S parallels the similar decline observed in vivo and occurs irrespective of the quality of CFU-S transferred. In both the in vivo and in vitro transfer regimes there is little or no loss of quality of CFU-S as a result of one 'transfer' although there may be a reduction in the total numbers of CFU-S in the mouse. However, a second and third transfer in vivo or in vitro leads to a rapid decline in the quality (self-renewal ability) of the CFU-S. Furthermore, despite the fact that the cells are transferred in vitro to a new adherent layer there is no recovery of the quality lost in the second transfer of the CFU-S. This fact implies that self-renewal potential of the CFU-S is a property intrinsic to the cell. The data presented here appear to exclude mitotic history and proliferative stress as factors determining the loss of self-renewal in CFU-S. They also fail to implicate stromal involvement in the decline. It may be that the dilution of an accessory cell or simply the disaggregation of the marrow may be major factors. The work presented indicates that the loss of self-renewal and repopulating ability of haemopoietic stem cells as a result of marrow transplantation may be studied using the long-term marrow culture and yield results relevant to in vivo marrow transplantation.

Animals↗
PubMed1984

Haemopoietic stem cells and the problem of self-renewal.

Haemopoiesis occurs in association with a complex stromal cell network in which all levels of haemopoietic cell development can be found. In order to understand the interaction between stromal cells and growth factors with the processes of self-renewal and differentiation, we have carried out a series of experiments attempting to define the circumstances in which self-renewal occurs in long-term marrow cultures. We have found that highly purified (FACS sorted) CFU-S do not undergo significant self-renewal in vitro when inoculated onto marrow stromal cells that can support self-renewal of unfractionated CFU-S. We have examined the effects of expression of the src oncogene on self-renewal of CFU-S. We have found that, following infection of long-term cultures with a retrovirus carrying the src oncogene, there is expression of src in certain of the stromal cells. There is also a selection for CFU-S that have an extended self-renewal capacity in vivo and in vitro. These CFU-S are non-leukaemic and can reconstitute haempoiesis in irradiated mice. Cells from src-infected cultures can also be induced to proliferate and form cell lines in vitro in the presence of interleukin 3 (IL-3). The cell lines produced are multipotential and non-leukaemic. From such data we conclude that expression of the src oncogene has (directly or indirectly) permanently altered the stem cells in such a way that they can undergo extensive self-renewal in situations that are unfavourable for growth and self-renewal of normal stem cells.

Animals↗
PubMed1983

The stem cell system.

The stem cell is defined as that cell in a tissue which, under normal circumstances, maintains its own population, undiminished in function and size, and furnishes daughters to provide new functional cells of that tissue. The daughters may, or may not, have to undergo further differentiation and/or maturation in order to achieve their functional stage. The fundamental characteristic of a stem cell, therefore, is self-renewal. Evidence is presented which implicates the microenvironment as a major component of the stem cell system, without which stem cells cannot be maintained. Furthermore, it is suggested that stem cell properties do not reside in one specific cell type in the population but, when necessary, cells other than those normally playing the stem cell role, can have stem cell function imposed upon them by the appropriate microenvironment. The stem cell "niche" hypothesis is presented to explain the dependence of stem cells upon their microenvironment. The postulate is offered that there are no cells which are intrinsically stem cells but that a range of cells in a tissue possess stem cell potential to a greater or lesser extent.

Animals↗
PubMed1980

Self-maintenance capacity of CFU-S.

The numbers of CFU-S which developed in spleen colonies were measured 11 days after injection of irradiated mice with marrow from normal mice or mice which had been treated in one of a variety of ways. The broad spread of CFU-S numbers, seen by other authors, in colonies derived from normal marrow was confirmed. However, the range and distribution of CFU-S per colony was generally different in colonies derived from the marrow of mice which were recovering or had recovered from some form of depopulation. From the data obtained, the mean CFU-S/colony, M1, and the probability of self-renewal, p, of the CFU-S were calculated. These values are used to calculate the number of cell cycles undergone during development of the colony and, by making certain assumptions, the cell cycle time of the CFU-S. The plot of p against log M for the various samples measured should be linear if all CFU-S proliferate at the same rate in a growing colony. It is not linear, however, so that CFU-S obtained under different experimental conditions do not all undergo the same number of cycles. In general, treatments given to the mice result in a lowering of the capacity for self-renewal of their CFU-S and also to a shortening of their cell cycle time. Some of the possible implications of these findings are discussed.

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