# Cell Lineage Affiliation During Hematopoiesis

## TL;DR

This review discusses how and when hematopoietic stem cells commit to specific blood cell lineages during development.

## Contribution

The paper reviews contrasting views on the timing and mechanism of lineage commitment in hematopoietic stem cells.

## Key findings

- There is uncertainty about when hematopoietic stem cells become affiliated with a single cell lineage.
- Two main views exist: late stepwise commitment or early continuous lineage affiliation.
- The review considers how much lineage-affiliated stem cells contribute to blood cell production.

## Abstract

By the mid-1960s, hematopoietic stem cells (HSCs) were well described. They generate perhaps the most complex array of functionally mature cells in an adult organism. HSCs and their descendants have been studied extensively, and findings have provided principles that have been applied to the development of many cell systems. However, there are uncertainties about the process of HSC development. They center around when and how HSCs become affiliated with a single-cell lineage. A longstanding view is that this occurs late in development and stepwise via a series of committed oligopotent progenitor cells, which eventually give rise to unipotent progenitors. A very different view is that lineage affiliation can occur as early as within HSCs, and the development of these cells to a mature end cell is then a continuous process. A key consideration is the extent to which lineage-affiliated HSCs self-renew to make a major contribution to hematopoiesis. This review examines the above aspects in relation to our understanding of hematopoiesis.