Seven ways to study human development
Much is known about how organisms – including humans – develop. How has this knowledge been obtained?
Developmental processes have been meticulously documented for centuries. A contemporary of Charles Darwin, Ernst Haeckel, was a noted illustrator and natural historian and recorded embryonic development of numerous species (unfortunately, with a great deal of creative licence).
Visual records provide an important foundation for work on the biological mechanisms of development. Such work continues today, with ‘virtual embryo’ projects providing digital images of different stages of animals’ development.
2. Cell labelling
More detailed information can be obtained through experiments in which cells are labelled – for instance using fluorescent proteins – and the fate of their descendants tracked. This technique can be used to track cell migration and also to identify a cell’s descendants or ancestors.
3. Tissue explants
Early embryological research relied heavily on the experimenter moving parts of embryos, either around the same embryo or between embryos. The differences in form and function of different parts could then be observed and recorded. Such work identified key areas of the embryo that controlled the development of neighbouring regions (organising centres).
Genetic approaches aim to identify the genes controlling developmental processes. Typically, the aim is to identify a genetic variation (sometimes called a mutation) associated with a specific phenotypic change. The nature of the phenotypic defect provides a clue to the function of the gene – if an altered allele stops a head forming, it can be assumed the gene it is a part of is normally involved in head formation.
Since the 1980s genetic approaches have revealed much about the development of model organisms such as the fruit fly, nematode worm, zebrafish and mouse. Particularly important has been the ability to ‘knock out’ (eliminate) the function of specific genes (and, more recently, to ‘knock in’ new genes). Lately, it has even been possible to knock out genes at particular times in development or in specific tissues.
5. Comparative studies
The common evolutionary origins of different organisms mean that results in one animal can be compared with those from another. The function of a human gene implicated in an inherited disease, for example, can be analysed in mice or zebrafish.
6. Functional studies
Genetic studies can identify genes involved in developmental processes; their sequences may provide clues to their function. Generally, though, cellular and biochemical studies need to be carried out to find out what role a gene has in the cell.
7. Mathematical modelling
Mathematical approaches to development were proposed by computing pioneer Alan Turing in the 1950s. Today the goal is to develop mathematical representations that model the genetic and molecular control networks that create different morphologies during development. The growth of systems biology – looking at how many different components act together – is stimulating much activity in this area.Lead image:
Professor Bill Harris/Wellcome Images CC BY NC ND