Artwork depicting neuronal migration

Seven ways to study human development

Much is known about how organisms – including humans – develop. How has this knowledge been obtained?

1. Observation

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).

4. Genetics

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:

Artwork depicting many very young neurons that have been produced in the neuroepithelium migrating to their appropriate destinations in the brain. This image highlights the future of neuroscience showing different classes of cells through colour coding. There is no available technique to do this now, but it is not far off considering the advances that have been made with ‘brainbow’ mice. The brainbow technique allows for different cell types to be tagged with fluorescent proteins to track their development and connections with other cells.

Professor Bill Harris/Wellcome Images CC BY NC ND

References

Further reading

About this resource

This resource was first published in ‘How We Look’ in November 2014.

Topics:
Cell biology, Careers, Genetics and genomics
Issue:
How We Look
Education levels:
16–19, Continuing professional development