66834 - Development Biology

Learning outcomes

At the end of the course, the student has knowledge on some developmental processes through the study of embryonic development in different model organisms; it also acquires an integrated and historical vision of the experimental approaches that have allowed the development of this discipline and of the contributions that this discipline has made to the study of evolution.

Course contents

This course examines the principles that explain how a single cell gives rise to an organism with organised structures and distinct cell types. Its central question is that of patterning: how cells acquire information about their position and translate it into different developmental programmes.

The course introduces the foundations of gene regulation, with particular attention to transcription factors and gene regulatory networks. It examines how cells with the same genome acquire different identities, and how those identities are specified, maintained or changed. Stem cells, differentiation and induction provide a framework for discussing the relationship between a cell's developmental potential, its history and signals from its surroundings.

A central theme is the transformation of continuous spatial information into distinct cell identities: the problem of positional information and patterning. The course considers molecular gradients and how cells interpret the strength and duration of a signal. The response depends not only on signal concentration but also on the gene regulatory networks already active in a cell and on interactions with neighbouring cells. Activation and mutual repression among transcription factors can amplify initially small differences, stabilise cell identities and sharpen the boundaries between domains. We will examine how networks within and between cells translate continuous signals into distinct, coordinated responses.

Specification of the anterior–posterior axis in Drosophila and dorsal–ventral patterning of the vertebrate neural tube will serve as two examples of this shared problem. In the first, we will examine how gradients of maternal factors, including Bicoid, help organise domains of gene expression in the embryo. In the second, we will consider how ventral SHH signals and dorsal signals from the BMP family contribute to the specification of neural progenitor domains. Comparing these systems will reveal a shared principle while allowing for differences in the signals and regulatory mechanisms involved.

Fertilisation and early development provide the setting in which these principles first operate. Cleavage, gastrulation and formation of the germ layers will be considered in relation to cell fate specification and the movements that organise the embryo. The course also covers sex determination as an example of a developmental decision shaped by the interaction of signals and genetic programmes.

Further aspects of these principles will be explored by comparing model organisms. The sea urchin provides a way to examine the specification of embryonic territories and interactions between cells during early development. Early vertebrate development allows comparison of different strategies for organising the embryo and establishing its body axes.

Developmental genomics introduces approaches for observing gene expression and cell states across time and space. Guided discussion of research papers will connect theoretical models with experimental evidence: which observations support a model of patterning, which experiments distinguish between alternative explanations, and what limits the conclusions that can be drawn.

The evolutionary component considers how developmental processes change across species. Comparisons between organisms will ask which components of gene regulatory networks are conserved and which have changed, for example through changes in regulatory elements, interactions between transcription factors or the use of existing signals in new contexts. The course will examine how changes in networks can alter when, where and how strongly genes are expressed, thereby contributing to the evolution of anatomical structures. It will also consider the limits of superficial similarity: the use of the same genes in different species does not necessarily mean that their developmental processes are identical.

By the end of the course, students should be able to explain how cellular networks interpret gradients and contribute to pattern formation; apply these concepts to key events in embryonic development; compare mechanisms across model organisms and consider their evolutionary changes; and critically evaluate the experimental evidence presented in a research paper.

Readings/Bibliography

Developmental Biology, Gilbert.

Office hours

See the website of Roberto Feuda