The notion of identity involves the dual concepts of sameness and individuality. This can be applied to a wide range of biological entities, including cells, tissues/organs, organisms, or populations. For example, the distinct somatic cells within an individual organism have the same genetic material but distinct cellular identities, defined as a given cellular state, such as differentiated cell types with specific functional and morphological properties (neurons, muscles or liver cells…).. The notion of identity in human and social sciences also involves the reconciliation between sameness and individuality: what makes a person distinct from other persons and how does their identity persist over time and space?

Decades of genetic and molecular studies have highlighted the crucial importance of the genetic information contained within the organisms or cells to define their identity. However, a given genotype can give rise to several different phenotypes, dictated by complex mechanisms of gene expression regulation. In addition, it is increasingly clear that the epigenome (i.e. the complement of all chromatin modifications, DNA methylation and RNA transcripts) is as important as genome in defining cellular identity. In addition, both genome and epigenome respond dynamically to changes in the local environment. As such, identity is determined by a complex interplay between genome, epigenome, signaling networks and environmental cues.

Disruptions in this finely regulated interplay such as mutations affecting the genome sequence, epigenetic modifications affecting gene expression or inappropriate environmental cues, are responsible for many human diseases, which can therefore be described as loss or alterations in identity. As such, understanding the determinants of identity will allow to re-examine pathologies in terms of identity loss and to explore therapeutic approaches based on re-establishing identities.

This symphonic interplay of the determinants of identify (genome, epigenome and environment) creates the complexity and adaptability that define living systems, their physiological condition and more generally: ‘who we are’. A lot of questions remain unanswered and a clear and integrated view of the establishment, control, plasticity and transmission of identity through interrelationships of these determinants is still missing.

The Who am I?-Exploring Identity labex is constructed around these issues with the ambition to create an inter-disciplinary intellectual environment to generate advances in knowledge and scientific progress in this fascinating field.

The project is built around five central thematic axes:

  • the maintenance and integrity of molecular and cellular identities
  • the establishment and transmission of identity to subsequent generations
  • evolution in terms of cumulative changes in identity over time and through populations
  • the impact of environment (at the chemical and cellular level) on defining identities
  • the pathological consequences of deregulation of these mechanisms (loss of identity)

Biological systems have the inherent stability and robustness necessary to sustain the sameness defining their identities trough the transmission and expression of unaltered genetic and epigenetic information.

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An essential feature of life is the generation of phenotypic variation and transmission to subsequent generations. This raises questions about the continuity of experience and memory, both at the cellular level, but also for whole organisms.

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A key feature of living organisms is their capacity to change over time and to adapt to their environment. The identity of contemporary organisms or cells is therefore also the result of their evolutionary history. Who am I? partner teams will explore the patterns of evolutionary change that lead to the present-day species, especially human beings.

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Cellular identities can be modulated by external factors, such as chemical/hormonal signals or physical cues from the environment such as mechanical constraints. Interestingly, not all cells respond to stimuli in the same way, implying the mechanical induction of distinct cellular identities by integrated signals still to be discovered. The collaboration between biochemists, cell biologists and biophysicists within Who am I? aims at developing new devices and quantitative methods for analyzing and modeling these events.

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