Periodic Reporting for period 4 - CellSex (The importance of cellular sex in physiology and the underlying mechanisms)
Berichtszeitraum: 2024-11-01 bis 2025-06-30
Sex differences represent the most pronounced phenotypic dimorphism within species. In humans, they underlie disparities in disease risk, incidence, and treatment response. While sex hormones from reproductive organs play central roles, our work has revealed the critical contribution of cell-intrinsic mechanisms linked to sex chromosomes. We previously demonstrated that the sex of intestinal stem cells determines adult gut size and sex-specific tumour susceptibility—offering proof-of-principle that sex chromosomes can shape adult tissue physiology independently of hormones. Yet, key questions remain: What are the full phenotypic consequences of cellular sex? Which genes and mechanisms are involved, and where do they act? Our ERC project aimed to answer these questions using Drosophila as a model to investigate how cellular sex impacts physiology at the organismal level. The project pursued three main objectives: 1-Identify new cellular sex pathways influencing body size and behaviour, 2-Explore how changes in sex-determining genes drive trait evolution, and 3-Develop the first organ-specific Y chromosome deletion and use it to study Y-linked contributions to sex differences in longevity.
Over five years, our work uncovered conserved biological principles demonstrating that intrinsic cellular and neuronal sex identity—independent of hormones—regulates longevity, metabolism, homeostasis, and tumour susceptibility. We redefined key concepts including the role of the Y chromosome, dosage compensation, and cellular sex identity. Major findings include:
Over five years, our work uncovered conserved biological principles demonstrating that intrinsic cellular and neuronal sex identity—independent of hormones—regulates longevity, metabolism, homeostasis, and tumour susceptibility. We redefined key concepts including the role of the Y chromosome, dosage compensation, and cellular sex identity. Major findings include:
This work has led to five major original research articles, three of which are already published and two in final stages of submission. We also produced two review articles to disseminate our conceptual advances, along with five collaborative publications extending the impact of our tools and findings to other areas of biology. Dissemination and outreach were central to this project. Findings were presented at over 35 national and international conferences by all members of the team, reaching diverse scientific communities including developmental biology, genetics, cancer biology, and sex differences in health. We also engaged extensively with the public throughout the grant period via science outreach initiatives, particularly targeting middle and high school students.
The genetic and conceptual tools developed in this project offer a powerful foundation for researchers investigating sex differences in both model organisms and human biology. By combining classical Drosophila genetics, innovative genome engineering, and high-resolution functional genomics, we uncovered five major findings over the 5-year duration of the project:
1. Refuting the “Toxic Y” Hypothesis & Establishing the Role of Phenotypic Sex in Longevity
Using novel genetic tools, we showed the Y chromosome does not shorten male lifespan, challenging the long-standing "toxic Y" hypothesis. Instead, phenotypic sex, controlled by a master regulator, determines lifespan and other physiological traits—independently of chromosomal sex. This suggests conserved lifespan regulation by sex-determining pathways across species.
2. Discovery of a Citrate-Dependent Pathway Linking Metabolism to Stem Cell Differentiation
In male germ cells, we uncovered a new axis where citrate uptake fuels Acetyl-CoA production, enabling N-terminal acetylation by NatB, which protects key proteins from degradation and supports sperm differentiation. This reveals a conserved link between metabolism and proteome stability.
3. Demonstrating the Universality and Function of Cellular Sex Identity
Contrary to the mosaic model, we showed that every somatic cell has a defined sexual identity driven by a binary genetic switch. This intrinsic sex identity regulates organ size, reproduction, and species-specific traits—marking the first organism-level demonstration of its physiological significance.
4. Redefining the Role of X Chromosome Dosage Compensation
A targeted screen of over 150 perturbations revealed that dosage compensation is essential in specific adult stem cells, notably in the respiratory system, but dispensable in many other tissues. This challenges the notion that X monosomy lethality results from cumulative gene mis-regulation and highlights polyploidy as a protective mechanism.
5. Identifying a Neural Basis for Sex Differences in Tumour Susceptibility
We showed that gut tumour vulnerability is governed by the intrinsic sexual identity of a central brain circuit, rather than by hormones or tumour cell sex. This fruitless-positive circuit regulates tumour-promoting ILP3 secretion from the visceral muscle via brain–gut projections—demonstrating, for the first time, a neural–tumour axis shaped by neuronal sex.
Together, these results not only reshape long-held views of sex determination and sexual dimorphism but also provide conceptual and technical advances that can be exploited across biological disciplines.
The genetic and conceptual tools developed in this project offer a powerful foundation for researchers investigating sex differences in both model organisms and human biology. By combining classical Drosophila genetics, innovative genome engineering, and high-resolution functional genomics, we uncovered five major findings over the 5-year duration of the project:
1. Refuting the “Toxic Y” Hypothesis & Establishing the Role of Phenotypic Sex in Longevity
Using novel genetic tools, we showed the Y chromosome does not shorten male lifespan, challenging the long-standing "toxic Y" hypothesis. Instead, phenotypic sex, controlled by a master regulator, determines lifespan and other physiological traits—independently of chromosomal sex. This suggests conserved lifespan regulation by sex-determining pathways across species.
2. Discovery of a Citrate-Dependent Pathway Linking Metabolism to Stem Cell Differentiation
In male germ cells, we uncovered a new axis where citrate uptake fuels Acetyl-CoA production, enabling N-terminal acetylation by NatB, which protects key proteins from degradation and supports sperm differentiation. This reveals a conserved link between metabolism and proteome stability.
3. Demonstrating the Universality and Function of Cellular Sex Identity
Contrary to the mosaic model, we showed that every somatic cell has a defined sexual identity driven by a binary genetic switch. This intrinsic sex identity regulates organ size, reproduction, and species-specific traits—marking the first organism-level demonstration of its physiological significance.
4. Redefining the Role of X Chromosome Dosage Compensation
A targeted screen of over 150 perturbations revealed that dosage compensation is essential in specific adult stem cells, notably in the respiratory system, but dispensable in many other tissues. This challenges the notion that X monosomy lethality results from cumulative gene mis-regulation and highlights polyploidy as a protective mechanism.
5. Identifying a Neural Basis for Sex Differences in Tumour Susceptibility
We showed that gut tumour vulnerability is governed by the intrinsic sexual identity of a central brain circuit, rather than by hormones or tumour cell sex. This fruitless-positive circuit regulates tumour-promoting ILP3 secretion from the visceral muscle via brain–gut projections—demonstrating, for the first time, a neural–tumour axis shaped by neuronal sex.
Together, these results not only reshape long-held views of sex determination and sexual dimorphism but also provide conceptual and technical advances that can be exploited across biological disciplines.
My team has uncovered novel cell-autonomous sexual differentiation mechanisms in Drosophila melanogaster, revealing how sex differences manifest across diverse cell types and tissues beyond the gonads. While classical genetic studies in flies established the genetic framework of sex determination and served as a model for other animals, our research took a critical step forward by showing how cellular sex identity impacts organ physiology throughout the body. We explored a largely uncharted question in biology: how sex, once determined, is expressed at the cellular level. Unlike the well-studied gonadal differentiation, little was known about how intrinsic sexual identity shapes phenotypes in non-reproductive organs. One reason for this gap is the technical challenge of dissecting sex chromosome effects outside the context of hormonal signalling. To overcome this, we developed advanced genetic tools enabling precise manipulation of sex and sex chromosomes in specific tissues. These tools include methods for generating mosaic animals with genetically defined cellular sex and for modulating the size and number of Y chromosomes in targeted organs. We also disentangled the role of the primary sex determinant from its canonical downstream targets, identifying novel, tissue-specific mechanisms that operate independently of traditional sex differentiation pathways. These innovations led to a suite of genetic stocks, methods, and models that are now being adopted by the wider research community. Our work challenged long-standing models and assumptions:
-We demonstrated that the presence of a Y chromosome does not reduce male lifespan, refuting the widely accepted "toxic Y" hypothesis.
-We showed that every somatic cell actively expresses its sexual identity through the production of the sex determinant, overturning the classical mosaic model of sexual differentiation.
-We revised the traditional two-gene model of Drosophila sexual differentiation, showing that it fails to account for widespread, hormone-independent sexual identity across tissues.
Through these discoveries, our work not only redefined key concepts in sex determination but also opened new avenues for understanding how cellular sex and metabolism interact to shape physiology and disease.
-We demonstrated that the presence of a Y chromosome does not reduce male lifespan, refuting the widely accepted "toxic Y" hypothesis.
-We showed that every somatic cell actively expresses its sexual identity through the production of the sex determinant, overturning the classical mosaic model of sexual differentiation.
-We revised the traditional two-gene model of Drosophila sexual differentiation, showing that it fails to account for widespread, hormone-independent sexual identity across tissues.
Through these discoveries, our work not only redefined key concepts in sex determination but also opened new avenues for understanding how cellular sex and metabolism interact to shape physiology and disease.