A Drosophila immune response against Ras-induced overgrowth
Thomas Hauling1, Robert Krautz, Robert Markus
1Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, S-10691 Stockholm, Sweden.
Abstract:
Our goal is to characterize the innate immune response against the early stage of tumor development. For this, animal models where genetic changes in specific cells and tissues can be performed in a controlled way have become increasingly important, including the fruitfly Drosophila melanogaster. Many tumor mutants in Drosophila affect the germline and, as a consequence, also the immune system itself, making it difficult to ascribe their phenotype to a specific tissue. Only during the past decade, mutations have been induced systematically in somatic cells to study the control of tumorous growth by neighboring cells and by immune cells. Here we show that upon ectopic expression of a dominant-active form of the Ras oncogene (Ras(V12)), both imaginal discs and salivary glands are affected. Particularly, the glands increase in size, express metalloproteinases and display apoptotic markers. This leads to a strong cellular response, which has many hallmarks of the granuloma-like encapsulation reaction, usually mounted by the insect against larger foreign objects. RNA sequencing of the fat body reveals a characteristic humoral immune response. In addition we also identify genes that are specifically induced upon expression of Ras(V12). As a proof-of-principle, we show that one of the induced genes (santa-maria), which encodes a scavenger receptor, modulates damage to the salivary glands. The list of genes we have identified provides a rich source for further functional characterization. Our hope is that this will lead to a better understanding of the earliest stage of innate immune responses against tumors with implications for mammalian immunity.
Insights
Fruit flies reveal early tumor immune responses. Ectopic Ras(V12) expression in Drosophila melanogaster salivary glands triggers encapsulation and humoral immunity, identifying new genes like santa-maria involved in tumor damage modulation.
Area of Science:
- Developmental Biology
- Immunology
- Genetics
Background:
- Drosophila melanogaster is a key model for studying tumor development and immune responses.
- Investigating early tumor stages requires precise control over genetic mutations in specific tissues.
- Previous studies often confounded tumor phenotypes due to germline mutations affecting the immune system.
Purpose of the Study:
- To characterize the innate immune response during early tumor development.
- To identify genes involved in the immune reaction to oncogene-induced tumors.
- To explore the role of specific genes in modulating tumor-associated damage.
Main Methods:
- Ectopic expression of dominant-active Ras (Ras(V12)) in Drosophila imaginal discs and salivary glands.
- Analysis of tissue morphology, metalloproteinase expression, and apoptotic markers.
- RNA sequencing of the fat body to identify humoral immune responses.
- Functional validation of identified genes, such as santa-maria.
Main Results:
- Ras(V12) expression induced salivary gland enlargement, metalloproteinase expression, and apoptosis.
- A cellular immune response resembling granuloma-like encapsulation was observed.
- A characteristic humoral immune response was detected in the fat body.
- The scavenger receptor gene santa-maria was identified as modulating salivary gland damage.
Conclusions:
- Drosophila provides a valuable model for dissecting early anti-tumor innate immunity.
- Ras(V12) oncogene expression elicits complex immune reactions, including cellular encapsulation and humoral responses.
- The identified genes, including santa-maria, offer new targets for understanding tumor-immune interactions with potential relevance to mammalian immunity.
