HINLOD

Roles of Homeoproteins in Lymphoid Organ Development

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 Obiettivo del progetto (Objective)

'Lymphoid organ development results from a complex interplay of genetically controlled molecular and cellular networks. While most of the molecular mechanisms underlying lymphoid organogenesis remain unknown, recent findings demonstrate that homeodomain transcription factors are essential to these processes. One such homeoprotein is Pbx1 that binds DNA with a subset of Hox proteins, including the Hox11 oncoprotein aberrantly accumulated in T-cell acute leukemia. Like Hox11, Pbx1 was originally isolated as a proto-oncogene in pre-B-cell leukemia. By using knockout mouse models, cellular and biochemical approaches, we demonstrated that Pbx1 and Hox11 loss of function mutations result in reduced spleen mesenchymal proliferation accompanied by spleen agenesis. Furthermore, we established a genetic network regulating spleen mesenchymal expansion and demonstrated the essential role of the Pbx1-Hox11 transcriptional pathway during spleen ontogeny. Although a few Pbx1- and Hox11-targets have been identified, the growth-related transcriptional networks orchestrated by these homeoproteins during lymphoid organogenesis remain mostly unknown. Our research objective is to perform a comprehensive search for direct Pbx1 and Hox11 growth-related target genes and de-convolute the global gene regulatory network governed by these homeoproteins during lymphoid organogenesis. We plan perform a comprehensive analysis to uncover genes differentially expressed in wild type and single Pbx1 and Hox11 mutant embryonic spleens. Next, our studies will focus on those direct downstream targets that are likely responsible for the cellular proliferation/differentiation defects observed in these mutant spleens. We will validate these potential targets by performing in situ hybridization and immunohistochemistry analysis on embryonic spleen sections and further corroborate whether Pbx1 and/or directly control these targets by chromatin immunoprecipitation and transcriptional assays.'

Introduzione (Teaser)

Cancer biology examines how normal cellular functioning is altered. To understand this we first need to have a better picture of normal developmental biology.

Descrizione progetto (Article)

It is known that many oncogenes and tumour suppressors encode for transcription factors essential for regulating developmental processes. Most of the molecular mechanisms behind lymphoid organogenesis are still unknown, but recent research indicates that homeodomain transcription factors are essential to these processes. One such homeoprotein is Pbx1. This binds DNA with a subset of Hox proteins, including the Hox11 oncoprotein that is accumulated in T-cell acute leukaemia.

The 'Roles of homeoproteins in lymphoid organ development' (Hinlod) project has so far used mouse models and cellular and biochemical approaches to describe the effects of Pbx1 and Hox11 activity. The researchers have established a genetic network regulating spleen mesenchymal expansion and were able to demonstrate the critical role of the Pbx1-Hox11 pathway during spleen ontogeny.

The project's main objective has been to identify and characterise novel molecular networks regulated by oncogenic transcription factors during organogenesis. This has included a detailed search to identify growth-related target genes and regulatory networks governed by Pbx1 and Hox11 homeoproteins during lymphoid organogenesis.

During the first 24 months of the project, the use of microarray analysis identified genes regulated by a set of oncogenic transcription factors during organ development. Also, a bioinformatic analysis was performed and team members identified potential target genes of those transcription factors. The project is currently working to validate target genes via reverse-transcription polymerase chain reaction (RT-PCR) and immunohistochemical analyses.

Hinlod has succeeded in verifying several potential targets and uncovering developmental pathways controlled by the transcription factors under investigation. Study results show that some target pathways are associated with proliferation and differentiation of progenitor cells during organogenesis. The project's final goal is to arrive at an all-inclusive understanding of the genetic and transcription networks behind organ development.

The project partners believe that if oncogenic transcription factor target genes and developmental pathways can be identified during organogenesis, this will enhance understanding of how activity at a molecular level induces cellular transformation and tumour progression.