Date of Award

2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular Biology

Abstract

In insects and vertebrates, hormone titers drive cellular proliferation and differentiation events that guide proper development. Nuclear receptors (NR) respond to these hormone signals by activating cascades of gene expression, along with coregulator protein complexes. In Drosophila melanogaster, fluctuating titers of the steroid hormone ecdysone are responsible for coordinating the timing of organismal development. Despite major advances in our understanding of Drosophila NR activities, we lack essential knowledge of the coregulators that are required for their proper function.

We have recently identified the Drosophila cara mitad (cmi) (`dear half') gene. The deduced CMI protein is closely related to the N-terminal half of the ALR-1/MLL-2 vertebrate NR coactivator that functions in several hormone regulated response pathways. The Drosophila TRR protein is an ortholog of the ALR-1 C-terminus that encodes a histone methyltransferase required for hormone-stimulated transcription. The evolutionary split of ALR-1 raises interesting questions regarding the conserved functions of each `half'.

We have shown that CMI serves as an essential coactivator of the hormone response pathway using genetic, molecular and biochemical tools. Genetic studies using cmi mutants, RNA-mediated gene silencing and over-expression of the wild type gene revealed that cmi is essential throughout development. Loss of function phenotypes include early lethality and morphological defects consistent with reduced hormone signaling. Over-expression of cmi revealed a variety of phenotypes in different tissues, suggesting widespread roles for cmi in body patterning. Biochemical experiments have shown that CMI can act directly in concert with hormone response regulators.

The BMP/TGFβ signaling pathway is highly conserved among higher eukaryotes and is essential for various cellular processes. In Drosophila, the DPP (TGFβ) signaling pathway is used to control many aspects of hormone regulated development. Our study revealed an important role of CMI in wing patterning through the regulation of dpp transcription. This regulation of dpp happens through both the 3' regulatory region at the larval stage and the 5'regulatory region at the pupal stage by a novel mechanism of dpp transcriptional regulation. Our study is the first one to describe the role of TRR in wing patterning. This function of TRR is synergistic with CMI and is likely through the DPP signaling pathway. The results from this study open new avenues to study the mechanisms involved in dpp transcription and DPP signaling. It also opens avenues to explore the DPP signaling pathway in wing patterning and in the patterning of other tissues where DPP signal is known to play a critical role.

Our study provides a unique insight into possible mechanisms of regulation of the evolutionarily conserved DPP/BMP signaling pathway by the mammalian ALR-1.

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Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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