Welcome to the Homepage of Max Luis Tejada Ph.D.!                                            

The past seven years: a thrillogy! 

I undertook my Ph.D. studies under the supervision of Dr. Roger Deeley, the director of the Cancer Research Laboratories and Stauffer Research professor here at Queen's University. Roger's research interests include the identification, cloning and characterization of novel gene regulatory proteins and proteins involved in the development of drug resistance in various types of cancer. If you are interested please click on the appropriate link.

My project  involved trying to unravel the mechanisms controlling expression of the avian apo very low density lipoprotein II (apoVLDLII) gene. Several characteristics make the apoVLDLII gene a particularly interesting model for investigating mechanisms that determine the tissue specificity and hormone dependence of gene expression. Expression of apoVLDLII is liver specific and absolutely dependent on estrogen. In addition, competence to activate this gene in the liver is acquired at a very discrete and experimentally accessible early stage of development.

My work focused on a very interesting avian homeodomain protein discovered in this laboratory a few years back. This protein, designated Avian Knotted-Related or AKR, has been classified as a member of the TALE (three-amino acid loop extension) family of homeodomain proteins. However, it is quite distinctive from other members of this family in that: (i) its DNA-binding domain is situated at the N-terminus of the protein, (ii) it contains a highly unusual Ile at position 50 of the recognition helix of the homeodomain, (iii) it has a highly unusual recognition element 5'-TGACAT-3' found within a 6 base-pair core region of site located within the proximal promoter region of apoVLDLII which was designated F'.

AKR was cloned due to its ability to interact with the core of the F' site. Deletion or mutation of this region results in a greater than 5-fold reduction in the estrogen-dependent activation of the gene (1). The initial transfection experiments performed using Hep3B cells indicated that AKR was capable of downregulating the expression and hence the activity of luciferace reporter constructs under the regulatory control of a proximal promoter fragment of the apoVLDLII promoter. In addition, AKR-mediated repression was found to occur through interactions with the F' region, as deletion or mutation of this site decreased the ability of AKR to downregulate reporter activity. This strongly suggested that both positive and negative regulatory factors affected expression of the apoVLDLII gene through their interactions with F' (2).

PCR-assisted target site selection demonstrated that AKR binds optimally to a site designated Opt-1 (5'-TGACAG-3') that matches the sequence of the F' core at 5/6 residues. AKR exhibits high binding affinity to both F' (Kd = 3.7 x 10^-10 M) and Opt-1 (Kd = 5.2 x 10^-11 M) as determined by scatchard plot analyses. To obtain some insights into the structural features that determined AKR binding specificity the recognition helix was modeled and then complexed with Opt-1 (view this model). The model was then tested by examining the consequences that mutating amino acid residues in helix 3 and the NH₂-terminal arm had upon the binding specificity of the homeodomain (view these figures in PDF format) (3).

As of August 29, 2000 I am still composing this    part, I seem to be having a bit of difficulty uploading the giffs. I apologize for the inconvenience - more science to come! 

At present, I am working for Dr. Virginia Walker as a post-doctoral fellow in the Department of Biology here at Queen's University. I am making use of the 1-hybrid system to clone out transcription factors  that bind to a putative juvenile hormone (JH) response element discovered in the promoter of a JH-responsive gene designated Jhp21 (4). As well, my wife and I are working on a collaborative product involving a novel transcription factor in the fission yeast Schizosaccharomyces pombe. Working on this project I have acquired experience performing 2-hybrid screens as well as a variety of techniques in manipulating fission yeast.

Please contact me at [email protected]

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My technical expertise: just exactly what I am good GREAT at!