
	1999 Summer Scholars Program

Previous: Jessica Straatmann

A Test of the Interaction of HP2 with HP1

By William Wooten
Mentors: Carolyn Craig, Chris Shaffer, and Sarah Elgin
Department of Biology, Washington University, St. Louis, MO

The chromosomes of any eukaryotic nucleus have two distinct structural environments: heterochromatin and euchromatin. My research deals with the heterochromatic regions of the chromosome. The heterochromatin is primarily made up of highly repetitive DNA sequences and is gene poor. Heterochromatin protein 1 (HP1) is a conserved, non-histone chromosomal protein that is associated with the pericentric heterochromatin, the small fourth chromosome, the telomeres, and some sites in the euchromatic arms, notably region 31. HP1 plays an important role in position effect variegation (PEV). PEV is a clonally inherited pattern showing gene silencing in some of the cells normally expressing the gene, caused by the insertion or rearrangement of a euchromatic gene into the vicinity of heterochromatin. Using a yeast two-hybrid screen, we recently identified a protein that interacts with HP1 called HP2. HP2 is also located in the pericentric heterochromatin and the small fourth chromosome. HP2 has a more limited distribution than HP1, which seems to provide more low-level staining in the euchromatin. My research goal was to discover how HP1 and HP2 interact on the chromosome by testing for HP2 function in the absence of HP1.

We attacked this question using mutations in HP1 through the following procedure. We set up genetic crosses between Su(var) 2-5⁰² males and Su(var) 2-5⁰⁵ virgin females, and between Su(var) 2-5⁰⁴ virgin females and Su(var) 2-5⁰⁵ males. Su(var) 2-5⁰⁴ and Su(var) 2-5⁰⁵ are both HP1 deficient. Su(var) 2-5⁰², a point mutation, has a weak chromocenter signal, yet displays other sites as usual. After these crosses were complete and enough time had passed for the Drosophila to grow to the third instar larval phase, I extracted the salivary glands, fixed with formaldehyde and squashed the polytene chromosomes onto a microscope slide. The squashed polytene chromosomes were stained with mouse (ascites purified) anti-HP1 and rabbit anti-HP2 for the first antibody. The second florescent antibody was goat anti-mouse-TRSC (red) and goat anti-rabbit-FITC (green). The results showed that HP2 does not need HP1 to bind to heterochromatin. It remained associated with the pericentric chromocenter and the fourth chromosome without the presence of HP1. My research also proved the theory that HP2 is more selective than HP1 and provided information concerning the Su(var) genetic crosses. The 05x02 cross produced smaller polytene chromosomes than the 05x04 cross, which suggests that the 05x02 cross has a shorter life span and a larger larval lethality rate.

In the future, I believe more information will be discovered concerning the function and structure of HP2. Currently, another student in my lab is screening for a deletion in the HP2 gene to study how HP2 affects position effect variegation.

Previous: Jessica Straatmann

Scholars Index

This page was last updated on Fri, Jun 16, 2000 at 2:17:01 PM by Tom Elgin with Userland Frontier.