Dr. Thomas Hammond    

Research Topics

Meiotic Silencing by Unpaired DNA (MSUD)

In N. crassa, and possibly many other organisms, MSUD carefully examines the locations of genes between pairs of homologous chromosomes.   Any gene found to be out of place is prevented from being expressed.  Although the mechanism behind this remarkable feat is essentially unknown, we do know that it requires several proteins that surround the nucleus (Figure A).  Next, we hope to identify and characterize MSUD proteins that interact directly with chromosomes, as they must be directly involved in detecting genes that are in the wrong place.

Figure A. Fluorescent protein-tagged MSUD proteins surround the cell nucleus during meiosis.

The Neurospora Spore Killers

While MSUD may defend genomes from external invaders, like viruses, genomes can also fall prey to internal agents, such as their own genes.  Spore killer is an example of what can happen when a genome’s own gene (or group of genes) becomes selfish.   Spore killer is a member of a broad class of DNA molecules called meiotic drive elements, examples of which exist in a diverse array of organisms, including plants, flies, and mammals. Through studies of Spore killer, we hope to learn more about meiotic drive elements and the cellular processes that have evolved to protect genomes from them.

Figure B. In crosses between Spore killer strains and normal strains, only spores with a Spore killer genotype are produced. Each meiotic cell (ascus) depicted in figure 'B' contains no more than 4 viable spores, instead of the normal 8 viable spores. This is becuase the 4 non-Spore killer spores have been killed by Spore killer.


Meiotic Drive in Fusarium Fungi

Maize is one of the world’s most important food and energy crops.  Fusarium verticillioides is both an endophyte and pathogen of maize that produces a group of teratogenic and carcinogenic mycotoxins.   Some of these mycotoxins, such as the fumonisins, have been linked to birth defects and esophageal cancer in humans.  Unfortunately, the current strategies used to prevent contamination of maize with fumonisins are ineffective.  Through a collaboration with Dr. Daren Brown at the USDA-ARS-National Center for Agricultural Utilization Research in Peoria, we are investigating the possibility of using meiotic drive elements to eliminate fumonisin production genes from agricultural populations of F. verticillioides. If successful, this strategy will safely eliminate fumonisin contamination of maize without the use of fungicides.  It will also provide knowledge on how to apply meiotic drive-based control systems to other toxigenic and/or pathogenic fungi.

The figure below shows two maturing asci from a cross between an F. verticillioides Sk+ strain and an F. verticillioides Sk- strain. Note that only 4 developing ascospores are visibile in each ascus. The other 4 have been killed by the Sk locus.