Research in the LaMunyon Lab focuses on two areas of nematode biology
Sperm Developmental Genetics
Our research investigates the control of sperm activation. The timing of sperm activation is incredibly important – delays cause a lag in the race to fertilize the eggs, and premature activation reduces stored energy before it can be used in the race. In C. elegans, an activating molecule stimulates a signaling pathway that downregulates a number of "brake" proteins, allowing activation. During this process, the spherical spermatids undergo a dramatic cellular reorganization to produce an amoeboid, crawling cell – all within about 2 minutes! We have identified several genes that encode the brake proteins. One is spe-4, a homolog of the human protein Presenilin1, which when mutated causes early onset Alzheimer's Disease. Another gene is spe-46, which we will be describing in an upcoming paper. spe-46 mutants have prematurely activated sperm, but they also have numerous other sperm defects including chromosomal segregation problems that cause aneuploidy. A third gene that we have identified as encoding a brake protein actually associates with mitochondria. It is very unusual for a gene expressed only in sperm to associate with mitochondria – studies of this gene, and a paralog, are ongoing. We are also investigating numerous additional brake protein mutants.
In collaboration with the laboratory of Dr. Hamid M. Said at the UC Irvine Medical School and the VA Medical Center in Long Beach, we investigate vitamin transporters in C. elegans. Our studies so far have involved the folate transporter folt-1. Knockout worms are sterile and metabolically compromised as a result of folate deficiency. Surprisingly, thiamin supplementation makes them better. We are also investigating two riboflavin transporters. When the two transporters are knocked out, the worms suffer even more detrimental effects. We will soon begin using vitamin transporter knockouts as a novel means of controlling pest nematodes. These transporters will be described in an upcoming paper.
In both of these studies, the laboratory employs modern molecular biological techniques in engineering GFP reporter constructs and using homologous recombination to integrate them into the worm’s chromosomes, designing plasmids to create RNA interference, sequencing whole genomes via next generation sequencing, and creating transgenic worms.
Former Research Projects
While we no longer work on these projects, we do think about them at times....
Sperm Competition in Nematodes
In C. elegans, hermaphrodites normally reproduce by self fertilization, but when they mate with a male, the male's sperm displace the hermaphrodite's own sperm and predominate in fertilization. We found that male sperm take precedence becasue they are larger than hermaphrodite sperm, and larger sperm crawl faster and physically displace smaller sperm. Across species, larger sperm correlate with greater risk of sperm competition. Experimentally, we found that increased sperm competition resulted in the evolution of larger sperm over the course of 60 generations.
Sperm Competition in Moths
Females of the arctiid moth Utetheisa ornatrix mate numerous times, but they generally lay eggs sired by only one of their mates: the largest. We found evidence that the female herself controls movement of sperm within her reproductive tract, and thus may choose the sperm of her largest mate, based on his ejaculate size.
Psychological Adaptation to Sperm Competition in Humans
In the past, our laboratory has collaborated with that of evolutionary psychologist Dr. Todd Shackelford at Oakland University to investigate how sperm competition has influenced the behavioral adaptations of both men and women.