The 1998 Summer Research Fellows at Davidson are listed below, along with the name and abstract of their research project and the name of their faculty mentors:
Lindsay
Cohen
Dr. Malcolm Campbell, mentor
Subcloning of the H+-ATPase pmh1 in Chlamydomonas reinhardtii
Chlamydomonas reinhardtii, or Chlamy, is a haploid, unicellular, biflagellated green alga. Chlamy differentiates into two mating types that attach flagella, fuse, and form a zygote only in the absence of nitrogen. It is an ideal organism used to study cell-cell interactions because of this unique mating system. In 1992, Dr. Ginger Armbrust isolated a mutant strain of Chlamy that cannot attach flagella. In subsequent experiments, Dr. Armbrust identified the wild-type version of the affected gene. From the sequence data that have been obtained, the genomic DNA appears to code for an H+-ATPase. Earlier this year, the wild-type gene was divided into two halves and was cloned into two different plasmids. Using the two halves, I constructed several intermediate plasmids. I used restriction enzymes to cleave the DNA at specific sites and then either religated the remaining plasmid or inserted the cleaved section into another plasmid. I also used PCR to add about 500 bp. to the gene's 3' end to include the polyadenylation signal. Although I did not combine the two halves to form the final constructs, I successfully shortened the two halves and cloned other constructs that were sequenced. The ultimate goal of the project is to transform the final wild-type constructs into the mutant Chlamy cells; this will tell us 1) if the wild-type genomic DNA can complement the mutation to allow the cells to mate and 2) how long the genomic DNA needs to be to do this.
Lauren
Freeman
Dr. Julio Ramirez, mentor
The effect if AIT-082 on hippocampal sprouting in rats
The loss of memory associated with Alzheimer¹s disease may result from the degeneration of cholinergic pathways in the hippocampal system. It has been demonstrated that unilateral lesions of the entorhinal cortex (UECX), a model of Alzheimer¹s disease in rats, promote a sprouting response in the cholinergic septodentara pathway, which projects to the dentate gyrus of the hippocampus. This sprounting response may contribute to the recovery of memory function. After injury to the central nervous system, purine nucleosides and nucleotides produced by injured and dying cells promote the sprouting neurites. A novel purine derivative, AIT-082, has been found to increase nerve growth factor-mediated neurite outgrowth from PC12 cells. This drug may also have memory enhancing capabilities, as shown in studies with normal and aged memory-deficient mice. Our laboratory has found that at 4 days post-lesion, intraperitoneal injections of AIT-082 significantly enhanced sprouting in the ventral hippocampus. We undertook this investigation to determine whether the enhancement is maintained at 10-15 days post-lesion. We observed a significant enhancement of sprouting in the dorsal dentate gyrus in the rUECX/SALINE and the rUECX/AIT-082 groups as compared to the SHAM/SALINE group. We observed a significant enhancement of the sprouting in the ventral dentate gyrus in the rUECX/SALINE and the rUECX/AIT-082 groups as compared to the SHAM/SALINE and SHAM/AIT-082 groups. No other intergroup differences were noted.
Charlotte
White
Dr. Julio Ramirez, mentor
The behavioral effects of medial septum lesions
The hippocampus is essential to learning and memory. It receives glutamatergic input from the entrorhinal cortex (EC) and cholinergic input form the medial septum/vertical limb of the diagonal band of Broca (MS/VDB). Individuals in the early stages of Alzheimer¹s disease show memory deficits coincident with cholinergic neuron loss in the hippocampus. Rats show deficits of spatial working memory following deafferentation of the hippocampus. Memory function returns following CNS sprouting to the hippocampus. This work evaluates the behavioral significance of the unilateral MS/VDB lesion in animals preoperatively trained on a Y-maze alternation task. Comparison of the hippocampi within lesioned subjects revealed a moderate to high anterior and posterior denervation in the ipsilateral hippocampus as compared to the contralateral hippocampus. Unilateral lesioning of the MS/VDB does not result in behavioral memory deficit. The results provide a basis for future studies of the functional significance of sprouting by the MS/VDB to the denervated hippocampus.
Kelly
Westbrook, Ellen Rockwell, Ned Robinson
Dr. Mark Stanback, mentor
Condition and mate choice in eastern bluebirds, Sialia sialis
A variety of sexual selection models have described the possible role of condition in mate choice. If female birds prefer mates of high genetic quality but are constrained in their choice by the choices of females in better condition, a positive correlation between male and female condition would be expected. However, if high quality females can seek copulations outside of the pair, they will not be as choosy about the quality of their mate. To distinguish between these predictions, we compared the condition of male and female Eastern Bluebirds, Sialia sialis, during the nestling phase of reproduction. We took five measurements of condition: mass, size-specific mass, hematocrit, bilateral asymmetry, and feather growth. Of these different condition indices, regressions comparing the male and female within a pair were significant for the mass and hematocrit measurements. These results indicate that females may choose males whose condition is similar to their own. Such pattern of mate choice suggests that females are constrained by the choices of higher quality females.
Russell
Bailey, Will White
Dr. Patricia Peroni, mentor
Ecological genetics of artificial buried seed banks from a white campion
(Silene latifolia) metapopulation.
Seed banks have the potential to buffer populations against environmental uncertainty and to serve as reservoirs of genetic variation. From the perspective of the metapopulation, these dormant propagule pools can lower extinction rates for population fragments by providing a means of maintaining demes that does not require long distance seed dispersal. We investigated the effects of 3.5 yr burial on the genetic composition of white campion (Silene latifolia) seed banks. Our study sites were located in southwestern Virginia, and the white campion populations in this region have served as the subject of a long term investigation into the dynamics of metapopulations. Samples of seeds were encased in porous fabric packets, buried to a depth of 5 cm in five randomly selected plots at each of two sites, and exhumed 3.5 yr later. An average of 41% of seeds survived 3.5 yr of burial, and germination during burial accounted for almost all losses from the seed bank. Seeds that remained ungerminated during burial showed 87% survival. Comparison of the seeds that survived 3.5 yr burial and the original seed crop indicate that females showed a greater tendency to remain in the seed bank than males. This result suggests that populations re-founded from seed banks may face constraints on genetic variation due to sex ratio biases that develop during burial. We also initiated the collection of genotype data at 7 isozyme loci for seedlings produced by seeds that survived burial and seedlings from the original seed crop. Technical difficulties related to the ongoing renovation of our building prevented us from collecting sufficient data to determine if persistence in the seed bank varied with the level of inbreeding.
1998 Summer Research Fellows at Davidson
Hughes Summer Research Fellows '97
