Biology

Student Honors Papers

The Student Honors Papers collection represents exemplary work in biology at Illinois Wesleyan University. The Ames Library is proud to archive these and other honors projects in Digital Commons @ IWU, the University's online archive of student, faculty and staff scholarship and creative activity.

Elucidating a Mechanism of Growth Cessation in Heterocysts of Anabaena sp. PC7120

by Blake Beehler

Anabaena sp. strain PCC 7120 is a filamentous, multicellular cyanobacterium that allows for the study of developmental factors that lead to the patterned differentiation of cell types. When given a source of fixed nitrogen, Anabaena grows in long strands of identical vegetative cells, all of which carry out photosynthesis to capture energy and fix carbon for the organism. However, under nitrogen-deplete conditions, approximately every tenth vegetative cell of a strand will terminally differentiate into a heterocyst, a non-dividing cell type with the ability to fix atmospheric nitrogen. This cell-type specific cessation of division indicates that there is a regulatory link between binary fission and heterocyst differentiation. In Anabaena, the location of the division plane for binary fission is determined by the interaction of MinC, MinD, MinE, and FtsZ. It is unknown how cell division is inhibited in heterocysts, but it has been shown that heterocysts lack polymerized FtsZ rings (Z-rings) normally responsible for for cytokinesis. To begin to understand FtsZ loss in heterocysts, mutant strains of Anabaena that displayed abnormal heterocyst morphology were screened for the presence of Z-rings. In mutant strains of interest, a copy of ftsZ, translationally fused with a yellow fluorescent protein (yfp), was introduced into the genome, and the cells were visualized by fluorescence microscopy. The results suggest that hetP may be responsible for inhibiting Z-ring formation in heterocysts, thus preventing division. Through a bacterial two-hybrid system and β-galactosidase assay, the interactions of HetP, Min proteins, and FtsZ have been qualitatively and quantitatively assessed. The results suggest an indirect interaction between HetP and cell division proteins as a possible mechanism for the cessation of growth in the heterocyst cell type of Anabaena. Forward genetic screening has lead to the establishment of a potential downstream target of HetP.

Comparison of regional eggshell porosity between the brood parasitic Brown-headed Cowbird (Molothrus ater) and its hosts: the Dickcissel (Spiza americana), and two non-parasitic relatives, the Red-winged Blackbird (Agelaius phoeniceus) and the Common Grackle (Quiscalus quiscula).

by Brittany Childs

The Brown-headed Cowbird (Molothrus ater) is a generalist brood parasite that lays eggs in the nests of many host species, including the Dickcissel (Spiza americana) and two non-parasitic relatives: the Red-winged Blackbird (Agelaius phoeniceus) and the Common Grackle (Quiscalus quiscula). Cowbird eggs reportedly hatch sooner than equivalently-sized host eggs, presumably via accelerated embryonic development enabled by a greater eggshell porosity and consequently greater gas exchange. However, the distribution of pores among apical, equatorial and basal eggshell regions within cowbirds and host species is undetermined. I tested the hypothesis that equatorial porosity would be greatest because respiratory gases primarily cross the eggshell pores and enter or exit the embryo’s circulatory system via the chorioallantoic membrane located in that region. I found that the equatorial region of eggs within species had significantly greater pore density, pore area, and porosity than the basal or apical regions of eggshells from cowbirds (P ≤ 0.006), Red-winged Blackbirds (P ≤ 0.002), and Dickcissels (P ≤ 0.005). Grackle eggshells did not follow this regional pattern, and porosity characteristics did not differ significantly between the equator and base (P > 0.05). Notably, cowbird eggshells had significantly greater pore area and porosity in equatorial regions compared to its three hosts (P ≤ 0.012). Cowbird eggshells had a greater apical pore area than that of the Dickcissel (P < 0.001) and grackle (P = 0.003), and did not have significantly greater eggshell basal pore area or porosity compared to either of its relatives. These observations demonstrate region-specific rather than global increases in eggshell porosity, which may further explain the accelerated embryonic development of cowbirds compared to host species.

A new species of frog (Strabomantidae: Pristimantis) from Peru with comments on its ectoparasites (Acari: Trombiculidae)

by Alan W. Brus

In South America, frogs of the genus Pristimantis are diverse and can be found from lowland forests to elevations of about 4000 m in the Andes. The 444 known species of Pristimantis belong to 16 species groups. One of these groups is the Pristimantis orestes Group, the 14 members of which inhabit the páramo, puna, and upper montane forests in southern Ecuador (3 species) and Peru (11 species). Species of the Pristimantis orestes Group are characterized by having snout-vent lengths ranging from 18.0 to 29.4 mm, short robust bodies, relatively short snouts, narrow digital discs, and areolate ventral skin. Some species have variously colored pale spots in the groin. Herein, I describe a new, diminutive species of Pristimantis from the Andes of northern Peru that I assign to the Pristimantis orestes Group. The new species, denoted Prsitimantis sp. 1, has a snout-vent length of 17.35–29.08 mm (n = 47) in adult females, and 14.39–22.97 mm (n = 40) in adult males, and it differs from all other members of the Pristimantis orestes Group in having prominent scapular tubercles. Ectoparasitic mites (Trombiculidae) of the new species were studied to determine any relation between the degree of infestations and body regions, size, sex, and age. No relationships were found among sexes or ages of frogs. Larger females were 3.85 times more likely to be infested than small females, but no difference was seen between different sized males. The throat had significantly more mites than other body regions and the legs had significantly fewer mites than other regions. Mites were examined using scanning electron microscopy and their morphology was compared to drawings of a previously described mite. The mite on Pristimantis sp. 1 was not Hannimania sp., the genus commonly reported to infest frogs.

Determining the Composition of the Dwelling Tubes of Antarctic Pterobranchs

by Lukasz J. Sewera

Pterobranchs are a group of marine invertebrates within the Hemichordata, which share characteristics with both chordates and echinoderms. Pterobranchs live in colonies of secreted tubes, coenicia, which are composed of a gelatinous material of unknown composition. Visually, the tubes appear similar to the tunic of tunicates, a group of invertebrates within the Chordata. The nonproteinaceous tunic of tunicates is composed of cellulose, which is unusual. The goal of this study was to determine the composition of the pterobranch coenicium. Some aspects of pterobranch phylogeny are still unclear even after multiple molecular and morphological studies. Identification of any new shared characteristics with either echinoderms or chordates would be valuable in determining clearer relationships among these taxa. Purification methods, histology, and microscopy techniques were used to study the structure and properties of the tube material. To date, the results indicate that that the tube material may be protein but the composition is unknown.

Nucleic acids and protein synthesis

by Sheldon Nicol

The unprecedented growth of interest in protein synthesis among biochemists is both a result of, and has contributed to, our rapidly advancing knowledge of the chemistry and metabolism of the nucleic acids. Over the past two decades, evidence has accumulated which points to an intimate association between cellular nucleic acid and protein synthetic activity. A large number of experiments in bacterial systems have shown that ribonuclease disrupts the cell's protein synthetic machinery and that ribonucleic acid (RNA) can frequently restore it. Studies of bacterial transformation (Hotchkiss, 1957) and the discovery of the autonomous infectivity of tobacco mosaic virus RNA (Gierer and Schramm, 1956) unequivocally established that nucleic acids alone contain the necessary information in their structure to direct the synthesis of new and genetically significant proteins. A large body of information on the fate of C14-amino acids in whole animal demonstrates conclusively that the initial and major site of incorporation of amino acids into protein are the cellular ribonecleoprotein particles (ribosomes). Thus it was clear, before cell-free systems has received much scrutiny, that nucleic acids had some intimate directive role in converting amino acids to protein and that the study of protein synthesis was inseparable from a study of the nucleic acids.

Myology of the Pectoral, Branchial, and Jaw Regions of the Ratfish Hydrolagus Colliei (Holocephali)

by Dominique Didier '87

The musculature of the jaw, branchial, and shoulder regions of the ratfish, Hydrolagus colliei, was dissected and described in an effort to determine possible homologous characters shared by the shark, a member of the subclass Elasmobranchii, and the ratfish, a member of the subclass Holocephali. The musculature of the ratfish jaw differs from the morphological pattern found in sharks in that the jaw muscles of the ratfish are located anterior to the orbit, unlike the jaw muscles of sharks, which are posterior to the orbit. It is suggested that this anterior musculature is a character that was shared by fossil ptyctodonts (Class Placodermi) and is not found in any other living fish today. It is further suggested that the labial cartilages of the ratfish may be remnants of the palatoquatrate cartilage which were excluded as the jaw became fused to the braincase. The morphology of the head of the ratfish best supports the hypothesis that ratfish and ptyctodonts are more closely related to each other than either taxon is to sharks or other jawed fishes.

The Anatomy of the Hyoid Region of Molossus Molossus and its Implication in Systematics

by Natawadee Prasertphon '91

The hyoid musculature and hyoid apparatus of a bat, Molossus molossus (Chiroptera: Molossidae) are dissected and described. A comparison is made with the hyoid structures of bats of the genera Rhinopoma, Emballonura, Nycteris, Megaderma, Rhinolophus, Pteronotus, Phyllostomus, and Eptesicus, which were previously described by my sponsor Gri'tfiths and associates. In Molossus, the geniohyoid and sternohyoid insertions, as well as the hyoglossus origin, have lifted off the basihyal bone and jointly retain a direct attachment to the basihyal via a small tendon. The hyoglossus is split into three distinct bellies: the most superficial originates from the basihyal raphe, the second originates from the basihyal bone, and the third originates from a very reduced thyrohyal bone. A part of the mylohyoideus has broken away from the main muscle, retaining its insertion on the basihyal--it is termed the mylohyoid profundus. The jugulohyoid muscle is absent, as is the stylohyoideus. The styloglossus muscle is split into two distinct bellies by the hyoglossus muscle. A cladistic analysis of these data gives preliminary support to Koopman's proposal in 1984 for a separation of the superfamilies Emballonuroidea and Rhinolophoidea from the superfamilies Phyllostomoidea and Vespertilionoidea. These data provide the first compelling support for Koopman's taxonomic group Yangochiroptera, comprising the superfamilies Phyllostomoidea and Vespertilionoidea.

Toward an Understanding of Alzheimer's Disease: The Effects of B-Amyloid(1-42) and Ibotenic Acid on the Retention of a Spatial learning Task in Rats F:ollowing Multiple Injections into the Hippocampus

by Jason Pequette '94

Neuropathologically, Alzheimer's disease (AD) is characterized by neuritic plaques and neurofibrillary tangles. Evidence has suggested that a protein called B-amyloid (BA) is a major component of the neuritic plaques and may playa role in the neurodegeneration seen in AD. The cellular mechanisms by which BA induces neurotoxicity, however, are still unclear. Recent evidence suggests that the aggregational state of BA may be relevant to its neurotoxicity. Whether portions of the BA protein or the entire sequence produces neurotoxicity in neurons, however, remains a controversy. Still another controversy is whether BA is directly neurotoxic to neurons or whether it increases the vulnerability of neurons. Recent evidence reported by Doman, Kang, McCampbell and Kang, that injections of BA(25-35) with a low dose of ibotenic acid into the hippocampus did disrupt the acquisition of spatial learning in the rat, supports the vulnerability hypothesis. They suggest that the synergistic effect between BA and ibotenic acid may have produced the neurotoxic effect. In light of recent evidence (McCampbell, Peterson and Tinkler, unpublished) that injections of BA(1-42) alone did not disrupt the retention of a spatial learning task, in this study we assessed the increased vulnerability hypothesis by co-injecting fiA(1-42) with a subthreshold dose of ibotenic acid into the hippocampus of male rats. Another problem related to fiA's neurotoxicity may concern the extent of hippocampal damage it produces. Therefore, we assessed the effects of multiple injections of fiA(1-42) and ibotenic acid into the hippocampus of male rats. Although preliminary, the results of this study conclude that coinjections of fiA(1-42) and ibotenic acid do not disrupt the retention of a spatial learning task.

Comparison of the Effects of Saporin-IgG Injections into the Nucleus Basalis Magnocellularis and Medial Septal Area of Male Rat as Assessed by the Morris Water Maze Task

by Alexander R. V. McCampbell '95

Alzheimer's disease currently afflicts approximately 4 million people in the United States, with 100,000 new cases being reported each year. As post mortem examination of AD patientsI brains has revealed a significant decrease in the number of cholinergic neurons, one approach we have taken is to look at the correlation between the depletion of certain cholinergic markers in animals and the resulting behavioral deficits. Two regions of specific interest are the medial septal area (MSA) and the nucleus basalis magnocellularis (NBM). These regions are important because they are the major source of cholinergic neurons in the brain, they are selectively targeted during aging and AD, and there have been many reports of their importance in learning and memory tasks. Therefore in this study we examined the effects on spatial learning, as assessed by the Morris water maze (MWM), in the male rat following intracerebral injections of the selective cholinergic neurotoxin, saporin-IgG. The results of this study indicate that saporin injections into the NBM impaired the performance in the MWM when compared to controls and injections of saporin into the MSA. This was revealed by significantly longer latencies to find a submerged platform and longer latencies during the spatial discrimination test.

Immunolesions Using Site Specific Injections of 192-lgG Saporin into the Basal Forebrain Fail to Affect Radial Arm Maze Performance in the Male Rat

by Lesley J. Hickman '96

In this study I investigated the effects of 192-lgG saporin injections into the medial septal area.(MSA) and nucleus basalis magnocel/ularis (NBM) on radial arm maze performance in the male rat. The results of the present study reveal that combined injections of 192-lgG saporin into the basal forebrain failed to disrupt RAM performance when compared to vehicle-injected controls. In addition, intraperitoneal injections using a muscarinic receptor blocker, scopolamine, failed to reveal a compensatory response of the cholinergic basal forebrain that may have explained the lack of behavioral effects of 192IgG saporin. Consequently, the results of this study suggest that a selective reduction in cholinergic transmission in the basal forebrain is, by itself, insufficient to account for the functional impairments observed in spatial learning in the rat. These data do not support the use of 192-lgG saporin as a viable approach to the elucidation of the neuropathological mechanisms that are associated with the cognitive deficits seen in Alzheimer's Disease.