SBE – Faculty Members

Digital Signal Analysis
In my work with circadian rhythms and heartbeat, I have adapted a number of digital signal analysis techniques for use with biological systems. One of these techniques is Maximum Entropy Spectral Analysis. More recently, I have adapted wavelet analysis techniques for use in circadian rhythms. I am currently investigating acoustic signals produced by male Drosophila during courtship. There is a great deal of species-specific information carried by these songs. I have adapted wavelet decomposition techniques for time-frequency of analysis of these signals as well. Wavelet analysis is a new method that holds promise for other biological signals, including heartbeat.

Circadian Rhythms
I continue my work on circadian and ultradian rhythms in collaboration with investigators at other institutions, principally Brandeis University. I am particularly interested in ultradian rhythms and their potential role underlying the 24-h oscillator, and have worked on the role of the cry gene in peripheral clocks and social interactions that can lead to resetting of the clock.

I am more broadly engaged in multidisciplinary research to increase the effectiveness of watershed management practices, including activities such as riparian restoration, dam removal, and the control of invasive species. With the Mitchell Center for Environmental and Watershed Science I work to maximize the usefulness of multidisciplinary environmental research by developing robust partnerships with key stakeholders involved in environmental decision-making. The Mitchell Center also serves as a forum for the discussion of controversial and complex environmental issues facing Maine and other regions.

A large variety of diseases, both inherited and acquired, affect muscle tissues in humans. In order to prevent and/or treat such disease, it is necessary to understand the pathology at the cellular and molecular level. Because each step of muscle specification and differentiation translates to a progressive refinement of functional physiology, studying muscle development may lead to therapeutic insights. The goal of our laboratory is to elucidate the signaling networks that underlie the muscle morphogenesis.

We study skeletal muscle morphogenesis during zebrafish development. Skeletal muscle is comprised of segmentally reiterated myotomes. Like the mammalian tendon, the zebrafish myotome boundary transduces force from muscle to the skeletal system. Thus, myotome boundary formation, as well as skeletal muscle morphogenesis, is critical for normal development and muscle function. Our research investigates the morphogenetic signaling networks that underlie skeletal muscle and myotome boundary formation.

The zebrafish is an excellent model system with which to integrate the genetic, molecular, and cell biological mechanisms that underlie muscle development. Because the signaling networks that regulate muscle development are remarkably conserved among vertebrates, our studies may lead to novel insights into development of therapeutics for muscle and tendon diseases.

Most of my current work concerns the physiology and ecology of actinorhizal plants. These plants are woody dicots that form nitrogen-fixing root nodules with Frankia, an actinomycete. They are found in 23 genera in 8 families and include alders (Alnus spp.), sweet gale (Myrica gale), bayberry (Myrica pensylvanica), and sweet fern (Comptonia peregrina). Actinorhizal plants commonly grow vigorously in nitrogen-poor soils where most plants grow only poorly or not at all. Such soils include raw mineral soils, sandy soils found on glacial outwash plains and along shores, and wet soils along streams and shores and in swamps and peatlands.

Presently we are examining the role that hemoglobin plays in Frankia including its localization within the cell and its interaction with oxygen. In addition we are examining the conditions needed for seedling establishment in common Maine actinorhizal plants.

The long-term goal of my work is the biological control of a cosmopolitan, soil-borne plant pathogen, Rhizoctonia solani.

Species of Rhizoctonia cause economically important diseases on most of the world's major field and vegetable crops, fruit and forest trees, turfgrasses, and ornamental plants. Thus, characterization of genetic factors regulating virulence in R. solani could have a significant impact on a wide spectrum of plant related human endeavor.

My research group has shown that particular double-stranded RNA (dsRNA) genetic elements are associated with a dramatically decreased disease-producing capacity (e.g., hypovirulence) in R. solani. Sequencing analysis of these dsRNA's suggested that they carry an RNA polymerase gene which allows them to replicate in the host cell, but most importantly they carry nucleotide sequences that are genetically related to genes involved in different metabolic pathways. Sequencing analysis of a hypovirulence-associated dsRNA (M2) has enabled me to put forward the following hypothesis: The M2 dsRNA down-regulates the shikimic acid (shikimate) pathway, which is responsible for the synthesis of the aromatic amino acids (AAA). R. solani produces a "toxin" (phenyl acetic acid, PAA) associated with the rhizoctonia disease syndrome in potato. PAA is a derivative of one of the AAA, phenylalanine. Thus, down-regulation of AAA biosynthesis leads to a decreased production of PAA and, in turn, to a diminished degree of pathogenicity (hypovirulence).

It appears that dsRNAs in fungi (and in other organisms) are involved in gene regulation of the host cell. My research program revolves around this hypothesis. Knowledge gained in this area will lead to the development of biocontrol-based strategies of plant disease management that will fulfill the need for sustainable and nonpolluting agricultural practices. Our project is part of a multifaceted, worldwide effort aimed at making agriculture more sustainable, and congruent with the ever-growing societal aspiration to nurture the environment in which we live.

Heart rhythms

Cardiac rhythms of Drosophila originate in a myogenic pacemaker. My collaborator, Dr. Harold Dowse (this Department) and I have identified two ion channels central to this pacemaker: A voltage-gated "OPQ-Type" Calcium channel, and a fast Calcium-gated potassium channel encoded by the slowpoke gene. Other Potassium channels may be involved, but sodium channels do not play a role in heartbeat. We have found several mutants with severe cardiac arrhythmias: slowpoke, no-action-potential, amnesiac, Dopa decarboxylase, and ether-a-go-go. We have also found that serotonin, octopamine, norepinephrine, dopamine, and acetylcholine are cardioacceleratory, while a pentapeptide from Limulus slows heartbeat.

Female sexual receptivity

Receptivity is switched on in young adults. I am studying the genetic and endocrine program underlying the switch-on, using a combination of genetic, physiological, and ethological approaches. A few genes are known to be crucial to receptivity; I am utilizing two, apterous (ap) and icebox. apterous mutants are deficient in JH, and therefore develop receptivity very slowly. icebox, discovered to be a behavioral mutation in this lab, exerts a stronger effect on receptivity than any other known gene. I also use JH analogs and JH inhibitors in these studies. I characterize the "microresponses" of females---the frequency and details of their signals to sexually active males---by analyzing videotaped behavior.

My work with actinorhizal nodules concerns the regulation of gas exchange and the function of nodule hemoglobins. These hemoglobins are similar to the myoglobins of animal muscle tissue, but their function is unknown. I have shown that hemoglobins are present in high concentrations in the nodules of some actinorhizal species, and in low concentrations in other species. My working hypothesis is that hemoglobins are needed for the extremely high rates of respiration and gas exchange that occur in root nodules. We have recently shown that Frankia produces hemoglobin when grown in pure culture. Current research focuses on the establishing the function of this hemoglobin, both in the free-living and symbiotic states of Frankia.

My major foci at present are on recruitment and ecology of fucoid algae, especially Ascophyllum nodosum, and on the growth and reproductive ecology of green sea urchins. The alga is long-lived and the dominant intertidal alga throughout much of the North Atlantic ocean. Studies are directed towards understanding the mechanisms of attachment and the role of recruitment and dispersal on population regulation. Sea urchins are the second major marine resource in Maine. However, overharvesting created a boom and bust phenomenon, and understanding growth and reproductive processes may be crucial to recovery. Aspects of algal-herbivore interactions, including foraging behavior of invertebrates and their influence on the structure of intertidal assemblages, continue to be a component of my work. Behavioral studies on herbivores are an important but somewhat neglected aspect of community studies.