Hox Genes as Molecular Determinants of Neuronal Development
The body of an animal has an amazingly large variety of cell types with very different shapes and functions. However, all the cells of an animal contain the same genes. During embryonic development, cells become different because they start to express different sets of genes. As a consequence, only a relatively small fraction of all the genes are expressed in each individual cell. Transcription factors are regulatory genes that play a crucial role in defining cell types by controlling the expression of other genes. The Hox genes are a well-studied family of transcription factors that code for proteins containing a DNA-binding motif called the homeobox or homeodomain. The Hox genes seem to be present in all animals, including organisms that are as diverse as humans, insects, worms and jellyfish. Early during embryonic development, the Hox genes specify positional information along the anterior-posterior body axis. At later stages of development, the Hox genes are also expressed within specific domains of the nervous system.
Of all the organ systems in an animal, the nervous system contains the largest variety of cell shapes and behaviors. The mechanisms that generate this diversity determine nervous system development and pathology. Since the discovery of the Hox genes in 1984, our knowledge of embryonic development has improved tremendously. However, we have a more limited understanding of how Hox genes function at the cellular level, particularly in the nervous system. As a consequence, it is very valuable to be able to examine and manipulate the expression of these genes in individual, identified neurons whose properties are well known. For these reasons, we are studying the Hox genes in the leech Hirudo medicinalis, an organism well suited for neurobiological research. Leeches have a simple nervous system with large, hardy neurons that are easy to study.
The goal of our research is to examine the functions of Hox genes in the development of the central nervous system. There are at least nine different leech Hox (Lox) genes. Some of these genes have been cloned, allowing us to raise antibodies against their proteins and study their expression. The Lox genes are expressed in different but overlapping subsets of neurons within the central nervous system of the embryo, where they may act in a combinatorial way to determine neuronal identities. We are currently examining the normal patterns of expression of Lox genes in the nervous system, as well as the effects of experimentally altering their expression in neurons. Part of this work is carried out as a collaboration with Eduardo Macagno of Columbia University.
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The focus of research in my laboratory is comparative studies of neural mechanisms underlying monogamous mating systems and paternal behavior. Paternal care has a significant impact on the health and survival of offspring in monogamous species, including humans. Although this behavior in males and females appears to be similar, the mechanisms that stimulate and maintainit are different between the sexes. Compared to maternal behavior, relatively little is know about the brain mechanisms that regulate paternal behavior. The animal models we use are small rodents commonly known as voles. Voles are excellent prototypes for comparative studies because they have species that are genetically similar, but remarkably different in their mating systems and parental behavior. For example, prairie voles have a monogamous mating system. The breeding pairs form life-long pair bonds, share a nest, and cooperate in parental care of young. In contrast, meadow voles have a promiscuous mating system. The breeding pairs do not form a bond and males are not parental.
To understand brain mechanisms that regulate monogamy and paternal care, we are looking at a neural circuit that utilizes vasopressin. Vasopressin, acting as a neurotransmitter in the brain, is shown to communicate information about pair bonding in monogamous species and paternal behavior. Previous studies have indicated that injection of vasopressin into the brain of the monogamous prairie voles stimulated behaviors associated with pair bonding. In addition, injection of vasopressin into specific sites within the brain induced paternal responsiveness in sexually inexperienced male prairie voles that are not normally paternal. Interestingly, the levels of vasopressin production and release within specific sites of the prairie-vole brain change significantly during the mating period, a time in which pair bonding occurs. These data suggest that vasopressin plays an important role in shaping monogamous relationships and paternal behavior. However, the mechanisms by which vasopressin affects these behavior remain unknown.
Ongoing experiments in my laboratory aim to identify the behavioral and physiological factors that stimulate changes in vasopressin production and release during parenthood. We attempt to understand whether vasopressin activity in the brain is directly related to paternal responsiveness or is involved in processing signals that stimulate paternal behavior. Our studies are taking a closer look at the activity of vasopressin in the brain to see if there are changes in production, release or sensitivity to vasopressin in response or as a result of behavioral changes. In addition, we are identifying parts of the neural circuit in which vasopressin acts to influence paternal behavior. We are taking a multidisciplinary approach by combining behavioral, physiological, neuroanatomical, and histochemical studies. We use a range of techniques including: behavioral anaylsis, neuroanatomy (traditional and viral tract tracing), histochemistry (immunocytochemistry, receptor autoradiography, and in situ hybridization), and computerized image analysis. Visit Website
Invited Papers:
Basile, D.V. Physiological effects of Methylobacterium sp. On rice, Oryza sativa [L.] growth and development. 96th General Meeting of the American Society of Microbiology, New Orleans, LA, 1996. Visit Webpage
One of the most interesting microbe-plant interactions is the symbiosis between nitrogen fixing bacteria rhizobia and leguminous plants. The growth of a healthy plant depends on a lot of different factors, the availability of fixed nitrogen source such as ammonia is one. Most plants, except for the legume group, depend on the presence of a fixed nitrogen such as ammonia for their growth so that most of the plants are limited to grow in nutrient rich environments. Leguminous plants have developed a unique approach to solve this dependence on fixed nitrogen by forming a symbiosis with nitrogen fixing bacteria. Leguminous plants develop root nodules in the presence of rhizobia and those nodules are then colonized by rhizobia. The carbon and other nutrients provided by the plant support the growth of bacterial cells whose primary activity is to convert atmosphere nitrogen into ammonia as nitrogen source for the plant growth. The agriculture and environmental significance of this symbiosis has made the Sinorhizobia meliloti-alfalfa interaction one of the best understood model systems for microbe-plant interaction.
The successful establishment of the symbiosis appears to depend on intricate exchanges of chemical signal between S. meliloti cells and alfalfa, their plant host. Such signal exchanges would likely be the basis for the strict symbiotic relationship between S. meliloti and alfalfa, and the ability of alfalfa to prevent pathogenic bacteria in soil from colonizing its root nodules. It is currently understood that the start of this symbiosis is trigged by the exchange of the bacterial Nod factor and plant flavonoids. Like all other leguminous plants, alfalfa produces flavonoids and secrets into soils sounding their roots. The flavonoids elicit the production of the Nod factor by S. meliloti cells in the soil surrounding the roots. When the S. meliloti nod factor is sensed, alfalfa will form curled root hairs and infection thread inside these curled root hairs that will allow the bacterial cells to enter and colonize root nodules. One crucial question is how does alfalfa know when and where to form infection threads and selectively allow only its symbiotic rhizobial cells to enter the infection threads?
The introduction of the fluorescence labeling technology allowed us to focus on the process of the infection thread formation and bacterial entry to the infection threads. We discovered that the formation of infection thread depends on the presence of a bacterial polysaccharide, succinoglycan. We have introduced a jellyfish gene into rhizobial cells so that S. meliloti cells are constitutively producing green fluorescence protein that turns transparent bacterial cells into green under UV light. The green fluorescence protein does not interfere with the ability of the rhizobial cells to symbiosis with its plant host. By comparing symbiosis of rhizobial mutants that fail to produce a bacterial polysaccharide, succinoglycan, to those of their wild type parental strains, we were able to determine that the presence of succinoglycan is crucial for plant to form infection threads. The production of succinoglycan by the rhizobia is regulated by a bacterial sensor protein on the surface of S. meliloti cells, which suggest S. meliloti has the ability to regulate the production of succinoglycan based on the signals it senses in its environment. The signals can be either plant products or changes of environment when S. meliloti cells colonized the surface of alfalfa root hairs cells. All together, our preliminary results suggest that the formation of infection threads could be the result of another signal exchange between S. meliloti and alfalfa. We are currently investigating the role of succinoglycan in eliciting the formation of infection threads inside the alfalfa root hairs with a grant from the National Institute of Health. Visit Webpage
Goldberg, J., Gonzalez, H., Jensen, T.E. and Corpe, W.A. Quantitative analysis of the elemental composition of bacterial polyphosphate bodies using STEM-EDX. Submitted.
Jensen, T.E. and Corpe, W.A. (1999) The study of enigmatic microbial communities. In Enigmatic Microorganisms and Life in Extreme Environments. Seckback, J., editor. Kluwer Academic Publishers, the Netherlands. 187-194.
Goldberg, J. and Jensen, T.E. (1998) Quantitative elemental analysis of the components of Pb exposed cells of Plectonema boryanum using regular and overplus cells: an energy dispersive x-ray spectroscopy study. Proc. 56th Ann. Meeting Microsc. Microanal. 4 (Suppl. 2: Proceedings). San Francisco Press, CA. 262-263.
Seckbach, J., Jensen, T.E., Matsuno, K., Nakamura, H., Walsh, M.M. and Chela-Flores, J. (1998) Is there an alternative path in eukaryogenesis? In Exobiology: Matter, Energy, and Information in the Origin and Evolution of Life in the Universe. Chela-Flores, J. and Raulin, F., eds. Kluwer Academic Publishers. The Netherlands. 235-240.
Torrez, M., Goldberg, J. and Jensen, T.E. (1998) Heavy metal uptake by living and killed cell components in Plectonema boryanum (Cyanophyceae). Microbios 96: 141-147.
Gonzalez, H. and Jensen, T.E. (1998) Nickel sequestering by polyphosphate bodies in Staphylococcus aureus. Microbios 93:179-185.
Goldberg, J., Gonzalez, H., Jensen, T.E. and Corpe, W.A. (1996) Quantitative elemental analysis of bacterial polyphosphate bodies using scanning transmission electron microscopy and energy dispersive x-ray spectroscopy. Proc. 54th Ann. Meeting Microscopy Soc. Amer., San Francisco Press, CA. Pp. 802-803.
Corpe, W.A. and Jensen, T.E. (1996) The diversity of bacteria, eukaryotic cells and viruses in an oligotrophic lake. Applied Microbiology and Biotechnology 46: 622-630.
Jensen, T.E. (1994) Fine structure of elongate polyhedral bodies (carboxysomes) in two Oscillatoria (cyanophyceae) isolates. Microbios. 79: 203-214.
Jensen, T.E. and Corpe, W.A. (1994) Picoplanktonic cyanophytes from three small lakes. Arch. Hydrobiol. Suppl. Algological Studies 75: 149-156.
Jensen, T.E. and Corpe, W.A. (1994) Elemental analysis of non-living particles in picoplankton fractions from oligotrophic lake water. Water Research 28: 901-907.
Jensen, T.E. (1993) A morphometric study of natural and laboratory grown Gloeotrichia sp. Microbios 74: 219-226.
Rai, L.C., Jensen, T.E., and Rachlin, J.W. (1990) A morphometric and x-ray energy dispersive approach to monitoring pH altered cadmium toxicity in Anabaena flos-aquae. Arch. Env. Cont. Tox. 19: 479-487. Visit Webpage
My career as a graduate student, postdoctoral fellow and now as an Assistant Professor has been dedicated to working on disorders that are developmental as their origin. As a graduate student I worked in Dr. Pat Levitt's laboratory examining changes in cortical development due to prenatal exposure to cocaine. It was here that I was first exposed to behavioral disorders in children. We developed an animal model to use to examine what happens to the brain if it is exposed to cocaine in-utero. Cocaine affects the dopaminergic, serotonergic, and neuroepinepherine systems. We chose to examine how cocaine affects two of these systems by examining cortical areas that receive input from one or the other neurotransmitter. We chose to examine the dopaminergic system and the serotonergic system by looking at cellular development in the anterior cingulate cortex, medial prefrontal and primary visual cortex. The anterior cingulate cortex and the medial prefrontal cortex receives a dopaminergic innervation and is important in processing information dealing with learning, memory, attention and social behaviors. Primary visual cortex receives a dense serotonergic innervation and is a primary sensory region. Our work showed that disruption of the developing dopaminergic system leads to changes in outgrowth of dendrites in pyramidal cells. This work led me to want to better understand the dopaminergic system.
Current projects in my laboratory are aimed at better understanding the etiology of schizophrenia. Schizophrenia appears to be a neurodevelopmental disorder affecting the dopaminergic and serotonergic systems. My laboratory uses classical and more modern techniques to better understand the changes in different cortical areas that may bring about the disease. The primary project in the laboratory examines dendritic morphology of projection neurons in the dorsolateral prefrontal cortex an area known to be involved in schizophrenia. We use immunohistochemistry as well as tract tracing methods to perform density and three-dimensional morphological analysis of the neurons.
We are also examining Huntington's Chorea using similar techniques. This is an inherited genetic disorder. This is a progressive disease that can manifest itself at any age but is usually seen in adults.
Future work in the lab is aimed at expanding on the present data for both projects as well as moving into new areas. I am currently working on a grant to get funding to look at cellular architecture in Autism. There are a few brain banks that have tissue available to do postmortem work. We will be submitting a grant to NIH in June to look at dendritic morphology in autism. Visit Website
My research interest is in the area of biologically active phytochemicals. Plants produce a myriad of unusual compounds that are not used for primary metabolism, but are thought to be used for plant survival to various environmental challenges. The biological activities of these phytochemicals, also known as secondary products or natural products, have been harnessed by humans for millennia as medicines. The research conducted in my laboratory examines phytochemicals for novel biological actions. I am specifically interested in phytochemicals with antioxidant activity that may help to prevent cancer and cardiovascular disease.
The Phytochemistry Laboratory at Lehman College is a newly renovated facility in Davis Hall, room 119. It is fully equipped with instruments used for the identification and purification of natural products, including a gas chromatograph (HP 6890 with head space sampler), high performance liquid chromatographs (two Waters 2690 with 996 and one Waters 600 controller with 2487 dual wavelength detector), and a LC-MS (Finnigan Mat MS with Waters 2690 and 486 detector).
The Phytochemical Laboratory maintains collaborations with students of the CUNY Ph. D. Subprogram in Plant Sciences and Biochemistry, as well as with The New York Botanical Garden and The Richard and Hinda Rosenthal Center for Complementary & Alternative Medicine, Columbia University College of Physicians and Surgeons. Visit Website
Dr. Dwight Kincaid is a plant ecologist whose research interests have increasingly become canalized to urban taxa and habitats. He has produced 12 PhDs from his laboratory and currently advises two doctoral students. Current research involves quantitative ecololgical inventory and modeling, floristics, urban riparian forests, invasive species, and tropical dendrochronology. Visit Website
Recent Publications:
Muntzel, M. , Lewis, S. J. and Johnson, A. K. (1996). Anteroventral third ventricle lesions attenuate pressor responses to seratonin in anesthetized rats. Brain Research, 714: 104-110
Muntzel, M:, Thunhorst, R. L. and Johnson, A. K. (1996). Effects of Subfornical Organ Lesions on Sympathetic Nerve Responses to insulin. Hypertension, 29: 1020-1024
Muntzel, M., Abe, A. and Petersen, J. S. (1997). Effects of adrenergic, cholinergic and autonomic blockade on metformin-induced depressor responses in spontaneously hypertensive rats. Journal of Pharmacology and Experimental Therapeutics, 281: 618-623
Muntzel, M., Barrett, S. and Hamidou, 1. (1998). Metformin attenuates salt-induced hypertension in spontaneously hypertensive rats (SHR). Hypertension, in press.
Muntzel, M., Nyeduala, B. and Barrett, S. (1998). High dietary salt enhances acute depressor responses to metformin. Submitted to American Journal of Hypertension. Visit Website
Fish Ecology - Population Dynamics and Niche Overlap
Fish Systematics - Phylogeny and Cytogenetics
Aquatic Ecology
Estuarine Ecology
Fish and Invertebrate sub-fossils from an archaeological site, Ghazi Shah, Pakistan
The long-range activities of this laboratory are to understand the phylogenetic relationships, interactions, and general life histories of both freshwater and marine aquatic organisms. Among the techniques employed are the use of cytogenetics in studies of the interrelationships of monophyletic genera and species, mathematical models for evaluating population dynamics and life histories, and the development of new approaches for the understanding of resource partitioning in aquatic environments. We will also be exploring the use of high-end computer graphics for studies of the comparative morphology of aquatic organisms, and to develop virtual models for studies of form and function. Visit Website
Research in the Wurtzel laboratory is directed at solving a global health problem of vitamin A deficiency that affects 250,000,000 children worldwide and leads to increased childhood mortality. World wide Vitamin A deficiency is linked to diets deficient specifically in pro-vitamin A carotenoids. To alleviate this public health problem, our research is focused on the use of genomic tools and natural plant diversity to understand how crop plants control their chemistry; for a plant to make novel medicinal compounds or vitamins requires expression of genes controlling specific biosynthetic pathways. To harness the untapped potential of plants to provide nutraceuticals or even yet to be discovered drugs to treat disease or new sources of energy, requires investigation of biosynthetic pathways using tools of molecular biology, genomics, bioinformatics, chemistry, and biochemistry, combined with classical botanical phylogenetic studies. Current research in the Wurtzel laboratory incorporates such tools to investigate carotenoid accumulation in important food crops such as maize, wheat, and rice. The present goal is to understand, at the molecular and biochemical level, how plants regulate the biosynthesis and accumulation of provitamin A carotenoids in the seed endosperm tissue. This research is leading to improved strategies for predicting plant chemistry and enhancing provitamin A carotenoid content.
ROP small GTPase signaling in plant nutrient and hormone responses
Small GTPases (monomeric GTP-binding proteins) are pivotal molecular switches in signal transduction that controls various cellular processes such as cell polarity, cytoskeletal organization and cell cycle in eukaryotic organisms. There are two forms of GTPases. The GDP-bound form is inactive, but in response to extracellular signals, GDP is exchanged with GTP, resulting in the formation of GTP-bound, active form that leads to the activation of downstream signaling events (Figure 1). Once activated, GTP is hydrolyzed and thus the GTP-bound form is converted to the GDP-bound form, switching off the signal. In mammals, the Ras superfamily of signaling small GTPases consists of Ras and Rho family.
Plants are non-motile, photoautotrophic organisms and therefore they must respond and adapt to constantly changing environments (such as light, temperature, water, CO2 and nutrients). Plants are not only the major food suppliers for human nutrition, but also provide a good model system to study GTPase signaling. However, in plants there is no Ras homolog. Instead, plants possess a Rho subfamily termed ROP that is distinct from the other three subfamilies: RHO, CDC42 and RAC. In Arabidopsis thaliana, the model plant also called “plant Drosophila”, there are eleven members of ROP, each with distinct and somewhat overlapping expression patterns and functions. Accumulating evidence suggest that in plants, ROP probably acts as Ras and Rho GTPases in the control of cell morphogenesis, cytoskeletal organization, and response to hormones and biotic and abiotic stresses. My current research is focused on the ROP-controlled signaling network through which plants constantly monitor and precisely respond to the fluctuations of the environments. Two specific aspects of the signaling are addressed in parallel: cytoskeletal organizations in the cell cortex and control of gene expression in the nucleus.
Figure 1. ROP GTPase as a molecular switch in hormone and nutrient signaling in plants. Our lab uses a combination of genetic, genomic, molecular and cellular tools to dissect signaling pathways of ROP GTPase-controlled hormone and nutrient balance responses. Shown on the right is the rop10-1 mutant which is more sensitive to the inhibition of seedling growth by ABA, compared to the Arabidopsis wild-type (Ws).
Microtubule and microfilament cross-talk during root hair tip growth.Root hairs are long, thin tubular-shaped outgrowths from root epidermal cells called trichoblasts. Although they are not essential for plant growth and development, root hairs are important for the anchorage of the root to the soil and the uptake of water and nutrients by dramatically increasing the root surface areas. Importantly, root hair tip growth is one of the few extreme types of highly dynamic, polarized growth and has been used as a unique model system for the study of cell polarity. This dynamic process requires the well-organized cytoskeletons such as microfilaments and microtubules, to facilitate active organelle and vesicle transport. Constitutive activation of ROP2 and other members of ROP GTPases have been shown to disrupt the root hair tip growth, likely as a result of the alteration of microtubule and microfilament organizations. To identify novel components of the ROP2-regulated microtubule and microfilament cross-talk, we have initiated a forward genetic screen. We are using molecular genetic, cell biological and other tools to dissect the molecular mechanisms by which ROP2 integrates signals or signaling pathways to coordinate microtubule and microfilament organizations.
ROP10 small GTPase-gated ABA signaling. Abscisic acid (ABA) is a “master” stress hormone that modulates a variety of growth and developmental processes and stress responses, including seed dormancy/germination, stomatal movement, and drought, salt and cold responses. Although there are quite a large number of genes found to be involved in ABA responses, very few of them are connected in a signal transduction pathway. We first reported that gain-of-function mutants of ROP2 altered ABA responses. Using a loss-of-function mutant, we then showed that ROP10 small GTPase is a negative regulator specifically involved in ABA responses (Figure 1). Furthermore, the plasma membrane localization is required for ROP10 function. However, the signaling components regulated by ROP10 remain to be identified. Therefore, one of our goals is to understand what specific ABA signaling pathway(s) are switched on/off by ROP10, leading to the changes of gene expression in the nucleus.
Figure 2. C- and N-dependent activation of gene expression in S deficiency response. The putative thioglucosidase gene promoter is fused to the GUS reporter gene, and transgenic plants expressing the fusion construct are used in the C, N and S interaction study. This gene is activated by S deficiency predominantly in the root tissues, dependent on the availability of C which shows a synergistic interaction with N. For more details, please read a recent paper by Dan et al. (2007) in Plant Molecular Biology