Welcome to the Unguez Lab
Research in the Unguez lab focuses on understanding how intrinsic and extrinsic factors influence the properties expressed by excitable cells that make up the neuromuscular system: skeletal muscle fibers and motor neurons. We place a special emphasis on studying the mechanisms by which these cells regulate the maintenance and plasticity of their diverse biochemical, morphological, and physiological characteristics. To address fundamental questions regarding the cellular and molecular mechanisms regulating the differentiated phenotype of neuromuscular components, we have been studying electric fish.
Electric fish offer a unique case in the study of skeletal muscle plasticity in that during normal development, some skeletal muscle fibers lose their contractile apparatus and convert into the non-contractile, current-producing cells of the electric organ (EO) called electrocytes. Mature electrocytes retain a partial muscle phenotype and this capacity to maintain some muscle genes while down-regulating others is a most favorable, yet intriguing, model system to further our understanding of processes that control the expression of distinct protein systems in the myogenic program.
Our work using electric fish as our model system has led us into several research areas that use different experimental approaches and techniques that address fundamental questions regarding the mechanisms underlying the maintenance of the differentiated components of neuromuscular system and its evolution into distinct motor systems. Areas of active research in our lab include:
• Regulation of muscle gene expression in muscle-like electrocytes
• Neuronal control of the myogenic program in muscle and electric organ
• Differentiation of motor neuronal diversity in electric fish
• Mechanisms of tissue regeneration in electric fish
• Isolation and characterization of myogenic stem cells from electric fish
Regulation of muscle gene expression in muscle-like electrocytes
Given that activation of the vertebrate muscle program is under transcriptional control, and that in mature electrocytes some muscle genes are down regulated while others continue to be expressed, our aim has been to characterize the expression of the MyoD family of myogenic regulatory factors (MRFs) and their co-regulators MEF2 and Id genes in muscle fibers and electrocytes (Kim et al., 2004; Kim et al., 2008). We reason that the level to which the muscle program is manifested in these cells (Cuellar et al., 2006) might be associated with distinct expression levels of the MRFs and/or MRF co-factors. Current studies center on the characterization of MRFs and MEF2 gene products at the transcript and protein levels in the mature and developing stages using S. macrurus-specific probes.
Neuronal control of the myogenic program in muscle and electric organ
It is well established that the nervous system has significant influence on the skeletal muscle phenotype by regulating the kind and amount of specific muscle proteins. Studies have also demonstrated that the neural influence is exerted largely through the electrical activation pattern imposed on the muscles. However, the specific signaling pathways and regulatory molecules that link electrical activity to changes in muscle-specific gene expression remain largely unknown. Similar to skeletal muscle fibers, the electrocyte phenotype is influenced by neuronal input (Unguez and Zakon, 1998). Removal of neuronal input results in the detection of sarcomeric proteins and formation of sarcomeres de novo (Unguez and Zakon, 1998). Hence, manipulation of the EO phenotype provides an excellent model to study the neural regulation of clearly defined subsets of muscle proteins. Current studies include manipulations of neuronal input to determine the nature of the neuronal signal (i.e., activity-dependent versus activity-independent factors). Considerable effort is also focused on elucidating the signaling pathways that may function as mediators in the regulation of muscle specific proteins by neural input.
Differentiation of motor neuronal diversity in electric fish
Mature electrocytes are innervated by specialized electromotoneurons (EMNs) believed to derive from spinal and/or cranial motor neurons, and which exert a continuous activation pattern that ranges from 50 to 200 Hz. How electrocytes and EMNs evolved from their precursor cells to form a functional electromotor system is unknown. Ultimately, our goal is to understand the mechanisms underlying the differentiation of distinct phenotypic fates among muscle-derived cells and specific synapse formation by their corresponding innervating motor neurons in S. macrurus. Current focus is on the characterization of the biochemical and morphological properties of mature EMNs and their formation during tail regeneration. These data will be instructive in studies designed to elucidate the patterns of synapse formation in the both motor systems during tail regeneration.
Mechanisms of tissue regeneration in electric fish
Electric fish are among the most highly regenerative teleost species known. S. macrurus can inexhaustibly regenerate its spinal cord dermis, skeleton, vessels, muscle, and electric organ following repeated amputations without scar formation. Restoration of tissues amputated in S. macrurus occurs through a blastema-dependent regeneration process. Data from our ongoing immunolabeling and intracellular dye tracing studies are consistent with a muscle and EO regeneration process in which myogenic satellite cells respond to tail amputation by reentry to the cell cycle and contribute to the restoration of these myogenic tissues. Since these results depart from the cell dedifferentiation-dependent regeneration commonly reported in other vertebrates, current studies include evaluating the incidence of cell dedifferentiation to determine the contribution of this process to the robust regeneration capacity of S. macrurus.
Isolation and characterization of myogenic stem cells from electric fish
Skeletal muscle and electric organ contain “satellite-like” cells that proliferate following tail amputation and contribute to the regeneration of these tissues, indicating the presence of pre-existing myogenic precursor cells in adult tissues. Current studies aim to characterize the biological function of these muscle precursor cells after injury and determine their role in the robust regeneration response by S. macrurus. These studies include the isolation of undifferentiated single cells from adult and regenerating tissues to test their capacity to replicate and differentiate into multinucleated muscle fibers.