Adaptive Evolution of Nearctic Deepwater Fish Vision: Implications for Assessing Functional Variation for Conservation.

Intraspecific functional variation is critical for adaptation to rapidly changing environments. For visual opsins, functional variation can be characterized in vitro and often reflects a species' ecological niche but is rarely considered in the context of intraspecific variation or the impact of recent environmental changes on species of cultural or commercial significance. Investigation of adaptation in postglacial lakes can provide key insight into how rapid environmental changes impact functional evolution.

Phagocyte dynamics in a highly regenerative urochordate: insights into development and host defense.

Phagocytosis is a cellular process by which particles and foreign bodies are engulfed and degraded by specialized cells. It is functionally involved in nutrient acquisition and represents a fundamental mechanism used to remove pathogens and cellular debris. In the marine invertebrate chordate Botryllus schlosseri, cell corpse engulfment by phagocytic cells is the recurrent mechanism of programmed cell clearance and a critical process for the successful execution of asexual regeneration and colony homeostasis.

Asexual propagation and regeneration in colonial ascidians.

Regeneration is widely distributed among the metazoans. However, clear differences exist as to the degree of regenerative capacity: some phyla can only replace missing body parts, whereas others can generate entirely new individuals. Ascidians are animals that possess a remarkable regenerative plasticity and exhibit a great diversity of mechanisms for asexual propagation and survival.

Suppression of programmed cell death regulates the cyclical degeneration of organs in a colonial urochordate.

The survival of animal tissues and organs is controlled through both activation and suppression of programmed cell death. In the colonial urochordate Botryllus schlosseri, the entire parental generation of zooids in a colony synchronously dies every week as the asexually derived generation of buds reaches functional maturity. This process, called takeover, involves massive programmed cell death (PCD) of zooid organs via apoptosis followed by programmed removal of cell corpses by blood phagocytes within approximately 1 day.

Identification of a novel gene involved in asexual organogenesis in the budding ascidian Botryllus schlosseri.

Development via regeneration or budding shares some known genetic pathways with embryogenesis, but no concerted effort has been made to identify genes unique to asexual development. We have identified a novel gene that plays a role in cyclical bud formation and asexual organogenesis in the colonial ascidian Botryllus schlosseri. Athena mRNA is transcribed at high levels during the 24- to 36-hr interval of programmed cell death and new bud initiation at the conclusion of the budding cycle (takeover).

Cyclical generation and degeneration of organs in a colonial urochordate involves crosstalk between old and new: a model for development and regeneration.

Botryllus schlosseri is a colonial marine urochordate in which all adult organisms (called zooids) in a colony die synchronously by apoptosis (programmed cell death) in cyclical fashion. During this death phase called takeover, cell corpses within the dying organism are engulfed by circulating phagocytic cells. The "old" zooids and their organs are resorbed within 24-36 h (programmed cell removal).

A morphological study of nonrandom senescence in a colonial urochordate.

Botryllus schlosseri is a clonally modular ascidian, in which individuals (zooids) have a finite life span that is intimately associated with a weekly budding process called blastogenesis. Every blastogenic cycle concludes with a synchronized phase of regression called takeover, during which all zooids in a colony die, primarily by apoptosis, and are replaced by a new generation of asexually derived zooids. We have previously documented that, in addition to this cyclical death phase, entire colonies undergo senescence during which all asexually derived individuals in a colony, buds and zooids, die in concert.

Introduction of high-alcohol beer in Ontario: preliminary observations on its use by underage drinkers.

Preliminary data are reported on the use of high-alcohol beer by underage drinkers in Ontario. Students in grades 11 and 12 with a valid driver's licence completed a questionnaire between January and May, 1994 (i.e.

16S mitochondrial ribosomal RNA degradation is associated with apoptosis.

The use of mitochondrial RNA as an indicator of apoptosis was investigated. Exposure of HA-1 fibroblastic cells to 10 micromol H(2)O(2) per 10(7) cells induced nuclear fragmentation, cell shrinkage, and internucleosomal DNA fragmentation, all characteristics of apoptosis. RNA extracted from control and apoptotic cultures, and analyzed by Northern blot hybridization, revealed a significant increase in the degradation of mitochondrial 16S ribosomal RNA (rRNA) that was associated with apoptosis.

Evidence for transcriptional modulation but not acid phosphatase expression during programmed cell death in the colonial tunicate Botryllus schlosseri.

Botryllus schlosseri is a clonally modular ascidian in which asexually derived adults (zooids) exhibit developmental synchrony. At the conclusion of the blastogenic (asexual) cycle every 5 days at 21 degrees C, all zooids within a colony die simultaneously in 24 hours and are replaced by a new asexual generation of zooids. This cyclical process, called takeover, involves the selective destruction of the zooid's visceral tissues which include the pharynx, esophagus, stomach, intestine, endostyle, neural complex and heart, whereas bud tissues and mesenchymal components (muscle and blood cells) remain unaffected.

Isolation of biologically functional RNA during programmed death of a colonial ascidian.

The blastogenic (asexual) cycle of the colonial ascidian Botryllus schlosseri (Tunicata, Ascidiaceae) concludes in a cyclical phase of programmed cell and zooid death called takeover, in which all asexually derived adults die synchronously by apoptosis. The characterization of developmentally regulated genes whose expression patterns are selectively modulated during this process could pave the way to understand how this model organism dies. However, isolation of biologically functional RNA in this and other colonial ascidians with conventional phenol/chloroform-based procedures is hampered by extensive contamination of RNA preparations by pigments.

A morphological and immunohistochemical study of programmed cell death in Botryllus schlosseri (Tunicata, Ascidiacea).

The blastogenic cycle of the colonial ascidian Botryllus schlosseri concludes in a phase of selective cell and zooid death called takeover. Every week, all asexually derived parental zooids synchronously regress over a 30-h period and are replaced by a new generation. Here we document the sequential ultrastructural changes which accompany cell death during zooid degeneration.

A cyclical, developmentally-regulated death phenomenon in a colonial urochordate.

Botryllus schlosseri is a colonial ascidian whose asexually derived, clonally modular systems of zooids exhibit developmental synchrony. The blastogenic cycle culminates in a phase of programmed cell and zooid death called takeover, in which all functional zooids die over a 30 hr period, and are replaced by a new generation of individuals. Because of the weekly recurrence and magnitude of visceral death in this model organism, we have begun to characterize the mechanisms that govern takeover.

Evidence for a programmed life span in a colonial protochordate.

The variety of theories that have attempted to define the mechanisms of aging and life span can be broadly divided into two alternative but nonexclusive viewpoints. The first stipulates that random changes of cellular and molecular structures lead to death following progressive "wear and tear." The second argues that life span is, at least in part, genetically programmed, and therefore aging may also result from time-dependent intrinsic processes.

The role of T cell receptors in non-MHC-restricted cytotoxicity.

The relationship between natural killer cells (NK) and cells of the T lineage has been obscured by the existence of poorly characterized clones of presumed NK origin. We have analyzed nine of these cloned cell lines displaying varying levels of cytotoxic activity against NKS YAC-1 target cells for rearrangement and expression of the genes encoding the alpha, beta, and gamma chains of the T cell receptor for antigen. Rearrangements at both the TcR beta and gamma loci were detected in all clones often at both alleles.

An expanded population of natural killer cells in mice with severe combined immunodeficiency (SCID) lack rearrangement and expression of T cell receptor genes.

Mice with severe combined immunodeficiency syndrome (SCID) exhibit an impairment in both T and B cell maturation, whereas myelopoiesis remains unaffected. We report here that spleens from SCID mice have undergone phenotypic expansion of cells bearing the NK-2 and asialo GM1 markers (70-80%) characteristic of NK cells and this expansion is accompanied by a 3-4-fold enrichment in NK cytolytic activity over their normal C.B-17 littermates.

T cell receptor gene rearrangements in cells with natural killer activity in the mouse.

Cell-mediated recognition can operate at different levels of complexity and specificity based largely on the time of appearance of effector mechanisms during the course of evolution. Antigen-specific cytotoxic T lymphocytes require both T cell receptor genes and lectin-like cell adhesion molecules (LFA-1, LFA-2, lymphocyte function-associated) to initiate and maintain stable effector target cell conjugates. Natural killer (NK) cells, on the other hand, do not require expression of T cell receptor genes in the recognition and killing of tumor cells and virally infected cells.

Segregation of the NK-sensitive phenotype in human x mouse somatic cell hybrids reveals separate genetic control of recognition and postrecognition determinants.

In an attempt to investigate the nature of tumor cell-derived membrane surface determinants involved in natural killer cell (NK) recognition or postrecognition events, we have constructed human X mouse interspecies somatic cell hybrids. Highly NK-sensitive (NKs) human tumor cells were fused with NK resistant (NKr) mouse fibroblasts (LMTK-) in polyethylene glycol and selected in hypoxanthine/aminopterin/thymidine medium and ouabain. Hybrids generated from NKs erythroleukemia cells (K-562) or NKs retinoblastoma cells (Y-79) with LMTK- displayed an intermediate NK-sensitive phenotype.

Gene rearrangement in cells with natural killer activity and expression of the beta-chain of the T-cell antigen receptor.

The mammalian host defence system can be divided broadly into adaptive and non-adaptive immunity. Adaptive immunity is acquired and is mediated by B and T lymphocytes. Non-adaptive immunity is mediated in part by a small subclass of heterogeneous peripheral blood mononuclear cells.

Natural killer cell-mediated lysis involves an hydroxyl radical-dependent step.

The role of oxygen radicals in lysis of K562 target cells by human natural killer (NK) cells was determined by addition of scavengers of these free radicals. Lysis was greatly reduced under hypoxic conditions. Superoxide dismutase and cytochrome c, scavengers of superoxide anions, and catalase and scavengers of hypochlorite had no effect on lysis.