▪ Abstract Animals may be camouflaged by a coloration that matches their surroundings or by a combination of color and shape. Some species make themselves conspicuous and rely upon bold and bright coloration as a means of warning off their potential predators. Population biologists have accumulated information on the adaptive significance of coloration for a large number of species. To elucidate the mechanisms underpinning such natural selection events, it is necessary to understand the visual systems of interacting organisms. Molecular genetic analyses on the human opsin genes by Nathans and his colleagues made it possible to characterize the opsin genes of various vertebrates. A striking level of diversity in the opsin gene sequences reflects adaptive responses of various species to different environments. Comparative analyses of opsins reveal that gene duplications and accumulation of mutations have been important in achieving that diversity. The analyses also identify amino acid changes that are potentially important in controlling wavelength absorption by the photosensitive molecules, the visual pigments. These hypotheses can now be rigorously tested using tissue culture cells. Thanks to the molecular characterization of the opsin genes, it is now possible to study the types of opsins associated with certain environmental conditions. Such surveys will provide important first molecular clues to how animals adapt to their environments with respect to their coloration and behavior.
We have isolated and sequenced genes from the blind cave fish, Astyanaxfasciatus, that are homologous to the human red and green visual pigment genes. The data strongly suggest that, like human, these fish have one red-like visual pigment gene and multiple green-like visual pigment genes. By comparing the DNA sequences of the human and fish visual pigment genes and knowing their phylogenetic relationship, one can infer the direction of amino acid substitutions in the red and green visual pigments. The results indicate that the red pigments in human and fish evolved from the green pigment independently by identical amino acid substitutions in only a few key positions.
The motility of cilia and flagella is powered by dynein ATPases associated with outer doublet microtubules. However, a flagellar kinesin-like protein that may function as a motor associates with the central pair complex. We determined that Chlamydomonas reinhardtii central pair kinesin Klp1 is a phosphoprotein and, like conventional kinesins, binds to microtubules in vitro in the presence of adenosine 5 -[,␥-imido]triphosphate, but not ATP. To characterize the function of Klp1, we generated RNA interference expression constructs that reduce in vivo flagellar Klp1 levels. Klp1 knockdown cells have flagella that either beat very slowly or are paralyzed. EM image averages show disruption of two structures associated with the C2 central pair microtubule, C2b and C2c. Greatest density is lost from part of projection C2c, which is in a position to interact with doublet-associated radial spokes. Klp1 therefore retains properties of a motor protein and is essential for normal flagellar motility. We hypothesize that Klp1 acts as a conformational switch to signal spoke-dependent control of dynein activity.Chlamydomonas ͉ cilia ͉ motility ͉ radial spoke ͉ RNA interference
Serotonin (5HT) plays major roles in the physiological regulation of many behavioral processes, including sleep, feeding, and mood, but the genetic mechanisms by which serotonergic neurons arise during development are poorly understood. In the present study, we have investigated the development of serotonergic neurons in the zebrafish. Neurons exhibiting 5HT-immunoreactivity (5HT-IR) are detected from 45 h postfertilization (hpf) in the ventral hindbrain raphe, the hypothalamus, pineal organ, and pretectal area. Tryptophan hydroxylases encode rate-limiting enzymes that function in the synthesis of 5HT. As part of this study, we cloned and analyzed a novel zebrafish tph gene named tphR. Unlike two other zebrafish tph genes (tphD1 and tphD2), tphR is expressed in serotonergic raphe neurons, similar to tph genes in mammalian species. tphR is also expressed in the pineal organ where it is likely to be involved in the pathway leading to synthesis
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