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  • Cell & Developmental Biology  (6)
  • genome organization  (1)
  • 1
    ISSN: 1573-5028
    Keywords: Arabidopsis ; cysteine tRNA genes ; genome organization ; in vitro transcription ; Nicotiana
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have recently characterized Nicotiana cytoplasmic (cyt) tRNAGCA Cys as novel UGA suppressor tRNA. Here we have isolated its corresponding (NtC1) and a variant (NtC2) gene from a genomic library of Nicotiana rustica. Both tRNACys genes are efficiently transcribed in HeLa cell nuclear extract and yield mature cyt tRNAsCys. Sequence analysis of the upstream region of the RAD51 single-copy gene of the Arabidopsis thaliana genome revealed a cluster of three tRNACys genes which have the same polarity and comprise highly similar flanking sequences. Of the three Arabidopsis tRNACys genes only one (i.e. AtC2) appears to code for a functional gene which exhibits an almost identical nucleotide sequence to NtC1. These are the first sequenced nuclear tDNAsCys of plant origin.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 173 (1982), S. 137-158 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The function of major features of the skull of Varanus exanthematicus during feeding was examined using cineradiography and electromyography. During the initial stages of feeding, Varanus grabs and orients a prey item in the mouth with no mastication, tearing of the prey, or killing bite. Ingestion is through a highly stereotyped movement, inertial feeding. The tongue plays no role in food transport. Once the prey is in the pharyngeal region, the hyoid apparatus squeezes the prey into the esophagus and stomach. Activity of jaw adducting muscles during prey orientation and inertial feeding is strikingly different. In prey orientation, the adductor musculature is active over long periods, and intermuscular differentiation and unilateral activity are common. During these phases the musculature is producing force against the resistance of the prey item held between the teeth. In inertial feeding, the jaw musculature functions to close the jaws rapidly against little resistance. A consistent pattern of intramuscular differentiation is present, with some portions of the musculature being active during both jaw opening and closing. Activity of the Mm. adductor mandibulae externus and pterygoideus is indistinguishable. Neither meso- nor metakinetic movement was observed during inertial feeding; resolution of interacranial movement was less certain during power phases. The quadrate moved during jaw opening and closing in inertial feeding. However, its movement was not linked with that of the palatomaxillary segment. These data are discussed in three contexts: cranial kinesis, intramuscular differentiation, and the mechanics of whole muscles.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 187 (1986), S. 261-287 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The morphology and function of the tongue and hyoid apparatus in Varanus were examined by anatomical and experimental techniques. Morphological features unique to Varanus include a highly protrusible tongue that has lost a roughened dorsal surface, an exceptionally strong and mobile hyobranchial apparatus, a well-defined joint between the ceratohyal and anterior process, and a series of distinct muscles inserting at the anterior hyobranchial region. Varanus is also unusual among lizards in a number of feeding behaviors; it ingests prey entirely by inertial feeding, as the tongue does not participate in food transport. Further specializations include an increased reliance on hyobranchial movements in drinking and pharyngeal packing and compression. The long, narrow tongue is most likely related to the mechanics of tongue protrusion; the increased amount, strength, and complexity of hyobranchial movement is related to the fact that the hyobranchium in Varanus replaces the tongue in many functions. Previous hypotheses for the origin of these adaptations are discussed, and the difficulties of attributing these specializations to any specific scenario of adaptation or constraint are emphasized.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 205 (1990), S. 307-324 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Tongue musculature in 24 genera of snakes was examined histologically. In all snakes, the tongue is composed of a few main groups of muscles. The M. hyoglossus is a paired bundle in the center of the tongue. The posterior regions of the tongue possess musculature that surrounds these bundles and is responsible for protrusion. Anterior tongue regions contain hyoglossal bundles, dorsal longitudinal muscle bundles and vertical and transverse bundles, which are perpendicular to the long axis of the tongue. The interaction of the longitudinal with the vertical and horizontal muscles is responsible for bending during tongue flicking. Despite general similarities, distinct patterns of intrinsic tongue musculature characterize each infraorder of snakes. The Henophidia are primitive; the Scolecophidia and Caenophidia are each distinguished by derived characters. These derived characters support hypotheses that these latter taxa are each monophyletic. Cylindrophis (Anilioidea) is in some characters intermediate between Booidea and Colubroidea. The condition in the Booidea resembles the lizard condition; however, no synapomorphies of tongue musculature confirm a relationship with any specific lizard family. Although the pattern of colubroids appears to be the most biomechanically specialized, as yet no behavioral or performance feature has been identified to distinguish them from other snakes.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 196 (1988), S. 157-171 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The morphology of the tongue of agamid lizards is reviewed and discussed in the context of its functional and phylogenetic significance. It is shown that in several features, including the development of the central musculature of the tongue into a ring muscle and the presence of a genioglossus internus muscle in adults, the tongue in most agamids is derived relative to that in other squamates. In some features, such as the vertical connective tissue septa, agamids share primitive features with Sphenodon. Some conditions found in agamids are also found in anoline iguanids. Two genera, Uromastyx and Leiolepis, differ significantly from other agamids in intrinsic tongue musculature.The functional significance of the unique tongue morphology is that agamids utilize a different mechanism of tongue protrusion from that of other lizards. This mechanism involves the production of force against the lingual process, leading to an anterior slide of the tongue, and is detailed in this paper. Finally, I discuss the mechanical basis for the transformation series of tongue protrusion mechanisms from agamids to chamaeleonids. It is suggested that the mechanism of tongue protrusion in chamaeleonids is not unique, but is a highly derived state of the condition found in agamids.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 215 (1993), S. 119-149 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The pattern of onset and general rate of cranial ossification are compared in two marsupials, Monodelphis domestica (Didelphidae) and Macropus eugenii (Macropodidae). In both species a similar suite of bones is present at birth, specifically those surrounding the oral cavity and the exoccipital, and in both postnatal events follow a similar course. The facial skeleton matures more rapidly than the neurocranium, which is characterized by an extended period of ossification. Most dermal bones begin ossification before most endochondral bones. Endochondral bones of the neurocranium are particularly extended in both the period of onset of ossification and the rate of ossification. These data confirm suggestions that morphology at birth is conservative in marsupials and we hypothesize that the pattern of cranial osteogenesis is related to two distinct demands. Bones that are accelerated in marsupials are correlated with a number of functional adaptations including head movements during migration, attachment to the teat, and suckling. However, the very slow osteogenesis of the neurocranium is probably correlated with the very extended period of neurogenesis. Marsupials appear to be derived relative to both monotreme and placental mammals in the precocious ossification of the bones surrounding the oral cavity, but share with monotremes an extended period of neurocranial osteogenesis. © 1993 Wiley-Liss, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 222 (1994), S. 149-173 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Development of craniofacial muscles of Monodelphis domestica (Marsupialia, Didelphidae) is described. In a period of 4-6 days all craniofacial muscles in M. domestica progress from myoblast condensation, to striated myofibers that are aligned in the direction of adult muscles and possess multiple, lateral nuclei. This process begins 1 to 2 days before birth and continues during the first few days after birth. Compared to other aspects of cranial development, muscle development in M. domestica is rapid. This rapid and more or less simultaneous emergence of craniofacial muscles differs from the previously described pattern of development of the cranial skeleton in marsupials, which displays a mosaic of acceleration and deceleration of regions and individual elements. Unlike the skeletal system, craniofacial muscles show no evidence of regional specialization during development. M. domestica resembles eutherian mammals in the relatively rapid and more or less simultaneous differentiation of all craniofacial muscles. It differs from eutherian taxa in that most stages of myogenesis occur postnatally, following the onset of function. The timing of the development of muscular and skeletal structures is compared and it is concluded that the relatively early development of muscle is not reflected by any particular acceleration of the differentiation or growth of skeletal structures. Finally, the difficulties in accounting for complex internal arrangements of muscles such as the tongue, given current models of myogenesis are summarized. © 1994 Wiley-Liss, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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