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11.
Synopsis The early development of the southern mouthbrooder,Pseudocrenilabrus philander, is documented from activation until the early stages of the juvenile period. The duration of the embryonic period is about 14 days at 25°C. Development is direct and there is accelerated exogenous feeding into the embryonic period. The pattern of development and the timing of ontogenetic events and structure formation are a reflection of both internal and external environmental conditions. During mouthbrooding, oxygen uptake is facilitated by embryonic respiratory plexuses and flapping of the pectoral fins. At the time of first release from the buccal cavity, the embryos are in an advanced state of development. The switch-over from the temporary embryonic respiratory system to the adult branchial system has occurred. The yolksac serves as a supplemental source of nutrition as the embryos develop their external food-gathering abilities. The skeletal and sensory systems are sufficiently developed to allow the young to return to the safety of the female's buccal cavity. Pigmentation may provide disruptive colouration. The rate and pattern of development of another mouthbrooding cichlid,Oreochromis mossambicus, is similar to that ofP. philander despite their phylogenetic differences, and may be a consequence of similar life-history styles. 相似文献
12.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
13.
14.
J A Taylor C J Bruton J K Anderson J E Mole F C De Beer M L Baltz M B Pepys 《The Biochemical journal》1984,221(3):903-906
The rat serum protein that undergoes Ca2+-dependent binding to pneumococcal C-polysaccharide and to phosphocholine residues, and that is evidently a member of the pentraxin family of proteins by virtue of its appearance under the electron microscope, has been variously designated as rat C-reactive protein (CRP) [de Beer, Baltz, Munn, Feinstein, Taylor, Bruton, Clamp & Pepys (1982) Immunology 45, 55-70], 'phosphoryl choline-binding protein' [Nagpurkar & Mookerjea (1981) J. Biol. Chem. 256, 7440-7448] and rat serum amyloid P component (SAP) [Pontet, D'Asnieres, Gache, Escaig & Engler (1981) Biochim. Biophys. Acta 671, 202-210]. The partial amino acid sequence (45 residues) towards the C-terminus of this protein was determined, and it showed 71.7% identity with the known sequence of human CRP but only 54.3% identity with human SAP. Since human CRP and SAP are themselves approximately 50% homologous, the level of identity between the rat protein and human SAP is evidence only of membership of the pentraxin family. In contrast, the much greater resemblance to human CRP confirms that the rat C-polysaccharide-binding/phosphocholine-binding protein is in fact rat CRP. 相似文献
15.
In vivo synthesised protein with norleucine occupying one half of the normal methionine loci was prepared using a methionine auxotroph of Escherichia coli K12. The extent of charging of the analogue onto both tRNAmet species and subsequent incorporation into soluble protein was monitored with a double-labelling system comprising [G-3H]norleucine and [35S]methionine. Further experiments established that norleucine can be formylated in vivo once charged onto the initiator tRNAfmet. An N-terminal analysis of the crude soluble protein revealed that formylnorleucyl-tRNAfmet can initiate protein synthesis and that the formyl group is then removed from the nascent polypeptide. We were also led to conclude that the N-terminal methionine-amino peptidase does not recognise the analogue in this position. Slow growth rates on the methionine analogue have been partly attributed to limiting levels of charged tRNAmmet, resulting in turn from the inefficiency of norleucine charging by methionyl-tRNA synthetase. Finally no evidence has been found for the production of aberrant protein as a result of norleucine incorporation, implying that limited growth on the analogue is due to its inability to replace methionine as the precursor of S-adenosyl methionine. 相似文献
16.
Methionyl-tRNA synthetase from Escherichia coli. Primary structure of the active crystallised tryptic fragment 总被引:14,自引:0,他引:14
A 3300-base segment of Escherichia coli chromosomal DNA, cloned into pBR322, will complement a methionine auxotroph in which the lesion is a defective methionyl-tRNA synthetase with a much reduced affinity for methionine. Crude extracts of these transformants contain elevated levels of a protein which has a subunit molecular weight of 66 000, methionyl-tRNA synthetase aminoacylation activity in vitro and which cross-reacts with anti-(methionyl-tRNA synthetase) antibodies. This polypeptide is very slightly larger than the well-characterised and crystallised tryptic fragment of methionyl-tRNA synthetase. A DNA sequence of 1750 residues at one end of the cloned insert codes for a non-terminated open reading frame in which we can locate a large number of methionyl-tRNA synthetase tryptic and chymotryptic peptides. We have also sequenced 300 nucleotides upstream of this coding segment where we find a large invert repeat in the putative methionyl-tRNA synthetase promoter region. 相似文献
17.
The rufous colouring on the feathers of the under parts of adult bearded vultures Gypaetus barbatus , studied by scanning electron microscopy, energy-dispersive X-ray microanalysis and X-ray diffraction analysis, is caused by an external deposit of iron oxide in the ferrihydrite state. Unstained feathers, e.g. in captive birds, are pure white. The feathers of young birds have similar coatings of iron oxide to those of adults, but because the feathers are pigmented pale to dark brown (dependent on age), the rusty colour is partly or totally obscured. The intensity of the colour in adult birds varies between individuals and within individuals with time; the more worn the feathers the more iron oxide they can hold. After heavy rainfall up to 30% of adult birds can become appreciably paler. Birds take about 6 days (range–9 days) to regain normal colouring. Iron oxide accumulates mainly in the axes of shafts and barbs, barbs and barbules and barbules and hamuli, and forms blob-like deposits at the ends of barbs and barbules on the outer layers of feathers. Iron oxide is probably acquired passively when bearded vultures come into contact with deposits in caves and on ledges on cliffs. The colour is then spread by preening. Iron oxide imparts camouflage to adult birds, but also reduces wear on the outer layer of feathers, makes feathers more rigid and probably helps control ectoparasites. 相似文献
18.
The distribution of the genus SelenopeltisHawle & Corda throughout the Selenopeltis Province shows the presence during the Arenig of northern and southern species «groups, and a Llandeilo migration of the latter is identified within the Median Armorican synclinorium. New material of S. macrophthalmus (Kloucek) is described from Brittany together with S. gallicus gallicus nov. sp., nov. subsp. and S. gallicus irroratus nov. sp., nov. subsp. 相似文献
19.
An account is given of some aspects of the biology of Tilapia mossambica Peters in Lake Sibaya, South Africa. Lake Sibaya is a warm shallow coastal lake with extensive shallow terraces in the littoral which shelve abruptly into underwater valleys. The substrate is predominantly sandy. Aquatic macrophytes are generally restricted to water 1–7 m deep. Adult fishes (over 8 cm standard length) are usually absent from water deeper than 12m and shallower than 0–5 m, whereas juveniles may occur at all depths, and fry only in very shallow water.
T. mossambica inhabits the littoral and sublittoral in the warm and transition periods (August–April) but moves into deep water in the cool season (May–July). Exposed and sheltered areas are utilized for different purposes by adult fishes, the former for nesting, and latter for feeding and mouth–brooding. Habitat selection by males is governed by the availability of suitable nest sites. Nests are most common in sparsely–vegetated sheltered areas. Brooding females preferred sheltered littoral areas but ventured onto the terrace to release the fry. Juveniles and fry inhabited exposed shores with a temperature gradient which reversed diurnally. The breeding, shoaling and feeding behaviour is described. The biology of T. mossambica in Lake Sibaya is compared to data on the same, and similar species, in other systems. The utilization of available resources in the lake by T. mossambica is discussed and reference is made to the importance of the retention of generalized characters for the successful habitation of the cyclically–renewed habitat of the littoral. 相似文献
T. mossambica inhabits the littoral and sublittoral in the warm and transition periods (August–April) but moves into deep water in the cool season (May–July). Exposed and sheltered areas are utilized for different purposes by adult fishes, the former for nesting, and latter for feeding and mouth–brooding. Habitat selection by males is governed by the availability of suitable nest sites. Nests are most common in sparsely–vegetated sheltered areas. Brooding females preferred sheltered littoral areas but ventured onto the terrace to release the fry. Juveniles and fry inhabited exposed shores with a temperature gradient which reversed diurnally. The breeding, shoaling and feeding behaviour is described. The biology of T. mossambica in Lake Sibaya is compared to data on the same, and similar species, in other systems. The utilization of available resources in the lake by T. mossambica is discussed and reference is made to the importance of the retention of generalized characters for the successful habitation of the cyclically–renewed habitat of the littoral. 相似文献
20.
Michaela R. Bruton Nicholas O’Dwyer Roger Adams 《Journal of electromyography and kinesiology》2013,23(4):747-758
Potential sex differences in patterns of movement of recreational and competitive athletes were investigated in a systematic review of lower limb kinematics, muscle activation and stiffness during landing and hopping tasks. Little support for sex-specific lower limb kinematic patterns was found in 17 studies retrieved on landing and hopping. Ten studies retrieved on muscle activation during landing provided no support for sex-specific patterns. Four articles retrieved on leg stiffness established that absolute stiffness was lower in females, but differences in stiffness normalized to body mass were less clear. The wider literature indicates that a combination of biological, environmental and sociocultural constraints may shape movement patterns differently in females and males. Sociocultural factors differentially affect accumulated motor experience, practice opportunities and focus of attention in females, leading to differences in motor skill that confound the comparison of female and male movements. The findings of the review support the hypothesis that such sex differences in athletic performance are likely to diminish or disappear with increasing skill. In everyday movement tasks, however, where level of skill is a less meaningful dimension than in sport, differences in movement patterns observed between females and males point instead to the influence of subtle societal expectations on movement patterns. 相似文献