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1.
The role of laminin and the laminin/fibronectin receptor complex in the outgrowth of retinal ganglion cell axons 总被引:9,自引:0,他引:9
Chick embryo retinal ganglion cell (RGC) axons grow to the optic tectum along a stereotyped route, as if responding to cues distributed along the pathway. We showed previously that, in culture, RGCs from embryonic Day 6 retina are responsive to the neurite-promoting effects of the extracellular matrix glycoprotein laminin and that this response is lost by RGCs at a later stage of development. Here we report that, before axon outgrowth is initiated in vivo, laminin, is expressed along the optic pathway at nonbasal lamina sites that are accessible to the growth cones of RGC axons. The distribution of laminin within the pathway is consistent with its localization at the end-feet of neuroepithelial cells that line the route, and it continues to be expressed at these marginal sites during the first week of embryonic development. At later stages, concomitant with the loss of response by RGCs in culture, laminin becomes restricted to basal laminae at the retinal inner limiting membrane and pial surface of the optic pathway. Neurofilament-positive RGC axons bind a monoclonal antibody, JG22, which recognizes the laminin/fibronectin receptor complex, and continue to do so throughout embryonic development. We show that, in vitro, the JG22 antigen expressed by RGCs appears to function as a laminin receptor, by demonstrating that JG22 antibody blocks neurite outgrowth on a substrate of laminin. These findings are consistent with the possibility that laminin defines a transient performed pathway specifically recognized by early RGC growth cones as they navigate toward their central target. 相似文献
2.
Purification and characterization of proteolytic fragments of lipocortin I that inhibit phospholipase A2 总被引:3,自引:0,他引:3
K S Huang P McGray R J Mattaliano C Burne E P Chow L K Sinclair R B Pepinsky 《The Journal of biological chemistry》1987,262(16):7639-7645
Human lipocortin I is a 38.5-kDa phospholipase A2 inhibitor that has been produced in Escherichia coli in large quantities by recombinant DNA technology (Wallner, B.P., Mattaliano, R.J., Hession, C., Cate, R. L., Tizard, R., Sinclair, L.K., Foeller, C., Chow, E.P., Browning, J.L., Ramachandran, K.L., and Pepinsky, R.B. (1986) Nature 320, 77-80). To localize the region within the protein responsible for its inhibitory activity, we generated a series of fragments of the recombinant product by limited proteolysis with elastase and characterized their structure by sequencing and peptide mapping. Five active fragments have been analyzed in detail. The smallest is an 18-kDa fragment derived from the amino-terminal half of lipocortin. Three of the larger fragments contain this region. The fifth fragment is missing 83 amino acids from the amino terminus. A region common to all the active fragments (amino acid residues 97-178) is 70% homologous with the corresponding region from a second member of the lipocortin family which recently was cloned (Huang, K-S., Wallner, B.P., Mattaliano, R.J., Tizard, R., Burne, C., Frey, A., Hession, C., McGray, P., Sinclair, L.K., Chow, E.P., Browning, J.L., Ramachandran, K.L., Tang, J., Smart, J.E., and Pepinsky, R.B. (1986) Cell 46, 191-199) and thus presumably is important for activity. In addition to inhibitory fragments, we have isolated a 3-kDa proteolytic fragment from the amino terminus of lipocortin I that contains the known phosphorylation site for protein-tyrosine kinases. Because of sequence homology of the 3-kDa fragment with biologically active synthetic peptides from pp60v-src and middle T antigen, its release by proteases may represent an important part of the activity of lipocortin. 相似文献
3.
4.
Wolterbeek, H. Th. and De Bruin, M. 1986. Xylem and phloem importof Na+, K+ , Rb+, Cs+ and in tomato fruits: differential contributions from stem and leaf.J.exp. Bot. 37: 928939. The transport of Na+, K+, Rb+, Cs+ and into developing fruits of tomato (an inbred lineof Lycopersicon esculentum Mill. cv. Tiny Tim) was measured.Element solutions were introduced into the transpiration streamthrough the cut stem bases of plant parts consisting of a stempart with single green fruit, both with and without attachedfully expanded leaf. Measurements were carried out of the accumulationin the fruit of the gamma-ray emitting radiotracers 24Na+, 42K+,86Rb+, 134Cs+ and The transport into the fruit was expressed by a single parameter taking intoaccount volume flows varying with time and experiments. Xylemto phloem transfer in the stem as a source of fruit elementsupply was shown to be inversely related with the velocity offlow of the stem xylem. The results also indicated that thetransfer system in the stem was more rapidly equilibrated thanit was in the leaf. Stem loading of the phloem is suggested as a possible mechanismregulating the solute influx in fruits under varying flow velocitiesof the stem xylem, while fruit influx of phloem solutes, whichwere loaded in the leaf, may play a major role in influx regulationunder conditions of varying solute concentrations. Key words: Alkali ions, tomato fruits, stem and leaf phloem loading 相似文献
5.
Prevost, I. and Le PageDegivry, M. Th. 1985. Changesin absicisic acid content in axis and cotyledons of developingPhaseolus vulgaris embryos and their physiological consequences.J.exp. Bot. 36: 19001905.Changes in abscisic acid (ABA)content with time were measured in embryonic axes and in cotyledonsof Phaseolus vulgaris embryos using a radioimmunoassay.During embryogenesis, a similar pattern was observed in bothtissues: ABA increased to a maximum 29 d after an thesis, followedby a decrease as the seed matured. The level of ABA in the cotyledonswas always much higher than that in the axes. In in vitro cultures,the duration of the lag phase before germination of isolatedembryonic axes increased with ABA content. The presence of cotyledonsalways lengthened the lag phase; longer lag phases were associatedwith greater concentrations of ABA in the cotyledons. Moreoverthe presence of cotyledons stimulated the growth of seedlings. Key words: ABA distribution, embryo maturation, axis and embryo germinability 相似文献
6.
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8.
Abstract.
- 1 The relative influences of temperature and availability of food on reproduction, survival and growth of all developmental stages of two carabid beetle species are discussed with special reference to the suggested relationship between availability of food, size of egg production and survival of adults from one breeding season to the next.
- 2 Temperature as well as food supply influence the length of larval growth and adult body size. Beetles grown at low temperatures and low amounts of food are smaller than those grown at higher temperature and with more food.
- 3 The number of eggs laid per female was correlated with the amount of food gathered. There was no inverse relationship (trade-off) between reproductive output and survival in the field until the next breeding season.
- 4 In 1980 no significant relationship was found between winter mortality and the amounts of food gathered by beetles in the period after reproduction and before winter diapause. However, in 1981 in C. melanocephalus a lower number of starved beetles survived the winter than the fed ones and‘field’beetles.
- 5 Only in the first part of the feeding activity period in autumn can enough food be gathered by C.melunocephalus for successful hibernation. In the second part of this period there is not enough food to build up the fat reserves needed to survive the winter.
- 6 Difference in population fluctuations of both species are discussed in relation to their life histories.
9.
Summary The Linnaean nameCryptozo?n proliferum
Hall was proposed in 1883 for a previously undescribed life-form preserved in spectacular exposures of Cambrian limestones in
New York State, USA. It is now recognised that these are exposures of stromatolitic microbialites, laminated organosedimentary
structures formed from interaction between a benthic microbial community (BMC) and the environment. Microbialites are neither
fossil organisms nor trace fossils. These complex structures are the products of dissipative, self-organising systems involving
a BMC, the external environment and the accreting microbialite. Functionally analogous BMCs of different species compositions
may build similar structures in similar environments in quite separate periods. The type exposures ofCryptozo?n proliferum show objects composed of complex, concentric rings, up to a metre in diameter, that have grown laterally without any restriction
other than that provided by neighbouring structures. They are not the relicts of domes truncated by penecontemporaneous erosion
or Pleistocene glaciation, but depositional forms in which upward growth was restricted. Analogous modern structures occur
on a reef platform along the north east shore of hyposaline Lake Clifton, Western Australia. These are tabular thrombolitic
microbialites that vary lakeward across the reef platform from low, compound structures to discrete, concentric structures
up to 50 cm high. The Lake Clifton forms are, in turn, morphological analogues of microatolls found on coral reef platforms.
Coral microatolls are coral colonies with flat, dead tops and living perimeters in which upward growth is constrained by the
sea surface. In shallow water they form circular rims of laterally growing coral around a dead centre. In deeper water they
form coral heads that develop flat tops on reaching sea level. It is concluded that both the tabular microbialites of Lake
Clifton and the type exposures ofCryptozo?n proliferum are analogous to coral microatolls in both form and origin-structures that have been able to grow laterally, but in which
upward growth is restricted by subaerial exposure. Similar microatoll microbialites have been described from other modern
environments, including Great Salt Lake, Utah, USA and Stocking Island, Exuma Cays, Bahamas. Ancient examples may include
some of the “tufa” deposits of the Basal Purbeck Formation in Dorset, UK, as well as the coalesced domal bioherms of the Upper
Cambrian Arrinthrunga Formation of the Georgina Basin, Central Australia, and the “washbowl” structures described from the
B?tsfjord Formation of the Varanger Peninsula, north Norway. Progress towards a reliable interpretation of ancient microbialites
depends on an understanding of modern environments in which analogous structures are forming. This study of microatolls has
demonstrated that other sessile life forms may create colonial ecomorphs that, used cautiously, can serve as analogues for
understanding the factors controlling the growth and form of microbialites. The surprising lack of pre-Pleistocene examples
of microatolls recorded to date has simply been due to their lack of recognition in the geological record. They occur in sequences
from the Proterozoic onwards, and provide powerful environmental indicators of ancient reef platforms on which biological
growth was adjusted to contemporary sea level. 相似文献
10.
Fine structure of aphid stylet routes in plant tissues in correlation with EPG signals 总被引:8,自引:0,他引:8
Abstract. Plant penetration by Aphis fabae (Scopoli) was recorded by the electrical penetration graph (EPG) technique and followed by stylectomy during wave-forms that were suspected of indicating sieve element punctures. The severed stylets in the plant tissue were subsequently processed for transmission electron microscopy (TEM) and sectioned either transverse or longitudinal to the stylets. Two completely serially sectioned probes from the epidermis to the phloem were reconstructed.
In one probe the stylet pathway went to a sieve element and showed many empty branches of salivary sheath material. Breaks in cell walls filled with sheath material demonstrated that the majority of cells bordering the track had been punctured, which supports earlier evidence from EPGs. All types of cells showed punctures and the highest number was found inside the vascular bundle. Very few cells died, which would appear to be important for virus transmission, and in others cellular reactions remained limited to some callose formation. The route of the stylets was intercellular and passed through the secondary wall material. The role of pectinase in intercellular penetration, and previous evidence for intracellular tracks are discussed. Most sieve elements had been punctured but only one was eventually accepted. Thus, reaching a sieve element in a host plant does not automatically imply its acceptance though the reason remains unclear. Gelation of phloem proteins was shown in the stylet canal.
In a second probe, plant cytological and morphological correlations with the EPG were emphasized. Probes by other aphid-plant combinations showed great similarity. 相似文献
In one probe the stylet pathway went to a sieve element and showed many empty branches of salivary sheath material. Breaks in cell walls filled with sheath material demonstrated that the majority of cells bordering the track had been punctured, which supports earlier evidence from EPGs. All types of cells showed punctures and the highest number was found inside the vascular bundle. Very few cells died, which would appear to be important for virus transmission, and in others cellular reactions remained limited to some callose formation. The route of the stylets was intercellular and passed through the secondary wall material. The role of pectinase in intercellular penetration, and previous evidence for intracellular tracks are discussed. Most sieve elements had been punctured but only one was eventually accepted. Thus, reaching a sieve element in a host plant does not automatically imply its acceptance though the reason remains unclear. Gelation of phloem proteins was shown in the stylet canal.
In a second probe, plant cytological and morphological correlations with the EPG were emphasized. Probes by other aphid-plant combinations showed great similarity. 相似文献