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1.
Leah Edelstein 《Differentiation; research in biological diversity》1982,23(1-3):1-9
Abstract. The selection of polarity in cells of the cambium in higher plants is a regulated process of development which results in horizontally or vertically oriented cells. A set of mathematical equations suggestive of this developmental dichotomy is given a new biologic interpretation. As a result, a molecular scheme capable of acting as a biochemical switch is suggested. The model features two structural protein monomers whose synthesis is controlled autogenously by feedback repression. The implications of this and similar mechanisms to other differentiating systems is discussed. 相似文献
2.
3.
S. J. Edelstein 《Human Evolution》1987,2(2):169-174
Biological clock data from protein sequences indicate times for the divergence of humans and African apes that are only 2–3 million years before the present and hence inconsistent with the generally accepted view ofAustralopithecus on the evolutionary line toHomo. This inconsistency has been reconciled for most investigators by postulating a slowing of the biological clock among higher primates. However, there is no independent evidence for such a slowing, and for a number of reasons a specific slowing is unlikely. Therefore, an alternative paradigm is considered here based on the hypothesis that the molecular clock data are correct. The main consequence of this hypothesis is the placement ofA. afarensis in a position ancestral to African apes. An argument in support of this alternative paradigm is formulated concerning the evolution of knuckle-walking in African apes from ancestors whose bipedalism was already well developed. Published data are cited, particularly concerning the structure of the wrist, which accommodate poorly the evolution of African apes from palmigrad-walking or brachiating ancestors resemblingProconsul africanus orPongo. These arguments suggest that an alternative paradigm of hominoid evolution placingA. afarensis ancestral toHomo, Gorilla, andPan warrants further consideration. 相似文献
4.
High level of divergence of male-reproductive-tract proteins, between Drosophila melanogaster and its sibling species, D. simulans 总被引:1,自引:0,他引:1
We compared male-reproductive-tract polypeptides of Drosophila melanogaster
and D. simulans by using two-dimensional gel electrophoresis. Approximately
64% of male-reproductive-tract polypeptides were identical between two
randomly chosen isofemale lines from these two species, compared with 83%
identity for third-instar imaginal wing-disc polypeptides. Qualitatively
similar differences were found between reproductive tracts and imaginal
discs when D. sechellia was compared with D. melanogaster and with D.
simulans. When genic polymorphism was taken into account, approximately 10%
of male- reproductive-tract polypeptides were apparently fixed for
different alleles between D. melanogaster and D. simulans; this proportion
is the same as that found for soluble enzymes by one-dimensional gel
electrophoresis. Strikingly, approximately 20% of male-reproductive- tract
polypeptides of either D. melanogaster or D. simulans had no detectable
homologue in the other species. We propose that proteins of the Drosophila
male reproductive tract may have diverged more extensively between species
than have other types of proteins and that much of this divergence may
involve large changes in levels of polypeptide expression.
相似文献
5.
Plasma high-density lipoproteins (HDL) can provide rat ovary steroidogenic tissue with cholesterol for steroid hormone production, but the mechanism of cholesterol transfer is unknown. To test the importance of apolipoprotein A-I (the major HDL apolipoprotein) in HDL-cell interactions, we examined the ability of canine-human HDL hybrids containing various proportions of canine apolipoprotein A-I and human apolipoprotein A-II to stimulate steroidogenesis by cultured rat ovary granulosa cells. We observed that as the apolipoprotein A-II to apolipoprotein A-II ratio decreased, the ability of the hybrid particles to stimulate granulosa cell progestin (progesterone and 20 alpha-dihydroprogesterone) production diminished. However, granulosa cell progestin (progesterone and 20 alpha-dihydroprogesterone) production diminished. However, apolipoprotein A-I was not necessary for cholesterol transfer, since hybrids with less than 5% of their total apolipoprotein mass as apolipoprotein A-I stimulated progestin production 30% as effectively as canine HDL, which contained essentially only apolipoprotein A-I. These data indicate that the delivery of cholesterol from HDL into the rat ovary cell for steroidogenesis is not strictly dependent on the presence of a specific HDL apolipoprotein. 相似文献
6.
Induction of tumors and generation of recovered sarcoma viruses by, and mapping of deletions in, two molecularly cloned src deletion mutants. 总被引:9,自引:9,他引:0
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td108 , a transformation-defective (td) deletion mutant of the Schmidt-Ruppin strain of Rous sarcoma virus of subgroup A (SR-A), was molecularly cloned. Two isolates of td viruses, td108 -3b and td108 -4a, obtained by transfection of the molecularly cloned td108 DNAs into chicken embryo fibroblasts, were tested for their ability to induce tumors and generate recovered avian sarcoma viruses ( rASVs ) in chickens. Both td viruses were able to induce tumors with a latency and frequency similar to those observed previously with biologically purified td mutants of SR-A. rASVs were isolated from most of the tumors examined. The genomic RNAs of those newly obtained rASVs were analyzed by RNase T1 oligonucleotide fingerprinting. The results showed that they had regained the deleted src sequences and contained the same set of marker src oligonucleotides as those of rASVs analyzed previously. The src oligonucleotides of rASVs are distinguishable from those present in SR-A. We conclude that those rASVs must have been generated by recombination between the molecularly cloned td mutants and the c-src sequence. The deletions in the td mutants were mapped by restriction enzyme analysis and nucleotide sequencing. td108 -3b was found to contain an internal src deletion of 1,416 nucleotides and to retain 57 and 105 nucleotides of the 5' and 3' src coding sequences, respectively. td108 -4a contained a src deletion of 1,174 nucleotides and retained 180 and 225 nucleotides of the 5' and 3' src sequences, respectively. Comparison of sequences in the 5' src and its upstream region of td108 -3b with those of SR-A, rASV1441 (a td108 -derived rASV analyzed previously), and c-src suggested that the 5' recombination between td108 and c-src occurred from 7 to 20 nucleotides upstream from the beginning of the src coding sequence. 相似文献
7.
Proteolytic processing and compartmentalization of the primary translation products of mammalian apolipoprotein mRNAs 总被引:1,自引:0,他引:1
J I Gordon H F Sims A W Strauss A M Scanu C Edelstein R E Byrne 《CRC critical reviews in biochemistry》1986,20(1):37-71
The steps involved in the initial assembly of apolipoproteins and lipids into supramolecular arrays (nascent lipoprotein particles) are largely unknown. Examination of the proteolytic processing and compartmentalization of the primary translation products of apolipoprotein mRNAs represents one approach to deciphering the molecular details of lipoprotein assembly. The structures of the primary translation products of seven mammalian apolipoprotein mRNAs has been determined in the past several years. The organization of apolipoprotein signal peptides is typical of eukaryotic prepeptides, although an unusual degree of sequence conservation is present among the signal segments of apo AI, AIV, and E. For those apolipoprotein sequences studied in detail, SRP-dependent cotranslational translocation and proteolytic processing appears to be highly efficient and results in sequestration of the processed protein within the lumen of the endoplasmic reticulum (ER). However the mechanism by which these lipid-binding proteins avoid arrest during their translocation through the lipid bilayer of the ER membrane remains obscure. The two principal human HDL apolipoproteins undergo novel extracellular post-translational proteolytic processing, which results in removal of nonhomologous propeptides. The proteases responsible for proapo AI and AII processing appear to be different. The processing of these proapolipoproteins provides a potential series of steps for regulating the ordered assembly of HDL constituents. 相似文献
8.
A model for growth of a tissue culture consisting of cell clumps is given. A set of equations for following the size distribution of clumps is used to determine total biomass accumulation. Existence and uniqueness of a solution to the equations is proved, and estimates of the biomass growth is given in a number of situations. 相似文献
9.
10.
Wesley Hicks Robert Ward David Edelstein Leon Hall Anthony Albino Robert Hard Bonnie Asch 《Cell biology international》1995,19(4):301-306
The cytokertatins in respiratory epithelial cells (REC) of human nasal polyps and turbinates were analyzed by immunohistochemistry. Cytokeratin 19 (CK19) was present in all REC, CK5 and 14 were expressed primarily in basal cells, and CK7, 8, and 18 were found in suprabasal cells. Differences in cytoplasmic locations were also apparent among the individual cytokeratins. CK13 was not detected in any REC of these tissues. The results indicate the profile of cytokeratins in REC of human nasal polyps and turbinates is essentially identical to that of REC in the more distal respiratory tract. 相似文献