MITOTIC CONTROL IN ADULT MAMMALIAN TISSUES

Mitotic homeostasis: Mitotic control is maintained by the interaction of a tissue-specific mitosis-inhibiting chalone, which permeates the whole tissue, and a non-tissue-specific mitosis-promoting mesenchymal factor, which originates in the connective tissue and acts only on connective-tissue-adjacent cells. In the basal layer of the epidermis the mitotic rate is determined by the relative concentrations of these two substances; in the distal layers the chalone is dominant so that all cells must become post-mitotic, age, and die. Thus the perfect balance between cell gain and cell loss that is maintained equally in hypoplasia, normality, and hyperplasia is ensured by the fact that all cells forced distally by mitotic pressure enter a chalone concentration that is high enough to direct them into post-mitosis and so to their deaths. The mitotic rate of the basal epidermal cells and the ageing rate of the distal cells are both inversely related to the chalone concentration. A change in the mitotic rate is matched by an equal change in the ageing rate so that, within limits, epidermal thickness (or mass) remains constant. Epidermal thickness is determined by the tissue-specific ratio, mitotic rate: ageing rate; it is influenced by the mitotic rate only when this exceeds a certain critical level. Evidently all epithelial tissues, even when these form solid masses (e.g. liver hepato-cytes), have a similar control mechanism, the ‘basal cells’ being those that are connective-tissue-adjacent and the ‘distal cells' those that are not. Tissues that are not connective-tissue-based (e.g. erythrocytes and granulocytes) have specialized mechanisms involving differentiation from relatively undifferentiated stem cell populations, as also do the connective tissues themselves. Local tissue damage leads via local chalone loss to a temporarily and locally increased mitotic rate; chronic damage leads via chronic chalone loss to hyperplasia, the increase in tissue mass being limited by the reduced life-span of the post-mitotic cells. Compensatory hypertrophy When a tissue mass is so large (e.g. the hepatocytes) in relation to the total body mass that the escaping chalone forms a significant systemic concentration, extensive damage leads to compensatory hypertrophy. The reduced tissue mass (e.g. after partial hepatectomy) produces less chalone, leading to a reduced systemic concentration, and therefore a higher chalone loss from the surviving tissue. This results in a general mitotic response in that tissue, as the relative power of the mesenchymal factor increases, and thus to an increase in tissue mass. Growth ceases when the normal tissue mass is attained. When a large tissue suffers chronic damage (e.g. liver cirrhosis) the chronic chalone lack results in hypertrophy, which is limited by the reduced life-span of the post-mitotic cells. Tumour growth Mitotic control is lost when the chalone concentration falls so low that the ‘distal cells’ remain mitotic; cell gain then exceeds cell loss and a tumour appears. Such chalone loss is related to permanent membrane damage, which may be the central event in carcinogenesis. The evidence is that a tumour continues to produce and to respond to the chalone of its tissue of origin. As a tumour grows the systemic concentration of its chalone rises steadily so that there is an increasing mitotic inhibition, first, in the parent tissue, and second, in the tumour itself. Thus tumour growth may be described as an exponential process limited by an exponential retardation. This means that, if the host survives, the tumour growth will cease and the tumour mass will reach a plateau. This is a negative feedback mechanism which differs from compensatory hypertrophy only in that, at the plateau, the mass attained is greater than normal, and also in that, at any time, further cell damage may cause the tumour to ‘progress’. When this happens the new and higher plateau may be unattainable before the host is killed. Tumour growth is normally slower than would be expected if the mitotic advantage were the only factor involved; clearly tumour growth is usually inhibited by factors other than the chalone, in particular perhaps by the immune response to the altered cell membrane. It is an especial pleasure to acknowledge the constant help and encouragement that has been given by Johanna U. R. Deol.     

THE METABOLIC SYSTEMS INVOLVED IN DISSIMILATION OF CARBOHYDRATE RESERVES IN BAKERS' YEAST

Evidence is presented showing that the dissimilation of carbohydrate reserves in two strains of bakers'' yeast, Saccharomyces cerevisiae, is a purely respiratory process. Endogenous respiration is KCN-labile. Our own experiments together with various accounts and data given in the literature show that the same "oxygen-transporting mechanism" functions in both endogenous and exogenous metabolism. However, the lack of sensitivity of the endogenous system of reactions to low concentrations of monoiodoacetic acid, the absence of anaerobic CO₂ production, and the absence of alcohol production, demonstrate that fermentation is not involved in the dissimilation of the carbohydrate reserves. Throughout the experiments the endogenous respiration behaved functionally as a unitary system of reactions. The O₂ consumption and CO₂ production were parallel at all times; i.e., the R. Q. was consistently 1. Monoiodoacetic acid and KCN in concentrations from 10^–5 to 10^–1 molar affected both O₂ uptake and CO₂ production to the same extent. The only agents known to alter the value of the R. Q. were those which disrupted the normal protoplasmic structure, viz. grinding the cells with sand, plasmolyzing them with toluol and hypertonic salt solutions, or pressing them in a hydraulic press. These agents brought about a vigorous anaerobic CO₂ production accompanied by an accumulation of alcohol in the medium. The unitary character of endogenous respiration is exhibited only when the normal structure of the cell is kept intact; apparently it depends upon the maintenance of a chambered (or compartmental) architecture of the cell.     

ENZYMES OF ENERGY-CONVERTING SYSTEMS IN INDIVIDUAL MAMMALIAN NERVE CELL BODIES1

Abstract— The activities of 7 enzymes (hexokinase, phosphofructokinase, glucose-6-P dehydrogenase, 6-P-gluconic dehydrogenase, NADP linked isocitric dehydrogenase, malic dehydrogenase and lactic dehydrogenase) were measured in individual nerve cell bodies of 8 different neuronal types: pyramidal cells from cerebral cortex and Amnion's horn, Purkinje cells, giant cells in the reticular formation, Deiters’nucleus cells, facial nucleus cells, anterior horn cells and dorsal root ganglion cells. Samples of similar size were analysed from the molecular layer of cerebellum. The cell bodies were dissected from frozen-dried tissue sections and weighed on quartz fibre balances. The weights ranged from 0–2 ng for the smallest pyramidal cells to 9 ng for the largest giant cells. The specific enzymatic reactions were carried out in small volumes (0–01–5 μl) under mineral oil (‘oil-well technique’). The NADPH₂ or NAD formed was amplified by‘enzymatic cycling’and measured fluorometrically. A new cycling method was used for measuring the NAD formed in three of the enzymatic methods. Double cycling was used to measure glucose-6-P and 6-P-gluconate dehydrogenases in the smallest cell bodies. Each type of neuron exhibited a unique enzyme pattern, but four general patterns could be distinguished. The most variable of the enzymes was glucose-6-P dehydrogenase which was nearly 10-fold higher in anterior horn cells than in pyramidal cells from the cerebral cortex. Malic dehydrogenase was the most constant, with a 3-fold range from the highest (Purkinje cells) to the lowest (dorsal root ganglion cells).     

硬骨鱼类促性腺激素的分泌及其调节机制

美国动物学会和加拿大动物学会为纪念著名鱼类生理学家Dr.W.S.Hoar,于1980年12月28日在美国西雅图市联合举行一次“鱼类繁殖”的专题学术会议。会上,美国、加拿大、法国、日本和新加坡的学者围绕鱼类繁殖的行为和内分泌问题发表了十一篇科学论文和综述,反映了当前对鱼类繁殖生理研究取得的新进展。现仅就比较普遍感兴趣的硬骨鱼类促性腺激素的分泌及其调节机制问题做一综合介绍。       

GENETIC CONTROL OF VERY EARLY MAMMALIAN DEVELOPMENT

The overall picture of mammalian preimplantation development is one of complex but integrated molecular activity. As development progresses from the 1 cell stage, blastomeres acquire properties that differ from those of cells of previous stages and eventually differ from one another even at the same stage. The evidence concerning the role of the embryonic genome during this process can be summarized under two headings:
(1) Expression of embryonic genome
(a) Quantitative and qualitative changes in RNA and protein synthesis begin to occur soon after fertilization.
(b) Changes in structural proteins (enzyme activities, transport systems and intercellular junctions) occur throughout early development.
(c) Paternal gene products can be detected as early as the 2-cell stage.
(2) The need for expression of the embryonic genome
(a) Inhibitors of RNA and protein synthesis result in abnormal and lethal development.
(b) Several mutations ( T/t, A^y, Os, c^25H, Om, Ts ) are lethal during early development.
(c) Chromosomal imbalance (monsomy, haploidy, nullisomy) has adverse effects on early development.
Even though studies in vitro on the inhibition of translation indicate that stable maternal messenger RNAs are present in the developing mouse embryo, the evidence outlined in this article strongly supports the belief that embryonic gene expression occurs very early in development (at least by the 2 cell stage) and that this expression is required for normal development.     

菌株 Cy－1 代谢产物中激素类物质分析测定

应用生物学方法对所研制的防治棉花等作物土传病害的微生物制剂进行了分析测定,结果表明制剂中含有生长素、细胞分裂素和赤霉素等激素类物质。     

菌株Cy-1代谢产物中激素类物质分析测定

应用生物学方法对所研制的防治棉花等作物土传病害的微生物制剂进行了分析测定,结果表明制剂中含有生长素、细胞分裂素和赤霉素等激素类物质。     

中国兽类生态学的进展

对近代的兽类学来说,我国虽然从本世纪二十年代即已开始分类研究,三十年代也有了生态学的论文,但是经过抗日战争的破坏,新中国建立之始,实际上处于空白状态。在建立兽类学开始之时,就比较注意兽类生态学的研究。初期的工作自不免朴素粗放一些,但对生态学的发展起到一定的作用。代表的著作可举出纪树立等(1951)的黄鼠研究和杨新史(1951)的《家鼠及其防治》,二者都是从防治医学角度进行工作的,以后此二人也都未再作此类工作。从五十年代中期大量的工作就开始了。涉及到农、林、医、牧以及基础理论的诸多方面,今就以下各方面分述于后。     

哺乳动物抗菌肽研究进展

自昆虫中发现抗菌肽以来,迄今已有约2000多种抗菌肽在生物体中被分离,仅在哺乳动物中就发现了上百种抗菌肽,哺乳动物抗菌肽是哺乳动物抵抗外界病原物质侵染而产生的一系列非专一性免疫应答物,它具有分子量低,热稳定,广播谱抗菌等特点,本文就近年来发现的哺乳动物的抗菌从分类,结构、生物学特性,表达控制,作用机制及应用前景方面作一介绍。     

MICROTUBULAR CRYSTALS IN MAMMALIAN CELLS

Periwinkle alkaloids in very low concentrations cause an intracytoplasmic sequestration of microtubule protein in the form of symmetrical, microtubular bodies. These crystals, which may measure up to 8 µ in length, appear within 30 min in L-strain fibroblasts in vitro, but they increase in incidence and size with time of exposure to the alkaloids. Similarly, if exposed to these compounds, human leukocytes in vitro contain identical crystalline structures. Neither colchicine nor puromycin prevents the formation of these bodies; the latter compound, however, retards crystal growth.     

ANALYSIS OF MECHANISMS OF MICROEVOLUTIONARY CHANGE IN CEPPHUS GUILLEMOTS USING PATTERNS OF CONTROL REGION VARIATION

We surveyed population-level sequence variation in part of the mitochondrial control region for three species including eight subspecies of Cepphus guillemots (Charadriiformes: Alcidae) to test specific predictions about mechanisms of population differentiation. We found that sequences of spectacled guillemots (C. carbo) were more closely related to those of pigeon guillemots (C. columba; both found in the Pacific Ocean) than to those of black guillemots (C. grylle; Arctic and Atlantic Oceans), despite dissimilarities in plumage between spectacled guillemots and the other species. Distributions of species and timing of divergence events suggest that speciation involved allopatric and microallopatric populations isolated by Pleistocene glaciers. Control region sequences were significantly differentiated among populations within species and suggest that gene flow is low; however, populations are probably not in genetic equilibrium, so these results probably reflect historical isolation of colonies. In contrast, phylogenetic relationships among sequences within species were poorly resolved, probably because of a combination of incomplete lineage sorting and contemporary gene flow. Indices of genetic diversity provided no suggestion of recent bottlenecks in most populations, although two populations apparently underwent recent severe bottlenecks. Genetic divergence among populations was not correlated with geographic distance, which argues against isolation by distance. Results of these analyses, combined with breeding distributions and timing of divergence events, suggest that populations diverged during isolation in glacial refugia. Our results are consistent with earlier hypotheses posed by Storer and Udvardy.     

TRACTION EPIPHYSES IN TEH MAMMALIAN SKULL

Traction epiphyses in the mammalian skull are described for the first time, an account being given of the mastoid epiphysis of the otariid pinnipedes and of the lacrimal (antorbital) epiphysis in tapirs, elephants and rhinoceroses.