Comparison of the tissue-specific expression and developmental regulation of two closely linked rodent genes encoding cytosolic retinol-binding proteins

Cellular retinol-binding protein (CRBP) and cellular retinol-binding protein II (CRBP II) are two highly homologous cytoplasmic proteins that bind all-trans-retinol. We have recently demonstrated that the mouse genes encoding CRBP and CRBP II are closely linked on chromosome 9 and that both human genes are located on chromosome 3 (Demmer, L.A., Birkenmeier, E.H., Sweetser, D.A., Levin, M.S., Zollman, S., Sparkes, R.S., Mohandas, T., Lusis, A.J., and Gordon, J.I. (1987) J. Biol. Chem. 262, 2458-2467). We have now used RNA blot hybridization analysis to assess the degree to which these genes are coordinately expressed in fetal, suckling, weaning, and adult rat tissues. Both genes exhibit different developmental patterns of expression in liver, intestine, lung, kidney, testes, and placenta. In the intestine, CRBP mRNA was detected during the 16th day of gestation--prior to the development of a well-differentiated absorptive epithelium--and remained essentially unchanged throughout the peri- and postpartum periods. By contrast, the pattern of intestinal CRBP II mRNA accumulation closely parallels the times of first appearance, and subsequent proliferation, of the intestinal absorptive columnar epithelium, supporting the hypothesis that CRBP II is involved in the intestinal uptake or intracellular trafficking of this hydrophobic vitamin. In the fetal liver, both genes were expressed by gestational day 16. Whereas the concentration of hepatic CRBP mRNA increased markedly during the suckling and early weaning periods, CRBP II mRNA levels fell abruptly immediately after birth. These peripartum changes were not paralleled by remarkable alterations in the steady state levels of hepatic retinol. Marked changes in the expression of CRBP in the liver and of CRBP II in the intestine were also documented in pregnant and lactating female rats. These differences in CRBP/CRBP II gene expression strongly suggest that their proteins serve different physiological functions. The peripartum liver may provide a useful model for dissecting the relative roles played by these homologous proteins in retinoid metabolism as well as the factors which modulate activation and repression their genes.     

Influx of 5'-deoxy-5'-methylthioadenosine into HL-60 human leukemia cells and erythrocytes

The influx of 5'-deoxy-5'-methylthioadenosine (MeSAdo) into human HL-60 leukemia cells and erythrocytes was characterized in order to determine whether it is facilitated by the nonspecific nucleoside carrier system or by a separate transporter, as suggested by other reports. Initial velocities were measured at room temperature by means of inhibitor-stop and oil-stop assays. MeSAdo influx was strongly inhibited by Ado, dAdo, and nucleoside transport inhibitors including nitrobenzylthioinosine and dipyridamole. Ade was inhibitory only at concentrations in excess of 1 mM. Loss of nucleoside transport capacity during differentiation of HL-60 cells was accompanied by a corresponding decrease in MeSAdo influx rates. These results indicate that MeSAdo influx was mediated by the nonspecific nucleoside transport system. The kinetic data were consistent with a single saturable carrier and yielded Km values of 74 and 184 microM and Vmax values of 424 and 48 pmols/10(6) cells/min with HL-60 cells and erythrocytes, respectively, after correction for a substantial passive diffusion component, which accounted for over 50% of the influx of 1 mM MeSAdo. The passive diffusion of MeSAdo in the presence of a transport inhibitor was not rate-limiting for the salvage of 50 microM MeSAdo to methionine when HL-60 cells were cultured in methionine-deficient medium. The large contribution of passive diffusion to the influx of MeSAdo is consistent with its unusually high octanol/water partition ratio (5.7-fold greater than that of Ado).     

A genetical model for emergenesis: in memory of Laurence H. Snyder, 1901-86.

When a phenotype is determined by a specific gene combination of several loci, it is called an emergenic trait. Such a trait, although genetically controlled, does not usually run in families, since the specific gene combination can hardly be preserved in the process of reproduction. The present paper suggests a concrete genetical model to account for the phenomenon that there is little resemblance between siblings and parent-child pairs with respect to this trait. The genetical model is multiple homozygosis for all loci involved in the gene configuration. The properties of such a trait in a random mating population for all families, as well as for the segregating families only, are investigated. Some of the difficulties in estimating the genetical parameters on the basis of empirical data are also discussed.     

甘薯胚胎及果实发育的研究

本文研究甘薯的胚胎发育及果实的形成。授粉后10—30分钟花粉粒在柱头上萌发,2小时花粉管抵达珠孔,5—12小时左右完成双受精。授粉后12小时胚乳核开始第一次有丝分裂;15小时合子开始第一次有丝分裂,18小时形成顶细胞和基细胞;尔后分化成原胚,球形胚,心形胚,鱼雷形胚,成熟胚。在适宜温度下21天左右胚胎发育完成。果为蒴果,其内含有1—4粒种子。授粉后3—4天子房开始膨大形成果实,21—30天蒴果与种子成熟。     

三尖杉属受精作用的研究

三尖杉属的精原细胞有一类似银杏生毛体的星状体结构,它分裂产生的2个精子,在大小与形态上都基本相同,而且在精子细胞质中具有拟核仁颗粒存在。上述结构是三尖杉属的重要特点之一。本属植物的成熟卵细胞特别长,细胞质中有丰富的拟核仁结构,卵核下方具2—3团浓稠的细胞质团,这些结构很像穗花杉的卵细胞。三尖杉属的受精作用,属于有丝分裂后类型,这种类型只在松科和三尖杉科中发现。受精后,卵细胞发生强烈的极性分化,上部细胞质变成高度液泡化;相反,下部细胞质则聚集大量蛋白泡和拟核仁颗粒。     

山药化学成分的研究

从胡椒科植物山蒟中分得两个新木脂素类成分(Ia)和(Ⅱ),以及巴豆环氧素(Crorepoxide)(Ⅲ)和β-谷甾醇(Ⅳ)。经光谱分析及化学鉴定,(Ia)、(Ⅱ)为新结构,分别命名为山蒟素 B(hancinone)、山蒟素 C(hancinone C)。     

冬小麦春化过程中可溶性蛋白质组成的变化与形态发生的关系

冬小麦“农大139”经40天左右的春化处理才能迅速而整齐地抽穗,但经14—21天低温处理,已经具有在夏季抽穗的可能性,虽然抽穗推迟且极不整齐;再将春化时间延长,则抽穗百分比增加,且从播种到抽穗的时间缩短。这表明,春化过程中低温对发育的作用有两种效应:前期低温是诱发生理状态的转变,后期低温则只具有加速发育的作用,两个时期的转变是在春化的中期。蛋白质合成抑制剂乙基硫氨酸和对-氟苯丙氨酸能抑制冬小麦的春化,抑制时期也是在春化过程的中期。不同时间低温处理后冬小麦幼芽中可溶性蛋白质含量及组成发生了变化,春化过程中期(低温处理14天之后)不仅含量比对照增加了一倍,而且有新的蛋白质谱带出现。春麦中无类似现象,未经低温处理的春麦已含有冬麦中新出现的谱带。说明冬小麦春化过程的第14—21天左右是与春化过程有关的蛋白质合成的关键时期,该时期新合成的蛋白质与植株的发育状态之间存在着密切的相关关系。     

芦苇胚性愈伤组织的形成及植株的再生

以芦苇种子为外植体,其愈伤组织的诱导率最高。叶鞘和叶片不发生脱分化。培养基中最合适的蔗糖浓度为4%。维生素 B 类、肌醇对愈伤组织的生长起促进作用。而酵母提取物对愈伤组织的诱导和生长具有明显的抑制作用。这种抑制效应,将随酵母提取物浓度的提高而增大。愈伤组织的继代培养,随培养基中2,4-D 浓度的提高,其平均鲜重明显降低。脱分化培养基中2,4-D 浓度对胚性愈伤组织的诱导形成具有一定的相关性。胚性愈伤组织经30代继代培养依然具有90%的分化频率,只是每块愈伤组织的分化苗数减少。反之,非胚性愈伤组织则完全丧失形态发生的能力。对两类愈伤组织进行扫描电镜的观察,发现其表面结构有很大差异。其过氧化物酶、酯酶同工酶谱以及可溶性蛋白的含量均有明显的差别。