异细胞质中国春小麦与八倍体小偃麦杂交的细胞遗传研究

用5个异细胞质“中国春小麦”分别和八倍体小偃麦中_2、中_3,中_5杂交。F_1植株性状为两亲的中间型。D型细胞质和B型细胞质的作用基本相同。S型和G型细胞质严重影响F_1的育性,但二者表现不同,S型细胞质仅削弱花粉育性,而G型细胞质使有些杂交组合的F_1雄性完全不育。在中_3、中_5核基因组中存在G型细胞质雄性不育的育性恢复基因。M~t型细胞质可使所有杂交组合F_1植株大型化和抽穗期延长10—15天。此外,细胞遗传学分析表明,M~t型细胞质能促进同源染色体配对,而G型细胞质则促进部分同源染色体配对。G型细胞质对花粉母细胞减数分裂Ⅱ影响较大,产生许多异常四分体,最终引起雄性不育。上述杂交组合经连续回交,已育成异细胞质的八倍体小偃麦品系。     

Influence of spinal cord transection on the presence and axonal transport of CGRP-, chromogranin A-, VIP-, synapsin I-, and synaptophysin-like immunoreactivities in rat motor nerve

Using immunofluorescence and cytofluorimetric scanning (CFS), we investigated the short-term (1-7 days) influence of lower thoracic spinal cord transection on lumbar motor neurons. The content of calcitonin gene-related peptide- (CGRP) like immunoreactivity (LI), chromogranin A (Chr A) -LI, vasoactive intestinal polypeptide (VIP)-LI, Syn I-LI, and synaptophysin (p38)-LI in motor perikarya, and the anterograde and retrograde axonal transport of these substances in the sciatic nerve, were studied in nerve crush (6 h) experiments. During the week after transection, CGRP-LI in perikarya decreased, whereas Chr A-LI increased. VIP-LI, co-localized with Chr A-LI in motor perikarya, did not change after transection. The antero- and retrograde transport of CGRP-LI in the sciatic nerve, occurring in both motor and sensory axons, appeared unchanged in cytofluorimetric scanning (CFS) graphs, but the microscopical picture clearly showed that large motor axons had a decreased content of CGRP-LI at 3 and 7 days posttransection, whereas thinner axons were unchanged in fluorescence intensity. The anterograde transport of Chr A-LI, present in both motor and postganglionic adrenergic axons, was decreased 1 and 3 days after lesion, but returned to control by day 7. There was a marked decrease in anterograde transport of VIP-LI, present mainly in postganglionic sympathetic axons, at day 3, but at 7 days transport was normal. The amounts of transported p38, the synaptic vesicle marker, were in the normal range during the whole period. Syn I-LI accumulation anterogradely was somewhat decreased at 3 and 7 days posttransection, and at 1 day the retrograde accumulation was significantly increased. The results suggest that removal of supraspinal input to intact lower motor neurons causes alterations in metabolism and axonal transport of organelle-associated substances, partly probably related to the complex pattern of transmitter leakage from degenerating, descending nerve terminals. These alterations appear to take place also in postganglionic sympathetic neurons in the sciatic nerve, that originate in the lumbar sympathetic chain. © 1992 John Wiley & Sons, Inc.     

Characterization of potassium channels in pancreatic beta cells from ob/ob mice

The patch-clamp technique in the cell-attached mode was used to study the K channels present in the membrane of cultured pancreatic beta cells from ob/ob mice. Three types of K+ channels were regularly observed, with conductances of 64, 20 and 146 pS. The conduction and kinetic properties of the 64 pS channel were similar to those of the ATP-sensitive potassium channel from normal beta cells. Furthermore, glucose blocked the activity of this channel at the same concentrations as that reported for normal cells. The 20 pS and the 146 pS were insensitive to glucose. The latter K+ channel appears to be similar to the large conductance voltage-activated potassium channels described in normal rodent beta cells. Thus, potassium channels in ob/ob pancreatic beta cells in culture are in most respects normal. Other factors may account for the abnormal electrical response to glucose of ob/ob pancreatic islets, such as reversible impairment of their function in vivo or defects not related to potassium permeability.     

Fatty acyl-CoAs are potent inhibitors of the nuclear thyroid hormone receptor in vitro

We report that long-chain fatty acyl-CoAs are potent inhibitors of the thyroid hormone (T3) receptor isolated from rat liver nuclei. Both saturated and unsaturated fatty acyl-CoAs were similarly potent. Fifty per cent inhibition of T3 binding by the receptor was observed at an oleoyl-CoA concentration as low as 1.3 microM, and the affinity of oleoyl-CoA for the receptor (Ki) was estimated to be 0.45 microM. Fatty acyl-CoAs also promoted dissociation of the hormone bound to the receptor. The action of fatty acyl-CoAs was competitive for the hormone binding site, resulting in a reduction in the receptor's affinity for T3. These observations suggest that fatty acyl-CoAs modulate the binding of the thyroid hormone to its nuclear receptor, in vitro. Whether or not such events occur in vivo remains to be determined.     

Induction of F9 cell differentiation by transient exposure to retinoic acid.

The F9 cell is a mouse embryonal teratocarcinoma which can be induced to differentiate into visceral endoderm by treatment with retinoic acid (RA). Treatment with RA in conventional studies was carried out in the constant presence of RA. Here we demonstrate that treatment with RA can be as short as 3 hrs to induce differentiation of F9 cells. Morphology, alpha-fetoprotein gene activity, and temporal patterns of F9 cell differentiation are the same with both short- and long-term treatment with RA.     

A 21S enzyme complex from HeLa cells that functions in simian virus 40 DNA replication in vitro

A sedimentable complex of enzymes for DNA synthesis was partially purified from the combined low-salt nuclear extract-postmicrosomal supernatant solution of HeLa cell homogenates by poly(ethylene glycol) precipitation in the presence of 2 M KCl, discontinuous gradient centrifugation, Q-Sepharose chromatography, and velocity gradient centrifugation. In addition to the previously described 640-kDa multiprotein DNA polymerase alpha-primase complex [Vishwanatha et al. (1986) J. Biol. Chem. 261, 6619-6628], the enzyme complex also has associated topoisomerase I, DNA-dependent ATPase, RNase H, DNA ligase, a simian virus 40 origin recognition, dA/dT sequence binding protein [Malkas & Baril (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 70-74], and proliferating cell nuclear antigen. Essentially all of the T antigen dependent simian virus 40 in vitro replication activity in the combined nuclear extract-postmicrosomal supernatant solution resides with the sedimentable complex of enzymes for DNA synthesis. Sedimentation analysis on a 10-35% glycerol gradient in the presence of 0.5 M KCl indicates that the enzyme complex is 21S. The associated enzymes for DNA synthesis and in vitro simian virus 40 replication activity cofractionate throughout the purification of the 21S complex. The DNA polymerase and in vitro simian virus 40 replication activities are both inhibited by monoclonal antibody (SJK 132-20) to human DNA polymerase alpha and by 5-10 microM butylphenyl-dGTP, indicating that the association of DNA polymerase alpha with the 21S enzyme complex is essential for the initiation of SV40 DNA replication in vitro.     

Lipid-protein interactions in stacked and destacked thylakoid membranes and the influence of phosphorylation and illumination. Spin label ESR studies

The effects of membrane destacking, protein phosphorylation, and continuous illumination have been studied in pea thylakoid membranes using ESR spectroscopy of an incorporated spin-labelled phosphatidylglycerol. This spin-labelled analogue of an endogenous thylakoid lipid has previously been shown to exhibit a selectivity of interaction with thylakoid proteins. Neither destacking, phosphorylation nor illumination was found to change the ESR spectra appreciably, suggesting that for phosphatidylglycerol at least, neither the number of protein-associated membrane lipids nor their pattern of selectivity was altered. The redistribution of the thylakoid protein complexes in the membrane, under these various conditions, therefore takes place with conservation of the properties of the lipid/protein interface.     

Role of tRNA modification in translational fidelity

In transfer RNA many different modified nucleosides are found, especially in the anticodon region. In this region, pseudouridine (psi) is found in positions 38, 39 or 40 in a subset of tRNA species, 2-methylthio-6-hydroxyisopentenyladenosine (ms2io6A) is found in position 37 in tRNAs that read codons starting with U and 1-methylguanosine (m1G) is found in position 37 in tRNAs reading codons of the UCCNG type. We have used the mutants hisT, miaA and miaB and trmD, which are deficient in the biosynthesis of psi, ms2io6A, and m1G, respectively, to study the functional aspects of the respective modified nucleosides. We have shown: (1) Presence of psi improved the cellular growth rate, the polypeptide step-time, and the efficiency of an amber suppressor, but did not appreciably sense the codon context. (2) Presence of ms2io6A improved the cellular growth rate, the polypeptide step-time and the efficiency of several amber suppressor tRNAs. It also had a profound effect on the codon context sensitivity of the tRNA. (3) Presence of m1G improved the cellular growth rate and the polypeptide steptime and also prevented the tRNA from shifting the reading frame. Thus, these three modified nucleosides present in the anticodon region have apparently different functions.