Well-defined genome architecture in the human sperm nucleus

Using fluorescence in situ hybridization, conventional epifluorescence microscopy, and laser scanning confocal microscopy followed by three-dimensional reconstruction we describe a well-defined higher order packaging of the human genome in the sperm cell nucleus. This was determined by the spatial localization of centromere and telomere regions of all chromosomes and supported by localization of subtelomere sequences of chromosome 3 and the entire chromosome 2. The nuclear architecture in the human sperm is characterized by the clustering of the 23 centromeres into a compact chromocenter positioned well inside the nucleus. The ends of the chromosomes are exposed to the nuclear periphery where both the subtelomere and the telomere sequences of the chromosome arms are joined into dimers. Thus chromosomes in the human sperm nucleus are looped into a hairpin-like configuration. The biological implications of this nuclear architecture in spermatogenesis and male pronuclear formation following fertilization are discussed.     

A large-subunit mitochondrial ribosomal DNA sequence translocated to the nuclear genome of two stone crabs (Menippe)

Two DNA sequences that appear to be homologous to large-subunit mitochondrial ribosomal RNA genes have been identified in the stone crabs Menippe mercenaria and M. adina. Amplification from whole genomic DNA by polymerase chain reaction (PCR) with oligonucleotide primers based on conserved portions of large-subunit mitochondrial rRNA genes consistently amplified two products of similar length (565 and 567 bp). These products differed at 3% of their nucleotide bases, and could be distinguished by a HindIII site. Only one of these sequences (designated the A sequence) was detected by PCR in purified mitochondrial DNA. The other (designated the B sequence) hybridized to total genomic DNA at a level consistent with a nuclear genome location. It is unlikely that the type B product would have been recognized as a nuclear copy by examination of its sequence alone. This is the first report of a mitochondrial gene sequence translocated into the nuclear genome of a crustacean.      

Identification of genetic variants associated with maize flowering time using an extremely large multi‐genetic background population

Flowering time is one of the major adaptive traits in domestication of maize and an important selection criterion in breeding. To detect more maize flowering time variants we evaluated flowering time traits using an extremely large multi‐ genetic background population that contained more than 8000 lines under multiple Sino‐United States environments. The population included two nested association mapping (NAM) panels and a natural association panel. Nearly 1 million single‐nucleotide polymorphisms (SNPs) were used in the analyses. Through the parallel linkage analysis of the two NAM panels, both common and unique flowering time regions were detected. Genome wide, a total of 90 flowering time regions were identified. One‐third of these regions were connected to traits associated with the environmental sensitivity of maize flowering time. The genome‐wide association study of the three panels identified nearly 1000 flowering time‐associated SNPs, mainly distributed around 220 candidate genes (within a distance of 1 Mb). Interestingly, two types of regions were significantly enriched for these associated SNPs – one was the candidate gene regions and the other was the approximately 5 kb regions away from the candidate genes. Moreover, the associated SNPs exhibited high accuracy for predicting flowering time.     

Histone acetylation reduces nucleosome core particle linking number change

Nucleosome core particles differing in their levels of histone acetylation have been formed on a closed circular DNA that contains a tandemly repeated 207 bp nucleosome positioning sequence. The effect of acetylation on the linking number per nucleosome particle has been determined. With increasing levels of acetylation, the negative linking number change per nucleosome decreases from -1.04 +/- 0.08 for control to -0.82 +/- 0.05 for highly acetylated nucleosomes. These results indicate that histone acetylation has the ability to release negative supercoils previously constrained by nucleosomes into a closed chromatin loop and in effect function as a eukaryotic gyrase.     

Thylakoid protein kinase activity and associated control of excitation energy distribution during chloroplast biogenesis in wheat

The activity of thylakoid protein kinase and the regulation of excitation energy distribution between photosystems I and II was examined during chloroplast biogenesis in light-grown Triticum aestivum (wheat) leaves. The specific activity of the thylakoid protein kinase decreased some six-fold during development from the young plastids at the base of the 7-d-old leaf to the mature chloroplasts at the leaf tip. Appreciable activity was also detected in plastids isolated from etiolated leaves. In mature chloroplasts the majority of phosphate was incorporated into the M_r=26,000 apo-proteins of the light-harvesting chlorophyll a/b-protein complex (LHCP). However, at early stages of chloroplast development and in the etioplast, the phosphate was predominantly incorporated into a polypeptide of M_r=9,000 dalton. Immature thylakoids, isolated from the base of the leaf, had relatively low concentrations of LHCP and could perform a State 1-State 2 transition, as demonstrated by ATP-induced quenching of photosystem II fluorescence. Analyses of photosystem I and photosystem II fluorescence-induction curves from intact leaf tissue demonstrated that this transition occurs in vivo at early stages of leaf development and, therefore, may play an important role in regulating energy transduction during chloroplast biogenesis.     

Histochemical characterization of the surface mucoprotein of normal and abnormal human trophoblast

Synopsis The surface coating of normal and abnormal trophoblast has been studied histochemically. It has been found to contain a highly sulphated mucosaccharide which is probably present together with an acidic non-sulphated mucosaccharide; there are suggestions that the accompanying protein is highly basic. The only difference noted between the coat on the normal trophoblast and that of the hydatidiform mole and ectopic trophoblast was the presence ofvis-glycol groups in the normal which were not found in the abnormal. It is suggested that the presence of the sulphated mucoprotein on the surface of the trophoblast is involved in the protection of the trophoblast from immunological attack.     

Studies on the role and mode of operation of the very-lysine-rich histone H1 (F1) in eukaryote chromatin. The properties of the N-terminal and C-terminal halves of histone H1.

Restricted chymotrypsin digestion of calf thymus H1 histone gives two fragments, residues 1--106 and 107--C-terminal. These were studied by proton magnetic resonance and circular dichroism. The N-terminal fragment exhibited some salt-induced structure in aqueous solution, but this did not parallel the globular structure of the intact H1 molecule. Comparison of circular dichroism results with helix predictions for this portion of the molecule suggests that the secondary structure may be the same in this fragment as it is in the corresponding region of the whole molecule. The C-terminal fragments show very little salt-induced structure. The N-terminal fragments binds to DNA very weakly, but the C-terminal fragment binds as strongly as the whole molecule. In the C-terminal fragment, about one quarter of the lysine residues are not bound to the DNA in water, but initial increase of salt concentration causes them to become bound. This increasing binding occurs under the same ionic conditions that cause chromatin condensation and condensation of H1 - DNA complexes, and it is suggested that there may be a connection between these phenomena.