Developmental profiles of three embryo-lethal maize mutants lacking leaf primordia: ptd*-1130, cp*-1418, and bno*-747B

The defective kernel (dek) mutants of maize are altered in both their embryo and endosperm development. Earlier studies have indicated that some of the dek mutants are unable to form shoot apical meristems or leaf primoirda. We have examined three embryo lethal dek mutants of this type, ptd*-1130, cp*-1418, and bno*-747B, to obtain a developmental profile for each. Allelism tests show that these three mutants are not allelic. Embryos were examined in early, mid-, and late kernel development as well as at kernel maturity by dissection and sectioning procedures and also at kernel maturity by scanning electron microscopy. All three mutants lag behind normal embryos in their rate of development. Embryos of ptd*-1130 reached the transition stage by early kernel development and progressed no further but underwent cell enlargement and necrosis during late kernel development. Embryos of cp*-1418 reached an early coleoptilar stage by midkernel development. They subsequently increased in size but did not form any leaf primordia. At kernel maturity, they no longer had a shoot apical meristem but often had a well formed root meristem. They appeared to remain healthy and did not become necrotic. Embryos of bno*747B reached the early coleoptilar stage by early kernel development but progressed no further. By kernel maturity, they had grown into masses of irregularly shaped embryonic tissue that no longer resembled any normal embryo stage but were not necrotic. None of these three mutants responded to attempts to support continued embryo development when cultured, but all three mutants formed callus on N6 and MS media supplemented with 2,4-D. These results indicate that these mutants are all uniformly blocked at specific stages early in embryonic development, have different subsequent developmental fates, and represent three different genes performing unique functions that are essential for embryogenesis.     

Global Analysis of ATM Polymorphism Reveals Significant Functional Constraint

ATM, the gene that is mutated in ataxia-telangiectasia, is associated with cerebellar degeneration, abnormal proliferation of small blood vessels, and cancer. These clinically important manifestations have stimulated interest in defining the sequence variation in the ATM gene. Therefore, we undertook a comprehensive survey of sequence variation in ATM in diverse human populations. The protein-encoding exons of the gene (9,168 bp) and the adjacent intron and untranslated sequences (14,661 bp) were analyzed in 93 individuals from seven major human populations. In addition, the coding sequence was analyzed in one chimpanzee, one gorilla, one orangutan, and one Old World monkey. In human ATM, 88 variant sites were discovered by denaturing high-performance liquid chromatography, which is 96%-100% sensitive for detection of DNA sequence variation. ATM was compared to 14 other autosomal genes for nucleotide diversity. The noncoding regions of ATM had diversity values comparable to other genes, but the coding regions had very low diversity, especially in the last 29% of the protein sequence. A test of the neutral evolution hypothesis, through use of the Hudson/Kreitman/Aguadé statistic, revealed that this region of the human ATM gene was significantly constrained relative to that of the orangutan, the Old World monkey, and the mouse, but not relative to that of the chimpanzee or the gorilla. ATM displayed extensive linkage disequilibrium, consistent with suppression of meiotic recombination at this locus. Seven haplotypes were defined. Two haplotypes accounted for 82% of all chromosomes analyzed in all major populations; two others carrying the same D126E missense polymorphism accounted for 33% of chromosomes in Africa but were never observed outside of Africa. The high frequency of this polymorphism may be due either to a population expansion within Africa or to selective pressure.     

Stable Carbon Isotope Composition (deltaC), Water Use Efficiency, and Biomass Productivity of Lycopersicon esculentum, Lycopersicon pennellii, and the F(1) Hybrid

Three tomatoes, Lycopersicon esculentum Mill. cv UC82B, a droughttolerant wild related species, Lycopersicon pennellii (Cor.) D'Arcy, and their F₁ hybrid, were grown in containers maintained at three levels of soil moisture. Season-long water use was obtained by summing over the season daily weight losses of each container corrected for soil evaporation. Plant biomass was determined by harvesting and weighing entire dried plants. Season-long water use efficiency (gram dry weight/kilogram H₂O) was calculated by dividing the dry biomass by the season-long water use. The season-long water use efficiency was greatest in the wild parent, poorest in the domestic parent, and intermediate (but closer to the wild parent) in the F₁ hybrid. Instantaneous water-use efficiency (micromole CO₂/millimole H₂O) determined by gas exchange measurements on individual leaves was poorly correlated with season-long water use efficiency. However, the relative abundance of stable carbon isotopes of leaf tissue samples was strongly correlated with the season-long water use efficiency. Also, the isotopic composition and the season-long water use efficiency of each genotype alone were strongly negatively correlated with plant dry weight when the dry weight varied as a function of soil moisture.     

Benign dermal eccrine cylindroma. A pitfall in the cytologic diagnosis of adenoid cystic carcinoma

Aspiration cytology from four benign dermal eccrine cylindromas and five adenoid cystic carcinomas were compared. These two lesions were found to have so much in common morphologically that they may be indistinguishable on a purely cytologic basis. Accordingly, we recommend a restricted excision to obtain a histopathologic diagnosis before more extensive surgery is performed whenever a lesion is cytologically consistent with adenoid cystic carcinoma but clinically shows a picture that does not exclude dermal eccrine cylindroma.     

K‐Lysine acetyltransferase 2a regulates a hippocampal gene expression network linked to memory formation

Neuronal histone acetylation has been linked to memory consolidation, and targeting histone acetylation has emerged as a promising therapeutic strategy for neuropsychiatric diseases. However, the role of histone‐modifying enzymes in the adult brain is still far from being understood. Here we use RNA sequencing to screen the levels of all known histone acetyltransferases (HATs) in the hippocampal CA1 region and find that K‐acetyltransferase 2a (Kat2a)—a HAT that has not been studied for its role in memory function so far—shows highest expression. Mice that lack Kat2a show impaired hippocampal synaptic plasticity and long‐term memory consolidation. We furthermore show that Kat2a regulates a highly interconnected hippocampal gene expression network linked to neuroactive receptor signaling via a mechanism that involves nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐κB). In conclusion, our data establish Kat2a as a novel and essential regulator of hippocampal memory consolidation.     

Subcellular localization of seven VirB proteins of Agrobacterium tumefaciens: implications for the formation of a T-DNA transport structure.

Plant cell transformation by Agrobacterium tumefaciens involves the transfer of a single-stranded DNA-protein complex (T-complex) from the bacterium to the plant cell. One of the least understood and important aspects of this process is how the T-complex exits the bacterium. The eleven virB gene products have been proposed to specify the DNA export channel on the basis of their predicted hydrophobicity. To determine the cellular localization of the VirB proteins, two different cell fractionation methods were employed to separate inner and outer membranes. Seven VirB-specific antibodies were used on Western blots (immunoblots) to detect the proteins in the inner and outer membranes and soluble (containing cytoplasm and periplasm) fractions. VirB5 was in both the inner membrane and cytoplasm. Six of the VirB proteins were detected in the membrane fractions only. Three of these, VirB8, VirB9, and VirB10, were present in both inner and outer membrane fractions regardless of the fractionation method used. Three additional VirB proteins, VirB1, VirB4, and VirB11, were found mainly in the inner membrane fraction by one method and were found in both inner and outer membrane fractions by a second method. These results confirm the membrane localization of seven VirB proteins and strengthen the hypothesis that VirB proteins are involved in the formation of a T-DNA export channel or gate. That most of the VirB proteins analyzed are found in both inner and outer membrane fractions suggest that they form a complex pore structure that spans both membranes, and their relative amounts in the two membrane fractions reflect their differential sensitivity to the experimental conditions.     

Leaderless polypeptides efficiently extracted from whole cells by osmotic shock.

Three molecular foldases, DsbA, DsbC, and rotamase (ppiA), exhibited the unusual property of accumulating in an osmotically sensitive cellular compartment of Escherichia coli when their signal sequences were precisely removed by mutation. A mammalian protein, interleukin-1 (IL-1) receptor antagonist, behaved in a similar fashion in E. coli when its native signal sequence was deleted. These leaderless mutants (but not two control proteins overexpressed in the same system) were quantitatively extractable from whole cells by a variety of methods generally employed in the recovery of periplasmic proteins. A series of biochemical and genetic experiments showed that (i) leaderless DsbA (but not the wild type) was retained in a nonperiplasmic location; (ii) beta-galactosidase fusions to leaderless DsbA (but not to the wild type) exhibited efficient alpha complementation; (iii) none of the leaderless mutant proteins were substantially associated with cell membranes, even when they were overexpressed in cells; and (iv) leaderless DsbA was not transported to an osmotically sensitive compartment via a secA- or ftsZ-dependent mechanism. The observation that these proteins transit to some privileged cellular location by a previously undescribed mechanism(s)--absent their normal mode of (signal sequence-dependent) translocation--was unexpected. DsbA, rotamase, and IL-1, whose tertiary structures are known, appear to be structurally unrelated proteins. Despite a lack of obvious homologies, these proteins apparently have a common mechanism for intracellular localization. As this (putative) bacterial mechanism efficiently recognizes proteins of mammalian origin, it must be well conserved across evolutionary boundaries.     

Vertebrate Hedgehog signaling: cilia rule

The Hedgehog (Hh) signaling pathway differentially utilizes the primary cilium in mammals and fruit flies. Recent work, including a study in BMC Biology, demonstrates that Hh signals through the cilium in zebrafish, clarifying the evolution of Hh signal transduction.