Search for: All records

The B chromosome in maize is a supernumerary chromosome that due to its dispensability is present in only some lines of maize. Over its evolution, the B chromosome has developed a two-part drive mechanism that ensures its continued presence in maize populations. Its drive mechanism involves nondisjunction at the second pollen mitosis in which two sperm cells are produced and preferential fertilization by the sperm with the two B chromosomes more often joining with the egg as opposed to the central cell in the process of double fertilization. Previous work had suggested some lines of maize exhibit a different response and that this was controlled by the female parent. We sought to examine the variation for this trait by testing a wide spectrum of characterized maize lines. Most inbred lines exhibit the canonical preference for the egg cell, some appear to have random fertilization, and one inbred line (B73) shows a preference for the B containing sperm to fertilize the central cell.

Barbara McClintock recognized transposable elements originally by the movement of a site of chromosomal breakage, a genetic element calledDissociation(Ds) that was induced to break or transpose by another element she calledActivator. The chromosome breaking version, when analyzed on the molecular level was one transposon inside another. It is now known that transposition involving transposon termini in non-standard orientation with reference to each other results in chromosomal breakage. Here we used engineered transposon ends together with a phenotypic marker to cause targeted chromosomal breaks. The results indicate that engineered direct orientation of the naturally inverted repeats ofDissociationcan cause chromosomal breakage at the transgenic sites of insertion.

Gene duplications have long been recognized as a contributor to the evolution of genes with new functions. Multiple copies of genes can result from tandem duplication, from transposition to new chromosomes, or from whole-genome duplication (polyploidy). The most common fate is that one member of the pair is deleted to return the gene to the singleton state. Other paths involve the reduced expression of both copies (hypofunctionalization) that are held in duplicate to maintain sufficient quantity of function. The two copies can split functions (subfunctionalization) or can diverge to generate a new function (neofunctionalization). Retention of duplicates resulting from doubling of the whole genome occurs for genes involved with multicomponent interactions such as transcription factors and signal transduction components. In contrast, these classes of genes are underrepresented in small segmental duplications. This complementary pattern suggests that the balance of interactors affects the fate of the duplicate pair. We discuss the different mechanisms that maintain duplicated genes, which may change over time and intersect.

The genomic imbalance caused by varying the dosage of individual chromosomes or chromosomal segments (aneuploidy) has more detrimental effects than altering the dosage of complete chromosome sets (ploidy). Previous analysis of maize (Zea mays) aneuploids revealed global modulation of gene expression both on the varied chromosome (cis) and the remainder of the genome (trans). However, little is known regarding the role of microRNAs (miRNAs) under genomic imbalance. Here, we report the impact of aneuploidy and polyploidy on the expression of miRNAs. In general,cismiRNAs in aneuploids present a predominant gene-dosage effect, whereastransmiRNAs trend toward the inverse level, although other types of responses including dosage compensation, increased effect, and decreased effect also occur. By contrast, polyploids show less differential miRNA expression than aneuploids. Significant correlations between expression levels of miRNAs and their targets are identified in aneuploids, indicating the regulatory role of miRNAs on gene expression triggered by genomic imbalance.

The B chromosome of maize undergoes nondisjunction at the second pollen mitosis as part of its accumulation mechanism. Previous work identified 9-Bic-1 (9-B inactivated centromere-1), which comprises an epigenetically silenced B chromosome centromere that was translocated to the short arm of chromosome 9(9S). This chromosome is stable in isolation, but when normal B chromosomes are added to the genotype, it will attempt to undergo nondisjunction during the second pollen mitosis and usually fractures the chromosome in 9S. These broken chromosomes allow a test of whether the inactive centromere is reactivated or whether a de novo centromere is formed elsewhere on the chromosome to allow recovery of fragments. Breakpoint determination on the B chromosome and chromosome 9 showed that mini chromosome B1104 has the same breakpoint as 9-Bic-1 in the B centromere region and includes a portion of 9S. CENH3 binding was found on the B centromere region and on 9S, suggesting both centromere reactivation and de novo centromere formation. Another mini chromosome, B496, showed evidence of rearrangement, but it also only showed evidence for a de novo centromere. Other mini chromosome fragments recovered were directly derived from the B chromosome with breakpoints concentrated near the centromeric knob region, which suggests that the B chromosome is broken at a low frequency due to the failure of the sister chromatids to separate at the second pollen mitosis. Our results indicate that both reactivation and de novo centromere formation could occur on fragments derived from the progenitor possessing an inactive centromere.

The non‐essential supernumerary maize (Zea mays) B chromosome (B) has recently been shown to contain active genes and to be capable of impacting gene expression of the A chromosomes. However, the effect of the B chromosome on gene expression is still unclear. In addition, it is unknown whether the accumulation of the B chromosome has a cumulative effect on gene expression. To examine these questions, the global expression of genes, microRNAs (miRNAs), and transposable elements (TEs) of leaf tissue of maize W22 plants with 0–7 copies of the B chromosome was studied. All experimental genotypes with B chromosomes displayed a trend of upregulated gene expression for a subset of A‐located genes compared to the control. Over 3000 A‐located genes are significantly differentially expressed in all experimental genotypes with the B chromosome relative to the control. Modulations of these genes are largely determined by the presence rather than the copy number of the B chromosome. By contrast, the expression of most B‐located genes is positively correlated with B copy number, showing a proportional gene dosage effect. The B chromosome also causes increased expression of A‐located miRNAs. Differentially expressed miRNAs potentially regulate their targets in a cascade of effects. Furthermore, the varied copy number of the B chromosome leads to the differential expression of A‐located and B‐located TEs. The findings provide novel insights into the function and properties of the B chromosome.

Spinal cord injury (SCI), following explosive oxidative stress, causes an abrupt and irreversible pathological deterioration of the central nervous system. Thus, preventing secondary injuries caused by reactive oxygen species (ROS), as well as monitoring and assessing the recovery from SCI are critical for the emergency treatment of SCI. Herein, an emergency treatment strategy is developed for SCI based on the selenium (Se) matrix antioxidant system to effectively inhibit oxidative stress‐induced damage and simultaneously real‐time evaluate the severity of SCI using a reversible dual‐photoacoustic signal (680 and 750 nm). Within the emergency treatment and photoacoustic severity assessment (ETPSA) strategy, the designed Se loaded boron dipyrromethene dye with a double hydroxyl group (Se@BDP‐DOH) is simultaneously used as a sensitive reporter group and an excellent antioxidant for effectively eliminating explosive oxidative stress. Se@BDP‐DOH is found to promote the recovery of both spinal cord tissue and locomotor function in mice with SCI. Furthermore, ETPSA strategy synergistically enhanced ROS consumption via the caveolin 1 (Cav 1)‐related pathways, as confirmed upon treatment with Cav 1 siRNA. Therefore, the ETPSA strategy is a potential tool for improving emergency treatment and photoacoustic assessment of SCI.

A stable lean‐electrolyte operating lithium–sulfur (Li–S) battery based on a cathode of Li₂S in situ electrocatalytically deposited from L₂S₈catholyte onto a support of metallic molybdenum disulfide (1T‐MoS₂) on carbon cloth (CC) is created. The 1T‐MoS₂significantly accelerates the conversion Li₂S₈catholyte to Li₂S, chemically adsorbs lithium polysulfide (LiPSs) from solution, and suppresses crossover of the LiPSs to the anode. These experimental findings are explained by density functional theory calculations that show that 1T‐MoS₂gives rise to strong adsorption of polysulfides on its surface and is electrocatalytic for the targeted reversible Li–S conversion reactions. The CC/1T‐MoS₂electrode in a Li–S battery delivers an initial capacity of 1238 mAh g⁻¹, with a low capacity fade of only 0.051% per cycle over 500 cycles at 0.5C. Even at a high sulfur loading (4.4 mg cm⁻²) and low electrolyte/S (E/S) ratio of 3.7 µL mg⁻¹, the battery achieves an initial reversible capacity of 1176 mA h g⁻¹at 0.5C, with 87% capacity retention after 160 cycles. The post 500 cycles Li metal opposing 1T‐MoS₂is substantially smoother than the Li opposing CC, with XPS supporting the role of 1T‐MoS₂in inhibiting LiPSs crossover.

Stem cell therapies have made strides toward the efficacious treatment of injured endometrium and the prevention of intrauterine adhesions, or Asherman's syndrome (AS). Despite this progress, they are limited by their risk of tumor formation, low engraftment rates, as well as storage and transportation logistics. While attempts have been made to curb these issues, there remains a need for simple and effective solutions. A growing body of evidence supports the theory that delivering media, conditioned with mesenchymal stem cells, might be a promising alternative to live cell therapy. Mesenchymal stem cell‐secretome (MSC‐Sec) has a superior safety profile and can be stored without losing its regenerative properties. It is versatile enough to be added to a number of delivery vehicles that improve engraftment and control the release of the therapeutic. Thus, it holds great potential for the treatment of AS. Here, a new strategy for loading crosslinked hyaluronic acid gel (HA gel) with MSC‐Sec is reported. The HA gel/MSC‐Sec treatment paradigm creates a sustained release system that repairs endometrial injury in rats and promotes viable pregnancy.