The t(8;21)(q22;q22) translocation is one of the most common genetic abnormalities in acute myeloid leukemia (AML), identified in 15% of all cases of AML, including 40-50% of FAB M2 subtype and rare cases of M0, M1 and M4 subtypes. The most commonly known AML1-ETO fusion protein (full-length AML1-ETO) from this translocation has 752 amino acids and contains the N-terminal portion of RUNX1 (also known as AML1, CBFalpha2 or PEBP2alphaB), including its DNA binding domain, and almost the entire RUNX1T1 (also known as MTG8 or ETO) protein. Although alterations of gene expression and hematopoietic cell proliferation have been reported in the presence of AML1-ETO, its expression does not lead to the development of leukemia. Here, we report the identification of a previously unknown alternatively spliced isoform of the AML1-ETO transcript, AML1-ETO9a, that includes an extra exon, exon 9a, of the ETO gene. AML1-ETO9a encodes a C-terminally truncated AML1-ETO protein of 575 amino acids. Expression of AML1-ETO9a leads to rapid development of leukemia in a mouse retroviral transduction-transplantation model. More importantly, coexpression of AML1-ETO and AML1-ETO9a results in the substantially earlier onset of AML and blocks myeloid cell differentiation at a more immature stage. These results indicate that fusion proteins from alternatively spliced isoforms of a chromosomal translocation may work together to induce cancer development.

Background: An ongoing outbreak of coronavirus disease 2019 (COVID-19) has spread around the world. It is debatable whether asymptomatic COVID-19 virus carriers are contagious. We report here a case of the asymptomatic patient and present clinical characteristics of 455 contacts, which aims to study the infectivity of asymptomatic carriers. Material and methods: 455 contacts who were exposed to the asymptomatic COVID-19 virus carrier became the subjects of our research. They were divided into three groups: 35 patients, 196 family members and 224 hospital staffs. We extracted their epidemiological information, clinical records, auxiliary examination results and therapeutic schedules. Results: The median contact time for patients was four days and that for family members was five days. Cardiovascular disease accounted for 25% among original diseases of patients. Apart from hospital staffs, both patients and family members were isolated medically. During the quarantine, seven patients plus one family member appeared new respiratory symptoms, where fever was the most common one. The blood counts in most contacts were within a normal range. All CT images showed no sign of COVID-19 infection. No severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections was detected in 455 contacts by nucleic acid test. Conclusion:In summary, all the 455 contacts were excluded from SARS-CoV-2 infection and we conclude that the infectivity of some asymptomatic SARS-CoV-2 carriers might be weak. IntrodutionThe emergence of the coronavirus disease 2019 (COVID-19) since early December 2019, has spread to many countries recently and sparked world pandemic via mass gathering [1][2][3]. As of March 24, 2020, there have been 334981 confirmed cases and 14652 deaths globally [4].It has been proved that the pathogen of COVID-19 is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which has high homology with SARS-CoV [5]. Similar to SARS-CoV, the dominant SARS-CoV-2 transmission mode is human-to-human transmission [6]. Differently, the reproductive number (R0)

Central nervous system (CNS) involvement remains an important cause of morbidity and mortality in acute leukemia, the mechanisms of leukemic cell infiltration into the CNS have not yet been elucidated. The blood-brain barrier (BBB) makes CNS become a refugee to leukemic cells and serves as a resource of cells that seed extraneural sites. How can the leukemic cells disrupt this barrier and invasive the CNS, even if many of the currently available chemotherapies can not cross the BBB? Tight junction in endothelial cells occupies a central role in the function of the BBB. Except the well known role of degrading extracellular matrix in metastasis of cancer cells, here we show matrix metalloproteinase (MMP)-2 and -9, secreted by leukemic cells, mediate the BBB opening by disrupting tight junction proteins in the CNS leukemia. We demonstrated that leukemic cells impaired tight junction proteins ZO-1, claudin-5 and occludin resulting in increased permeability of the BBB. However, these alterations reduced when MMP-2 and -9 activities were inhibited by RNA interference strategy or by MMP inhibitor GM6001 in an in vitro BBB model. We also found that the disruption of the BBB in company with the down-regulation of ZO-1, claudin-5 and occludin and the up-regulation of MMP-2 and -9 in mouse brain tissues with leukemic cell infiltration by confocal imaging and the assay of in situ gelatin zymography. Besides, GM6001 protected all mice against CNS leukemia. Our findings suggest that the degradation of tight junction proteins ZO-1, claudin-5 and occludin by MMP-2 and -9 secreted by leukemic cells constitutes an important mechanism in the BBB breakdown which contributes to the invasion of leukemic cells to the CNS in acute leukemia.

There are a number ofagents which, when added to cultures of murine erythroleukemia cells (MELC), markedly increase the probability of commitment to express the characteristics of terminal erythroid differentiation, including loss of proliferative capacity and increased accumulation of globin mRNA and hemoglobin. Some characteristics of inducer-mediated commitment of MELC to terminal erythroid differentiation were examined by determining the effects of dexamethasone (an inhibitor of inducer-mediated MELC differentiation) and of hemin (an inducer of globin mRNA accumulation). Previously, it was shown that exposure of MELC to hexamethylene-bisacetamide (HMBA) leads to commitment, detectable within 12 hr. MELC cultured with both HMBA and dexamethasone do not express commitment. MELC transferred from culture with HMBA and dexamethasone to cloning medium without these agents express commitment to terminal erythroid differentiation, indicating that MELC retain a "memory" for some early HMBA-mediated changes leading to commitment which occur even in the presence of the inhibitory steroid. The kinetics of commitment in experiments in which exposure to HMBA is interrupted, or dexamethasone is added to the culture with HMBA, suggest that there is a rate-limiting step early in the commitment process. The memory for this step persists for more than one cell cycle. Addition ofhemin to cultures with HMBA and dexamethasone initiates accumulation of globin mRNA but does not reverse the steroid-mediated inhibition of terminal cell division (that is, the cells retain their proliferative capacity). Inducer-mediated MELC commitment is associated with accumu-

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Murine erythroleukemia cells (MELC) are virustransformed erythroid precursors that appear to be blocked at an erythroid precursor stage comparable to the erythroid colonyforming unit (CFU-e). These cells are useful in examining factors regulating terminal differentiation. Induced MELC are characterized by a coordinated program of gene expression, including commitment to terminal cell division, accumulation of globin mRNAs and corresponding hemoglobins, and accumulation of several other proteins, including the chromatin-associated protein H10. Two cloned variant cell lines, DR1O and RI, have been developed from inducer-sensitive DS19 cells by selection for inducer resistance.DRlO and RI cells fail to display commitment to terminal cell division when cultured with dimethyl sulfoxide (Me2SO), hexamethylene bisacetamide (HMBA), or butyric acid. Both cell lines are induced by all three agents to accumulate Hi1. DR1O cells are resistant to Me2SO-mediated accumulation of hemoglobin but are sensitive to HMBA-or butyric acid-mediated accumulation. RI cells are resistant to Me2SO-and HMBA-mediated accumulation of hemoglobin but are sensitive to butyric acid-mediated accumulation. Both DR1O and RI are commitment-negative MELC variants, displaying variable responses to inducers with respect to other features of terminal erythroid cell differentiation.Murine erythroleukemia cells (MELC) are virus-transformed erythroid cell precursors, approximating the erythroid colonyforming unit (CFU-e), that may be induced by dimethyl sulfoxide (Me2SO) (1), hexamethylene bisacetamide (HMBA) (2), and a variety of other agents to express characteristics of terminal erythroid cell differentiation (3). Induced differentiation of MELC line DSl9, a derivative of line 745A (2, 3), is characterized by the coordinated expression of commitment to terminal cell division (4, 5); accumulation of newly synthesized aand ,3globin mRNAs (6) and a-, 3mai-, and prminn-globins, hemoglobins major and minor (7,8), and erythrocyte surface proteins such as spectrin (9); augmentation of enzyme activities of the heme synthetic pathway (10); and increase in the level of H10, a chromatin-associated protein (11,12).Recently, we have shown that both inducer-mediated commitment to terminal cell division and increased globin gene expression involve multistep processes (12, 13). For example, in uninduced MELC there are alterations in the chromatin of the a,-and 8`mai-globin gene domains that, presumably, occurred at prior stage in the differentiation of these cells and are stably propagated. With exposure to HMBA or Me2SO, other alterations in chromatin structure occur at sites corresponding to the 5' flanking sequence of both the a,-and r4-globin genes (13)(14)(15). Whether these changes in chromatin reflect a nuclear site of action of HMBA or Me2SO or are secondary to inducermediated effects on other cellular functions is not established (16)(17)(18).

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Serum small extracellular vesicles (seVs) have recently drawn considerable interest because of the diagnostic and therapeutic potential of their miRnAs content. However, the characteristics of human, mouse and rat serum sEVs and their differences in small RNA contents are still unknown. In this study, through nanoparticle tracking analysis and small RNA sequencing, we found that human, rat, and mouse serum seVs exhibited distinct sizes and particle numbers as well as small RnA contents. Serum seVs contained not only abundant miRnAs but also a large number of tRnA fragments. Most serum miRnAs existed both inside and outside of seVs but were enriched in seVs. common serum seV miRNAs (188 miRNAs) and species-specific serum sEV miRNAs (265, 58, and 159 miRNAs, respectively) were identified in humans, rats, or mice. The serum sEVs contained miRNAs from tissues and organs throughout the body, with blood cells as the main contributors. In conclusion, our findings confirmed the rationality of exploring serum sEV miRNAs as noninvasive diagnostic markers and revealed great differences in serum sEV small RNAs between humans, rats, and mice. Inadequate attention to these differences and the contribution of blood cells to serum sEV miRNAs could hinder the clinical translation of basic studies. Circulating RNAs, especially microRNAs (miRNAs) have recently emerged as non-invasive disease biomarkers. miRNAs are endogenous small noncoding RNAs of approximately 22 nt that regulate gene expression posttranscriptionally by binding to target mRNA and repressing mRNA translation or increasing mRNA cleavage. Abnormally expressed miRNAs have been associated with multiple diseases. In 2008, Chen et al. reported that human serum contained numerous stable miRNAs that might originate in tissues throughout the body. The expression profiles of these miRNAs exhibit great potential to serve as novel noninvasive biomarkers for the diagnosis of cancer and other diseases 1. To date, their study has been cited more than 4,000 times, which reflects the intensive interest of researchers in serum miRNAs as noninvasive biomarkers. Exosomes are small extracellular vesicles (sEVs) (30-150 nm) that are secreted by fusion of multivesicular bodies to the plasma membrane 2. These extracellular vesicles are functional vehicles carrying a complex cargo of proteins, lipids, and nucleic acids 3. Serum exosomes are regarded as the main vector for circulating RNAs, and RNAs within exosomes are more stable and are protected from degradation by RNA enzymes 4. Increasing interest has been focused on serum exosome miRNAs as potential biomarkers for the detection of various cancers and other diseases. In the past decade, the number of publications on serum exosomal miRNAs has increased dramatically. However, there are still some questions that need to be addressed in the field. First, many studies addressing the diagnostic or therapeutic potential of serum exosomal miRNAs have been carried out with mice or rats models 5-7 , but to what extent the mouse and rat serum ex...