ACTN1 mutations cause congenital macrothrombocytopenia

Congenital macrothrombocytopenia (CMTP) is a heterogeneous group of rare platelet disorders characterized by a congenital reduction of platelet counts and abnormally large platelets, for which CMTP-causing mutations are only found in approximately half the cases. We herein performed whole-exome sequencing and targeted Sanger sequencing to identify mutations that cause CMTP, in which a dominant mode of transmission had been suspected but for which no known responsible mutations have been documented. In 13 Japanese CMTP-affected pedigrees, we identified six (46%) affected by ACTN1 variants cosegregating with CMTP. In the entire cohort, ACNT1 variants accounted for 5.5% of the dominant forms of CMTP cases and represented the fourth most common cause in Japanese individuals. Individuals with ACTN1 variants presented with moderate macrothrombocytopenia with anisocytosis but were either asymptomatic or had only a modest bleeding tendency. ACTN1 encodes α-actinin-1, a member of the actin-crosslinking protein superfamily that participates in the organization of the cytoskeleton. In vitro transfection experiments in Chinese hamster ovary cells demonstrated that altered α-actinin-1 disrupted the normal actin-based cytoskeletal structure. Moreover, transduction of mouse fetal liver-derived megakaryocytes with disease-associated ACTN1 variants caused a disorganized actin-based cytoskeleton in megakaryocytes, resulting in the production of abnormally large proplatelet tips, which were reduced in number. Our findings provide an insight into the pathogenesis of CMTP.

Modification of the trypsin cleavage site of rotavirus VP4 to a furin-sensitive form does not enhance replication efficiency

The infectivity of rotavirus (RV) is dependent on an activation process triggered by the proteolytic cleavage of its spike protein VP4. This activation cleavage is performed by exogenous trypsin in the lumen of the intestines in vivo. Here, we report the generation and characterization of a recombinant RV expressing cDNA-derived VP4 with a modified cleavage site (arginine at position 247) recognized by endogenous furin as well as exogenous trypsin. Unexpectedly, the mutant virus (KU//rVP4-R247Furin) was incapable of plaque formation without an exogenous protease, although the mutant VP4s on virions were efficiently cleaved by endogenous furin. Furthermore, KU//rVP4-R247Furin showed impaired infectivity in MA104 and CV-1 cells even in the presence of trypsin compared with the parental virus carrying authentic VP4 (KU//rVP4). Although the total titre of KU//rVP4-R247Furin was comparable to that of KU//rVP4, the extracellular titre of KU//rVP4-R247Furin was markedly lower than its cell-associated titre in comparison with that of KU//rVP4. In contrast, the two viruses showed similar growth in a furin-defective LoVo cell line. These results suggest that intracellular cleavage of VP4 by furin may be disadvantageous for RV infectivity, possibly due to an inefficient virus release process.

Two different pathways for the transport of primitive and definitive blood cells from the yolk sac to the embryo in humans

During the early human embryonic period nutrients and blood cells are temporarily provided by the extraembryonic yolk sac (YS). The YS before week six is involved not only in primitive but also in definitive erythropoiesis. While the destiny of primitive erythroid cells that fill the blood vessels of the YS is well known, the final destination of erythrocytes present in the endodermal vesicular system is unknown. In the present study we have investigated, step by step, the destiny of the erythrocytes present in the endodermal vesicles during the embryonic period. Twelve human YSs and their corresponding yolk stalks were analyzed between weeks 4 and 7 of embryonic age by light and scanning electron microscopy. It is shown that erythrocytes (according to their size and morphological features) located within the endodermal vesicles of the YS wall are pulled out through endodermal pits into the YS cavity, from where they reach the lumen of the primitive gut of the embryo through the vitelline duct, a temporary pathway communicating both compartments. During the study period no erythrocytes were seen within the embryo's vascular network where only primitive erythroblasts were identified. Our results indicate that the vitelline duct plays an important transient role as a pathway for the transport of nutrients and blood cells between the YS and the embryo before week five of embryonic development that ends just at the time when YS-embryo circulation becomes established.

Budding and direct division of adult human erythrocytes in serum-free cultures

This paper documents the budding and division process of human erythrocytes in vitro using time-lapse light microscopy of hanging-drop preparations. The erythrocytes were prepared from normal adult human peripheral blood. Red blood cells showed cytoplasmic budding, segmentation, and direct division with delayed addition of erythropoietin in serum-free Dulbecco's modified Eagle's medium/nutrient mixture F-12 Ham. These observations are thought to be useful for developing model of definitive erythropoiesis and simple expansion of human erythrocytes.

Observation of non-nucleated erythrocytes in the peripheral blood of medaka, Oryzias latipes

The medaka, Oryzias latipes is a useful animal model for the study of vertebrate developmental genetics. Using May-Grünwald-Giemsa stain, we found non-nucleated erythrocytes in the peripheral blood of medaka. Eleven of 50 fish occasionally showed non-nucleated erythrocytes in their peripheral blood. We expect that this observation will be useful in future studies involving screening for hematologic mutants.

Light and electron microscopic observation of presumptive erythropoietic foci in the medaka yolk sacs

The medaka, Oryzias latipes is a useful animal model for the study of primary vasculature in vertebrate embryos. Using benzidine stain for erythroid cells, we found presumptive erythropoietic foci in the yolk sac vitellolysis zone at stage 39. These foci were present in the yolk syncytial layer, in the extravascular and vitellolysis zone from 9 days post fertilization (dpf) to 11 dpf, and then declined between 12 to 13 dpf with yolk mass depletion. A table of previous reports on various species of fish showing yolk sac erythropoiesis is also presented.

Histochemical study of the definitive erythropoietic foci in the chicken yolk sac

It is well known that avian yolk sac is involved in both primitive and definitive erythropoiesis during embryonic development. Definitive erythropoiesis is first detected at about 4-5 days incubation and its maximum activity is reached between day 10 and 15 of incubation, ending between days 18 and 20 of incubation. We confirmed the definitive erythropoietic foci in the chicken yolk sac throughout the 5th to 19th day of incubation by histochemical light and electron microscopy. The definitive erythropoietic foci were observed in the yolk sac endodermal layer from day 5 until day 19, just before hatching. Ultrastructurally, definitive erythropoietic foci were observed extravascularly in the yolk sac endodermal cell layer in direct contact with the vitellolysis zone. These findings provide a basis for clarifying definitive erythropoiesis in vertebrates.

Redistribution of microtubules in dendrites of hippocampal CA1 neurons after tetanic stimulation during long-term potentiation

It is now well accepted that the trafficking of AMPA receptors to the postsynaptic plasma membrane plays an essential role in long-term potentiation at the hippocampal Schaffer collateral synapses on CA1 pyramidal cells, but the motor mechanism of trafficking is unknown. We suspected that this trafficking of AMPA receptors during long-term potentiation may be carried out along microtubules by their motors. To ascertain this hypothesis, we light- and electron-microscopically studied the distribution of microtubules in dendrites of CA1 neurons of non-stimulated and stimulated rat hippocampal slices by using very strong tetanic stimulation for inducing long-term potentiation. As a result, we observed the following changes: 1. In immunofluorescence for microtubules and IP3 receptor using ultrathin-cryosections, linear signals of microtubules in main dendritic shafts were changed into fragmented. 2. Many spotty signals of microtubules emerged at the peripheral area of dendrites. Electron-microscopically, there was redistribution of microtubules in dendritic spines and dendritic shafts, and the thickening of post-synaptic density. 3. Many microtubules concentrated to thickened postsynaptic density in spines and new ones emerged, going to spines from dendritic shafts. These results strongly suggest that new tracks of microtubules from cell bodies to the stimulated postsynaptic membranes were produced after tetanic stimulation during long-term potentiation. This newly produced microtubules between stimulated postsynaptic membranes and the cell body must be the most promising candidate of the track for the trafficking of AMPA receptors to the stimulated postsynaptic plasma membrane.

Presence of erythrocytes in the villous trophoblast cell layer of normal first trimester and term human placentae

Light and electron microscopic examination of first-trimester and term human placental tissues were performed to identify erythrocytes containing hemoglobin in the villous trophoblast cell layer. Erythrocytes were not identified in chorionic villous epithelium at week 7 of gestation. These cells first appeared in the villous cytotrophoblast at week 8, and continued to be present in the villous cytotrophoblast until week 9, as shown by benzidine staining. At week 12 gestation, a cluster of erythrocytes was present in a villous syncytial sprout. At 40 and 41 weeks gestation, erythrocytes were located in the villous cytotrophoblast cell layer. Electron microscopic observations focused on the cytoplasm of villous cytotrophoblast at week 8, the syncytial sprout at week 12 and the cytotrophoblast cell layer at term, confirmed the presence of erythrocytes at an extravascular location, as observed by light microscopy.

Appearance of erythrocyte-like globules in the mouse visceral yolk sac endodermal cells on embryonic day 12, with special reference to blood islands

The mouse visceral yolk sac (VYS) is widely known to play an important role as erythropoietic tissue during embryonic periods. Mouse VYS from embryonic days 9 to 12 was examined by light microscopy, electron microscopy and histochemical analysis with benzidine to detect the presence of hemoglobin with special reference to the development of VYS, the disappearance of the blood islands in VYS, and the appearance of a novel structure in the form of erythrocyte-like globules in VYS endodermal cells. The villous appearance of VYS became complicated by the development of VYS endodermal cells. The blood islands positive for the benzidine reaction were light microscopically detected on embryonic days 9, 10, and 11. They disappeared on embryonic day 12, however. Erythrocyte-like globules positive for the benzidine reaction were not observed in VYS endodermal cells on embryonic days 9, 10, and 11, but then appeared on embryonic day 12, by light and electron microscopy. Erythrocyte-like globules in VYS endodermal cells, which appear after the disappearance of blood islands in VYS, may participate in erythropoiesis during embryonic development.

A light and electron microscopic study of the mouse visceral yolk sac endodermal cells in the middle and late embryonic periods, showing the possibility of definitive erythropoiesis

Hematological studies have revealed the importance of the visceral yolk sac (VYS) in the primitive erythropoiesis of mouse embryos at an early stage before day 12. We examined the possibility of the occurrence of extra-embryonic erythropoiesis at a stage later than embryonic day 12 by light and electron microscopic analyses. Surprisingly, a novel structure in the form of erythrocyte-like globules was observed in the VYS endodermal cells. They were consistently present in the VYS endodermal cells from embryonic day 12 until day 18 (birth is day 19), by immunocytochemical and enzyme histochemical analyses. They were immuno-positive for mouse erythrocyte antibody and also positive for the benzidine reaction showing the presence of hemoglobin. The erythrocyte-like globules were shown to be the erythrocytes present in the cytoplasm. These results indicated that erythropoiesis in the VYS endodermal cells continues from the early embryonic stage, as primitive erythropoiesis, until the late stage.