Search

Platelet GPIIbIIIa is only synthesized in megakaryocyte or in cell lines with megakaryocytic features. The sequence for GPIIb and GPIIIa have recently been derived from cDNAs obtained from HEL cells. The sequence of these proteins produced by the megakaryocyte, has however, not been determined yet. This study describes full length cDNAs for GPIIb and GPIIIa isolated from megakaryocyte cDNA libraries. The cDNA sequences indicate the presence of nucleotide differences, between the sequence of the GPIIIa cDNAs from HEL cells, endothelial cells and megakaryocytes. One difference was also observed between HEL and megakaryocyte GPIIb at position 633 where a cystein in the megakaryocyte GPIIb, is replaced by a serine in the HEL sequence. The mRNA species for GPIIb (3.4kb) and GPIIIa (6.1 kb) were of the same size in HEL cells and human megakaryocytes. [ABSTRACT FROM AUTHOR]

Emerging evidence indicates that microtubule-associated proteins (MAPs) are implicated in synaptic function; in particular, mice deficient for MAP6 exhibit striking deficits in plasticity and cognition. How MAP6 connects to plasticity mechanisms is unclear. Here, we address the possible role of this protein in dendritic spines. We find that in MAP6-deficient cortical and hippocampal neurons, maintenance of mature spines is impaired, and can be restored by expressing a stretch of the MAP6 sequence called Mc modules. Mc modules directly bind actin filaments and mediate activity-dependent stabilisation of F-actin in dendritic spines, a key event of synaptic plasticity. In vitro, Mc modules enhance actin filament nucleation and promote the formation of stable, highly ordered filament bundles. Activity-induced phosphorylation of MAP6 likely controls its transfer to the spine cytoskeleton. These results provide a molecular explanation for the role of MAP6 in cognition, enlightening the connection between cytoskeletal dysfunction, synaptic impairment and neuropsychiatric illnesses. Microtubule-associated protein 6 (MAP6) is known to be important for synaptic plasticity and cognition, supposedly via interaction with microtubules. Here, the authors found that MAP6 is crucial for the stabilisation of enlarged synapses through its association with a different cytoskeletal element, actin. [ABSTRACT FROM AUTHOR]

The crosstalk between microtubules and actin is essential for cellular functions. However, mechanisms underlying the microtubule-actin organization by cross-linkers remain largely unexplored. Here, we report that tau, a neuronal microtubule-associated protein, binds to microtubules and actin simultaneously, promoting in vitro co-organization and coupled growth of both networks. By developing an original assay to visualize concomitant microtubule and actin assembly, we show that tau can induce guided polymerization of actin filaments along microtubule tracks and growth of single microtubules along actin filament bundles. Importantly, tau mediates microtubule-actin co-alignment without changing polymer growth properties. Mutagenesis studies further reveal that at least two of the four tau repeated motifs, primarily identified as tubulin-binding sites, are required to connect microtubules and actin. Tau thus represents a molecular linker between microtubule and actin networks, enabling a coordination of the two cytoskeletons that might be essential in various neuronal contexts. [ABSTRACT FROM AUTHOR]