No abstract

A limited number of glycoproteins including luteinizing hormone and carbonic anhydrase-VI (CA6) bear N-linked oligosaccharides that are modified with ␤1,4-linked N-acetylgalactosamine (GalNAc). The selective addition of GalNAc to these glycoproteins requires that the ␤1,4-N-acetylgalactosaminyltransferase (␤GT) recognize both the oligosaccharide acceptor and a peptide recognition determinant on the substrate glycoprotein. We report here that two recently cloned ␤GTs, ␤GT3 and ␤GT4, that are able to transfer GalNAc to GlcNAc in ␤1,4-linkage display the necessary glycoprotein specificity in vivo. Both ␤GTs transfer GalNAc to N-linked oligosaccharides on the luteinizing hormone ␣ subunit and CA6 but not to those on transferrin (Trf). A single peptide recognition determinant encoded in the carboxyl-terminal 19-amino acid sequence of bovine CA6 mediates transfer of GalNAc to each of its two N-linked oligosaccharides. The addition of this 19-amino acid sequence to the carboxyl terminus of Trf confers full acceptor activity onto Trf for both ␤GT3 and ␤GT4 in vivo. The complete 19-amino acid sequence is required for optimal GalNAc addition in vivo, indicating that the peptide sequence is both necessary and sufficient for recognition by ␤GT3 and ␤GT4.

Surprisingly little is known about the development of connections within a functional area of the cerebral cortex. We examined the postnatal growth of connections in mouse barrel cortex during the second and third weeks after birth, coinciding with the period of rapid synaptogenesis that occurs just after the barrels first form. A barrel is a group of neurons in layer 4 of somatosensory cortex that is part of a cortical column. Each whisker/barrel column is linked anatomically and functionally to a homotopic whisker on the contralateral face. Radial groups of cortical neurons were labeled with the neuronal tracer biotinylated dextran amine in mice ranging in age from postnatal day 8 (P8; P0 is the date of birth) to adulthood. The spatial distributions of retrogradely labeled neurons in different laminae were analyzed. The barrel map in layer 4 was used as a template to compare quantitative data from different animals and to account for substantial changes in barrel and barrel field size during development. Intrinsic projections 1) innervate increasingly more distant targets within barrel cortex up to 3 weeks of age; 2) continue to form in targets after 3 weeks, effectively strengthening existing connections; 3) follow a timetable for growth that is layer-specific; 4) link more distant barrel columns in layer 4 from neurons that are found preferentially in the barrel side and the septa between barrels; and 5) form over the shortest distances between the barrel columns. These data indicate that intrinsic connections in mouse barrel cortex develop by the progressive addition of neuronal connections rather than by sculpting preliminary connections. We describe statistically significant changes in connectivity during development that may be applied to model and assess the development of connections after a variety of experimental perturbations, such as to the environment and/or the genome.

Surprisingly little is known about the development of connections within a functional area of the cerebral cortex. We examined the postnatal growth of connections in mouse barrel cortex during the second and third weeks after birth, coinciding with the period of rapid synaptogenesis that occurs just after the barrels first form. A barrel is a group of neurons in layer 4 of somatosensory cortex that is part of a cortical column. Each whisker/barrel column is linked anatomically and functionally to a homotopic whisker on the contralateral face. Radial groups of cortical neurons were labeled with the neuronal tracer biotinylated dextran amine in mice ranging in age from postnatal day 8 (P8; P0 is the date of birth) to adulthood. The spatial distributions of retrogradely labeled neurons in different laminae were analyzed. The barrel map in layer 4 was used as a template to compare quantitative data from different animals and to account for substantial changes in barrel and barrel field size during development. Intrinsic projections 1) innervate increasingly more distant targets within barrel cortex up to 3 weeks of age; 2) continue to form in targets after 3 weeks, effectively strengthening existing connections; 3) follow a timetable for growth that is layer-specific; 4) link more distant barrel columns in layer 4 from neurons that are found preferentially in the barrel side and the septa between barrels; and 5) form over the shortest distances between the barrel columns. These data indicate that intrinsic connections in mouse barrel cortex develop by the progressive addition of neuronal connections rather than by sculpting preliminary connections. We describe statistically significant changes in connectivity during development that may be applied to model and assess the development of connections after a variety of experimental perturbations, such as to the environment and/or the genome.

We have identified a new gene in Drosophila on the basis of a mutation that affects both behavior and neuronal excitability. This mutation, called bemused (bem) is the result of a P element insertion at cytological position 85D. Flies defective at bem display greatly reduced coordination, flight ability and fertility. The bem mutation also affects synaptic transmission at the larval neuromuscular junction. In particular, bem larvae display a more rapid onset of augmentation than bem+ larvae. This effect is potentiated by the potassium channel blocking drug quinidine. The increased transmitter release that occurs in bem mutants following repetitive nerve stimulation is accompanied by the appearance of extra action potentials in the motor neuron. We conclude that the bem mutation increases neuronal excitability, possibly as a result of a defect in an ion channel structural or regulatory gene.