Neuroectodermal specification and regionalization of the Spemann organizer in Xenopus.

During gastrulation in Xenopus convergence and extension movements, mediated by mediolateral intercalations, are the driving force for early neural plate morphogenesis. Here we show that the winged helix transcriptional regulator, Xfd-12' is dynamically expressed in medial neural plate precursors that undergo convergence and extension movements. These medial neuraxial progenitors are specified in and beyond the Spemann organizer prior to specification of the basal anlage of the neural plate.

Retroviral capture of c-erbB proto-oncogene sequences: rapid evolution of distinct viral genomes carrying mutant v-erbB genes with different transforming capacities.

The evolution of oncogene-transducing retroviruses was followed by studying the genomes of five new, erbB carrying retroviruses. These viruses, isolated from cells of one chicken infected with Rous Associated virus 1 (RAV-1), had captured c-erbB sequences as a consequence of RAV-1 integration into the host genome. Their genome structures were distinct; however, their v-erbB genes had sustained identical 5' and 3' deletions and the v-erbB-env junctions were identical at the nucleotide level.

Detection of avian hematopoietic cell surface antigens with monoclonal antibodies to myeloid cells. Their distribution on normal and leukemic cells of various lineages.

The isolation and characterization of monoclonal antibodies reacting with cell surface antigenic determinants of normal and leukemic avian hematopoietic cells is described. The antibodies were produced by immunizing mice with normal macrophages, as well as with myeloid cells transformed with the avian acute leukemia viruses MC29, AMV and E26. Eleven antibodies were characterized for their reactivity with a variety of normal and leukemic cells of the myeloid, B- and T-lymphoid and of the erythroid cell lineage.

Erythroblast cell lines transformed by a temperature-sensitive mutant of avian erythroblastosis virus: a model system to study erythroid differentiation in vitro.

A continuous chicken erythroblast cell line transformed by the temperature-sensitive mutant ts34 of avian erythroblastosis virus was developed. This cell line, designated HD3, could be induced to terminally differentiate by shift to the nonpermissive temperature. The differentiated cells resembled erythrocytes as judged by morphology, expression of hemoglobin as determined by benzidine staining and radioimmunoassay, and by the expression of differentiation-specific cell surface antigens.

Mutant of avian erythroblastosis virus defective for erythroblast transformation: deletion in the erb portion of p75 suggests function of the protein in leukemogenesis.

Previous studies have shown that td359 AEV, a mutant of avian erythroblastosis virus (AEV), is unable to transform erythroblasts in vitro or in vivo but is capable of transforming fibroblasts in vitro and of causing sarcomas in chicks. In this paper we show that the mutant synthesizes a gag-gene related protein (delta p75) which is about 1000 daltons smaller than the protein, p75, induced by wild-type AEV. The mutant protein lacks 3 of the approximately 53 lysine-arginine tryptic peptides resolved in p75 and also contains an additional peptide.