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A J Brothers

Publications and source records attributed to A J Brothers.

8 recordsLinked to original sources
PubMed1992

The marginal zone of the 32-cell amphibian embryo contains all the information required for chordamesoderm development.

The formation of the amphibian organizer is evidenced by the ability of cells of the dorsal marginal zone (DMZ) to self-differentiate to form notochord and to induce the formation of other axial structures from neighboring regions of the embryo. We have attempted to determine when these abilities are acquired in the urodele, Ambystoma mexicanum (axolotl), and in the anuran, Xenopus laevis, by removing the mesodermalizing influence of the vegetal hemisphere at different stages of development and culturing the animal hemisphere isolate. This was possible, even at the 32 and 64-cell stage, through the use of embryos with rare cleavage patterns. Cultured isolates were analyzed for morphological differentiation of mesodermal and neural structures, and for biochemical differentiation of the tissue-specific enzyme, acetylcholinesterase (AChE). Large amounts of mesodermal and neural structures, and normal expression of AChE were found in isolates made as early as the 32-cell stage in both species. Only a small increase in the percentage of isolates developing mesoderm was detected when isolations were made at later cleavage or blastula stages. The amount of mesoderm formed did not depend on the stage of isolation. Mesoderm differentiation was usually limited to the notocord and muscle. The isolates rarely formed pronephros, mesothelium, or mesenchyme, derivatives of ventral mesoderm, during normal development. The results indicate that the marginal zone of the cleavage-stage embryo contains all of the information needed for the formation of the organizer. The formation of dorsal mesoderm does not require subsequent interaction with the cells of the vegetal hemisphere, although the presence of those cells is likely to play a role in normal pattern formation.

Acetylcholinesterase↗
PubMed1988

Dorsal and ventral cells of cleavage-stage Xenopus embryos show the same ability to induce notochord and somite formation.

Cells in the dorsal marginal zone of the amphibian embryo acquire the potential for mesoderm formation during the first few hours following fertilization. An examination of those early cell interactions may therefore provide insight on the mechanisms important for organization of axial structures. The formation of mesoderm (notochord, somites, and pronephros) was studied by combining blastomeres from the animal pole region of Xenopus embryos (32- to 512-cell stages) with blastomeres from different regions of the vegetal hemisphere. The frequency of notochord and somite development was similar in combinations made with dorsal or ventral blastomeres, or with both. Our results show that during early cleavage stages the ventral half of the vegetal hemisphere has the potential to organize axial structures, a property previously believed to be limited to the dorsal region.

Animals↗
PubMed1976

Stable nuclear activation dependent on a protein synthesised during oogenesis.

A protein synthesised during oogenesis seems to be essential for the activation, during blastulation, of the nuclear genes essential for gastrulation and organogenesis. Nuclear transplantation experiments show that this interaction between the protein and the blastula nucleus produces a heritable state of nuclear activation.

Age Factors↗