Establishment of the organizing activity of the lower endodermal half of the dorsal marginal zone is a primary and necessary event for dorsal axis formation in Cynops pyrrhogaster.

The formation of the head and trunk-tail organizers in the dorsal marginal zone (DMZ) of an amphibian embryo is thought to require spatial and temporal interactions between the Nieuwkoop center and the DMZ. Recent studies of the Xenopus embryo suggested that intra-DMZ interaction is also needed to establish the regional specificity of the DMZ. However, it is not yet clarified when and how the final pattern of the head and trunk-tail organizers is established.

Study of Cynops pyrrhogaster notochord differentiation using a novel monoclonal antibody.

Two monoclonal antibodies which reacted specifically with the notochord of the early Cynops pyrrhogaster embryo were screened. The antigen molecules were detected within and around the notochord. They were first found mostly between the neural plate and the dorsal part of the notochord in the early neurula (stage 15).

Establishment and movement of egg regions revealed by the size class of yolk platelets in Xenopus laevis.

Sizes of yolk platelets were measured in sections of oocytes and embryos in Xenopus. It was found that the average size of the largest group of platelets in cells differed between germ layers of neurulae. It was small (3 to 5 μm) in the ectoderm, medium-sized (5 to 8 µm) in the mesoderm, and large (over 8 μm) in the endoderm.

Possible mechanisms in the rearrangement of non-yolk cytoplasmic materials during maturation of theXenopus laevis oocyte.

Using the monoclonal antibody (MoAb) Xa5B6 as probe, the authors examined the mechanisms of cytoplasmic rearrangement occurring during maturation of theXenopus oocyte. The antigen molecules recognized by the MoAb are arranged in radial striations of the oocyte cytoplasm. The radial striations were disorganized in vitro by progesterone treatment, and the antigen molecules were uniformly distributed, predominantly in the animal hemisphere.

Formation of the Neural Plate and the Mesoderm in Normally Developing Embryos of Xenopus laevis: (Xenopus laevis/neurogenesis/mesoderm formation/organizer/mesoplasm).

Normally developing embryos of Xenopus were fixed at various stages between the blastula and early tail bud stage, and their serial sections were examined. The marginal belt of the blastula was characterized by abundance of cells with RNA-rich peripheral cytoplasm called mesoplasm. At the early gastrula stage, the marginal belt was folded into two layers giving rise to mesodermal material and marginal ectoderm.

Appearance and Distribution of RNA-Rich Cytoplasms in the Embryo of Xenopus laevis during Early Development: (germinal vesicle material/dorsal yolk-free cytoplasm/blastulation/mesoderm formation/Xenopus laevis).

The occurrence of the dorsal yolk-free cytoplasm in the fertilized egg of Xenopus was re-examined, and the appearance and the distribution of RNA-rich cytoplasms in Xenopus embryos during early development were examined with their paraffin sections. The results show that the dorsal yolk-free cytoplasm does not occur solely in the dorsal part of the embryo but is continuous to similar cytoplasmic mass in the central and the ventral part. The whole mass of this continuous cytoplasm is denoted here as the mesoplasm.

Distribution of the Germinal Vesicle Material during Progesterone-Induced Oocyte Maturation in Xenopus and in Cynops: (germinal vesicle material/oocyte maturation/Xenopus laevis/Cynops pyrrhogaster).

The distribution of the germinal vesicle material in the oocyte during progesterone-induced maturation was studied in Xenopus and in Cynops. In both species, two distinctive masses of yolkfree cytoplasm appear in specific areas of the oocyte and at definite stages of maturation. One, the primary cytoplasmic mass, is formed at the basal side of the germinal vesicle during early maturation and is very RNA-rich.

Accumulation of Annulate Lamellae in the Subcortical Layer during Progesterone-induced Oocyte Maturation in Xenopus Laevis: (annulate lamellae/oocyte maturation/Xenopus laevis).

Changes in the fine structure, the location and the number of stacks of annulate lamellae during progesterone-induced maturation of oocytes of Xenopus were determined by electron microscopy. longitudinal sections of full-grown oocytes, about 260 stacks of annulate lamellae were observed with marked concentration in the subcortical layer, particularly in the vegetal hemisphere. After exposure to.

CHANGES IN NUCLEOLI AT MATURATION OF NEWT OOCYTE.

Changes in the nucleoli of maturing oocytes and the eggs of Cynops pyrrhogaster were studied with light and electron microscopy. Extrachromosomal nucleoli moved toward the center of the germinal vesicle in response to the maturation stimulus, released presumed ribosomal ribonucleoprotein, and further moved toward the center of the nucleus to form an aggregate with chromosomes which behaved in a similar manner. A few.

OCCURRENCE AND FINE STRUCTURE OF SUBCORTICAL CYTOPLASMIC ISLETS IN FERTILIZED EGGS OF CYNOPS PYRRHOGASTER.

Fertilized and unfertilized eggs of Cynops pyrrhogaster were examined by light and electron microscopy. In fertilized eggs that have just been laid, there are numerous small cytoplasmic patches free of granules in the pigmented layer of the animal hemisphere. Many of these granule-free cytoplasmic islets gradually grow out subcortically from the pigmented layer and fuse to form a subcortical layer of yolk-free cytoplasm of varying thickness by the time of the first cleavage division.

POSSIBLE SIGNIFICANCE OF NUCLEAR VOLUME CHANGE DURING EARLY DEVELOPMENT OF NEWT EMBRYOS.

The nuclear volumes at several stages of development were measured on Triturus pyrrhogaster embryos and changes in the fine structure and reactivity towards alkaline fast green of the nuclei were also examined. It was shown that the blastula nuclei were reduced about 80% to reach a constant volume of about 1,400 μm by the tail bud stage in ectomesodermal parts of the embryos. In the endoderm, the decrease in the nuclear volume was slightly delayed.