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Karyomere formation in cleaving eggs of Tetradontophora bielanensis (Collembola)

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Klag J., Jura C., Krzysztofowicz A., Kisiel E.

Folia Biologica

1995

vol. 43

issue 1-2

61-67

The term "karyomere"designates a p[articular kind oforganization of the telophase nucleus, in which each individual chromosome is surrounded by a typical nuclear envelope, thus representing a small nuclear structure.In T.bielenensis they are formed during firts prophase and subsequently change into chromosomes making a metaphase plate.Each metaphase chromosome is completly enclosed by a double envelope, similar to a nuclear one but devoid of nuclear pores.The only place on the chromosome where the envelope is not complete is the region of the kinetochore.Anaphase starts with the division of the chromosome into chromatids and subsequent decondensation of the latter.During anaphase, te process of decondensation of the chromatids starts at the leading ends of each chromatid and hence, they acquire a tennis racket-like appearance.As a result, on the spindle poles two groups of the chromosome vesicles or karyomeres are gethered.Each karyomere has the appearance of a typical nucleus enclosed by a double envelope pierced by nucleus pores filed with nucleoplasm containing patches ofchromatin.It is suggested that karyomeres are formed only in species with a large amount of chromatin in their nuclei.

Predetermination of cytokinesis and transition from holoblastic to partial superficial cleavage in early embryonic development of Tetrodontophora bielanensis (Collembola)

88%

Klag J., Krzysztofowicz A., Jura C., Kisiel E.

Folia Biologica

2000

vol. 48

issue 3-4

137-142

In the T. bielanensis embryo, only karyokinesis occurs during the first cleavage division, and a two-nuclear syncytial embryo forms. Then, two cytoplasmic concentrations in the form of elongated rolls perpendicular to each other develop below the periplasm at the animal pole of the egg. The second cleavage division is also associated with karyokineses only. After the embryo reaches the four-nuclear stage, cytokineses occur at its animal pole, and two cleavage furrows perpendicular to each other develop in the periplasm above the cytoplasmic concentrations. The cell membranes forming within the furrows do not invade the cytoplasmic concentrations, but their growing tips push them into the egg interior, where they merge and form the central cytoplasmic concentration. The developing cell membranes do not invade the central cytoplasm; they band and grow above its surface. Four pyramidal blastomeres form as a result of this. The eight-blastomere embryo forms through both karyokinesis and cytokinesis, but the growing cell membranes now band below the previous ones and cut off anucleate parts of the mother blastomeres, which fuse with the central cytoplasm. Thus, during this phase of development the transition from holoblastic to partial superficial cleavage is initiated. Morphological analysis suggests that the formation of the first two cytokineses is predetermined by and depends on factors connected with the animal pole periplasm. It also suggests that the central cytoplasm constitutes the morphological field, inducing the transition from holoblastic to partial superficial cleavage.

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2 Folia Biologica

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Karyomere formation in cleaving eggs of Tetradontophora bielanensis (Collembola)

Predetermination of cytokinesis and transition from holoblastic to partial superficial cleavage in early embryonic development of Tetrodontophora bielanensis (Collembola)