Related Experiment Video
Updated: May 27, 2026
14:27
A Cell-Free Assay Using Xenopus laevis Embryo Extracts to Study Mechanisms of Nuclear Size Regulation
Published on: August 8, 2016
Mitotic chromosome size scaling in Xenopus
Esther K Kieserman1, Rebecca Heald
1Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA.
Cell Cycle (Georgetown, Tex.)
|November 11, 2011
Summary
Mitotic chromosome size scales during embryonic development. This study shows that chromosome size decreases by the neurula stage, suggesting epigenetic changes during DNA replication influence scaling.
Area of Science:
- Cell Biology
- Developmental Biology
- Genetics
Background:
- Rapid embryonic cell divisions reduce cell size without growth.
- Mitotic chromosome size must scale down to ensure proper segregation.
- Previous work showed nuclear and spindle size scaling in Xenopus egg extracts.
Purpose of the Study:
- Investigate the phenomenon of mitotic chromosome size scaling during embryonic development.
- Determine if chromosome size changes correlate with cell size changes during development.
- Explore the mechanisms underlying chromosome size scaling.
Main Methods:
- Combined nuclei from different stage Xenopus laevis embryos with egg extracts.
- Assembled mitotic chromosomes in vitro.
- Compared chromosome dimensions at various developmental stages.
- Investigated the role of cell cycle progression and DNA replication.
Main Results:
- Isolated sperm chromosomes did not show size differences between species.
- Mitotic chromosomes from early embryos (cleavage to blastula) were similar in size to sperm chromosomes.
- Chromosome area decreased by approximately 50% by the neurula stage.
- Swelling G2 nuclei did not increase mitotic chromosome size.
- Full cell cycle progression in egg extract increased mitotic chromosome size.
Conclusions:
- Chromosome scaling occurs during Xenopus embryonic development, with size decreasing by the neurula stage.
- Epigenetic mechanisms influencing chromosome size can be altered during DNA replication.
- In vitro assembly of chromosomes of varying sizes provides a model for studying underlying molecular mechanisms.
Related Concept Videos
01:51Lampbrush Chromosomes
In 1882, Flemming observed lampbrush chromosomes (LBC) in salamander eggs. Later in 1892, Rückert observed LBCs in shark egg cells and coined the term "lampbrush chromosomes" because they looked like brushes used to clean kerosene lamps.
LBCs are made up of two pairs of conjugating homologous chromatids. Each chromatid consists of alternatively positioned regions of condensed-inactive chromatin and loosely placed-active side loops, which can be contracted and extended. The loops resemble the...
LBCs are made up of two pairs of conjugating homologous chromatids. Each chromatid consists of alternatively positioned regions of condensed-inactive chromatin and loosely placed-active side loops, which can be contracted and extended. The loops resemble the...
02:04Polytene Chromosomes
Polytene chromosomes are giant interphase chromosomes with several DNA strands placed side by side. They were discovered in the year 1881 by Balbiani in salivary glands, intestine, muscles, malpighian tubules, and hypoderm of larvae Chironomus plumosus. Hence, these are also called "Salivary gland chromosomes." These are found in insects of the order Diptera and Collembola; in certain organs of mammals; and synergids, antipodes of flowering plants. Polytene chromosomes are also regularly...
02:36Cells Coordinate Growth and Proliferation
Cell size is a significant factor impacting cellular design, function, and fitness. There exists some internal coordination by which cells double their masses before division, thus, achieving homeostasis. Coordination between cell growth and proliferation depends on the checkpoints in between cell cycle phases. Loss of coordination or failure in the checkpoint mechanism can drive the cell to uncontrolled growth and loss of cellular function. Like dividing cells that coordinate cellular growth,...
02:02Meiosis II
Meiosis II entails cell division and segregation of the sister chromatids, resulting in the production of four unique haploid gametes. The steps for meiosis II are similar to mitosis, except that meiosis II occurs in haploid cells, whereas mitosis occurs in diploid cells.
The timing and cell division patterns of meiosis differ between males and females. In male meiosis, the centrosomes are part of the formation of the meiotic spindle. However, in oocytes, including that of humans, Drosophila,...
The timing and cell division patterns of meiosis differ between males and females. In male meiosis, the centrosomes are part of the formation of the meiotic spindle. However, in oocytes, including that of humans, Drosophila,...
01:57Meiosis II
Meiosis II is the second and final stage of meiosis. It relies on the haploid cells produced during meiosis I, each of which contain only 23 chromosomes—one from each homologous initial pair. Importantly, each chromosome in these cells is composed of two joined copies, and when these cells enter meiosis II, the goal is to separate such sister chromatids using the same microtubule-based network employed in other division processes. The result of meiosis II is two haploid cells, each containing...
02:57Meiosis vs. Mitosis
Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
Before the start of mitosis and meiosis I, the cell synthesizes DNA, resulting in two homologous copies of each chromosome. DNA synthesis is...
Before the start of mitosis and meiosis I, the cell synthesizes DNA, resulting in two homologous copies of each chromosome. DNA synthesis is...