A novel technique for observing the internal ultrastructure of human chromosomes with known karyotype

Area of Science:

• Cell Biology
• Genetics
• Microscopy

Background:

• Observing human chromosome internal ultrastructure via transmission electron microscopy (TEM) is challenging due to difficulties in detaching chromosome spreads from slides.
• Existing methods limit detailed ultrastructural analysis of specific chromosomal regions.

Purpose of the Study:

• To develop and validate a novel method for preparing human metaphase chromosome spreads for transmission electron microscopy (TEM).
• To enable detailed examination of the internal ultrastructure of various chromosomal regions, including centromeres, telomeres, and fragile sites.

Main Methods:

• Metaphase chromosome spreads were prepared on flexible thermoplastic (ACLAR) film.
• Chromosomes were stained with diamidino-phenylindole for karyotyping, fixed, stained with tannic acid, dehydrated, and embedded in epoxy resin.
• The resin sheet containing whole chromosome spreads was detached for TEM observation.

Main Results:

• The new method successfully produced detachable resin sheets with intact chromosome spreads.
• TEM revealed detailed ultrastructural patterns of human lymphocyte chromosomes, including centromeres, telomeres, and fragile sites.
• Discernible features included electron-dense boundaries, less dense internal regions, and peripheral chromatin loops.

Conclusions:

• This method overcomes previous limitations in preparing chromosome spreads for TEM.
• It facilitates comprehensive examination of human chromosome internal ultrastructure and its relation to function.
• The technique is valuable for advancing research into chromosomal organization and dynamics.