Soft x-ray lithographic studies of interphase chromosomes.

Area of Science:

• Cell Biology
• Biophysics
• Microscopy

Background:

• Understanding the 3-dimensional organization of chromatin within human nuclei is crucial for comprehending cellular function.
• Conventional microscopy techniques have limitations in resolving the fine structural details of nuclear and chromosomal organization.

Purpose of the Study:

• To investigate the 3-dimensional structure of purified interphase human nuclei and chromosome arrays using soft x-ray absorption lithography.
• To compare the effectiveness of soft x-ray absorption lithography with conventional imaging methods for visualizing nuclear and chromosomal structures.

Main Methods:

• Soft x-ray absorption lithography was employed to pattern purified human nuclei and chromosome arrays on PMMA resists.
• Scanning electron microscopy (SEM) was used to image the resulting patterns.
• Comparisons were made with transmission electron microscopy (TEM), SEM, high-voltage electron microscopy (HVEM), and light microscopy.

Main Results:

• Soft x-ray resist images displayed orderly 3-dimensional arrays of absorption profiles.
• Dense chromatin at the nuclear edge showed aligned periodic peaks (approx. 2200 Å diameter) with substructure.
• Periodicity and alignment of interphase chromosomes were consistent with birefringent data, indicating high 3-dimensional order, even in nuclei with minimal protein content beyond DNA and histones.
• Dispersed chromosome fibers exhibited similar absorption periodicities.

Conclusions:

• Soft x-ray absorption lithography provides significant new insights into the ordered structure of human nuclei and chromosomes.
• The technique effectively visualizes the 3-dimensional organization of chromatin and chromosome fibers.
• This method offers a valuable tool for studying the structural basis of nuclear organization.