Polarization Microscopy - Biomedical Optical Phase Microscopy and Nanoscopy - page 302

Figure 15.1
Live sperm head of cave cricket viewed between crossed polarizers. The helical regions of the DNA,
wound in a coil of coil within the chromosomes, appear bright or dark depending on their
orientation with respect to the crossed polarizer (P) and analyzer (A). Bars indicate junctions of
chromosomes that are packed in tandem in the needle-shaped sperm head (width approximately
1

m). This is the first (and virtually only) mode of microscopy by which the packing arrangement
of DNA and the chromosomes have been clearly imaged in live sperm of any species. (The sperm
head is immersed in DMSO (dimethyl sulfoxide) for index matching and imaged with a high-
resolution polarizing microscope using rectified optics (97

μ

/1.25NA).) Source: From Ref. [1] .

3

(B) (C) (D)

(E) (F) (G) (H)

Figure 15.2
Birefringence of spindle, asters, and fertilization envelope in the early zygote of a sea urchin,
Lytechinus variegatus, observed between crossed polarizers (A, P) and a compensator (C, the arrow
indicates slow axis orientation), using a traditional polarizing microscope. In panels (B) through
(F), near the center of the cell, birefringent figures appear that represent arrays of parallel MTs of
varying density and orientation. Densely packed spindle MTs extend horizontally and appear
bright, while the less dense arrays of astral MTs extend radially centered near the spindle poles.
Because astral MT arrays are radially arranged, they appear either bright (horizontal orientation)
or dark (vertical orientation) as their birefringence either adds to or subtracts from the
birefringence of the compensator. The mitotic chromosomes exhibit negligible birefringence due to
the tight winding of DNA around histones. The fertilization envelope that surrounds the cell is
composed of tangentially aligned paracrystalline polymers inducing a strong birefringence that is
visible in all panels and appears brighter or darker in different quadrants due to the action of the
compensator. Source: Reproduced from Ref. [2] .