The Role of Phase Contrast Microscopy in Cell Cycle Observation

Every cell, regardless of whether it is animal or plant in origin, undergoes the cell cycle, a process that involves growth and cell division. As mitosis or meiosis occurs, minute changes in the cell’s structure and in its components also take place. Prior to the observation technique provided by phase contrast microscopy, it was difficult to observe the cell cycle under a microscope primarily because the process required living cells. In traditional microscopy, it was necessary to stain the cell in order to produce enough contrast with which to observe progress in the cell cycle. The only problem is that staining often kills the cell. With phase contrast microscopy, observing living cells became a possibility.

The use of phase contrast microscopy in cell cycle observation
A phase contrast microscope allows users to view specimens without the need for staining the sample. This makes it an ideal tool to use for studying and observing the cell cycle, capable of revealing essential changes during cell division. Phase contrast microscopy provides an enhanced contrast mode, where the cell’s outline and any movements in the cell components may be easily viewed and identified. The changes may even be viewed using a time-lapse sequence so the cell cycle may be observed as a continuous process, where any break down, remodeling or replication may be seen.

Since cells undergo several phases during the cycle, any minute changes that may occur may be noted. The cell cycle phases (prophase, metaphase, anaphase, telophase) show significant alterations in the structure of a cell, changes that may be easily observed using phase contrast microscopy. This series of changes occur between the formation of the cell and its replication, something that can be easily monitored because the cell cycle is directional and sequential. It never occurs in reverse.

Observing the cell cycle is essential to understanding how the process of cellular differentiation occurs and what kind of changes contribute to what type of characteristics later on. In stem cell research, the cell cycle is an important component in the study on how differentiated cells may be maintained when they reach maturity.

How the phase contrast microscopy works
In conventional microscopy, light travels through and interacts with the medium. This interaction causes changes in the medium’s phase and amplitude, something that is affected by the properties of that medium. Colors and how the object appears will depend on the wavelength with which light travels and is absorbed.

The differences in the specimen’s composition and density will also affect the phase of light that passes through it. To the human eye using a more conventional microscope, changes in the object’s phase is difficult to observe. In a cell cycle, these changes, albeit minute, contain very important information. With phase contrast microscopy, light that passes through the specimen may be observed along with a reference. The interference can then provide the sample’s phase structure.

Some unstained objects or specimens are called phase objects because they do not absorb light and therefore change the phase of light that is diffracted by the object itself. They do this by retarding the light by about ¼ wavelength, which results to a phase difference that the human eye or even the camera film is not capable of detecting. In traditional optical microscopy, the image produced at the level of the eyepiece does not contain a lot of contrast, which makes details difficult to see and identify.

This problem was corrected when phase contrast microscopy was developed, allowing unstained specimens to produce contrast images that provided more details. Phase contrast microscopy is especially effective in observing the cell cycle because cells are often transparent, so any phase shifts that occur in the light that passes through the specimen may be easily converted to image contrast changes or amplitude.

The reason why phase contrast microscopy works so well with cell cycle observation is because of the way it manipulates light to process an image. Staining an object meant introducing a substance that is often toxic to the cells, so essentially, a stained specimen is really just a dead or fixed cell. With phase contrast microscopy, living cells may be viewed and cell cycle can be observed. The refractive index of the cell’s structure is altered because of differences found in the biochemical composition of living cells. This results to an image where cellular structures are seen as light and dark regions.

Phase contrast microscopy was invented in the 1930s by Frits Zernike, who later received the Physics Nobel Prize for his invention. Today, phase contrast microscopy remains as one of the most advanced and commonly used microscopy techniques for the observation of living cells, organisms and other transparent specimens.