Category: DNA

Nucleolus via Fibrillarin

3/16/2017

Z-stack

High magnification timelapse (cell division)

Figure 1. Movies of fibrillarin in Nucleoli. Left: Z-stack of live hiPS cells expressing mEGFP tagged fibrillarin imaged on a spinning-disk confocal microscope. Images start from the bottom of the cells and end at the top. Right: Timelapse movie of live hiPS cells expressing mEGFP tagged fibrillarin. Images were collected in 3D every 3 minutes for 1.5 hours on a spinning-disk confocal microscope. Image is a maximum intensity projection. Playback speed is 900x real time.

Figure 2. Time series of cell division. A single cell going through cell division taken from the movie on the right.

Observations

Fibrillarin marks the dense fibrillar component (DFC) of the nucleolus, the nuclear subcompartment where ribosome biogenesis occurs.
During much of interphase the nucleolus exists in 1-2 large, textured clusters within the nucleus of hiPS cells. During cell division, the nucleolus appears to ‘melt’ and then dissociate. After cell division, the nucleolus reassembles, first into small particles and progressing into the larger textured clusters observed during interphase. Low levels of fibrillarin are visible on chromosomes during chromosome segregation in mitosis.

Nuclear envelope visualized via lamin B1

3/10/2017

Low magnification timelapse

High magnification timelapse

Figure. Timelapse movies of hiPSC cells expressing mEGFP tagged Lamin B1. Images were collected in 3D every 3 minutes for 12 hours (left) or every 35 seconds for 23 minutes (right) on a spinning-disk confocal microscope. Images are maximum intensity projection (left) or single slices from the middle of the z-stack (right). Playback speed is 1800x (left) and 350x (right) real time.

Observations

Lamin B1 is a member of the lamin family of proteins that make up the nuclear lamina, located just inside the inner nuclear envelope. - In hiPS cells, nuclei in these cells occupy 30-50% of the cell volume making them very prominent. In the center of cells the nuclei occupy almost the entire cytoplasm such that a ‘bird’s eye view’ of the cell monolayer shows nuclei that appear tightly packed together.
As the cells enter mitosis, the lamin B1-containing nuclear envelope is seen to ruffle and take on a wavy morphology as it begins to breakdown. However the nuclear envelope does not completely breakdown during mitosis. As the nuclear envelope reforms, invaginations are seen that can look like spots within the nucleus. These spots decrease and disappear over time suggesting that they may be cell cycle related. These invaginations are also seen with Sec61B, which labels the ER including the peripheral ER surrounding the nucleus (See ER section).

Cell Structure Observations

Nucleolus via Fibrillarin

Nuclear envelope visualized via lamin B1

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