Summary: The uneven division during the first cell cycle of C. elegans embryogenesis is illustrated as an example cell biology research. Images, movies, matching animations and bioclips are provided to help understand this phenomenon.

The Phenomenon

Image I: anterior (A) <-> posterior (P)

Image II: A <-> P


Image III: A (with mouth) <-> P (with tail)

Image I is a one-cell C. elegans embryo (right after sperm enters oocyte). Image II is a 2-cell C. elegans embryo. An adult C. elegans is in image III. In a single-cell embryo, the difference in anterior and posterior is already established. In the 2-cell embryo these differenences are more pronounced (large vs small cells). In the adult worm, there are very distinct structures in the anterior versus posterior.

Helpful information for understanding the early C. elegans embryo

Basic components in embryoG

Use mouse-over each of the titles to observe the components.


Additional Information

ZygoteG: This is taken soon after paternal (dad) pro-nucleusG entered the egg.
This is still an one-cell embryo (instead of 2-cell) with mother pro-nucleus at the left and father pro-nucleus at the right. The cleavage in the middle of the embryo is pseudo-furrow although it looks like 2 cells.
The yellow bumps in the embryo are the refractile cytoplasmic organelles. They move around as the embryo divides.

A close look with animation

Click on either images to see the movie

One-cell embryoG
develops into two-cell embryo

Matching Animation

Animation and Bioclips of cell polarity & Cell division

(Click the image to visit bioclipG page)


From the phenomenon and cell polarity animation, polarizationG can be observed as the generation of two unequal-size daughter cells and the unequal distribution of cellular components in the two daughter cells, e.g.: components on cell membraneG (notice the distribution of the purple and orange lines).

Research questions

1) What components are distributed differently?

2) How important is it to have the cellular components polarized?

3) What are the functions of the polarized cellular components?

4) What are the spatial and temporal relationship between the polarized and non-polarized components?


1. Images of 1-cell and 2-cell embryo: Kevin O’Connell, National Institute of Diabetes & Digestive & Kidney Diseases (NIDDK).

2. Image of the adult worm: Bob Goldstein, The University of North Carolina at Chapel Hill
Chapel Hill.


Bioclip: a self-contained animations with in-depth presentation of biology concepts to help convey the research focus of a laboratory.

Embryo: the early developmental stage of an organism (C. elegans in this case) after fertilization and before hatching.

Membrane: permeability barrier surrounding cells or organelles and consists of a phospholipids bilayer, together with associated membrane proteins.

Polarization: the action/process of establishing polarity.

Pro-nucleus: one of two haploid nuclei in a newly fertilized embryo (one maternal and one paternal). (The Cell – A Molecular Approach. Geoffrey M. Cooper 1997)

Zygote: a fertilized egg; diploid cell resulting from fusion of a male and female gamete. (Molecular Cell Biology/Harvey Lodish [et al.] – 4th)

Egg Shell Cell Border Nuclei Spindles Poles Polar Body