Question

1. Describe the stages of C. elegans development, and indicate how you would differentiate between these stages?

Answer 1

Embryonic development:

Once the oocyte is fertilized, the zygote undergoes rotational holoblastic cleavage. An anterior-posterior axis is formed with the entry of the sperm in the oocyte. The sperm pronucleus migrates to the region committed to becoming the posterior pole of the embryo. The migration of the pronucleus is also accompanied by the asymmetric distribution of PAR proteins, which leads to asymmetric cell division.

Axis formation

The first asymmetric cell division results in two daughter cells one has PAR-3 and PAR -6 and is called AB cell and the other one has PAR-1 and PAR-2 and is called as P1 cell. In the second cell division, the AB cell divides to give rise to Aba and Abp cells while the P1 cell divides to form P2 and EMS cell. This division establishes the dorso-ventral axis.

Gastrulation

Once the embryo reaches 26-cell stage gastrulation occurs. An opening is formed in blastula followed by the involution of the cells into the blastopore.

Post-embryonic development:

The eggs hatched into larvae which subsequently transform into L1, L2, and L3 stages. However, under unfavorable conditions, it enters an alternative third larval stage, dauer stage. The stress resistance Dauer larvae can be identified by their sealed mouth and thin body structure. This stage lasts for nearly few months.