Somatic cells make up the structural components of an animal, such as skin, muscle, and nerves.
The germ cells are the reproductive cells that will create the offspring of the animal. During development, the somatic cell lineages will enter a variety of differentiative pathways to generate the somatic structures of the adult. Each step along these paths will increasingly narrow the developmental potential of each cell type, preventing, for example, a hematopoietic stem cell from becoming anything other than a type of blood cell. Germ cells, in contrast, must refrain from undergoing any somatic differentiation so they can remain totipotent - they have to be the source of all cell types in the next generation. My lab is using the nematode Caenorhabditis elegans as a model genetic system to address this question.