The stage specific appearance of a retravirus, termed the Intracisternal
A particle (IAP) is a normal feature of early preimplantation development.
To date, all feral and laboratory strains of Mus musculus and even Asian
species such as Mus cervicolor and Mus pahari express the particles during
the 2-8 cell stages. IAP form by budding into the endoplasmic reticulum and
appear singly or as groups of donut-shaped particles within the cisternae
(fig. 1). IAP are also produced in large numbers in several neoplastic cells
such as certain plasmacytomas and rhabdomyosarcomas. The role of IAP, either
in normal development or in neoplastic behavior, is unknown.
The mouse intracisternal A particle-promoted placental gene retrotransposition is mouse-strain-specific.
