In early embryos, there is a low level of homogeneous MSN mRNA expression, presumably maternally contributed , with a concentration of transcript in the pole plasm. At gastrulation, strong expression is seen in the invaginating mesoderm . Later the strongest expression is seen in the visceral mesoderm, with weak expression also present in the central nervous system . The msn expression pattern during embryogenesis includes many cells that undergo migration or shape changes.
Pole cells migrate around the embryo, at first passively and then actively.
Mesodermal cell elongate and invaginate during gastrulation. The sections of the gut elongate to meet each other, and the endoderm then migrates along the visceral mesoderm. Cells in the CNS undergo both migration and exon outgrowth. A role for msn in these cell movements has yet to be demonstrated, since msn is maternally expressed and is essential for oogenesis. Cloning and characterization of human protein kinase with homology to Ste20.