Hertwig rule

Introduced by the German zoologist Oscar Hertwig in 1884, the rule emphasizes the cell shape as a default mechanism of spindle apparatus orientation.

Hertwig noticed that elongated egg divides not randomly, but orthogonally to its long axis.

The studied systems include the mouse embryo,[2] Drosophila epithelium,[3] Xenopus blastomeres (Strauss 2006), MDCK cell monolayers[4] and plants (Gibson et al., 2011).

It is at this rounding stage that the decision on the orientation of the cell division is made by the spindle apparatus.

The orientation of TCJs remains stable, independent of the shape changes associated with cell rounding.

Cartoon of the dividing epithelium cell surrounded by epithelium tissue. Spindle apparatus rotates inside the cell. The rotation is a result of astral microtubules pulling towards tri-cellular-junctions (TCJ), signaling centers localized at the regions where three cells meet.