How is keratin formed in cells?

Keratinocytes are skin cells that form in the basal layers
of the cell, becoming squamous (flattened) as they rise up toward the skin's surface,
and are eventually shed. While we know the life cycle of these cells well, there is
still work to be done on exactly how they form keratin, and what factors determine
whether a specific basal cell will become a keratinocyte or
not.

Keratin is a fibrous protein which is present in the
cytoskeleton of many different types of cells; what distinguishes keratinocytes is not
only the amount of keratin present in their cytoskeletons, but also the arrangement of
the fibers. Currently the leading theory is that the keratin in keratinocytes is
arranged in bundles of parallel fibers; this arrangement helps explain how these cells
can be both strong and flexible at the same time, and also why they flatten as the
amount of keratin increases.  As the keratin is created, cell organelles go into stasis,
and a fully keratinized cell is dead by the time it reaches the outer layers of the
skin.