Final answer:
Keratinocytes in the stratum spinosum layer retain their nuclei and organelles and begin producing keratin. As they move to the stratum granulosum, they die and contribute to the formation of skin's upper layers and hair and nails.
Step-by-step explanation:
Keratinocytes that retain their nuclei and organelles and begin the production of keratin are found in the stratum spinosum layer of the epidermis. These cells are responsible for releasing a water-repelling glycolipid that helps prevent water loss, making the skin relatively waterproof. As keratinocytes are produced in the stratum basale, they get pushed upwards into the stratum spinosum where they start synthesizing keratin.
Further up, in the stratum granulosum, keratinocytes continue to change, their cell membranes thicken, and they generate large amounts of keratin and keratohyalin. This gives the stratum granulosum its grainy appearance. Eventually, in this layer, the nuclei and other cell organelles disintegrate, and the cells die, leaving behind keratin, keratohyalin, and cell membranes that contribute to the formation of the stratum lucidum or stratum corneum and the accessory structures of hair and nails.