What are the types of keratinocytes?

Keratinocytes exist in the epidermis, which is composed of 95% keratinocyte cells. Within the epidermis, keratinocytes are organized into four different layers: the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. 

1. The stratum basale is the layer of the epidermis which covers the keratinocyte stem cells and differentiating keratinocytes. Cell proliferation and division occur in this layer. Stratum basale keratinocytes are bound to the basal lamina by hemidesmosomes. These connections assist to maintain the integrity of the epithelium as well as regulating proliferation and differentiation of keratinocytes. Keratinocyte stem cells are columnar in shape, and are about 6-10 micrometers in size.
2. The stratum spinosum is found above the stratum basale. This layer has 8-10 sheets of keratinocytes that have a reduced potential for cell division. It is composed of polyhedral keratinocytes of about 10-15 micrometers in size and also show more eosinophilic cytoplasm and 1-2 visible nuclei. In this layer, keratinocytes are known as spinous keratinocytes because they share manu desmosomes and adherent junctions. These cell-cell junctions exist through the plasma membrane and are connected by tonofibrils. In the more superficial region of the stratum spinosum, keratinocytes become more flattened as they move towards the surfac due to the change in the type of synthesized keratins. 
3. In the outer layers of the stratum spinosum, keratinocytes change their gene expression and generate kerato-hyalin granules, ultimately forming the stratum granulosum. This layer is about 15 micrometers thin, and keratinocytes are flattened and show many kerato-hyalin granules in the cytoplasm. The granulas are polygonal, and highly basophilic. The keratin filaments progressively grow more abundant, which makes the epidermal barrier stronger. These processes are the starting point for cornification, or keratinization, of keratinocytes. 
4. The stratum corneum is composed of the degenerated keratinocytes (corneocytes). Corneocytes are connected by desmosomes to one another and exist in the ECM in non-polar lipids organized in layers. During the last stages, corneocytes lose their nucleus, are filled with keratin, and are surrounded by a layer of proteins and lipids. The more keratinocytes that are produced in the stratum basal, the more thickness there is in the stratum corneum. The dead cells in the stratum granulosum lead to the loss of desmosomes along the stratum corneum, making cell-cell junctions weaker and cursing cell fragments to peel off from the epidermis. Keratin and filaggrin make up for 80-90% of protein of the stratum corneum.