Final answer:
After injecting labelled keratin subunits into cultured skin cells, they are integrated into keratinocytes, particularly in the stratum spinosum. Over time, these cells move towards the skin surface and can be tracked using laboratory methods. This process is part of normal skin cell turnover but can occur more rapidly in conditions like psoriasis.
Step-by-step explanation:
After injecting labelled keratin subunits into cultured skin cells, a few minutes later, the keratin subunits will begin to integrate into the existing keratinocytes. Keratinocytes are cells that synthesize the fibrous protein keratin, which is essential for the structure and function of hair, nails, and the outer layer of the skin. These labelled keratin subunits will start to be incorporated into the cytoplasm of the keratinocytes, particularly those in the stratum spinosum, which is responsible for initiating keratin synthesis. In a chase experiment, after about 3 hours, the labelled subunits can usually be seen within the nuclei of interphase cells, but not in the cells that were in mitosis. Over time and with the natural turnover of skin cells, these newly formed keratins would migrate upwards as the cells move towards the stratum corneum, where keratinocytes eventually die and are sloughed away. This integration can be seen using tracking methods in the laboratory, whereby after several hours, some cells show the presence of the labelled keratin.
This natural process of keratinocyte turnover typically takes a month, but in some conditions like psoriasis, it can occur much more rapidly, resulting in skin patches that develop due to an accelerated rise of skin cells to the surface. By using labelled keratin, researchers can study the dynamics of keratin integration, cell division in the stratum basale, and cell death in the stratum corneum, helping to understand skin diseases and the effectiveness of potential treatments.