Biology Reference
In-Depth Information
A
B
C
SC
GL
SL
SG
SC
HG
IRS
SG
SC
ORS
BL
Mx
IRS
DP
BM
DP
SCD
ACD
Figure 7.2
Illustration of skin lineages. (A) The epidermis comprises of four layers:
basal layer (red, BL), spinous layer (black, SL), granular layer (black, GL), and stratum
corneum (black, SC). Stem cells are located in the basal layer, residing on a basement
membrane (BM). They undergo symmetric cell division (SCD) to double their popula-
tion or asymmetric cell division (ACD) to self-renew and generate another daughter for
terminal differentiation. (B) Hair follicle and their associated sebaceous glands are
appendages of the epidermis. Stem cells (orange, SC) reside in the bulge stem cell
niche. They move upward to become progenitor cells for the sebaceous gland (light
blue, SG-P) and subsequently terminally differentiated to sebaceous gland cells (dark
blue, SG-M). In the hair follicle lineage, stem cells give rise to outer root sheath (dark
green, ORS), matrix (light green, Mx), inner root sheath (purple, IRS), and eventually
hair shaft. Derma papilla (DP) is a cluster of mesenchymal cells surrounded by the hair
bulb. (C) At the telogen, the secondary hair germ (HG) is formed at the base of the
bulge and directly interacts with the DP. Inner root sheath (IRS) is generated directly
from the stem cells.
With over two decades of molecular genetic analyzes of the epidermis
and HFs, there is extensive knowledge of the signaling circuitry and physi-
ologically relevant changes in gene expression that occur, not only during
normal adult homeostasis and embryonic development but also in wound
repair and tumorigenesis. This provides an exceptional foundation for
dissecting how miR-mediated regulation fine-tunes these molecular events
in mammalian stem cell and tissue biology.
5. Insights into the Global Role of miRs
in the Skin Epithelium: Conditional
Ablation of Dicer
Not surprisingly, the first insights of the importance of miRs in the
skin epithelium came from profiling the ones that are expressed in this tissue
and examining the consequences of conditionally ablating
Dicer
in this tissue
