Flashcards in Chapter 4: Developmental Biology of the Skin Deck (46):
____________________ are immune cells that reside predominantly in the epidermis, and internalize and present potentially harmful antigens encountered in the environment to initiate an immune response.
___ is a transcription factor with multiple isoforms that is perhaps the central regulator of epithelial identity.
____ is very important to hair follicle formation and function.
It is critically important for the development of appendages
EDAR (ectodysplasin A receptor)
BMP (bone morphogenic protein) ligands are a family of ligands that bind BMP receptors and, among other functions, regulate _______________
hair follicle cycling and growth
____________ transcription factor family is important in large-scale body patterning
The cell that composes the majority of the epidermis is the ___________, so named because the structural protein keratin is abundant in that cell
While keratins are the protein most abundant in the epidermis, _________ are the most abundant protein in the dermis.
The primary cell of the dermis is the _________, which produces collagens but has a large repertoire of other functions
The third trimester runs from weeks ________ and is when most development completes, including the formation of the _________ from the skin whose function is thought to lubricate for the pas- sage through the birth canal
26 to 40
The morula divides to form a more complicated structure called a ______, which has 2 main parts
inner cell mass (embryo)
The _________ forms eventually the epidermis and melanocytes, but also the nervous system
Neural crest development initiates during the _______ of fetal life when the ectoderm forms the neural plate within it
Although they mostly contribute to the axial skeleton and muscles, early somite fibroblasts are also precursors for ___________
Many of these fibroblasts—especially from body locations such as the back—originate from the dorsolateral portions of the somite, which is also called the _______________.
Non–melanocyte-related diseases of neural crest migration include _________________________ where 22q11.2 deletion results in defects in cardiac, craniofacial, and endocrine organs, among others.1
Skin forming begins when the ectoderm converts to a single layer known as the _____________—a cuboidal, mitotically active and undifferentiated layer.
It expresses the gene _____, which is vital for epidermal differentiation and also corrupted in the EEC syndrome.
Genes that control periderm formation include _____, _____, and IKKα, likely partially through the nuclear factor kappa B (NF-κB) pathway.
Recent evidence suggests it is also a protective layer that prevents pathologic adhesions to adjacent epithelium, so that lack of periderm formation leads to the _________________
human cocoon syndrome
The dermis is formed from the mesodermal layer of the embryo; consequently, it is referred to as ___________
Whereas fibroblasts from the ventral body are thought to derive from _______________, fibroblasts from the head are thought to develop more from ____________________, and those, for example, of back skin are more likely to develop from _________ (and more specifically dermatomyotomes).
lateral plate mesoderm
neural crest precursors
In particular, fibroblasts are programmed with a specific combination of ________, which, even after culturing of fibroblasts, are retained to specify,
The upper dermal fibroblast progenitor (PDGFRa+, _______, Dlk−, ____) become dermal papillae (a ball of fibroblasts that control hair keratinocytes), arrector pili muscle (muscle attached to hair that causes goosebumps), and the fibroblast of the upper dermis termed ______________.
The lower dermal fibroblast progenitor (PDGFRa+, Blimp1−, Dlk1+) give rise to not only adipocytes but to the _________ (lower density and biased _______ over col- lagen III production).
Even though peroxisome- proliferator-activated receptor γ (PPARγ) is an important transcription factor for both white and brown adipose development, ______ appears to be uniquely important for brown adipose development
Hallmark clinical syndromes of defects in mesenchymal development include focal dermal hypoplasia or ________ caused by mutations in the PORC gene,
Analogous clinical syndromes for adipose tissue include the lipodystrophy syndromes such as Berardinelli-Seip where a lack of adipose development occurs from defects in the lipid synthesizing ________
Melanocytes can be detected by the _________ estimated gestational age (EGA) in human epidermis
Their (melanocyte) precursor is a __________ progenitor, which also can differentiate into glial cells in addition to melanocytes.
These precursor cells actually can lose expression of MITF and KIT to revert to a ___________—the adult melanocyte stem cells—that live in the _________ bulge stem cell compartment
In addition to populating hair follicles, melanoblasts are thought to home to sweat glands where they might contribute to ___________.
These melanocyte stem cells supply interfollicular melanocytes as well, most dramatically during ultraviolet light therapy for patients with ________
dermal melanocytes are thought to persist after birth in several locations, including the dorsa of the hands and feet, the _________, and the scalp. These areas are clinically important because they are also common sites for ________.
Another example of defective melanocyte development is piebaldism where disrupted melanocyte _________ secondary to defects in, for example, __________ signaling lead to areas of albinism
c-kit growth factor
In the skin, sensory neurons develop from the ________ (head) or __________ (elsewhere)
dorsal root ganglia
Merkel cells are found as early as ________ EGA with particular high density at volar sites, appendages, and ________
The earliest morphologic changes are the formation of a hair placode in the epidermis, where the keratinocytes become thinner, columnar, and tightly packed. This occurs around ___________
75 days EGA
The following stage is the hair germ phase (___________; sometimes referred to as hair bud), which is the more pronounced downward movement of epithelium forming a ___________, followed by continued downward epithelial invasion through the peg stage (100 days EGA).
During the peg stage, the epithelium begins to wrap around and encompass the associated inductive fibroblast population, which is now called the _______________
80 days EGA
The activity of ________ is perhaps the most important for appendage development
Downstream genes that are activated and necessary for morphogenesis include the ________ and ________ functions.
ectodysplasin ligand (EDA) and receptor (EDAR)
Sebaceous glands develop during the bulbous peg phase from _____ ______ hair follicle keratinocyte stem cells during 13th to 14th weeks of fetal life.
**Interestingly, while sebaceous glands have a dip in activity during childhood, they are more active during embryogenesis (in the production of the vernix caseosa) and puberty
Nail development also requires HOX programming as is evident by patients with nail-patella with mutations in the __________.
HOX gene LMX1b.
Volar dermatoglyphics development begins around ______ EGA when protuberances in palms and soles, called volar pads, appear
Following this, they arborize and sprout to extend themselves to mature in reactions involving ________ and _________.
__________ is required for the recruitment of associated cells such as pericytes
TGF-β and platelet-derived growth factor (PDGF)
While the EphrinB2 released by arteries as a ligand for ______ receptor on veins is important to maintain the arteriovenous (A-V) plexus, how arteries and veins are juxtaposed has only recently been elucidated.
In one current model, the signaling agent ______ is produced from arterial endothelial cells, and stimulates chemotaxis and expression of _____, a G-protein–coupled receptor, on venous endothelial cells to promote A-V alignment.
Lymphatic development occurs through the maturation of established venous endothelial cells that express ______.
These cells bud and migrate off to establish lymph vessels, first in regions of _______ expression in the _____________.
One hallmark disease is the Sturge-Weber syndrome where defects in the gene _______ cause prominent port-wine stains on the ______, as well as __________ anomalies leading to seizures and mental retardation, among other symptoms, and which is more concerning than the port-wine stains
The yolk sac also generates some important myeloid lineages, such as the skin-specific antigen presenting cells known as the Langerhans cell --> are detectable by ________ of gestation.
The second wave of development of hematopoietic cells occurs in the ________, with later contributions from the liver