Integument Development: Lectures 20 & 21

Question 1

What is the difference between cytodifferentiation and histogenesis?

Answer 1

cytodifferentiation
-cell specialization (morphological, metabolic, biochemical)

histogenesis
-coordinated differentiation of cells into a tissue

Question 2

describe the formation of a multiple layered epidermis, including the derivatives from the intermediate layer

Answer 2

periderm - first epidermal structure, single layer of ectodermal cells. Formed by end of first month

By end of the 3rd month it has become a 3 layered structure.

1. basal layer - metabolically active
2. intermediate layer - stratum spinosum and stratum granulosum
3. superficial peridermal layer - with surface blebs

transition from a single layer to the triple layer requires activation of p63 (induced by inferior mesenchyme?). INactivation of p63 in required for diassociation of the basal layer from the intermediate layer. -upward movement of new layers of skin

Question 3

How is apoptosis related to epidermal development?

Answer 3

peridermal cells undergo apoptosis and fetal epidermis becomes barrier against the envrioment

Question 4

epidermal ridges and dermatogylphs

Answer 4

epidermal ridges start first as volar pads, which show up by 6.5 weeks and extend to the fingers at 7.5 weeks. The volar pad sets shape for ridges on epidermis.

Location of the volar padd influences shape of fingerprint: high and round -> whorls
low pad -> arch

TIming also influences shape:
early formation -> whorls
later formation -> arches

Question 5

what is the molecular basis for albanism?

Answer 5

albanism is from the lack of melanocytes migrating into the epidermis/dermis or lack of enzyme for melanin production

Question 6

what are the major groups of immigrant cells? Where do they derive from and what are their functions?

Answer 6

Langerhans’ cells

• from BM
• are APCs

Merkel Cells

• from neural crest
• slow-adapting mechano-receptors

Question 7

what embryonic tissue type do melanocytes develop from?

Answer 7

neural crest

Question 8

what’s the origin of dermal cells for the dorsal surface, ventral and lateral surface, and cranial and anterior neck surfaces of the body?

Answer 8

dorsal surface - mesenchyme from dermatome

ventral and lateral surface - mesenchyme from lateral plate mesoderm

cranial and anterior neck surface - mesenchyme from neural crest (not mesoderm)

Question 9

what signalling induces dermal cell formation?

Answer 9

Wnt signalling to mesenchymal cells which then express Dermo 1

Question 10

Dermal cell characters

Answer 10

expresses Dermo 1
loosly aggregated
interconnected by tight junctions, secretes thin watery matrix rich in glycogen and hyluronic acid

Question 11

What do trunk dermis, limb dermis and fance and anterior neck dermis derive from?

Answer 11

trunk -> somatic dermatomes

limb dermis -> from lateral plate mesoderm

face and anterior neck -> neural crest

Question 12

what is the composition of trunk dermis, and potentially all??, by the end of the 3rd month?

Answer 12

sensory innervation at wk 8

vascularizaiton

fibroblasts develop from mesenchymal cells, collagens 1 and 3, and elastic fibers are secreted

Question 13

What is instructive induction and how it relates to dermis and epidermis development?

Answer 13

early in development the dermis influences the epidermis development and it’s derivatives. THe epidermis then influences further development of the dermis

one tissue tells another how to develop

Question 14

what are the epidermal derivatives and their commonalities?

Answer 14

derivatives - hair, nails, mammary glands

commonalities
-development involves entodermal-merodermal interactions and inductions

• begin as epidermal downgrowths into mesenchyme
• mesenchyme: hair papilla, outer hair follicle and arrector muscles
• ectoderm: hair follicle, hair shaft, sebaceous glands, nails, eponychium, and secretory and duct components of mammary glands

Question 15

what are the proteins involved with hair development and distribution

Answer 15

epidermal placode forms first from wnt-11, FGF and Eda with inactivation of BMP. Eda causes expression of Edar

BMP inhibits follice development and dickkopf inhibits wnt, making a hairless interfollicular zone

dermal papilla induced by shh (edar receptor) from epidermal placode

then downgrowth

Question 16

what’s the adult hair cycle?

Answer 16

anagen - growth
catagen - follicular regression
telogen - resting
exogen - shedding

Question 17

What are milk lines? what developmental protein are they related to?

Answer 17

two bands of thickened wolffiane ridge ~6 weeks

Related to an expression of different Wnt proteins in the ectodermal cells

Question 18

what role do Wnts, neurogluin-3, tbx-3, PTH, BMP, and Msx-2 play in mammarygland development?

Answer 18

wnts - expressed along milkline

neurogulin-3: placode development

tbx-3 - location of ^^ marked by it’s expression

PTH - increases sensitivity of underlying mesenchymal cells to BMP-4

BMP4 - stimulates downgrowth of epithelial bud and expression of msx-2

Msx2 - inhibits the formation of hair follicles

Question 19

What is testicular feminization and how is it related to mammary gland development?

Answer 19

testicular femininization is when a genetic male is insensitive to testostrone due to a missing receptor and develop female phenotype.

Testosterone inhibits/regresses mammary gland development and the mesoderm mediates testosterone effect on the gland. The receptor is in the mesoderm.

Question 20

what hormones finalize mammary gland development?

Answer 20

increased estrogen - induce proliferation in mammary ducts and and enlargement of fatty tissue (works paracrine-ly from mesoderm)

pregnancy - progestrone stimulate formation of secretory alveoli in the ducts

baby suckingly sends a nerve signal to hypothalamus which signals the anterior pituitary to secrete prolactin and cause milk synthesis and the posterior pituitary to release oxytocin which causes milk ejection.