Download Bio 127 Section 4 Outline

Bio 127 Section 4 Outline
Ch. 11 Paraxial and Intermediate Mesoderm
-mesoderm forms all organs between ectodermal wall and endodermal tissues
-mesoderm helps both the ectoderm and the endoderm form their own tissues
-anterior to trunk mesoderm is head mesoderm
-consist of unsegmented paraxial mesoderm and prechodal mesoderm
-provides head mesenchyme that forms tissues and musculature of face and eyes
-muscles form differently than muscles formed from somites
I) Trunk mesoderm of neurala-stage embryo subdivided into 4 regions
A) Chordamesoderm
1) Central region
2) forms notochord
B) Paraxial (somatic) mesoderm
1) tissues from this region located in back of embryo surrounding spinal cord.
2) Cells form somites, muscle, and connective tissues of the back
C) Intermediate mesoderm
1) forms urogenital system which includes kidneys, gonads, and associated ducts
D) Lateral plate mesoderm
1) Farthest away from notochord.
2) Forms heart, blood vessels, and blood cells of circulatory system
3) Lines body cavities
4) Helps form extra embryonic membranes important for transporting nutrients
E) The 4 regions specified along mediolateral axis by different amounts of BMPs
1) More lateral mesoderm expresses higher levels of BMP4 than midline areas
2) It is thought that different BMP concentrations may cause differential expression of
Forkhead (Fox) family of transcription factors
II) Paraxial Mesoderm: Somites and Their Derivatives
A) Somite formation
1) cells of paraxial mesoderm forms somites by antagonism of BMP signaling by
Noggin protein.
2) Mesoderm cells organize into whorls of cells that are split apart by fissures
3) Outer cells join into an epithelium while inner cells remain mesenchymal
4) Important components of somitogenesis
(i) Periodicity: “clock and wave” mechanism. Clock provided by Notch and Wnt
pathways. Rostral-caudual gradient provides wave of FGF
(ii) Fissure formation: Eph tyrosine kinase and ephrin proteins
(iii)Epithelialization: Ectodermal signals cause somatic cells to undergo
mesenchymal-epithelial transition. N-cadherin links cells into epithelium and
fibronectin matric with Eph and ephrin promote separation of somites from each
other
(iv) Specification: form different structures and pecified by Hox genes they express
(v) Differentiation: commitment of cells within somite occurs relatively late.
Specification of multipotent cells depend on location.
(a) ventromedial portion of somite induced to become sclerotome by paracrine
factors (Noggin and Shh) secreted from notochord.
(b) Remaining cells make dermamyotome
(i) Central dermamyotome generates muscle precursors and tissue layer of
the back. Maintained by wnt signals from epidermis. Also generates
brown fat
(c) Myotome: portion of somite that gives rise to skeletal muscles. Made of
primaxial and abaxial component
B) Myogenesis: Generation of Muscle
1) Myogenic bHLH proteins (myogenic regulatory factors MRFs) bind to DNA and
activate muscle-specific genes.
2) Satellite cells within basal lamina respond to injury or exercise by proliferating into
myogenic cells to form mew muscle fibers
3) Myoblast fusion
(i) Begins when myoblast leaves cell cycle
(ii) Cells align into chain
(iii)Cell fusion
4) myostatin negatively regulates number and growth of muscle fibers
C) Osteogenesis: Development of Bones
1) Intramembranous ossification: direct conversion of mesenchymal tissue into bone
2) Endochondral ossification: mesenchymal cells differentiate into cartilage and are
replaced by bone.
(i) Characteristic of vertebrae, ribs, and limbs
(ii) Vertebrae and ribs form from somites; limb bones from lateral plate mesoderm
(iii)Divided into five stages
3) Vertebrae formation
(i) Notochord induce surrounding mesenchyme cells to secrete epimorphin that
attracts sclerotome cells which condense and differentiate into cartilage.
(ii) Resegmentation enables muscles to coordinate movement of the skeleton
D) Dorsal Aorta Formation
1) intraembryonic circulatory system begins with dorsal aorta formation
2) Composed of internal lining of endothelial cells + outer layer of smooth muscle cells
3) Posterior sclerotome provides cells for the dorsal aorta and inter-vertebral blood
vessels
E) Tendon Formation: the Syndetome
1) 4th most dorsal part of the sclerotome
2) express scleraxis gene and generate the tendons
III)
Intermediate Mesoderm: the Urogenital System
A) Progression of Kidney Types
1) Nephron is the functional unit
2) Mammalian kidney development progresses through 3 major stages; only 3rd persists
as a functional kidney
B) Specification of the Intermediate Mesoderm: Pax2/8 Lim1
1) Paraxial mesoderm induce kidney-forming ability in intermediate mesoderm
2) Interactions induce expression of Lim1, Pax2/8 that causes kidney formation
C) Reciprocal Interactions of Developing Kidney Tissues
1) Intermediate mesodermal tissues (ureteric bud and metanephrogenic mesenchyme)
reciprocally induce each other to form kidney
2) Mechanisms of reciprocal induction
(i) Formation of the metanephrogenic mesenchyme: foxes, hoxes, and wt1
(ii) Metanephrogenic sesenchyme secretes GDNF to induce and direct ureteric bud
(iii)Ureteric bud secretes FGF2 and BMP7 to prevent mesenchymal apaptosis
(iv) Wnt9b and 6 from ureteric bud induce mesenchyme cells to aggregate
(v) Wnt4 converts aggregated mesenchyme cells into a nephron
(vi) Signals from the mesenchyme induce branching of ureteric bud
Ch. 12 Lateral Plate Mesoderm and the Endoderm
I) Lateral Plate Mesoderm
A) Heart Development
1) Heart is first functional unit; circulatory system first functional system
2) Heart progenitor cells migrate through primitive streak to form two groups of cells in
lateral plate mesoderm at the level of the node
(i) The cells are specified buy not determined
(ii) Specification induced by endoderm adjacent to the heart through BMP and FGF
3) Posterior and anterior regions determined by concentration of retinoic acid (RA)
4) Fusion of heart rudiments and initial hearbeats
(i) Cell differentiation occurs independently iin the two heart forming promordia
(ii) Ventral splanchnic mesoderm cells express N-cadherin on their apices, detach
from mesoderm and join together to form epithelial layer that leads to formation
of pericardial cavity
(iii)Epithelial layer of splanchnic mesoderm forms myocardium that give rise to heart
muscles that pump
(iv) Endocardial cells formed from splanchnic mesoderm that delaminated from
epithelium.
(a) Produce heart valves, secrete proteins regulating myocardial growth, and
regulate placement of heart nervous tissue
5) Looping and Formation of Heart Chambers
(i) Looping converts anterior-posterior polarity of heart tube into right-left polarity
(ii) Direction of looping dependent on proteins Nodal and Pitx2
(iii)Requires cytoskeletal rearrangement, extracellular matrix remodeling, asymmetric
cell division
(iv) Septa separates atria and ventricle
B) Formation of Blood Vessels
1) vessels form independently of heart
2) form for embryonic needs as well as adult
3) constrained to evolution
4) adapts to laws of fluid dynamics
(i) large vessels move fluid with low resistance
(ii) diffusion requires small volumes and slow flow
(iii)superbranching small vessels control speed
5) vasculogenesis is initial formation of blood vessels
(i) de novo differentiation of mesoderm into endothelium
6) angeiogenesis remodels primary capillary networks; veins and arteries are made
7) lymphatic vessels form separate system of vessels for fluid drainage and lymphocyte
transportation.
(i) Forms when subset of endothelial cells from jugular vein sprout to form
lymphatic sacs. further sprouting forms peripheral vessels
C) Hematopoiesis: The Stem Cell Concept
1) The stem cells can divide to produce more stem cells or to replenish differentiated
cells.
2) HSC can produce all blood cells and lymphocytes
3) 1 in every 10,000
4) In amniotes originate in yolk sac, then bone marrow and fetal liver
5) Inductive microenvironments induce different sets of transcription factors that specify
cell paths
II) Endoderm
A) The Pharynx
1) Location of 4 pharyngeal pouches
2) Is where endoderm meets ectoderm
3) Shh prevents apoptosis of neural crest cells
B) The Digestive Tube and its Derivatives
1) Posterior to pharynx
2) Endoderm generate lining; mesechyme cells from splanchnic portion of lateral plate
surround tube to form muscles for peristalsis
3) Includes esophagus, stomach, duodenum, intestines, and branches of the thyroid,
thymus, pancreas, and liver
4) Specification by retinoic acid gradient and signals from lateral plated derived
mesenchymal cells
C) The Respiratory Tube
1) Laryngotracheal groove splits to form bronchi and lungs
2) Endoderm of laryngotracheal becomes lining of trachea, bronchi, and air sacs
3) Groove formation induced by RA
4) Wnt signaling required for lung formation
5) Lung formation among last organs to differentiate
D) The Extraembryonic Membranes
1) Epithelia divides unequally to create body folds that isolate embryo from yolk
2) Somatopleure forms amnion and chorion
3) Slanchnopleure forms yold sac and allantois
4) Mesoderm generates essential blood supply to and from the epithelium
5) Amnion secretes fluid to prevent dessication
6) Chorion allows exchange of gases
(i) Lines shells in reptiles and birds
(ii) Forms placenta in mammals
7) Allantois stores urinary wastes and facilitate gas exchange
(i) Contributes to placental in mammals
(ii) Birds and reptiles must have it
8) Choriallantoic membrane transports calcium from eggshell to embryo
9) Yolk sac stores nutrition for embryo.
(i) Proteins digested into amino acids by endodermal cells before passing on to blood
vessels
Ch. 13 Development of the Tetrapod Limb
I) Pattern Formation
A) Symmetry in archeture of limbs, size of opposite limbs, and development
B) Asymmetry in forelimb-hindlimb from rostral-caudal, left/right mirror image,
structural polarity
C) Occurs in 4 dimensions
II) Formation of the Limb Bud
A) Specification of limb fields
1) Limb field is area of cells capable of forming limb
(i) When first formed have ability to regenerate lost parts
2) Limb development begins with limb bud formed from mesenchymal cells
accumulated under ectodermal tissue.
B) Induction of early limb bud
1) Signal for bud formation comes from lateral plate mesoderm cells that secrete FGF10
2) FGF8 helps establish anerior-posterior axis and then is eliminated by RA secreted by
somites. FGF10 is then secreted.
3) Wnt proteins restrict FGF10 to regions of lateral plate mesoderm where limb will
form
C) Specification of Forelimb and hindlimb
1) Tbx4 and Pitx1 and Tbx5 help specify forelimb and hindlimbs
III)
Generating the Proximal-Distal Axis
A) Apical Ectodermal Ridge
1) Mesenchyme cells in limb field secrete FGF10 inducing formation of AER
2) AER runs along distal margin of limb bud; is a major signaling center
3) Proximal-distal growth and differentiation result from interaction between AER and
limb bud mesenchyme beneath it call the progress zone (PZ).
IV)
Specification of the Anterior-Posterior Axis
A) Specification of anterior-posterior axis by zone of polarizing activity (ZPA)
1) ZPA is a small block of mesodermal tissue near the posterior junction of the limb bud
and body wall
2) Specifies anterior-posterior axis through Shh
B) Shh also plays role in digit specification and identity
1) Depend more on the number of times Shh is express rather than concentration of Shh
2) However digit 2 depend solely on Shh concentration and digit 1 is independent of Shh
V)
Generation of the Dorsal-Ventral Axis
A) Axis determined by ectoderm
B) Wnt7 induces activation of Lim1
1) Wnt7 expressed in dorsal ectoderm of chick and mouse limb bud, but not ventral
2) Lim1 appears important in specifying dorsal cell fates.
VI)
Coordinating the 3 Axis
A) BMP responsible for shutting down AER, ZPA, and inhibiting wnt7 along dorsalventral axis.
VII) Cell Death and Formation of Digits and Joints
A) Cell death enables digit and joint formation
B) Necrotic zones: regions where cell death occurs through apoptosis to sculpt the limbs
C) In autopod blocking BMP signaling prevents apoptosis. Noggin may be a blocker of
BMP.
D) Joint formation
1) BMPs induce mesenchymal cells to undergo aposptosis or become cartilageproducing chondrocytes depending on stage of development, and cell death or
differentiation depending on the age of the target cell.
2) Both apoptosis and cartilage formation are used to form joints
3) Movement and muscular force are required for joint formation
4) Wnt proteins and blood vessels also important
VIII) Continued Limb Growth: Epiphyseal Plates
A) Cartilaginous piphyseal plates at the ends of bones that enables bone growth through
production of chondrocytes.
B) FGFs halt epiphyseal growth plate cell proliferation by instructing the cartilage
precursors to differentiate rather than divide.
C) Mutations in FGF receptors cause dwarfism by causing receptors to prematurely activate.
D) Low levels of estrogen stimulate skeletal growth while high levels stop bone growth by
causing growth plate closure.