Mesoderm, Endoderm, Gametogenesis

What is the mesoderm?

The mesoderm is one of the three primary germ layers in early embryonic development that gives rise to various structures in the body.

What are the distinct bands of mesodermal cells?

The distinct bands are axial (notochord) mesoderm, paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm.

What does the chordamesoderm (axial mesoderm) develop into?

It forms the notochord, which induces and patterns the neural tube and establishes the anterior-posterior body axis.

What is the function of paraxial mesoderm?

It produces muscle, connective tissues of the back, and skeletal elements like vertebrae and ribs.

What does the intermediate mesoderm give rise to?

It develops into the urogenital system, including kidneys, gonads, and associated ducts.

What structures arise from the lateral plate mesoderm?

It gives rise to the heart, blood vessels, blood cells, and the lining of body cavities.

What are somites?

Somites are transitory epithelial block-like clusters of cells derived from paraxial mesoderm that will form vertebrae, ribs, and muscles.

What are the cell types derived from somites?

The cell types include sclerotome (vertebrae), syndetome (tendons), and myotome (skeletal muscles).

What does the sclerotome develop into?

It develops into vertebrae and associated tendons and rib cartilage.

What is the role of the dermomyotome?

It gives rise to the myotome (skeletal muscles) and dermatome (dermis of the back).

What factors affect the specification of paraxial mesoderm?

Factors include increasing amounts of BMPs and decreasing amounts of Noggin (BMP inhibitor).

What is somitogenesis?

Somitogenesis is the formation of somites where precursor cells reorganize into an epithelium.

How is anterior-posterior specification determined in mesoderm?

It is determined by Hox genes, which are spatially and temporally organized in the genome.

What is the fate of cells in the ventromedial sclerotome?

They migrate to the notochord and form the vertebral body.

What do cells in the dorsomedial sclerotome form?

They form the spine and arch of the vertebrae.

What is the significance of Tbx6 in presomitic mesoderm?

Tbx6 promotes presomitic mesoderm fates by repressing Sox2 and neural fates.

What is mesogenin 1's role in presomitic mesoderm?

Mesogenin 1 is necessary for Tbx6 expression in presomitic mesoderm.

What does the anteriormost part of paraxial mesoderm become?

It becomes the head mesoderm, forming the skeleton, muscles, and connective tissues of the face and skull.

What is the function of the lateral plate mesoderm?

It gives rise to the pelvic and limb skeleton.

What is the fate of cells from the myotome?

They generate the skeletal muscles of the back, rib cage, and ventral body wall.

What happens during the maturation of somites?

Cells within a somite become committed to a particular cell fate only when the somite matures.

What is the role of BMPs in mesoderm specification?

BMPs are involved in specifying the mediolateral axis of the paraxial mesoderm.

What is the relationship between Hox genes and mesodermal development?

Hox genes determine the spatial and temporal expression patterns in mesodermal development.

What is the significance of somitomere numbering?

Somitomere numbering using Roman numerals indicates the sequential formation of somites.

How do cells detach from the lateral edge of the dermomyotome?

They detach to generate musculature of the forelimbs and hindlimbs.

What is the primary function of the notochord?

The notochord functions to induce and pattern the neural tube and establish the body axis.

What transition occurs during somitogenesis?

Mesenchymal-to-epithelial transition.

What role does the transcription factor Mesp play in somitogenesis?

Mesp is upregulated and contributes to the upregulation of Eph in the anterior portion of somitomeres.

What triggers the upregulation of ephrin in somitomeres?

Eph activity in the posterior half of more anterior somitomeres.

What is the significance of Eph-Ephrin signaling in somitogenesis?

It leads to epithelialization by regulating Rho GTPases and integrin/fibronectin interactions.

How does Eph-Ephrin signaling affect Rho GTPases?

It regulates cytoskeletal rearrangements by modulating Cdc42 activity.

What happens to Cdc42 activity in peripheral cells of the somitomere?

Activated Ephrin signaling suppresses Cdc42 activity, creating a box around remaining mesenchymal cells.

What is the relationship between Cdc42 activity and epithelialization?

Low Cdc42 activity promotes epithelialization, while high Cdc42 activity prevents it.

What is the role of integrin alpha 5 in somitogenesis?

Eph-Ephrin signaling enhances integrin alpha 5 activity, promoting fibronectin assemblies in the ECM.

What is the clock-wavefront model in somitogenesis?

It describes when and where somite boundaries form based on gradients of signaling molecules.

What are the FGF and RA levels in the anterior and posterior regions during somitogenesis?

Anterior: low FGF, high RA; Posterior: high FGF, low RA.

What is the effect of high Notch signaling in somitogenesis?

It induces boundary formation between somites.

What is the role of Pax1 in sclerotome development?

Pax1 is needed for the epithelial-to-mesenchymal transition (EMT) and subsequent differentiation into cartilage.

What factors induce the ventromedial portion of the somite to become sclerotome?

Notochord-derived paracrine factors, specifically Shh.

What is the importance of BMP antagonists in sclerotome development?

Absence of BMPs is critical for allowing Shh to induce cartilage function.

What does the dorsal sclerotome give rise to?

Syndetome, which develops into tendons.

What do mesenchymal cells in the center of the somite develop into?

Arthrotome, which gives rise to vertebral joints and proximal ribs.

What is the role of epimorphin in vertebrae formation?

It attracts sclerotome cells to the region around the notochord and neural tube.

How do sclerotome cells migrate to form the spinous process of the vertebra?

Platelet-derived growth factor induces dorsal migration of sclerotome cells over the neural tube.

What is the significance of the spinous process in vertebrae?

It serves as an attachment point for muscles and ligaments.

What happens to notochordal cells during adulthood?

Some die, while remaining cells develop into the nuclei pulposi of intervertebral discs.

What is the function of the nuclei pulposi?

They form a gel-like mass in the center of intervertebral discs.

What gene does syndetome express for tendon formation?

Syndetome expresses the scleraxis gene.

What is the source of the syndetome's signaling for tendon formation?

Myotome's secretion of Fgf8.

What is the role of the dermomyotome in development?

It generates muscle precursors and dermal cells of the back.

What does the term 'myotome' refer to?

The part of the somite that gives rise to skeletal muscles.

What are migratory myoblasts responsible for?

They produce the myotome.

What type of muscles do primaxial myoblasts form?

They form intercostal muscles and deep muscles of the back.

What type of muscles do abaxial myoblasts form?

They form body wall, limb, and tongue muscles.

Which factors regulate epithelial-mesenchymal transition (EMT) in dermomyotome development?

Neurotrophin 3 and Wnt1 secreted by the neural tube.

What happens if the neural tube is removed or rotated during development?

It prevents the formation of the dermis.

What do Wnt signals from the epidermis promote?

They promote the differentiation of dermatome cells into dermis.

What are myogenic regulatory factors (MRFs)?

Proteins that regulate muscle development, including MyoD, Myf5, myogenin, and MRF4.

How do primaxial myoblasts mature?

They align, fuse, and elongate to become deep muscles of the back.

What inhibits myofiber growth?

Myostatin, a member of TGF-Beta.

What is hyperplasia in muscle development?

An increase in the number of muscle fibers due to loss of myostatin function.

What is hypertrophy in muscle development?

An increase in the size of muscle fibers due to loss of myostatin function.

What are the two types of ossification in bone development?

Intramembranous ossification and endochondral ossification.

What is intramembranous ossification?

The direct conversion of mesenchymal tissue into bone tissue.

What is endochondral ossification?

The formation of cartilage tissue from mesenchymal cells, which is later replaced by bone.

What are the five stages of endochondral ossification?

Commitment, compaction, proliferation, growth, and chondrocyte death.

What occurs during the commitment stage of endochondral ossification?

Mesenchymal cells commit to becoming cartilage, influenced by Sonic hedgehog.

What happens during the compaction stage of endochondral ossification?

Committed mesenchyme cells condense into compact nodules, with inner cells generating cartilage and outer cells becoming bone.

What occurs during the proliferation stage of endochondral ossification?

Chondrocytes proliferate rapidly to form a cartilaginous model for the bone.

What is the role of Runx2 during the growth stage of endochondral ossification?

It determines the elongation rate of skeletal elements.

What factors do hypertrophic cartilage cells secrete?

VEGF and Indian hedgehog.

What is the function of VEGF in bone development?

It transforms mesodermal mesenchyme cells into blood vessels.

Which gene is expressed by the intermediate mesoderm?

The Pax2 gene.

What induces the formation of the pronephros?

The anterior region of the pronephric duct induces adjacent mesenchyme.

What happens to the pronephric tubules?

They degenerate.

What is the nephric duct also known as?

Wolffian duct.

What induces the formation of mesonephros?

The middle portion of the nephric duct.

What is the permanent kidney called?

Metanephros.

What does the metanephrogenic mesenchyme induce?

The formation of a branch called the ureteric bud from each nephric duct.

What is the role of the ureteric bud?

It induces metanephrogenic mesenchyme to condense and differentiate into nephrons.

What signals induce intermediate mesoderm to form kidneys?

Signals from the paraxial mesoderm, including Lim1, Pax2, and Pax8.

What is the function of Lim1 in kidney development?

It converts intermediate mesenchyme into nephric duct and forms the ureteric bud and nephrons.

What do the ureteric bud and metanephric mesenchyme do?

They reciprocally induce each other to form the kidney.

What factors do metanephric mesenchyme secrete to induce the ureteric bud?

Glial-derived neurotrophic factor (GDNF).

What is the role of Fgf2 and BMP7 in kidney development?

They prevent mesenchymal apoptosis and promote condensation of metanephric mesenchyme.

What is the outcome of GDNF, Wnt, Fgf, and BMP signaling?

They induce branching of the ureteric bud.

What does Wnt9 and Wnt6 from the ureteric bud do?

They transform metanephric mesenchyme into tubular epithelium (nephrons).

What is the somatopleure composed of?

Somatic mesoderm and ectoderm.

What is the splanchnopleure composed of?

Splanchnic mesoderm and endoderm.

What forms the body cavity (coelom)?

The space between the somatopleure and splanchnopleure.

What does the first heart field form?

The scaffold of the developing heart.

What does the second heart field form?

The anterior and posterior ends of the heart tube.

What signals are involved in blood vessel formation?

Vasculogenesis and angiogenesis.

What is vasculogenesis?

The initial formation of blood vessels.

What is angiogenesis?

The sprouting of blood vessels and remodeling into distinct capillary beds, arteries, and veins.

What activates the Etv2 transcription factor in lateral plate mesoderm cells?

BMP, Wnt, and Notch signals.

What determines whether hemangioblasts become blood cells or blood vessels?

High Notch levels lead to blood cells; low Notch levels lead to blood vessels.

What factors are responsible for initiating vasculogenesis?

Fgf2, vascular endothelial growth factors (VEGFs), and angioproteins.

What role does Notch signaling play in hemangioblast differentiation?

High Notch signaling leads hemangioblasts to become blood cells, while low Notch signaling leads them to become blood vessels.

Define hematopoiesis.

The formation of blood cells, involving more stem cells and progenitor cells that differentiate into various blood cell types.