Development of the Heart

What is the apical ectodermal ridge (AER)?

A structure at the distal tip of the limb bud that controls proximo-distal outgrowth.

How does the AER control limb growth?

By secreting fibroblast growth factors (FGFs) that maintain mesenchyme in a proliferative state.

What is the zone of polarizing activity (ZPA)?

A region in the posterior limb bud that controls the anterior-posterior axis.

What molecule does the ZPA express to control the anterior-posterior axis?

Sonic hedgehog (Shh).

What is the role of cell death in limb development?

Sculpting the limb by eliminating excess tissue between digits.

What is the progress zone model in limb development?

Cells acquire positional information based on time spent under AER influence.

What are the three main axes in limb development?

Proximo-distal, anterior-posterior, and dorsal-ventral.

What is the function of Hox genes in limb development?

Control differentiation along the proximo-distal axis.

What are the main components of the limb bud?

Ectoderm and mesenchyme.

What is the role of FGF10 in limb initiation?

Induces FGF8 expression in the ectoderm to initiate limb growth.

How does the dorsal-ventral axis develop in limbs?

Regulated by ectodermal signals like Wnt7a.

What is the significance of Tbx genes in limb identity?

Tbx5 for forelimbs and Tbx4 for hindlimbs.

What is the function of the ectoderm in limb development?

Provides signals for patterning and growth.

What is the role of somites in limb musculature development?

Provide myogenic progenitor cells.

What is the process of limb bud formation?

Initiated by FGF10 and FGF8 signaling.

How does apoptosis contribute to digit formation?

Eliminates interdigital tissue to separate digits.

What is the role of BMPs in limb development?

Involved in tissue morphogenesis and patterning.

What are the main stages of limb development?

Initiation, patterning, differentiation, and growth.

What is the function of the non-ridge ectoderm in limb development?

Influences dorsal-ventral patterning.

What is the significance of limb development as a model system?

Helps understand pattern formation in other embryonic structures.

What is the role of the lateral plate mesoderm in limb development?

Provides the core mesenchyme for limb formation.

How does the AER interact with the ZPA?

Through a positive feedback loop involving FGFs and Shh.

What are the consequences of disrupting the ZPA?

Alters digit patterning and can lead to polydactyly.

What is the significance of Hox gene expression in limb development?

Determines the identity of limb segments.

How does cell death influence limb morphogenesis?

Refines the shape and structure of the limb.