Molecular approaches to vertebrate limb morphogenesis.

Area of Science:

• Developmental Biology
• Molecular Biology
• Genetics

Background:

• Morphogen concentration gradients are proposed to specify cell fate during embryonic development.
• Retinoic acid (RA), the active form of vitamin A, is emerging as a key morphogen in vertebrate systems.
• RA influences embryonic limb patterning, as demonstrated by changes in chick wing digit formation.

Purpose of the Study:

• To review experimental evidence supporting retinoic acid as a morphogen in limb development.
• To evaluate the role of cellular retinoic-acid-binding protein (CRABP) in regulating retinoic acid receptor activity.
• To explore the relationship between retinoic acid and the spatio-temporal expression of homeobox genes in developing limbs.

Main Methods:

• Review of experimental data on retinoic acid's role in limb morphogenesis.
• Order of magnitude calculations to assess CRABP's effect on retinoic acid receptor binding.
• Analysis of spatio-temporal expression patterns of homeobox genes in developing limbs.

Main Results:

• Local application of retinoic acid to chick wing buds induces a mirror-image symmetrical digit pattern (432234) instead of the normal pattern (234).
• Limb buds possess high levels of CRABP, which may modulate retinoic acid signaling by affecting receptor occupancy.
• Retinoic acid's potential influence on the expression patterns of key homeobox genes is discussed.

Conclusions:

• Retinoic acid is a strong candidate morphogen involved in embryonic limb development and digit patterning.
• CRABP likely plays a regulatory role in retinoic acid signaling pathways within the developing limb.
• Further investigation into the interaction between retinoic acid and homeobox gene expression is warranted to understand limb morphogenesis.