Beyond homeosis--HOX function in morphogenesis and organogenesis.

Area of Science:

• Developmental Biology
• Genetics
• Evolutionary Biology

Background:

• Hox genes are conserved transcription factors crucial for anteroposterior axis patterning in both vertebrates and invertebrates.
• HOX proteins dictate segment identity by controlling the formation of specific structures within their expression domains.

Purpose of the Study:

• To review how HOX proteins regulate downstream targets and mediate segment-specific structure formation.
• To explore Hox-activated networks, realizator genes, and the impact of Hox mutations on organogenesis.
• To discuss the homeotic and non-homeotic functions of Hox genes and their evolutionary implications.

Main Methods:

• Review of existing data on HOX protein function and regulation.
• Analysis of Hox-activated gene networks and realizator genes.
• Examination of organogenesis in Hox mutants across species.

Main Results:

• HOX proteins integrate positional information with tissue-specific factors at target gene enhancers for localized activation.
• HOX proteins primarily regulate morphogenesis indirectly via gene networks but can directly control realizator genes.
• Hox mutations often cause non-homeotic transformations, affecting cell behaviors like proliferation and survival, crucial for organogenesis.

Conclusions:

• The non-homeotic function of Hox genes in regulating cell behaviors for morphogenesis is conserved across vertebrates and invertebrates.
• This non-homeotic role may represent the ancestral function of HOX genes, predating their role in homeotic transformations.