Target sequences for hunchback in a control region conferring Ultrabithorax expression boundaries

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• Ultrabithorax (Ubx) gene expression patterns are crucial for embryonic development.
• Long-range repression mechanisms, involving control regions like PBX or ABX, regulate Ubx boundaries.
• The precise molecular mechanisms underlying these regulatory processes are not fully understood.

Purpose of the Study:

• To investigate the role of PBX or ABX control regions in mediating Ultrabithorax expression boundaries.
• To identify the specific cis-regulatory sequences and transcription factors involved in this regulation.
• To elucidate the function of hunchback protein in specifying Ultrabithorax expression patterns.

Main Methods:

• Analysis of beta-galactosidase expression patterns driven by PBX or ABX control regions in transgenic embryos.
• Dissection of the PBX control region to identify distinct cis-regulatory subfragments.
• Identification of transcription factor binding sites within these subfragments, particularly for hunchback protein.
• Functional assays using zygotic and maternal hunchback mutants to assess its role in PBX expression.

Main Results:

• Both PBX and ABX control regions confer an early expression band restricted along the anteroposterior axis, followed by a similar stripe pattern.
• Distinct cis-regulatory sequences within separate PBX subfragments confer these two distinct expression patterns.
• Multiple hunchback protein binding sites are present in both PBX subfragments, and zygotic hunchback is required to prevent ectopic PBX expression.

Conclusions:

• Hunchback protein directly binds to the PBX control region.
• Hunchback protein acts as a repressor to specify the boundary positions of the PBX expression pattern.
• These findings reveal a direct role for hunchback in the precise spatial regulation of Ultrabithorax expression.