Cdx1 and Cdx2 are functionally equivalent in vertebral patterning.

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• Cdx transcription factors regulate anterior-posterior (AP) vertebral patterning, partly by controlling Hox gene expression.
• Functional overlap exists between Cdx family members, but a complete understanding is limited by the absence of a Cdx2 null mutant.
• Redundancy in Hox proteins complicates determining if Cdx members regulate identical or separate Hox genes.

Purpose of the Study:

• To directly assess functional redundancy and target gene specificity among Cdx family members.
• To investigate the role of Cdx protein gradients in vertebral AP patterning.
• To develop novel genetic models for studying Cdx function.

Main Methods:

• Development of a Cdx2 "knock-in" mouse model, replacing Cdx1 with Cdx2.
• Generation of Cdx1 BAC transgenic mice to create a gain-of-function model for altered Cdx1 dosage.
• Analysis of skeletal defects and Hox gene expression in mutant and transgenic mouse models.

Main Results:

• Cdx2 "knock-in" mice perfectly complemented the Cdx1-null phenotype, showing no skeletal defects or altered Hox gene expression.
• Cdx1 BAC transgenic mice overexpressed Cdx1 but did not exhibit discernible effects on vertebral patterning or Hox gene expression in a wild-type background.
• These findings support functional redundancy among Cdx family members.

Conclusions:

• Functional redundancy between Cdx1 and Cdx2 is demonstrated through the "knock-in" model.
• Vertebral AP patterning is robust to moderate alterations in Cdx protein levels, challenging the strict gradient hypothesis.
• Cdx family members likely regulate distinct sets of Hox genes or downstream targets that converge on vertebral patterning events.