IQGAP3 is essential for cell proliferation and motility during zebrafish embryonic development

Area of Science:

• Cell Biology
• Developmental Biology
• Molecular Signaling

Background:

• IQGAP proteins are scaffolding molecules involved in actin dynamics, cell adhesion, and division.
• Three IQGAP family members exist in vertebrates: IQGAP1, IQGAP2, and IQGAP3.
• While IQGAP1's role in actin nucleation via growth factor receptors is established, IQGAP2 and IQGAP3 functions are largely unknown.

Purpose of the Study:

• To investigate the developmental roles and functions of IQGAP family members in zebrafish.
• To elucidate the specific functions of IQGAP3 during embryonic development.
• To determine IQGAP3's position within signaling pathways, particularly FGFR1-Ras-ERK.

Main Methods:

• In situ hybridization in zebrafish embryos to determine IQGAP1, IQGAP2, and IQGAP3 expression patterns.
• Morpholino-based knockdown of IQGAP1, IQGAP2, and IQGAP3 to assess their functional roles.
• Analysis of phenotypes resulting from IQGAP3 loss-of-function and rescue experiments with IQGAP3 mRNA.

Main Results:

• IQGAP1 and IQGAP2 are expressed in specific tissues, while IQGAP3 shows broad expression in proliferative cells.
• IQGAP1 and IQGAP2 knockdowns have minimal impact on zebrafish embryo morphology.
• IQGAP3 loss-of-function impairs cell proliferation and motility, mimicking phenotypes of dominant-negative Ras or FGFR1.
• Co-injection of IQGAP3 mRNA rescues dominant-negative FGFR1 or Ras phenotypes, confirming IQGAP3's role downstream.

Conclusions:

• IQGAP3 is essential for embryonic cell proliferation and motility in zebrafish.
• IQGAP3 functions as a downstream effector in the Fibroblast Growth Factor Receptor 1 (FGFR1)-Ras signaling pathway.
• These findings highlight a novel regulatory role for IQGAP3 in developmental signaling.