Functional characterization of male germ cell-specific CREM isoforms

Area of Science:

• Molecular Biology
• Reproductive Biology
• Gene Regulation

Background:

• Alternative splicing and promoter usage generate diverse cAMP-responsive element modulator (CREM) protein isoforms with varying functions.
• Two novel CREM isoforms, CREM-2-F-G-H-Ib and CREM-2-G-H-Ib, were recently identified in human germ cells.
• These novel isoforms possess a transactivation domain but lack a kinase-inducible domain (KID), potentially altering their function.

Purpose of the Study:

• To functionally analyze the novel CREM isoforms CREM-2-F-G-H-Ib and CREM-2-G-H-Ib.
• To investigate the translation initiation and DNA-binding capabilities of these isoforms.
• To determine the impact of these isoforms on cAMP-responsive gene expression.

Main Methods:

• Analysis of human testis RNA for in vitro and in vivo protein expression.
• Electrophoretic mobility shift assays (EMSAs) to confirm sequence-specific DNA binding.
• Luciferase reporter gene assays to assess protein kinase A (PKA) dependent activity.

Main Results:

• A novel upstream open reading frame in exon 2 allows for the translation of a full-length protein from the CREM-2-F-G-H-Ib isoform.
• Both novel isoforms initiate translation via downstream adeninethymine-guanines (ATGs).
• CREM-2-F-G-H-Ib inhibited PKA-dependent stimulation, while CREM-2-G-H-Ib did not.

Conclusions:

• The CREM-2-F-G-H-Ib isoform produces a functional, full-length protein capable of modulating gene expression.
• These novel CREM isoforms play distinct roles in regulating gene transcription during human spermatogenesis.
• The findings contribute to understanding the complex regulation of gene expression in male germ cells.