Functional characterization of SIM1-associated enhancers.

Area of Science:

• Genetics
• Neuroscience
• Endocrinology

Background:

• Haploinsufficiency of the single-minded homology 1 (SIM1) gene is linked to severe obesity in humans and mice.
• Altered SIM1 gene expression, potentially through regulatory elements like enhancers, may predispose individuals to obesity.

Purpose of the Study:

• To identify and characterize transcriptional enhancers that regulate SIM1 gene expression.
• To investigate the role of these enhancers in brain development and energy homeostasis.
• To explore potential links between genetic variations in these enhancers and obesity.

Main Methods:

• Comparative genomics was used to identify candidate SIM1 enhancers.
• Zebrafish and mouse transgenic enhancer assays were employed to test enhancer activity.
• Time course analysis and deletion series were used to characterize enhancer function and identify critical regions.
• Sequencing of enhancer regions in obese and lean cohorts was performed to identify single nucleotide polymorphisms (SNPs).

Main Results:

• Two SIM1 candidate enhancers (SCE2 and SCE8) demonstrated brain-enhancer activity in zebrafish.
• Both enhancers showed embryonic brain expression in mice, with SCE2 activity overlapping SIM1 expression from embryonic to adult stages, particularly in the hypothalamus.
• A critical region within SCE2 essential for developmental brain enhancer activity was identified.
• Obese individuals exhibited a higher prevalence of unique SNPs in this region, with one variant found to reduce developmental enhancer activity in zebrafish.

Conclusions:

• Two novel brain enhancers regulating the SIM1 gene locus were characterized.
• A specific set of obesity-associated SNPs within the SCE2 enhancer may contribute to obesity predisposition.
• These findings highlight the role of SIM1 regulatory elements in energy homeostasis and obesity.