Dynamic Interplay Between miR-124-3p and EGF in Regulating The 'Giant' Phenotype by RNA Signalling Mechanism

Epigenetic mechanisms and RNA signalling profoundly impact body growth during the early stages of embryonic development. Epigenetic modifications' critical role in determining which genes are activated or suppressed, thereby influencing the development. RNA molecules, like microRNAs, regulate gene expression, control cell fate, and coordinate cellular processes crucial for proper growth and development. These complex molecular processes work harmoniously to create the intricate symphony of early embryonic development, which lays the foundation for the organism's future growth and function. Mouse embryos that are microinjected with miR-124-3p (miR-124*) exhibit a significantly 'giant' phenotype before and after birth. Behavioural test results showed that miR-124* mice were more cognitively active. miR-124 is highly expressed in the brain; however, the molecular mechanism leading to the phenotypic changes mediated by miR-124-3p is unknown. This study aimed to investigate the role of epidermal growth factor (EGF) in developing a distinct phenotype ('giant and cognitive') in miR-124* mice. We established neurosphere (NS) culture from the hippocampus at E19.5 using EGF. In miR-124*, Doublecortin ( Dcx ) , Neurod1 (12 days old NS) and Sox8, Sox9, Sox10 (21 days old NS) are significantly overexpressed. Our results suggest that the addition of EGF likely leads to overexpression of transcription factors such as Sox8, Sox9 and Sox10 , while it decreased the expression of neurogenesis marker Dcx and neuronal differentiation marker Neurod1 when the culture period is extended up to 21 days in miR-124* NS. Following the microinjection of miR-124-3p into the embryo at the one-cell stage, EGF could have been activated and suppressed the expression of miR-124-3p, leading to early neurogenesis and neuronal differentiation in embryos. It led to the earlier emergence of mice with cognitively active and 'giant' phenotypes.