The roles and regulation of Mkrn3 in mouse hypothalamic neurons
Makorin Ring Finger Protein 3 (MKRN3) functions as a “pubertal brake,” and loss-of-function mutations in MKRN3 are the most common genetic cause of central precocious puberty, which sees activation of the reproductive axis at an abnormally young age. MKRN3 expression in the brain decreases significantly leading up to puberty, suggesting a repressive role on the hypothalamic GnRH which comprises the master regulator of reproduction. However, the factors driving this drop in MKRN3 levels, as well as its downstream targets are not known. Through extensive computational analysis of bulk and single cell RNA sequencing data from rodent brain samples across development, combined with experimental studies in a mouse GnRH neuronal cell line, we identified the developmentally upregulated receptor, Acvr1c, as a repressor of Mkrn3 expression though activation of Smad2/3 signaling. This repression involves the recruitment of the transcription factor Kap1, and the induction of repressive histone modifications at the Mkrn3 gene locus. Additionally, we generated and integrated various multi-omics data from GnRH-producing neurons: Mkrn3 protein and RNA interactomes, as well as proteome and transcriptome data following Mkrn3 overexpression. These analyses revealed a predominant role for Mkrn3 in regulating a large number of proteins, primarily via translation. Moreover, we found that Mkrn3 binds Gnrh1 mRNA, along with Igf2bp2 which interacts directly with Mkrn3, providing novel insights into the mechanisms through which Mkrn3 affects pubertal timing.
