OR04-06 Mkrn3, Dlk1 And Mecp2 Have Distinct Hypothalamic Expression Patterns Across Pubertal Maturation In Male And Female Mice

Disclosure: F.R. Tinano: None. S.A. Pereira: None. N.P. Boris: None. D.B. Macedo: None. A.P. Canton: None. A. Abreu: None. R.S. Carroll: None. A. Latronico: None. U.B. Kaiser: None. Context: Central precocious puberty (CPP) results from premature re-activation of the hypothalamic-pituitary-gonadal (HPG) axis. The most prevalent genetic cause of CPP is loss-of-function mutations in makorin ring finger 3 (MKRN3), with loss-of-function mutations in delta-like 1 homolog (DLK1) occurring less frequently. While the mechanisms by which MKRN3 regulates puberty onset have been partially elucidated in recent years, the manner by which DLK1 regulates HPG axis maturation remains unknown. Methyl CpG binding protein 2 (MeCP2) is associated with the neurodevelopmental Rett syndrome, with reports of early pubertal development among affected patients. Recently, rare variants in MeCP2 were identified in children with CPP with or without neurologic abnormalities. The pathways by which MECP2 may influence pubertal timing have not been determined. The aim of this study was to characterize Mkrn3, Dlk1 and Mecp2 expression patterns in the hypothalamus of male and female mice at different pubertal stages.Methods and Results: Male and female wild type C57BL/6 mice were euthanized at postnatal (P) age 10, 15, 22, 30 and 60 days. The mediobasal hypothalamus (MBH) and pre-optic area (POA) were isolated from the brains of each mouse. mRNA levels of Mkrn3, Dlk1 and Mecp2 were quantified by RT-qPCR and compared across the ages studied. Mkrn3 expression in both MBH and POA was highest at P10, then significantly lower at P15 and P22, remaining low until adulthood, with a similar pattern in male and female mice. In contrast, Dlk1 expression was higher at P60 compared to P22 in the MBH of male mice, while in female mice it was higher at P22 and P30 compared to P10. In the POA of male mice, Dlk1 expression was higher at P30 and P60 compared to P10, while no significant difference with age was seen in the POA of female mice. Mecp2 had higher expression in the MBH at P10 compared to P15 and P22 in male mice, and compared to P15, P30 and P60 in female mice. Mecp2 expression in the POA of both male and female mice was higher at P10 compared to all the other ages. No differences were observed in the hypothalamic expression of the three genes between male and female mice. Statistical significance was set at p < 0.05. Conclusions:Mkrn3 and Mecp2 had decreased hypothalamic expression in male and female mice with age, suggesting inhibitory roles on the HPG axis, consistent with the phenotype of CPP in patients with loss-of-function mutations in these genes. In contrast, hypothalamic expression of Dlk1 increased in both male and female mice toward adulthood, which is intriguing considering the association of loss-of-function mutations in this gene with CPP and suggests that the role of Dlk1 in the HPG axis is distinct from those of Mkrn3 and Mecp2. Defining the changes in hypothalamic expression of these three genes across pubertal development is critical to understanding their roles and mechanisms of action in regulating the HPG axis. Presentation: Thursday, June 15, 2023