High-throughput screens reveal putative regulators of MKRN3 in mouse neurons

Central precocious puberty (CPP) is often associated with loss-of-function mutations in the
gene encoding the putative RNA binding protein, Makorin Ring Finger Protein 3 (MKRN3).
Moreover, hypothalamic MKRN3 mRNA levels decrease before puberty, suggesting its
inhibitory role in puberty onset. Although this decrease is well established, the mechanisms
that mediate MKRN3 downregulation are unclear. To elucidate candidate genes that might
regulate MKRN3 expression in the hypothalamus, we analyzed publicly available RNA datasets
from brain samples of rats and mice through the juvenile to adulthood transition. The
bioinformatic screen identified 26 genes whose expression correlated with that of Mkrn3. One
of these candidates is the Activin receptor type 1C (Acvr1v) whose expression is negatively
correlated with that of Mkrn3 along development. To test if Acvr1c might be responsible for the
downregulation of Mkrn3, we expressed a constitutively active form of Acvr1c in a
hypothalamic GnRH secreting neuronal cell line (GT1-7), which led to a reduction in Mkrn3
mRNA levels. Furthermore, induction of the endogenous Acvr1c by either activin A or activin B,
reduced Mkrn3 expression in GT1-7 cells. Acvr1c signals through activation of the transcription
factors SMAD2/3, which harbor putative binding sites on the MKRN3 promoter, and we found
that knock down of SMAD2 increased Mkrn3 expression. These results suggest that Acvr1c-
mediated pathways might downregulate Mkrn3 expression during development to allow
puberty onset.