Fellow or Postdoc
Delphine Franssen, Alessandra Mancini, Jacob Haase, Katerina Corr, Lydie Naulé, Rona S Carroll, Ursula B Kaiser
Ursula B Kaiser
MKRN3 loss-of-function mutations represent the most frequent genetic cause of central precocious puberty. However, its mechanism of action and function remain poorly understood. Recently, our lab identified a potential role in neuronal plasticity. Mkrn3 deletion in a mouse model increased the number of hypothalamic dendritic spines. Moreover, we identified a specific interaction of MKRN3 with IGF2BP1, a key player in neuronal plasticity.
Here, we show that MKRN3-IGF2BP1 interaction is mediated by RNA in vitro, as their interaction was abrogated by RNase treatment. Using RNA co-IP, we found that MKRN3 and IGF2BP1 bind the same target, TAC3 mRNA (encoding NKB). NKB was increased in the hypothalamus of Mkrn3 KO mice. Here, we confirm in vitro that WT-MKRN3 leads to a decrease of NKB expression, while a mutation in the MKRN3 ubiquitin ligase motif reduces this effect.
To determine the role of MKRN3 in neuronal plasticity, we analyzed the dendritic arborization of hypothalamic neurons generated from wild-type and MKRN3-deficient hiPSCs. MAP2 staining revealed a trend to a higher number of tertiary dendrites in MKRN3-deficient cells.
In conclusion, MKRN3 interacts with IGF2BP1 and targets NKB to degradation via its ubiquitin ligase domain, with a potential role in neuronal plasticity.
Precocious puberty is clinically defined by the development of secondary sexual characteristics before the age of 8 years in girls. It is associated with higher risk of disease later in adult life, including breast, ovarian and endometrial cancers, and polycystic ovary syndrome (PCOS). The most common genetic cause of central precocious puberty is the mutation of a gene, MKRN3. However, the role and the mechanism of action of MKRN3 are still poorly understood. We identified that MKRN3 interacts with IGF2BP1, a key protein in neuronal development. We observed that both MKRN3 and IGF2BP1 bind to the same target, TAC3 mRNA. TAC3 encodes a neuropeptide, neurokinin B (NKB), which is essential for puberty onset. Using in vitro cellular experiments, we found that MKRN3 induced a decrease in NKB levels. In a transgenic mouse model and in hypothalamic cells derived from human induced pluripotent stem cells, we found that the absence of MKRN3 alters the projections and connectivity of hypothalamic neurons. Our findings have led to a better understanding of the mechanisms of action of MKRN3 and suggest a role in neuronal plasticity.