ESPE Yearbook of Paediatric Endocrinology

To read the full abstract: Disease Models & Mechanisms vol. 13,3 dmm040105. 13 Mar. 2020. doi: https://dmm.biologists.org/content/13/3/dmm040105.long

These authors developed an in vitro model to study human GnRH neuron transcriptome during developmental differentiation.

Gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus govern the hypothalamus-pituitary-gonadal (HPG) axis and regulate reproductive functions. Alteration of GnRH neuron development or signaling leads to congenital hypogonadotropic hypogonadism (CHH) or pubertal delay. However, the causal mechanisms are incompletely understood. A better understanding of the developmental differentiation of GnRH neurons is required to address this issue. During human fetal development, GnRH neurons differentiate from the nasal neuroepithelial compartment, which is derived from the olfactory placodes, and begin their migration to the hypothalamus (1). Neuronal progenitor subtypes that give rise to GnRH neurons have not been completely characterized yet.

Here, the authors generated a stable GnRH-TdTomato reporter cell line in human pluripotent stem cells (hPSCs) using CRISPR-Cas9 technology to model GnRH neuron development. CRISPR- Cas9 genome editing has recently become one of the key tools to study differentiation of specialized cell types, including GnRH neurons (2). To characterize the mRNA transcriptome, RNA-sequencing was performed on progenitors and differentiated GnRH neurons. This analysis revealed 6461 differentially-expressed genes. The findings highlight potential genes of interest regarding GnRH neuron development and disease, such as the transcription factor ISL1, a LIM/homeodomain family transcription factor with a known role as a specifying transcription factor in early spinal motor neurons (3). ISL1 was highly upregulated in TdTomato-expressing GnRH neurons and its expression was confirmed in human fetal tissues. In addition, they detected 15 differentially-expressed genes that are already implicated in CHH, such as TAC3, TAC3R, and ANOS1, and some genes with known relevance to human puberty timing, such as LEP and LEPR. The results of this study include a large number of differentially-expressed genes not previously described in GnRH neurons. This study provides new insights into the early stages of human GnRH neuron development, and greatly increases the list of potential regulators.

References:

1. Casoni F, Malone SA, Belle M, Luzzati F, Collier F, Allet C, Hrabovszky E, Rasika S, Prevot V, Chedotal A. et al. (2016). Development of the neurons controlling fertility in humans: new insights from 3D imaging and transparent fetal brains. Development 143, 3969–3981.

2. Yellapragada V, Liu X, Lund C, Ka?nsa?koski J, Pulli K, Vuoristo S, Lundin K, Tuuri T, Varjosalo M, Raivio T. (2019). MKRN3 interacts with several proteins implicated in puberty timing but does not influence GNRH1 expression. Front. Endocrinol. 10, 48. doi: 10.3389/fendo.2019.00048.

3. Rhee HS, Closser M, Guo Y, Bashkirova EV, Tan GC, Gifford DK, Wichterle H. (2016). Expression of terminal effector genes in mammalian neurons is maintained by a dynamic relay of transient enhancers. Neuron 92, 1252–1265.