The neuropeptide kisspeptin is a potent stimulator of GnRH neurons and has been implicated as a major regulator of the hypothalamus-pituitary-gonadal axis. There are mainly two anatomically segregated populations of neurons that express kisspeptin in the female hypothalamus: one in the anteroventral periventricular nucleus (AVPV) and the other in the arcuate nucleus (ARC). Distinct roles have been proposed for AVPV and ARC kisspeptin neurons during reproductive maturation and in mediating estrogen feedback on the hypothalamus-pituitary-gonadal axis in adults. Despite their pivotal role in the regulation of reproductive physiology, little is known about kisspeptin neuron connectivity. Although previous data suggest heterogeneity within the AVPV and ARC kisspeptin neuron populations, how many and which of these potential kisspeptin neuron subpopulations are actually communicating with GnRH neurons is not known. Here we used a combinatorial genetic transsynaptic tracing strategy to start to analyze the connectivity of individual kisspeptin neurons with the GnRH neuron population in female mice with a single-cell resolution. We find that only subsets of AVPV and ARC kisspeptin neurons are synaptically connected with GnRH neurons. We demonstrate that the majority of kisspeptin neurons within the AVPV and ARC does not communicate with GnRH neurons. Furthermore, we show that all kisspeptin neurons within the AVPV connected to GnRH neurons are estrogen sensitive and that most of these express tyrosine hydroxylase. Our data demonstrate functional specialization within the two kisspeptin neuron populations.

The neuropeptide kisspeptin is a major regulator of the hypothalamus-pituitary-gonadal axis. Although it has long been known that kisspeptin and its receptor G protein-coupled receptor 54 (GPR54) are expressed in the developing brain well before puberty onset, the potential role of kisspeptin/GPR54 signaling in the embryonic brain has remained mysterious. Recent studies in female mice have shown that kisspeptin neurons in the arcuate nucleus of the hypothalamus (ARC) already communicate with a subset of GnRH neurons in utero. Whether this specific neural circuit is also formed in the developing male brain is not known. Here, we used a combination of different genetic strategies to analyze the ontogeny and development of the kisspeptin/GPR54 system in the male mouse brain. We demonstrate orchestrated onset of kisspeptin and GPR54 expression in the male embryonic mouse brain and find that androgen receptor and estrogen receptor-α immunoreactivity within the male brain delineate the birthplace of kisspeptin neurons in the ARC. Using conditional transsynaptic tracing from kisspeptin neurons, we find that ARC kisspeptin neurons already communicate with a subset of GnRH neurons in utero and that the neural circuits between ARC kisspeptin and GnRH neurons in the male mouse brain are established before birth. Furthermore, we also show that the connectivity between kisspeptin and GnRH neurons does not depend on the spatial position of GnRH neurons. Our data delineate the maturing neural circuits underlying control of the reproductive axis in the male embryonic mouse brain.

The plane of division of granule neuron progenitors (GNPs) was analysed with respect to the pial surface in P0 to P14 cerebellum and the results showed that there was a significant bias towards the plane of cell division being parallel to pial surface across this developmental window. In addition, the distribution of β-Catenin in anaphase cells was analysed, which showed that there was a significant asymmetry in the distribution of β-Catenin in dividing GNPs. Further, inhibition of Sonic Hedgehog (Shh) signalling had an effect on plane of cell division. Asymmetric distribution of β-Catenin was shown to occur towards the source of a localized extracellular cue.

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