Rabconnectin-3α is required for the morphological maturation of GnRH neurons and kisspeptin responsiveness

A splice site variant in MADD affects hormone expression in pancreatic β cells and pituitary gonadotropes

MAPK activating death domain (MADD) is a multifunctional protein regulating small GTPases RAB3 and RAB27, MAPK signaling, and cell survival. Polymorphisms in the MADD locus are associated with glycemic traits, but patients with biallelic variants in MADD manifest a complex syndrome affecting nervous, endocrine, exocrine, and hematological systems. We identified a homozygous splice site variant in MADD in 2 siblings with developmental delay, diabetes, congenital hypogonadotropic hypogonadism, and growth hormone deficiency. This variant led to skipping of exon 30 and in-frame deletion of 36 amino acids. To elucidate how this mutation causes pleiotropic endocrine phenotypes, we generated relevant cellular models with deletion of MADD exon 30 (dex30). We observed reduced numbers of β cells, decreased insulin content, and increased proinsulin-to-insulin ratio in dex30 human embryonic stem cell-derived pancreatic islets. Concordantly, dex30 led to decreased insulin expression in human β cell line EndoC-βH1. Furthermore, dex30 resulted in decreased luteinizing hormone expression in mouse pituitary gonadotrope cell line LβT2 but did not affect ontogeny of stem cell-derived GnRH neurons. Protein-protein interactions of wild-type and dex30 MADD revealed changes affecting multiple signaling pathways, while the GDP/GTP exchange activity of dex30 MADD remained intact. Our results suggest MADD-specific processes regulate hormone expression in pancreatic β cells and pituitary gonadotropes.

The E3 ubiquitin ligase RNF216/TRIAD3 is a key coordinator of the hypothalamic-pituitary-gonadal axis

Recessive mutations in RNF216/TRIAD3 cause Gordon Holmes syndrome (GHS), in which dysfunction of the hypothalamic-pituitary-gonadal (HPG) axis and neurodegeneration are thought to be core phenotypes. We knocked out Rnf216/Triad3 in a gonadotropin-releasing hormone (GnRH) hypothalamic cell line. Rnf216/Triad3 knockout (KO) cells had decreased steady-state GnRH and calcium transients. Rnf216/Triad3 KO adult mice had reductions in GnRH neuron soma size and GnRH production without changes in neuron densities. In addition, KO male mice had smaller testicular volumes that were accompanied by an abnormal release of inhibin B and follicle-stimulating hormone, whereas KO females exhibited irregular estrous cycling. KO males, but not females, had reactive microglia in the hypothalamus. Conditional deletion of Rnf216/Triad3 in neural stem cells caused abnormal microglia expression in males, but reproductive function remained unaffected. Our findings show that dysfunction of RNF216/TRIAD3 affects the HPG axis and microglia in a region- and sex-dependent manner, implicating sex-specific therapeutic interventions for GHS.

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Rnf216/Triad3 controls GnRH production and intrinsic hypothalamic cell activity

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Rnf216/Triad3 knockout male mice have greater reproductive impairments than females

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Rnf216/Triad3 controls the HPG axis differently in males and females

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Rnf216/Triad3 knockout male mice have reactive microglia in the hypothalamus

Transcriptome Analysis Revealed Long Non-Coding RNAs Associated with mRNAs in Sheep Thyroid Gland under Different Photoperiods

The thyroid gland is a vital endocrine organ involved in the reproduction of animals via the regulation of hormone synthesis and secretion. LncRNAs have been proven to play important roles in reproductive regulation; however, the associated mechanism in the thyroid gland has not been clarified. In this study, we investigated to identify photoperiod-induced lncRNAs and mRNAs in the thyroid gland in Sunite ewes by comparing the expression profiles of short photoperiod (SP) and long photoperiods (LP). A total of 41,088 lncRNAs were identified in the thyroid gland through RNA-Seq. Functional analysis of differentially expressed lncRNAs using the R package revealed that reproductive hormone- and photoperiod response-related pathways, including the prolactin signaling, cAMP signaling, and circadian rhythm pathways, were significantly enriched. An mRNA-lncRNA interaction analysis suggested that the lncRNA LOC1056153S88 trans targets ARG2 and CCNB3, and the lncRNA LOC105607004 trans targets DMXL2, both of these might be involved in seasonal sheep breeding reproduction. Together, these results will provide resources for further studies on seasonal reproduction in sheep.

p140Cap Controls Female Fertility in Mice Acting via Glutamatergic Afference on Hypothalamic Gonadotropin-Releasing Hormone Neurons

p140Cap, encoded by the gene SRCIN1 (SRC kinase signaling inhibitor 1), is an adaptor/scaffold protein highly expressed in the mouse brain, participating in several pre- and post-synaptic mechanisms. p140Cap knock-out (KO) female mice show severe hypofertility, delayed puberty onset, altered estrus cycle, reduced ovulation, and defective production of luteinizing hormone and estradiol during proestrus. We investigated the role of p140Cap in the development and maturation of the hypothalamic gonadotropic system. During embryonic development, migration of Gonadotropin-Releasing Hormone (GnRH) neurons from the nasal placode to the forebrain in p140Cap KO mice appeared normal, and young p140Cap KO animals showed a normal number of GnRH-immunoreactive (-ir) neurons. In contrast, adult p140Cap KO mice showed a significant loss of GnRH-ir neurons and a decreased density of GnRH-ir projections in the median eminence, accompanied by reduced levels of GnRH and LH mRNAs in the hypothalamus and pituitary gland, respectively. We examined the number of kisspeptin (KP) neurons in the rostral periventricular region of the third ventricle, the number of KP-ir fibers in the arcuate nucleus, and the number of KP-ir punctae on GnRH neurons but we found no significant changes. Consistently, the responsiveness to exogenous KP in vivo was unchanged, excluding a cell-autonomous defect on the GnRH neurons at the level of KP receptor or its signal transduction. Since glutamatergic signaling in the hypothalamus is critical for both puberty onset and modulation of GnRH secretion, we examined the density of glutamatergic synapses in p140Cap KO mice and observed a significant reduction in the density of VGLUT-ir punctae both in the preoptic area and on GnRH neurons. Our data suggest that the glutamatergic circuitry in the hypothalamus is altered in the absence of p140Cap and is required for female fertility.

Heterogeneity in GnRH and kisspeptin neurons and their significance in vertebrate reproductive biology

Vertebrate reproduction is essentially controlled by the hypothalamus-pituitary-gonadal (HPG) axis, which is a central dogma of reproductive biology. Two major hypothalamic neuroendocrine cell groups containing gonadotropin-releasing hormone (GnRH) and kisspeptin are crucial for control of the HPG axis in vertebrates. GnRH and kisspeptin neurons exhibit high levels of heterogeneity including their cellular morphology, biochemistry, neurophysiology and functions. However, the molecular foundation underlying heterogeneities in GnRH and kisspeptin neurons remains unknown. More importantly, the biological and physiological significance of their heterogeneity in reproductive biology is poorly understood. In this review, we first describe the recent advances in the neuroendocrine functions of kisspeptin-GnRH pathways. We then view the recent emerging progress in the heterogeneity of GnRH and kisspeptin neurons using morphological and single-cell transcriptomic analyses. Finally, we discuss our views on the significance of functional heterogeneity of reproductive endocrine cells and their potential relevance to reproductive health.

The Differential Roles for Neurodevelopmental and Neuroendocrine Genes in Shaping GnRH Neuron Physiology and Deficiency

Gonadotropin releasing hormone (GnRH) neurons are hypothalamic neuroendocrine cells that control sexual reproduction. During embryonic development, GnRH neurons migrate from the nose to the hypothalamus, where they receive inputs from several afferent neurons, following the axonal scaffold patterned by nasal nerves. Each step of GnRH neuron development depends on the orchestrated action of several molecules exerting specific biological functions. Mutations in genes encoding for these essential molecules may cause Congenital Hypogonadotropic Hypogonadism (CHH), a rare disorder characterized by GnRH deficiency, delayed puberty and infertility. Depending on their action in the GnRH neuronal system, CHH causative genes can be divided into neurodevelopmental and neuroendocrine genes. The CHH genetic complexity, combined with multiple inheritance patterns, results in an extreme phenotypic variability of CHH patients. In this review, we aim at providing a comprehensive and updated description of the genes thus far associated with CHH, by dissecting their biological relevance in the GnRH system and their functional relevance underlying CHH pathogenesis.

Kisspeptin and GnRH interactions in the reproductive brain of teleosts

It is well known that gonadotropin-releasing hormone (Gnrh) has a key role in reproduction by regulating the synthesis and release of gonadotropins from the anterior pituitary gland of all vertebrates. About 25 years ago, another neuropeptide, kisspeptin (Kiss1) was discovered as a metastasis suppressor of melanoma cell lines and then found to be essential for mammalian reproduction as a stimulator of hypothalamic Gnrh and regulator of puberty onset. Soon after, a kisspeptin receptor (kissr) was found in the teleost brain. Nowadays, it is known that in most teleosts the kisspeptin system is composed of two ligands, kiss1 and kiss2, and two receptors, kiss2r and kiss3r. Even though both kisspeptin peptides, Kiss1 and Kiss2, have been demonstrated to stimulate gonadotropin synthesis and secretion in different fish species, their actions appear not to be mediated by Gnrh neurons as in mammalian models. In zebrafish and medaka, at least, hypophysiotropic Gnrh neurons do not express Kiss receptors. Furthermore, kisspeptinergic nerve terminals reach luteinizing hormone cells in some fish species, suggesting a direct pituitary action. Recent studies in zebrafish and medaka with targeted mutations of kiss and/or kissr genes reproduce relatively normally. In zebrafish, single gnrh mutants and additionally those having the triple gnrh3 plus 2 kiss mutations can reproduce reasonably well. In these fish, other neuropeptides known to affect gonadotropin secretion were up regulated, suggesting that they may be involved in compensatory responses to maintain reproductive processes. In this context, the present review explores and presents different possibilities of interactions between Kiss, Gnrh and other neuropeptides known to affect reproduction in teleost fish. Our intention is to stimulate a broad discussion on the relative roles of kisspeptin and Gnrh in the control of teleost reproduction.

Hypogonadotropic hypogonadism due to variants in RAB3GAP2: expanding the phenotypic and genotypic spectrum of Martsolf syndrome

Biallelic pathogenic variants in RAB3GAP2 cause Warburg Micro syndrome (WARBM) and Martsolf syndrome (MS), two rare, phenotypically overlapping disorders characterized by congenital cataracts, intellectual disability, and hypogonadism. Although the initial report documented hypergonadotropic hypogonadism (implying a gonadal defect), an adolescent girl with WARBM/MS was subsequently reported to have hypogonadotropic hypogonadism (implying a central defect in either the hypothalamus or anterior pituitary). However, in adult MS, hypogonadotropism has not been convincingly demonstrated. Additionally, the correlation between the pathogenic severity of variants in RAB3GAP2 and the phenotypic severity also remains unclear. Here we present a clinical report of a woman with congenital cataracts, apparent intellectual disability, and pubertal failure who underwent exome sequencing (ES) to determine a precise molecular diagnosis. Reproductive phenotypes reported previously in individuals with MS and the genotypic spectrum of previous RAB3GAP2 variants were also reviewed. The ES identified pathogenic compound heterozygous RAB3GAP2 variants (c.387-2A > G; p.(Arg428Glu)) combined with her phenotypic features, which enabled a unifying molecular diagnosis of MS. Reproductive evaluation confirmed a normosmic idiopathic hypogonadotropic hypogonadism. Review of the RAB3GAP2 allelic spectrum in WARBM/MS suggests that although variants resulting in complete abrogation of RAB3GAP2 protein function cause severe WARBM, variants associated with partially preserved RAB3GAP2 function cause milder MS. This report expands the genotypic and phenotypic spectrum of MS and demonstrates hypogonadotropic hypogonadism as a key pathophysiologic abnormality in MS. Genotype-phenotype associations of previously reported RAB3GAP2 variants indicate that variants that fully abolish RAB3GAP2 function result in WARBM, whereas MS is associated with variants of lesser severity with residual RAB3GAP2 function.

Biallelic DMXL2 mutations impair autophagy and cause Ohtahara syndrome with progressive course

Esposito et al. identify biallelic loss-of-function mutations in DMXL2, encoding a v-ATPase regulatory protein, in three sibling pairs exhibiting Ohtahara syndrome with a progressive course. Patient-derived fibroblasts and Dmxl2-silenced mouse hippocampal neurons show defective lysosomal function and autophagy, resulting in the latter in impaired neuronal development and synapse formation.

Rare copy number variations affecting the synaptic gene DMXL2 in neurodevelopmental disorders

Background

Ultra-rare genetic variants, including non-recurrent copy number variations (CNVs) affecting important dosage-sensitive genes, are important contributors to the etiology of neurodevelopmental disorders (NDDs). Pairing family-based whole-genome sequencing (WGS) with detailed phenotype data can enable novel gene associations in NDDs.

Methods

We performed WGS of six members from a three-generation family, where three individuals each had a spectrum of features suggestive of a NDD. CNVs and sequence-level variants were identified and further investigated in disease and control databases.

Results

We identified a novel 252-kb deletion at 15q21 that overlaps the synaptic gene DMXL2 and the gene GLDN. The microdeletion segregated in NDD-affected individuals. Additional rare inherited and de novo sequence-level variants were found that may also be involved, including a missense change in GRIK5. Multiple CNVs and loss-of-function sequence variants affecting DMXL2 were discovered in additional unrelated individuals with a range of NDDs.

Conclusions

Disruption of DMXL2 may predispose to NDDs including autism spectrum disorder. The robust interpretation of private variants requires a multifaceted approach that incorporates multigenerational pedigrees and genome-wide and population-scale data.

Dual role of DMXL2 in olfactory information transmission and the first wave of spermatogenesis

Gonad differentiation is a crucial step conditioning the future fertility of individuals and most of the master genes involved in this process have been investigated in detail. However, transcriptomic analyses of developing gonads from different animal models have revealed that hundreds of genes present sexually dimorphic expression patterns. DMXL2 was one of these genes and its function in mammalian gonads was unknown. We therefore investigated the phenotypes of total and gonad-specific Dmxl2 knockout mouse lines. The total loss-of-function of Dmxl2 was lethal in neonates, with death occurring within 12 hours of birth. Dmxl2-knockout neonates were weak and did not feed. They also presented defects of olfactory information transmission and severe hypoglycemia, suggesting that their premature death might be due to global neuronal and/or metabolic deficiencies. Dmxl2 expression in the gonads increased after birth, during follicle formation in females and spermatogenesis in males. DMXL2 was detected in both the supporting and germinal cells of both sexes. As Dmxl2 loss-of-function was lethal, only limited investigations of the gonads of Dmxl2 KO pups were possible. They revealed no major defects at birth. The gonadal function of Dmxl2 was then assessed by conditional deletions of the gene in gonadal supporting cells, germinal cells, or both. Conditional Dmxl2 ablation in the gonads did not impair fertility in males or females. By contrast, male mice with Dmxl2 deletions, either throughout the testes or exclusively in germ cells, presented a subtle testicular phenotype during the first wave of spermatogenesis that was clearly detectable at puberty. Indeed, Dmxl2 loss-of-function throughout the testes or in germ cells only, led to sperm counts more than 60% lower than normal and defective seminiferous tubule architecture. Transcriptomic and immunohistochemichal analyses on these abnormal testes revealed a deregulation of Sertoli cell phagocytic activity related to germ cell apoptosis augmentation. In conclusion, we show that Dmxl2 exerts its principal function in the testes at the onset of puberty, although its absence does not compromise male fertility in mice.