Kit ligand cytoplasmic domain is essential for basolateral sorting in vivo and has roles in spermatogenesis and hematopoiesis

Therapeutic modulation of KIT ligand in melanocytic disorders with implications for mast cell diseases

KIT ligand and its associated receptor KIT serve as a master regulatory system for both melanocytes and mast cells controlling survival, migration, proliferation and activation. Blockade of this pathway results in cell depletion, while overactivation leads to mastocytosis or melanoma. Expression defects are associated with pigmentary and mast cell disorders. KIT ligand regulation is complex but efficient targeting of this system would be of significant benefit to those suffering from melanocytic or mast cell disorders. Herein, we review the known associations of this pathway with cutaneous diseases and the regulators of this system both in skin and in the more well-studied germ cell system. Exogenous agents modulating this pathway will also be presented. Ultimately, we will review potential therapeutic opportunities to help our patients with melanocytic and mast cell disease processes potentially including vitiligo, hair greying, melasma, urticaria, mastocytosis and melanoma.

Combined analysis of mRNA-miRNA from testis tissue in Tibetan sheep with different FecB genotypes

Testis size is important for identifying breeding animals with adequate sperm production. The aim of this study was to survey the expression profile of mRNA and miRNA in testis tissue from rams carrying different FecB genotypes, including the wild-type and heterozygous genotypes in Tibetan sheep. Comparative transcriptome profiles for ovine testes were established for wild-type and heterozygote Tibetan sheep by next-generation sequencing. RNA-seq results identified 3,910 (2,034 up- and 1,876 downregulated) differentially expressed (DE) genes and 243 (158 up- and 85 downregulated) DE microRNAs (miRNAs) in wild-type vs heterozygote sheep, respectively. Combined analysis of mRNA-seq and miRNA-seq revealed that 20 miRNAs interacted with 48 true DE target genes in wild-type testes compared to heterozygous genotype testes. These results provide evidence for a functional series of genes operating in Tibetan sheep testis. In addition, quantitative real-time PCR analysis showed that the expression trends of randomly selected DE genes in testis tissues from different genotypes were consistent with high-throughput sequencing results.

Cell-extrinsic hematopoietic impact of Ezh2 inactivation in fetal liver endothelial cells

Despite the well-established cell-intrinsic role of epigenetic factors in normal and malignant hematopoiesis, their cell-extrinsic role remains largely unexplored. Herein we investigated the hematopoietic impact of inactivating Ezh2, a key component of polycomb repressive complex 2 (PRC2), in the fetal liver (FL) vascular niche. Hematopoietic specific (Vav-iCre) Ezh2 inactivation enhanced FL hematopoietic stem cell (HSC) expansion with normal FL erythropoiesis. In contrast, endothelium (Tie2-Cre) targeted Ezh2 inactivation resulted in embryonic lethality with severe anemia at embryonic day 13.5 despite normal emergence of functional HSCs. Ezh2-deficient FL endothelium overexpressed Mmp9, which cell-extrinsically depleted the membrane-bound form of Kit ligand (mKitL), an essential hematopoietic cytokine, in FL. Furthermore, Mmp9 inhibition in vitro restored mKitL expression along with the erythropoiesis supporting capacity of FL endothelial cells. These data establish that Ezh2 is intrinsically dispensable for FL HSCs and provides proof of principle that modulation of epigenetic regulators in niche components can exert a marked cell-extrinsic impact.

The production of glial cell line-derived neurotrophic factor by human sertoli cells is substantially reduced in sertoli cell-only testes

STUDY QUESTION

Do human Sertoli cells in testes that exhibit the Sertoli cell-only (SCO) phenotype produce substantially less glial cell line-derived neurotrophic factor (GDNF) than Sertoli cells in normal testes?

SUMMARY ANSWER

In human SCO testes, both the amounts of GDNF mRNA per testis and the concentration of GDNF protein per Sertoli cell are markedly reduced as compared to normal testes.

WHAT IS KNOWN ALREADY

In vivo, GDNF is required to sustain the numbers and function of mouse spermatogonial stem cells (SSCs) and their immediate progeny, transit-amplifying progenitor spermatogonia. GDNF is expressed in the human testis, and the ligand-binding domain of the GDNF receptor, GFRA1, has been detected on human SSCs. The numbers and/or function of these stem cells are markedly reduced in some infertile men, resulting in the SCO histological phenotype.

STUDY DESIGN, SIZE, AND DURATION

We determined the numbers of human spermatogonia per mm2 of seminiferous tubule surface that express GFRA1 and/or UCHL1, another marker of human SSCs. We measured GFRA1 mRNA expression in order to document the reduced numbers and/or function of SSCs in SCO testes. We quantified GDNF mRNA in testes of humans and mice, a species with GDNF-dependent SSCs. We also compared GDNF mRNA expression in human testes with normal spermatogenesis to that in testes exhibiting the SCO phenotype. As controls, we also measured transcripts encoding two other Sertoli cell products, kit ligand (KITL) and clusterin (CLU). Finally, we compared the amounts of GDNF per Sertoli cell in normal and SCO testes.

PARTICIPANTS/MATERIALS SETTING METHODS

Normal human testes were obtained from beating heart organ donors. Biopsies of testes from men who were infertile due to maturation arrest or the SCO phenotype were obtained as part of standard care during micro-testicular surgical sperm extraction. Cells expressing GFRA1, UCHL1 or both on whole mounts of normal human seminiferous tubules were identified by immunohistochemistry and confocal microscopy and their numbers were determined by image analysis. Human GDNF mRNA and GFRA1 mRNA were quantified by use of digital PCR and Taqman primers. Transcripts encoding mouse GDNF and human KITL, CLU and 18 S rRNA, used for normalization of data, were quantified by use of real-time PCR and Taqman primers. Finally, we used two independent methods, flow cytometric analysis of single cells and ELISA assays of homogenates of whole testis biopsies, to compare amounts of GDNF per Sertoli cell in normal and SCO testes.

MAIN RESULTS AND THE ROLE OF CHANCE

Normal human testes contain a large population of SSCs that express GFRA1, the ligand-binding domain of the GDNF receptor. In human SCO testes, GFRA1 mRNA was detected but at markedly reduced levels. Expression of GDNF mRNA and the amount of GDNF protein per Sertoli cell were also significantly reduced in SCO testes. These results were observed in multiple, independent samples, and the reduced amount of GDNF in Sertoli cells of SCO testes was demonstrated using two different analytical approaches.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

There currently are no approved protocols for the in vivo manipulation of human testis GDNF concentrations. Thus, while our data suggest that insufficient GDNF may be the proximal cause of some cases of human male infertility, our results are correlative in nature.

WIDER IMPLICATIONS OF THE FINDINGS

We propose that insufficient GDNF expression may contribute to the infertility of some men with an SCO testicular phenotype. If their testes contain some SSCs, an approach that increases their testicular GDNF concentrations might expand stem cell numbers and possibly sperm production.

STUDY FUNDING/COMPETING INTEREST(S)

This research was funded by the Eunice Kennedy Shriver National Institute for Child Health and Human Development, National Centers for Translational Research in Reproduction and Infertility Program (NCTRI) Grant 1R01HD074542-04, as well as grants R01 HD076412-02 and P01 HD075795-02 and the U.S.-Israel Binational Science Foundation. Support for this research was also provided by NIH P50 HD076210, the Robert Dow Foundation, the Frederick & Theresa Dow Wallace Fund of the New York Community Trust and the Brady Urological Foundation. There are no competing interests.

Comparative genomics of human stem cell factor (SCF)

Stem cell factor (SCF) is a critical protein with key roles in the cell such as hematopoiesis, gametogenesis and melanogenesis. In the present study a comparative analysis on nucleotide sequences of SCF was performed in Humanoids using bioinformatics tools including NCBI-BLAST, MEGA6, and JBrowse. Our analysis of nucleotide sequences to find closely evolved organisms with high similarity by NCBI-BLAST tools and MEGA6 showed that human and Chimpanzee (Pan troglodytes) were placed into the same cluster. By using JBrowse, we found that SCF in Neanderthal had a single copy number similar to modern human and partly conserved nucleotide sequences. Together, the results approved the gene flow and genetics similarity of SCF among human and P. troglodytes. This may suggest that during evolution, SCF gene transferred partly intact either on the basis of sequence or function from the same ancestors to P. troglodytes, the ancient human like Neanderthal, and then to the modern human.

The Role of Retinoic Acid (RA) in Spermatogonial Differentiation

Retinoic acid (RA) directs the sequential, but distinct, programs of spermatogonial differentiation and meiotic differentiation that are both essential for the generation of functional spermatozoa. These processes are functionally and temporally decoupled, as they occur in distinct cell types that arise over a week apart, both in the neonatal and adult testis. However, our understanding is limited in terms of what cellular and molecular changes occur downstream of RA exposure that prepare differentiating spermatogonia for meiotic initiation. In this review, we describe the process of spermatogonial differentiation and summarize the current state of knowledge regarding RA signaling in spermatogonia.

RNA-Seq identifies key reproductive gene expression alterations in response to cadmium exposure

Cadmium is a common toxicant that is detrimental to many tissues. Although a number of transcriptional signatures have been revealed in different tissues after cadmium treatment, the genes involved in the cadmium caused male reproductive toxicity, and the underlying molecular mechanism remains unclear. Here we observed that the mice treated with different amount of cadmium in their rodent chow for six months exhibited reduced serum testosterone. We then performed RNA-seq to comprehensively investigate the mice testicular transcriptome to further elucidate the mechanism. Our results showed that hundreds of genes expression altered significantly in response to cadmium treatment. In particular, we found several transcriptional signatures closely related to the biological processes of regulation of hormone, gamete generation, and sexual reproduction, respectively. The expression of several testosterone synthetic key enzyme genes, such as Star, Cyp11a1, and Cyp17a1, were inhibited by the cadmium exposure. For better understanding of the cadmium-mediated transcriptional regulatory mechanism of the genes, we computationally analyzed the transcription factors binding sites and the mircoRNAs targets of the differentially expressed genes. Our findings suggest that the reproductive toxicity by cadmium exposure is implicated in multiple layers of deregulation of several biological processes and transcriptional regulation in mice.

Spermatogonial behavior in rats during radiation-induced arrest and recovery after hormone suppression

Ionizing radiation has been shown to arrest spermatogenesis despite the presence of surviving stem spermatogonia, by blocking their differentiation. This block is a result of damage to the somatic environment and is reversed when gonadotropins and testosterone are suppressed, but the mechanisms are still unknown. We examined spermatogonial differentiation and Sertoli cell factors that regulate spermatogonia after irradiation, during hormone suppression, and after hormone suppression combined with Leydig cell elimination with ethane dimethane sulfonate. These results showed that the numbers and cytoplasmic structure of Sertoli cells are unaffected by irradiation, only a few type A undifferentiated (Aund) spermatogonia and even fewer type A1 spermatogonia remained, and immunohistochemical analysis showed that Sertoli cells still produced KIT ligand (KITLG) and glial cell line-derived neurotrophic factor (GDNF). Some of these cells expressed KIT receptor, demonstrating that the failure of differentiation was not a result of the absence of the KIT system. Hormone suppression resulted in an increase in Aund spermatogonia within 3 days, a gradual increase in KIT-positive spermatogonia, and differentiation mainly to A3 spermatogonia after 2 weeks. KITL (KITLG) protein expression did not change after hormone suppression, indicating that it is not a factor in the stimulation. However, GDNF increased steadily after hormone suppression, which was unexpected since GDNF is supposed to promote stem spermatogonial self-renewal and not differentiation. We conclude that the primary cause of the block in spermatogonial development is not due to Sertoli cell factors such (KITL\GDNF) or the KIT receptor. As elimination of Leydig cells in addition to hormone suppression resulted in differentiation to the A3 stage within 1 week, Leydig cell factors were not necessary for spermatogonial differentiation.

Genetic analysis of complex traits in the emerging Collaborative Cross

The Collaborative Cross (CC) is a mouse recombinant inbred strain panel that is being developed as a resource for mammalian systems genetics. Here we describe an experiment that uses partially inbred CC lines to evaluate the genetic properties and utility of this emerging resource. Genome-wide analysis of the incipient strains reveals high genetic diversity, balanced allele frequencies, and dense, evenly distributed recombination sites-all ideal qualities for a systems genetics resource. We map discrete, complex, and biomolecular traits and contrast two quantitative trait locus (QTL) mapping approaches. Analysis based on inferred haplotypes improves power, reduces false discovery, and provides information to identify and prioritize candidate genes that is unique to multifounder crosses like the CC. The number of expression QTLs discovered here exceeds all previous efforts at eQTL mapping in mice, and we map local eQTL at 1-Mb resolution. We demonstrate that the genetic diversity of the CC, which derives from random mixing of eight founder strains, results in high phenotypic diversity and enhances our ability to map causative loci underlying complex disease-related traits.

Kit ligand and Il7 differentially regulate Peyer's patch and lymph node development

Hematopoietic lymphoid tissue inducer (LTi) cells initiate lymph node (LN) and Peyer's patch (PP) development during fetal life by inducing the differentiation of mesenchymal organizer cells. The growth factor signals underlying LTi cell development and LN and PP organogenesis remain poorly understood. LTi cells express the Il7r and the receptor tyrosine kinase Kit, whereas organizer cells express their cognate ligands. To determine the relative significance of Il7 and Kit signaling in LTi cell homeostasis and PP and LN development, we have analyzed mice deficient for Kit (Kit(W/Wv)), Il7 (Il7(-/-)), or both (Il7(-/-) Kit(W/Wv)). Unlike Kit(W/Wv) and Il7(-/-) single mutants, Il7(-/-) Kit(W/Wv) mice were almost devoid of LTi cells in their mesenteric LN anlage. This LTi deficiency was associated with a block in mesenchymal LN organizer cell generation and the absence of almost all LNs. In contrast, intestinal LTi cell numbers, PP organizer cell generation, and PP development were strongly affected by impaired Kit signaling, but were independent of Il7. Hence, Kit and Il7 act synergistically in LN organogenesis, whereas Kit signaling, but not Il7, critically regulates PP organogenesis and LTi cell numbers in the intestine. Consistent with these differential growth factor requirements for PP and LN development, PP organizer cells expressed higher Kitl and lower Il7 levels than did LN organizer cells. Collectively, these results demonstrate that Kit and Il7 differentially control PP and LN organogenesis through the local growth factor-driven regulation of LTi cell numbers.