Expression of the adaptor protein m-Numb in mouse male germ cells

Septin 7 interacts with Numb to preserve sarcomere structural organization and muscle contractile function

Here, we investigated the mechanisms by which aging-related reductions of the levels of Numb in skeletal muscle fibers contribute to loss of muscle strength and power, two critical features of sarcopenia. Numb is an adaptor protein best known for its critical roles in development, including asymmetric cell division, cell-type specification, and termination of intracellular signaling. Numb expression is reduced in old humans and mice. We previously showed that, in mouse skeletal muscle fibers, Numb is localized to sarcomeres where it is concentrated near triads; conditional inactivation of Numb and a closely related protein Numb-like (Numbl) in mouse myofibers caused weakness, disorganization of sarcomeres, and smaller mitochondria with impaired function. Here, we found that a single knockout of Numb in myofibers causes reduction in tetanic force comparable to a double Numb, Numbl knockout. We found by proteomics analysis of protein complexes isolated from C2C12 myotubes by immunoprecipitation using antibodies against Numb that Septin 7 is a potential Numb-binding partner. Septin 7 is a member of the family of GTP-binding proteins that organize into filaments, sheets, and rings, and is considered part of the cytoskeleton. Immunofluorescence evaluation revealed a partial overlap of staining for Numb and Septin 7 in myofibers. Conditional, inducible knockouts of Numb led to disorganization of Septin 7 staining in myofibers. These findings indicate that Septin 7 is a Numb-binding partner and suggest that interactions between Numb and Septin 7 are critical for structural organization of the sarcomere and muscle contractile function.

Septin 7 Interacts With Numb To Preserve Sarcomere Structural Organization And Muscle Contractile Function

Here, we investigated mechanisms by which aging-related reductions of the levels of Numb in skeletal muscle fibers contribute to loss of muscle strength and power, two critical features of sarcopenia. Numb is an adaptor protein best known for its critical roles in development including asymmetric cell division, cell-type specification and termination of intracellular signaling. Numb expression is reduced in old humans and mice. We previously showed that, in mouse skeletal muscle fibers, Numb is localized to sarcomeres where it is concentrated near triads; conditional inactivation of Numb and a closely related protein Numb-like (NumbL) in mouse myofibers caused weakness, disorganization of sarcomeres and smaller mitochondria with impaired function. Here, we found that a single knockout of Numb in myofibers causes reduction in tetanic force comparable to a double Numb, NumbL knockout. We found by proteomics analysis of protein complexes isolated from C2C12 myotubes by immunoprecipitation using antibodies against Numb, that Septin 7 is a potential Numb binding partner. Septin 7 is a member of the family of GTP-binding proteins that organize into filaments, sheets and rings, and is considered part of the cytoskeleton. Immunofluorescence evaluation revealed a partial overlap of staining for Numb and Septin 7 in myofibers. Conditional, inducible knockouts of Numb led to disorganization of Septin 7 staining in myofibers. These findings indicate that Septin 7 is a Numb binding partner and suggest that interactions between Numb and Septin 7 are critical for structural organization of the sarcomere and muscle contractile function.

Role of adaptin protein complexes in intracellular trafficking and their impact on diseases

Adaptin proteins (APs) play a crucial role in intracellular cell trafficking. The 'classical' role of APs is carried out by AP1‒3, which bind to clathrin, cargo, and accessory proteins. Accordingly, AP1-3 are crucial for both vesicle formation and sorting. All APs consist of four subunits that are indispensable for their functions. In fact, based on studies using cells, model organism knockdown/knock-out, and human variants, each subunit plays crucial roles and contributes to the specificity of each AP. These studies also revealed that the sorting and intracellular trafficking function of AP can exert varying effects on pathology by controlling features such as cell development, signal transduction related to the apoptosis and proliferation pathways in cancer cells, organelle integrity, receptor presentation, and viral infection. Although the roles and functions of AP1‒3 are relatively well studied, the functions of the less abundant and more recently identified APs, AP4 and AP5, are still to be investigated. Further studies on these APs may enable a better understanding and targeting of specific diseases.APs known or suggested locations and functions.

Dysregulation of Notch-FGF signaling axis in germ cells results in cystic dilation of the rete testis in mice

Numb (Nb) and Numb-like (Nbl) are functionally redundant adaptor proteins that critically regulate cell fate and morphogenesis in a variety of organs. We selectively deleted Nb and Nbl in testicular germ cells by breeding Nb/Nbl floxed mice with a transgenic mouse line Tex101-Cre. The mutant mice developed unilateral or bilateral cystic dilation in the rete testis (RT). Dye trace indicated partial blockages in the testicular hilum. Morphological and immunohistochemical evaluations revealed that the lining epithelium of the cysts possessed similar characteristics of RT epithelium, suggesting that the cyst originated from dilation of the RT lumen. Spermatogenesis and the efferent ducts were unaffected. In comparisons of isolated germ cells from mutants to control mice, the Notch activity considerably increased and the expression of Notch target gene Hey1 significantly elevated. Further studies identified that germ cell Fgf4 expression negatively correlated the Notch activity and demonstrated that blockade of FGF receptors mediated FGF4 signaling induced enlargement of the RT lumen in vitro. The crucial role of the FGF4 signaling in modulation of RT development was verified by the selective germ cell Fgf4 ablation, which displayed a phenotype similar to that of germ cell Nb/Nbl null mutant males. These findings indicate that aberrant over-activation of the Notch signaling in germ cells due to Nb/Nbl abrogation impairs the RT development, which is through the suppressing germ cell Fgf4 expression. The present study uncovers the presence of a lumicrine signal pathway in which secreted/diffusible protein FGF4 produced by germ cells is essential for normal RT development.

MiR-31-5p promotes the cell growth, migration and invasion of colorectal cancer cells by targeting NUMB

The aim of this study was to investigate the role and specific molecular mechanism of miR-31-5 in colorectal cancer. The relative expression of miR-31-5p and NUMB in colorectal cancer tissues was analyzed by qRT-PCR. To knock down the expression of miR-31-5p, the transfection of miR-31-5p inhibitor was performed. The transfection with miR-31-5p mimic was used for miR-31-5p overexpression and pcDNA3.0-NUMB plasmid was used for NUMB overexpression. CCK-8 assay was used to analyze the cell proliferation. Flow cytometry was used to evaluate the cell apoptosis and cell cycle. Matrigel invasion assay was performed to assess the invasion potency and migration assay was performed to assess the migration potency. Hoechst 33258 staining assay was performed to analyze the cell apoptosis of HT29 cells after the indicated transfection. Luciferase activity assays were performed to confirmed the potential binding site for miR-31-5p in 3'-UTR region of NUMB. MiR-31-5p is highly expressed in colorectal cancer and is critical for the cell proliferation, cell cycle, migration, invasion and apoptosis. NUMB is target of miR-31-5p and NUMB overexpression inhibited the cell proliferation, migration, invasion and induced cell cycle arrest and apoptosis in HT29 colorectal cancer cells. In conclusion, miR-31-5p promoted the cell growth, migration and invasion by targeting NUMB in colorectal cancer cells.

Spermatogonial kinetics in humans

The human spermatogonial compartment is essential for daily production of millions of sperm. Despite this crucial role, the molecular signature, kinetic behavior and regulation of human spermatogonia are poorly understood. Using human testis biopsies with normal spermatogenesis and by studying marker protein expression, we have identified for the first time different subpopulations of spermatogonia. MAGE-A4 marks all spermatogonia, KIT marks all B spermatogonia and UCLH1 all Apale-dark (Ap-d) spermatogonia. We suggest that at the start of the spermatogenic lineage there are Ap-d spermatogonia that are GFRA1^High, likely including the spermatogonial stem cells. Next, UTF1 becomes expressed, cells become quiescent and GFRA1 expression decreases. Finally, GFRA1 expression is lost and subsequently cells differentiate into B spermatogonia, losing UTF1 and acquiring KIT expression. Strikingly, most human Ap-d spermatogonia are out of the cell cycle and even differentiating type B spermatogonial proliferation is restricted. A novel scheme for human spermatogonial development is proposed that will facilitate further research in this field, the understanding of cases of infertility and the development of methods to increase sperm output.

Numb modulates the paracellular permeability of intestinal epithelial cells through regulating apical junctional complex assembly and myosin light chain phosphorylation

Numb is highly expressed throughout the crypt-villus axis of intestinal mucosa and functions as cell fate determinant and integrator of cell-to-cell adhesion. Increased paracellular permeability of intestinal epithelial cells is associated with the epithelial barrier dysfunction of inflammatory bowel diseases (IBDs). The apical junctional complex (AJC) assembly and myosin light chain (MLC) phosphorylation regulate adherens junctions (AJ) and tight junctions (TJ). We determined whether and how Numb modulate the paracellular permeability of intestinal epithelial cells. Caco-2 intestinal epithelial cells and their Numb-interfered counterparts were used in the study for physiological, morphological and biological analyses. Numb, expressed in intestinal epithelial cells and located at the plasma membrane of Caco-2 cells in a basolateral to apical distribution, increased in the intestinal epithelial cells with the formation of the intestinal epithelial barrier. Numb expression decreased and accumulated in the cytoplasm of intestinal epithelial cells in a DSS-induced colitis mouse model. Numb co-localized with E-cadherin, ZO-1 and Par3 at the plasma membrane and interacted with E-cadherin and Par3. Knockdown of Numb in Caco-2 cells altered the F-actin structure during the Ca(2+) switch assay, enhanced TNFα-/INF-γ-induced intestinal epithelial barrier dysfunction and TJ destruction, and increased the Claudin-2 protein level. Immunofluorescence experiments revealed that NMIIA and F-actin co-localized at the cell surface of Caco-2 cells. Numb knockdown in Caco-2 cells increased F-actin contraction and the abundance of phosphorylated MLC. Numb modulated the intestinal epithelial barrier in a Notch signaling-independent manner. These findings suggest that Numb modulates the paracellular permeability by affecting AJC assembly and MLC phosphorylation.

The niche-derived glial cell line-derived neurotrophic factor (GDNF) induces migration of mouse spermatogonial stem/progenitor cells

In mammals, the biological activity of the stem/progenitor compartment sustains production of mature gametes through spermatogenesis. Spermatogonial stem cells and their progeny belong to the class of undifferentiated spermatogonia, a germ cell population found on the basal membrane of the seminiferous tubules. A large body of evidence has demonstrated that glial cell line-derived neurotrophic factor (GDNF), a Sertoli-derived factor, is essential for in vivo and in vitro stem cell self-renewal. However, the mechanisms underlying this activity are not completely understood. In this study, we show that GDNF induces dose-dependent directional migration of freshly selected undifferentiated spermatogonia, as well as germline stem cells in culture, using a Boyden chamber assay. GDNF-induced migration is dependent on the expression of the GDNF co-receptor GFRA1, as shown by migration assays performed on parental and GFRA1-transduced GC-1 spermatogonial cell lines. We found that the actin regulatory protein vasodilator-stimulated phosphoprotein (VASP) is specifically expressed in undifferentiated spermatogonia. VASP belongs to the ENA/VASP family of proteins implicated in actin-dependent processes, such as fibroblast migration, axon guidance, and cell adhesion. In intact seminiferous tubules and germline stem cell cultures, GDNF treatment up-regulates VASP in a dose-dependent fashion. These data identify a novel role for the niche-derived factor GDNF, and they suggest that GDNF may impinge on the stem/progenitor compartment, affecting the actin cytoskeleton and cell migration.

Musashi-1 post-transcriptionally enhances phosphotyrosine-binding domain-containing m-Numb protein expression in regenerating gastric mucosa

OBJECTIVE

Upregulation of the RNA-binding protein Musashi-1 (Msi1) has been shown to occur in rat gastric corpus mucosa after ethanol-induced mucosal injury. However, there is no direct evidence linking Msi1 with gastric regeneration. We examined the process of tissue repair after acute gastric mucosal injury with Msi1-knock-out (KO) mice to clarify the role of Msi1 and Msi1-dependent regulation of m-Numb expression in regenerating gastric mucosa.

METHODS

Acute gastric injury was induced in Msi1-KO and wild-type ICR mice by administering absolute ethanol. Expression of the splicing variants of m-Numb mRNA and protein in the gastric mucosa were analyzed by quantitative RT-PCR and western blotting, respectively.

RESULTS

We demonstrated that phosphotyrosine-binding domain-containing m-Numb expression was significantly upregulated at both the mRNA and protein levels in wild-type mice at 3 h after ethanol-induced acute gastric injury. In contrast, in Msi1-KO mice, the m-Numb protein was expressed weakly, and was associated with delayed regeneration of the injured gastric mucosal epithelium. In the Msi1-KO mouse, the ratio of m-Numb mRNA to total m-Numb mRNA in the heavy polysome fractions was lower than that in the wild-type mouse. Further, we showed that m-Numb-enhancement in gastric mucous cells induced the expression of prostate stem cell antigen and metallothionein-2. Under the m-Numb enhancing condition, the gastric cells exhibited enhanced cell proliferation and were significantly more resistant to H(2)O(2)-induced cell death than control cells.

CONCLUSIONS

Msi1-dependent post-transcriptional enhancement of m-Numb is crucial in gastric epithelial regeneration.

Distribution of GFRA1-expressing spermatogonia in adult mouse testis

In mice and other mammals, spermatogenesis is maintained by spermatogonial stem cells (SSCs), a cell population belonging to undifferentiated type A spermatogonia. In the accepted model of SSC self-renewal, Asingle (As) spermatogonia are the stem cells, whereas paired (Apaired (Apr)) and chained (Aaligned (Aal)) undifferentiated spermatogonia are committed to differentiation. This model has been recently challenged by evidence that As and chained (Apr and Aal), undifferentiated spermatogonia are heterogeneous in terms of gene expression and function. The expression profile of several markers, such as GFRA1 (the GDNF co-receptor), is heterogeneous among As, Apr and Aal spermatogonia. In this study, we have analysed and quantified the distribution of GFRA1-expressing cells within the different stages of the seminiferous epithelial cycle. We show that in all stages, GFRA1+ chained spermatogonia (Apr to Aal) are more numerous than GFRA1+ As spermatogonia. Numbers of chained GFRA1+ spermatogonia are sharply reduced in stages VII-VIII when Aal differentiate into A1 spermatogonia. GFRA1 expression is regulated by GDNF and in cultures of isolated seminiferous tubules, we found that GDNF expression and secretion by Sertoli cells is stage-dependent, being maximal in stages II-VI and decreasing thereafter. Using qRT-PCR analysis, we found that GDNF regulates the expression of genes such as Tex14, Sohlh1 and Kit (c-Kit) known to be involved in spermatogonial differentiation. Expression of Kit was upregulated by GDNF in a stage-specific manner. Our data indicate that GDNF, besides its crucial role in the self-renewal of stem cells also functions in the differentiation of chained undifferentiated spermatogonia.

Numb modulates intestinal epithelial cells toward goblet cell phenotype by inhibiting the Notch signaling pathway

Numb was originally identified as an important cell fate determinant that is asymmetrically inherited during mitosis and controls the fate of sibling cells by inhibiting the Notch signaling pathway in neural tissue. The small intestinal epithelium originates from the division of stem cells that reside in the crypt, which further differentiate into goblet cells, absorptive cells, paneth cells, and enteroendocrine cells. However, Numb's involvement in the differentiation process of intestinal epithelium is largely unknown. In the present study, we confirm that both the Numb mRNA and protein isoforms are expressed in adult mouse intestinal mucosa. Numb protein is ubiquitously expressed throughout the crypt-villus axis of the small intestinal epithelium and is mainly localized to the cytoplasmic membrane. Down-regulation of endogenous Numb using RNA interference in cultured intestinal LS174T cells increased Notch signaling, leading to the up-regulation of Hes1 and the down-regulation of Hath1. Knockdown of Numb alleviated MUC2 protein expression and led to loss of the goblet cell phenotype in LS174Tl cells. Our results provide the first evidence that Numb, an important cell fate determinant, modulates intestinal epithelial cells towards the goblet cell phenotype by inhibiting the Notch signaling pathway.

Numb deletion in POMC-expressing cells impairs pituitary intermediate lobe cell adhesion, progenitor cell localization, and neuro-intermediate lobe boundary formation

The pituitary gland contains six distinct hormone-secreting cell types that are essential for basic physiological processes including fertility and responding to stress. Formation of hormone-secreting cells during development relies on Notch signaling to prevent progenitors from prematurely differentiating. The nature of the signal curtailing Notch signaling in the pituitary is unknown, but a good candidate is the endocytic adaptor protein NUMB. NUMB targets Notch for proteolytic degradation, but it also has a broad range of actions, including stabilizing adherens junctions through interactions with cadherins and influencing cell proliferation by stabilizing expression of the tumor suppressor protein p53. Here, we show that NUMB and its closely related homolog, NUMBLIKE, are expressed in undifferentiated cells during development and later in gonadotropes in the anterior lobe and melanotropes of the intermediate lobe. All four isoforms of NUMB, are detectable in the pituitary, with the shorter forms becoming more prominent after adolescence. Conditionally deleting Numb and Numblike in the intermediate lobe melanotropes with Pomc Cre mice dramatically alters the morphology of cells in the intermediate lobe, coincident with impaired localization of adherens junctions proteins including E-CADHERIN, N-CADHERIN, β-CATENIN, and α-CATENIN. Strikingly, the border between posterior and intermediate lobes is also disrupted. These mice also have disorganized progenitor cells, marked by SOX2, but proliferation is unaffected. Unexpectedly, Notch activity appears normal in conditional knockout mice. Thus, Numb is critical for maintaining cell-cell interactions in the pituitary intermediate lobe that are essential for proper cell placement.

Spermatogonial stem cell regulation and spermatogenesis

This article will provide an updated review of spermatogonial stem cells and their role in maintaining the spermatogenic lineage. Experimental tools used to study spermatogonial stem cells (SSCs) will be described, along with research using these tools to enhance our understanding of stem cell biology and spermatogenesis. Increased knowledge about the biology of SSCs improves our capacity to manipulate these cells for practical application. The chapter concludes with a discussion of future directions for fundamental investigation and practical applications of SSCs.

Identification of spermatogonial stem cell subsets by morphological analysis and prospective isolation

Spermatogenesis is maintained by a pool of spermatogonial stem cells (SSCs). Analyses of the molecular profile of SSCs have revealed the existence of subsets, indicating that the stem cell population is more heterogeneous than previously believed. However, SSC subsets are poorly characterized. In rodents, the first steps in spermatogenesis have been extensively investigated, both under physiological conditions and during the regenerative phase that follows germ cell damage. In the widely accepted model, the SSCs are type Asingle (As) spermatogonia. Here, we tested the hypothesis that As spermatogonia are phenotypically heterogeneous by analyzing glial cell line-derived neurotrophic factor (GDNF) family receptor alpha1 (GFRA1) expression in whole-mounted seminiferous tubules, via cytofluorimetric analysis and in vivo colonogenic assays. GFRA1 is a coreceptor for GDNF, a Sertoli cell-derived factor essential for SSC self-renewal and proliferation. Morphometric analysis demonstrated that 10% of As spermatogonia did not express GFRA1 but were colonogenic, as shown by germ cell transplantation assay. In contrast, cells selected for GFRA1 expression were not colonogenic in vivo. In human testes, GFRA1 was also heterogeneously expressed in Adark and in Apale spermatogonia, the earliest spermatogonia. In vivo 5-bromo-2'-deoxyuridine administration showed that both GFRA1(+) and GFRA1(-) As spermatogonia were engaged in the cell cycle, a finding supported by the lack of long-term label-retaining As spermatogonia. GFRA1 expression was asymmetric in 5% of paired cells, suggesting that As subsets may be generated by asymmetric cell division. Our data support the hypothesis of the existence of SSC subsets and reveal a previously unrecognized heterogeneity in the expression profile of As spermatogonia in vivo.

Regulation of the spermatogonial stem cell niche

Spermatogonial stem cells (SSCs) reside within specialized microenvironments called 'niches', which are essential for their maintenance and self-renewal. In the mammalian testis, the main components of the niche include the Sertoli cell, the growth factors that this nursing cell produces, the basement membrane, and stimuli from the vascular network between the seminiferous tubules. This review focuses on signalling pathways maintaining SSCs self-renewal and differentiation and describes potential mechanisms of regulation of the spermatogonial stem cell niche.