Connexin30.3 is expressed in mouse embryonic stem cells and is responsive to leukemia inhibitory factor

Diversity in connexin biology

Over 35 years ago the cell biology community was introduced to connexins as the subunit employed to assemble semicrystalline clusters of intercellular channels that had been well described morphologically as gap junctions. The decade that followed would see knowledge of the unexpectedly large 21-member human connexin family grow to reflect unique and overlapping expression patterns in all organ systems. While connexin biology initially focused on their role in constructing highly regulated intercellular channels, this was destined to change as discoveries revealed that connexin hemichannels at the cell surface had novel roles in many cell types, especially when considering connexin pathologies. Acceptance of connexins as having bifunctional channel properties was initially met with some resistance, which has given way in recent years to the premise that connexins have multifunctional properties. Depending on the connexin isoform and cell of origin, connexins have wide-ranging half-lives that vary from a couple of hours to the life expectancy of the cell. Diversity in connexin channel characteristics and molecular properties were further revealed by X-ray crystallography and single-particle cryo-EM. New avenues have seen connexins or connexin fragments playing roles in cell adhesion, tunneling nanotubes, extracellular vesicles, mitochondrial membranes, transcription regulation, and in other emerging cellular functions. These discoveries were largely linked to Cx43, which is prominent in most human organs. Here, we will review the evolution of knowledge on connexin expression in human adults and more recent evidence linking connexins to a highly diverse array of cellular functions.

Connexin 45 is a novel suppressor of melanoma metastasis

The expression spectra of connexin (Cx) isoforms were investigated in three mouse melanoma cell lines: B16-F1 (F1), B16-F10 (F10), and B16-BL6 (BL6). Metastatic potential intensity was higher in the order of F1, F10, and BL6. A remarkable behavior of Cx45 was found among 20 isoforms. The expression level of Cx45 was highest in F1 and lowest in BL6. It was inductively predicted that Cx45 might be a novel suppressor of metastasis. A Cx45-overexpressing BL6 cell line (Cx45 +BL6) was developed and its properties were compared with those of a wild-type cell line of BL6 (W-BL6). Compared to W-BL6, Cx45 +BL6 showed reduced wound healing, Transwell® permeability, and matrix metalloproteinase 9 expression, suggesting the suppression of cellular migration and invasion. The expression of E-cadherin and integrin β1 in Cx45 +BL6 was also lower than in W-BL6, suggesting reduced cell adhesion. The decrease in cell adhesion was supported by the cell washing-out assay. In contrast, no difference between W-BL6 and Cx45 +BL6 was observed in cell proliferation, suggesting no effect on cell-cycle regulating factors. Finally, an in vivo assay revealed a significant decrease in the number of metastatic colonies of Cx45 +BL6 (176 ± 25/lung) in comparison with those of W-BL6 (252 ± 23/lung) in a mouse model. In conclusion, Cx45 is a novel suppressor of melanoma metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-022-00563-x.

Genome-wide characterization of gap junction (connexins and pannexins) genes in turbot (Scophthalmus maximus L.): evolution and immune response following Vibrio anguillarum infection

Gap junction (GJ), a special intercellular junction between different cell types, directly connects the cytoplasm of adjacent cells, allows various molecules, ions and electrical impulses to pass through the intercellular regulatory gate, and plays vital roles in response to bacterial infection. Up to date, the information about the GJ in turbot (Scophthalmus maximus L.) is still limited. In current study, 43 gap junction genes were identified in turbot, phylogeny analysis suggested that gap junctions from turbot and other species were clustered into six groups, GJA, GJB, GJC, GJD, GJE and PANX, and turbot GJs together with respective GJs from Japanese flounder, half-smooth tongue sole and large yellow croaker, sharing same ancestors. In addition, these 43 GJ genes distributed in different chromosomes unevenly. According to gene structure and domain analysis, these genes (in GJA-GJE group) were highly conserved in that most of them contain the transmembrane area, connexin domain (CNX) and cysteine-rich domain (connexin CCC), while PANXs contain Pfam Innexin. Although only one tandem duplication was identified in turbot gap junction gene, 235 pairs of segmental duplications were identified in the turbot genome. To further investigate their evolutionary relationships, Ka/Ks was calculated, and results showed that most ratios were lower than 1, indicating they had undergone negative selection. Finally, expression analysis showed that gap junction genes were widely distributed in turbot tissues and significantly regulated after Vibrio anguillarum infection. Taken together, our research could provide valuable information for further exploration of the function of gap junction genes in teleost.

The Relationship between the Connexin 32 and Connexin 43 Genes and the Pretreatment Stage and Short-term Follow-up of Patients with Acute Myeloid Leukemia

Background

Connexins (Cxs) are gap junction proteins involved in the communication between acute myeloid leukemia (AML) and stromal cells. They consist of intercellular channels termed "connexions", which can cause uncontrolled cell proliferation if dysregulated. This study aimed to evaluate the expression levels of the Cx32 and Cx43 genes and their correlations with other prognostic markers in patients with AML.

Methods

This cross sectional study was performed on peripheral blood samples from 60 newly diagnosed patients with AML and 40 healthy control subjects at Kasr Alainy School of Medicine, Cairo University, from June 2016 to December 2017. The quantitative real-time polymerase chain reaction (qRT-PCR) test was used to examine the relative expression level of Cx43 and Cx32 genes in the patients and the control subjects. The Chi square test or the Fisher exact test was employed to examine the relationship between qualitative variables, while the independent t test or the Mann-Whitney test was employed for quantitative data. All the tests were two-tailed, and a P value of less than 0.05 was considered significant.

Results

Among the patients with AML, 65% had a high Cx32 expression level, whereas 63.3% had a low Cx43 expression level. There was a statistically significant difference in the fold change values of Cx32 and Cx43 expression between the patient group and the control group (P=0.009 vs P=0.013, respectively). There was a remarkable association between both Cxs and CD34 and HLA-DR cells.

Conclusion

Cx expression in samples may add to the diagnostic workup of AML. Although we found a negative correlation between Cx43 expression and the peripheral blood blast percentage, the response after the first induction of chemotherapy showed no significant relationship with Cx43 and Cx32.

Overexpression of Gjb4 impairs cell proliferation and insulin secretion in primary islet cells

OBJECTIVE

Altered gene expression contributes to the development of type 2 diabetes (T2D); thus, the analysis of differentially expressed genes between diabetes-susceptible and diabetes-resistant mouse models is an important tool for the determination of candidate genes that participate in the pathology. Based on RNA-seq and array data comparing pancreatic gene expression of diabetes-prone New Zealand Obese (NZO) mice and diabetes-resistant B6.V-ob/ob (B6-ob/ob) mice, the gap junction protein beta 4 (Gjb4) was identified as a putative novel T2D candidate gene.

METHODS

Gjb4 was overexpressed in primary islet cells derived from C57BL/6 (B6) mice and INS-1 cells via adenoviral-mediated infection. The proliferation rate of cells was assessed by BrdU incorporation, and insulin secretion was measured under low (2.8 mM) and high (20 mM) glucose concentration. INS-1 cell apoptosis rate was determined by Western blotting assessing cleaved caspase 3 levels.

RESULTS

Overexpression of Gjb4 in primary islet cells significantly inhibited the proliferation by 47%, reduced insulin secretion of primary islets (46%) and INS-1 cells (51%), and enhanced the rate of apoptosis by 63% in INS-1 cells. Moreover, an altered expression of the miR-341-3p contributes to the Gjb4 expression difference between diabetes-prone and diabetes-resistant mice.

CONCLUSIONS

The gap junction protein Gjb4 is highly expressed in islets of diabetes-prone NZO mice and may play a role in the development of T2D by altering islet cell function, inducing apoptosis and inhibiting proliferation.

Effects of leukemia inhibitory factor receptor on the adipogenic differentiation of human bone marrow mesenchymal stem cells

Leukemia inhibitory factor (LIF) modulates various biological processes. Although previous studies have described the effects of LIF on adipocyte differentiation, the role of LIF receptor (LIFR) on adipocyte differentiation remains unclear. Using reverse transcription‑quantitative PCR (RT‑qPCR), LIFR expression was demonstrated to increase during adipogenic differentiation of human bone marrow mesenchymal stem cells (hMSCs), indicating that LIFR may be involved in this process. To further evaluate the association between LIFR and adipogenic differentiation, lentivirus‑mediated LIFR knockdown was performed in hMSCs. Cells were divided into two groups: Negative control group and LIFR‑knockdown group. During the adipogenic differentiation process, intracellular lipid accumulation was assessed with Oil Red O staining at various time points (days 3, 6 and 9). Additionally, the mRNA and protein expression levels of LIF, LIFR and three molecular indicators of adipogenesis, peroxisome proliferator‑activated receptor γ (PPARγ), CCAAT enhancer binding protein α (C/EBPα) and fatty acid binding protein 4 (FABP4/aP2), were assessed by RT‑qPCR and western blotting. The culture supernatant was collected to evaluate the concentration of LIF using ELISA. The present results suggested that LIFR expression progressively increased during adipogenic differentiation of hMSCs. Conversely, LIFR knockdown significantly suppressed this process. Additionally, PPARγ, C/EBPα and aP2 were inhibited following LIFR knockdown. In contrast with LIFR, the expression levels of LIF were significantly decreased after the initiation of adipogenic differentiation. Therefore, the expression levels of LIF and LIFR exhibited opposite trends. Collectively, the present results suggested that LIFR promoted adipogenic differentiation, whereas LIF may negatively regulate this process.

Enhancement of connexin30.3 expression in mouse embryonic stem cell line EB3 in response to cell-cell contacts

To clarify the potential role of gap junction in cell-cell contact response, the expression of connexin30.3 gene (Cx30.3), a specifically expressed isoform in undifferentiated state of mouse embryonic stem (ES) cell line EB3 was investigated under different cell-cell contact conditions. ES cells were cultured by hanging drop culture method to increase cell-cell contact frequency. As control, a single cell culture was conducted. After culture for 12 h, the Cx30.3 expression level in hanging drop culture reached 1.73-fold that of the control (p < 0.001). By contrast, connexin43 gene (Cx43), a ubiquitously expressed gene, showed no difference between both cultures. The experiment of E-cadherin inhibition and β-catenin knockdown suggested the action of E-cadherin upstream of the Cx30.3 regulating pathway. The cell-cell contacts with different cell lines such as HeLa cells and B16/BL6 caused no effect on the Cx30.3 in ES cells. These suggest a potential role of Cx30.3 as a cell-cell contact signal mediator partially regulated by E-cadherin signaling.

Comparison of different in vitro differentiation conditions for murine female germline stem cells

Objectives

In vitro differentiation of oocytes from female germline stem cells (FGSCs) has exciting potential applications for reproductive medicine. Some researchers have attempted to reveal the in vitro differentiation capacity of FGSCs. However, no systematic comparative study of in vitro differentiation conditions has been performed for murine FGSCs (mFGSCs).

Materials and Methods

mFGSCs line was cultured under five different conditions for in vitro differentiation. RT‐PCR was performed to detect the expression of Oct4, Fragilis, Blimp1, Mvh, Scp3 and Zp3. Immunofluorescence was carried out to test the expression of Mvh, Fragilis and Zp3. Two‐photon laser‐scanning microscope was used to analyze nucleus‐plasma ratio, and the proportion of chromatin of GV oocytes differentiated from mFGSCs in vitro (IVD‐GVO), GV oocytes from in vivo (GVO) and mFGSCs.

Results

RT‐PCR and immunofluorescence showed that mFGSC line expressed germ cell‐specific markers, but not a meiosis‐specific marker. By evaluating five different in vitro differentiation conditions, condition 5, which included a hanging drop procedure and co‐culture of mFGSCs with granulosa cells, was shown to be optimal. mFGSCs could be successfully differentiated into germinal vesicle (GV) ‐stage oocytes under this condition. 3D observation revealed that both the nucleus‐plasma ratio and proportion of chromatin were not significantly different between IVD‐GVO and GVO.

Conclusion

We evaluated five in vitro differentiation conditions for mFGSCs and successfully differentiate mFGSCs into GV‐stage oocytes using a three‐step differentiation process.

The role of connexins during early embryonic development: pluripotent stem cells, gene editing, and artificial embryonic tissues as tools to close the knowledge gap

Since almost 4 decades, connexins have been discussed as important regulators of embryogenesis. Several different members of the gene family can be detected in the preimplantation embryo and during gastrulation. However, genetically engineered mice deficient for every connexin expressed during early development are available and even double-deficient mice were generated. Interestingly, all of these mice complete gastrulation without any abnormalities. This raises the question if the role of connexins has been overrated or if other gene family members compensate and mask their importance. To answer this question, embryos completely devoid of any gap junctional communication need to be investigated. This is challenging because a variety of connexin genes are co-expressed and some null mutations lead to a lethal phenotype. In addition, maternal connexin transcripts were described to persist until the blastocyst stage. In this review, we summarize the current knowledge about the role of connexins during preimplantation development and in embryonic stem cells. We propose that the use of pluripotent stem cells, trophoblast stem cells, as well as artificial embryo-like structures and organoid cultures in combination with multiplex CRISPR/Cas9-based genome editing provides a powerful platform to comprehensively readdress this issue and decipher the role of connexins during lineage decision, differentiation, and morphogenesis in a cell culture model for mouse and human development.