Biology subjects

Zhang, X. M.

Publications and source records attributed to Zhang, X. M..

4 recordsLinked to original sources

bioRxiv2024

A minor impact of VGLUT1 expression level on quantal size revealed through the characterization of VGLUT1mEos2 knock-down new mouse model

Synaptic vesicles (SVs) are small organelles secreting neurotransmitters at synapses. By fusing a photoactivated fluorescent protein to VGLUT1, we generated a VGLUT1mEos2 knock-in mouse. VGLUT1mEos2 knock-in mice are viable and healthy, but exhibit a severe reduction in VGLUT1 expression levels. Using VGLUT1mEos2 expressing neurons, we established paradigms to trace individual SV mobility at the single-molecule level or via massive photoconversion. Hippocampal neurons with significantly diminished VGLUT1 expression maintain unaltered miniature glutamate release characteristics in terms of quantal size and frequency. We demonstrate that VGLUT1 expression level are not correlated in a linear fashion with the vesicular glutamate content. In conclusion, the VGLUT1mEos2 mouse line serves as a powerful tool for exploring SV mobility properties and elucidating the contributions of VGLUT1 to excitatory neurotransmission and cognitive processes.

neuroscience↗

bioRxiv2022

Jagged1 overexpression on T cells induces thymic regulatory T cells leading to thymic involution

We previously described a mouse model, tg66, with a severe defect resulting in diminished thymic size and complete involution by early adulthood. In the current study, we identified overexpression of Jagged1 as a mechanism for the alterations in thymic development in tg66 mice. T cells in the tg66 thymus were skewed towards CD8+ T cells, and within the CD4+ T cell compartment there was an over-representation of Foxp3+ cells. Regulatory Foxp3+ T cells (Tregs) isolated from tg66 mice had increased ST2 and CD103 expression. These Tregs could suppress proliferation to the same extent as conventional Tregs. Corroborating these results, tg66 mice were resistant to experimental induction of neuroinflammation in a common animal model for multiple sclerosis (EAE). Using bone marrow chimeras, we recorded a stark reduction in the number of thymocytes and a corresponding increase in Tregs in the thymus of mice receiving tg66 bone marrow. Conversely, through blocking Jagged1, the number of thymocytes was significantly increased, being concomitantly associated with a drop in the frequency of Tregs. We conclude that Tregs may play a role in thymic involution and could explain early thymic involution or loss as it is observed in diseases of thymic atrophy such as Down syndrome.

immunology↗

bioRxiv2020

HDAC6 regulates radiosensitivity of non-small cell lung cancer by promoting degradation of Chk1

We previously discovered that HDAC6 regulates the DNA damage response via modulating the homeostasis of a DNA mismatch repair protein, MSH2, through HDAC6s ubiquitin E3 ligase activity. Here, we have reported HDAC6s second E3 ligase substrate, a critical cell cycle checkpoint protein, Chk1. We have found that HDAC6 and Chk1 directly interact, and that HDAC6 ubiquitinates Chk1 in vivo. Typical Chk1 protein levels fluctuate, peaking at G2 and subsequently resolving via the ubiquitin-proteasome pathway. However, in HDAC6 knockdown cells, Chk1 is constitutively active and fails to resolve post-ionizing radiation (IR), leading to increased radiation sensitivity. Upon IR treatment, a greater proportion of HDAC6 knockdown cells accumulated at G2/M phase when compared with control cells. Depletion or inhibition of Chk1 in HDAC6 knockdown cells renders those cells radiosensitive, suggesting that persistently high level of Chk1 could lead cells to arrest at G2/M phase and eventually, apoptosis. Clinically, we found that high levels of phosphorylated Chk1 (p-Ser317) are associated with a better overall survival in a cohort of non-small cell lung cancer (NSCLC) patients, suggesting a link between active Chk1 and lung cancer development. Overall, our results highlight a novel mechanism of Chk1 regulation at the protein level, and a possible strategy for sensitizing NSCLC to radiation via inhibiting the activity of HDAC6s E3 ligase.

molecular biology↗

bioRxiv2018

Mammalian vesicular glutamate transporter VGLUT1 reduces synaptic vesicle superpool size and spontaneous release frequency.

Glutamate secretion at excitatory synapses is tightly regulated to allow for the precise tuning of synaptic strength. Vesicular Glutamate Transporters (VGLUT) accumulate glutamate into synaptic vesicles (SV) and thereby regulate quantal size. Further, the number of release sites and the release probability of SVs maybe regulated by the organization of active zone proteins and SV clusters. In the present work, we uncover a mechanism mediating an increased SV clustering through a tripartite interaction of VGLUT1, endophilinA1 and intersectin1. This strengthening of SV clusters results in a combined reduction of axonal SV super-pool size and miniature excitatory events frequency. Our findings support a model in which clustered vesicles are held together through multiple weak interactions between SH3 domains and proline rich sequences of synaptic proteins. In mammals, VGLUT1 gained a poly-proline sequence that recruits endophilinA1 and turns the transporter into a dual regulator of quantal release parameters at excitatory synapses.

neuroscience↗