Biology subjects

li, k.

Publications and source records attributed to li, k..

3 recordsLinked to original sources

bioRxiv2025

A new nitrogen biochemical process: Oxidization of ammonium into nitrogen gas using nitrate

The nitrifying bacteria oxidize ammonium into nitrite or nitrate under aerobic conditions, while the anaerobic ammonia-oxidizing bacteria utilize nitrite to oxidize ammonium into nitrogen gas under anaerobic conditions. There is no biochemical process that can directly oxidize ammonium into nitrogen gas using nitrate under anaerobic conditions. In this study, mature anaerobic ammonium oxidation (anammox) granular sludge was inoculated in an anaerobic nitrogen-removal system, while nitrate and ammonium were used as the influent substrates. The experiment was conducted for 537 days at a temperature of 30-32{degrees}C and a pH of 8.0-9.0. The transformation from nitrite-anammox to nitrate-anammox was stably achieved on the 350th day. The experimental results showed that, nitrate directly oxidized ammonium into nitrogen gas under anaerobic conditions. The produced gas consisted of 96.3% nitrogen and 3.7% carbon dioxide. The removal ratio of ammonium to nitrate was approximately 1.67:1, and the total inorganic nitrogen removal rate reached up to 290.20 mg/(L{middle dot}d). Unlike the nitrite-anammox reaction, this reaction was accompanied by an acid production process, which caused a decrease in pH. When the substrate was changed to nitrite and ammonium, the total nitrogen removal rate of only 1.1-1.3 mg/(L{middle dot}d) was achieved. This new biochemical reaction of nitrogen was defined as nitrate-anammox. The study reveals a new pathway of nitrogen transformation, providing novel insights into the global nitrogen cycle.

microbiology↗

bioRxiv2024

COCOA: A Framework for Fine-scale Mapping Cell-type-specific Chromatin Compartmentalization Using Epigenomic Information

Chromatin compartmentalization and epigenomic modification are crucial factors in cell differentiation and diseases development. However, mapping precise chromatin compartmental patterns across multiple cell types requires Hi-C or Micro-C data at high sequencing depth. Exploring the systematic relationship between epigenomic modifications and compartmental patterns remains a challenge. To address these issues, we present COCOA, a deep neural network framework that uses convolution and attention mechanisms to infer reliable fine-scale chromatin compartment patterns from six representative histone modification signals. COCOA achieves this by extracting 1-D track features through bi-directional feature reconstruction after resolution-specific binning epigenomic signals. These track features are then cross-fused with contact features using an attention mechanism. Subsequently, the contact features are transformed into chromatin compartment patterns through residual feature reduction. COCOA demonstrates accurate inference of chromatin compartmentalization at a fine-scale resolution and exhibits stable performance on test sets. In addition, we explored the impact of histone modifications on the chromatin compartmentalization through in silico epigenomic perturbation experiments. When using 1kb resolution high-depth experimental data, obscure compartments are observed, whereas COCOA can generate clear and detailed compartmental patterns. Finally, we demonstrated that COCOA enables cell-type-specific prediction of unrevealed chromatin compartment patterns in various biological processes. Thus, COCOA is an effective tool for gaining chromatin compartmentalization insights from epigenomics in a wide range of biological scenarios.

bioinformatics↗

bioRxiv2018

MiR-505-3p is a Repressor of the Puberty Onset in Female Mice

Puberty onset is a complex trait regulated by multiple genetic and environmental factors. In this study, we narrowed a puberty related QTL down to a 1.7 Mb region on chromosome X in female mice and inferred miR-505-3p as the functional gene.\n\nWe conducted ectopic expression of miR-505-3p in the hypothalamus of prepubertal female mice through lentivirus-mediated orthotopic injection. The impact of miR-505-3p on female puberty was evaluated by the measurement of pubertal events and histological analysis. The results showed that female mice with overexpression of miR-505-3p in the hypothalamus manifested later puberty onset timing both in vaginal opening and ovary maturation, followed by weaker fertility lying in the longer interval time between mating and delivery, higher abortion rate and smaller litter size. We also constructed miR-505-3p knockout mice by CRISPR/Cas9 technology. MiR-505-3p knockout female mice showed earlier vaginal opening timing, higher serum gonadotrophin and higher expression of puberty-related gene, as well as its target gene Srsf1 in the hypothalamus than their wild type littermates.\n\nSrsf1 was proved to be the target gene of miR-505-3p that played the major role in this process. The results of RIP-seq (RNA Immunoprecipitation-sequencing) showed that SF2, the protein product of Srsf1 gene, mainly bound to ribosome protein (RP) mRNAs in GT1-7 cells. The collective evidence implied that miR-505-3p/SRSF1/RP could play a role in the sexual maturation regulation of mammals.\n\nAuthor summaryThe puberty onset in mammals is a vital biological process that signals the acquisition of reproductive capacity. The initiation of puberty is triggered by the activation of hypothalamic pulsatile GnRH surge. The dysregulation of pubertal development shows relevance to later health risks of type 2 diabetes, cardiovascular disease, breast cancer and other health disorders. Recent progress indicates that a lot of genes play a role in the excitatory or inhibitory regulation of GnRH release. However, the detailed pathway of pubertal timing remains unclear. Our previous studies isolated an X-linked QTL that was associated with the timing of puberty in mice. In this study, we proved that miR-505-3p was a female puberty onset regulator based on data from positional cloning, ectopic expression and knockout mouse models. We also assigned Srsf1 as the functional target gene of miR-505-3p underlying this process. The results of RIP-seq showed that SF2, the protein of Srsf1 gene, preferential bound to ribosome protein (RP) mRNAs in GT1-7 cells. We propose that miR-505-3p/SF2/RP could play a role in the sexual maturation regulation of mammals.

genetics↗