The ADIPOQ gene-encoded adiponectin is a protein hormone produced exclusively by adipocytes (fat cells). It is transported through the bloodstream to muscle and liver cells. Adiponectin regulates various pathways related to fat storage and metabolism, including the modulation of blood glucose levels, fatty acid breakdown, brown adipocyte differentiation, and negative regulation of gluconeogenesis. By increasing insulin sensitivity and promoting fatty acid breakdown, adiponectin plays a crucial role in regulating glucose and fat metabolism. Additionally, it exhibits direct anti-diabetic, anti-atherosclerotic, and anti-inflammatory activities ^[1-2]. The mutation of the ADIPOQ gene is associated with adiponectin deficiency syndrome. Although the ADIPOQ gene is primarily expressed in adipose tissue, adiponectin is not only present in adipose tissue but is also widely distributed in various organs and tissues, including muscle, liver, intestines, male reproductive glands, and the brain ^[3-4]. The Adipoq-iCre mice are constructed by inserting a codon-improved Cre recombinase (iCre) element into the endogenous Adipoq gene of mice. The expression pattern of iCre recombinase is similar to the endogenous gene. When this strain is crossed with mice containing loxP sites, sequence recombination mediated by the Cre recombinase between loxP sites can occur in the white adipose tissue (WAT) and brown adipose tissue (BAT) of its offspring.

The AGRP gene encodes Agouti-related protein (AgRP), a neuropeptide synthesized by AgRP/NPY neurons predominantly located in the arcuate nucleus of the hypothalamus, as well as in the kidneys and adrenal glands. The expression of AGRP is modulated by various factors, including nutritional status and hormonal signals. Notably, AGRP expression is markedly upregulated during periods of starvation and rapidly downregulated following refeeding. AgRP is exclusively synthesized in the ventromedial part of the arcuate nucleus within neuropeptide Y (NPY)-containing cells, where it is co-expressed with NPY. This neuropeptide plays a pivotal role in enhancing appetite, reducing metabolic rate, and decreasing energy expenditure, making it one of the most potent and enduring appetite stimulators. AgRP exerts its orexigenic effects by antagonizing melanocortin receptor 4 (MC4R), thereby promoting food intake and inhibiting energy expenditure, which is crucial for weight regulation. Mutations in the AGRP gene have been implicated in conditions such as late-onset obesity and anorexia nervosa, underscoring its significant role in energy homeostasis and body weight control. The Agrp-IRES-CreERT2-P2A-tdTomato mouse model was generated by integrating the IRES-CreERT2-P2A-tdTomato gene expression cassette into the endogenous Agrp locus via gene editing technology. Under the control of the mouse endogenous Agrp gene regulatory elements, this mouse expresses tamoxifen-inducible CreERT2 recombinase. Additionally, the cassette includes a red fluorescent protein (tdTomato) for lineage tracing of Agrp-positive cells. In the absence of tamoxifen, CreERT2 recombinase remains cytoplasmic. Upon tamoxifen administration, CreERT2 translocates to the nucleus to mediate recombination. When Agrp-IRES-CreERT2-P2A-tdTomato mice are crossed with mice containing loxP sites, tamoxifen induction can trigger Cre recombinase-mediated sequence recombination between loxP sites in AgRP-positive neurons of the offspring.

The Cre-P2A cassette was inserted upstream of the ATG start codon.

The TAA stop codon was replaced with the P2A-CreERT2 cassette. CreERT2 recombinase is expressed under the regulatory control of Adgre1 gene elements. This model is a Tamoxifen-inducible Cre mouse, and when crossed with mice containing loxP sites, the offspring mice are expected to undergo sequence recombination between loxP sites mediated by Cre recombinase in macrophages following Tamoxifen induction.

The TGA stop codon was replaced with the P2A-CreERT2-WPRE-BGH pA cassette. CreERT2 recombinase is expressed under the regulatory control of Aqp5 gene elements. This model is a Tamoxifen-inducible Cre mouse, and when crossed with mice containing loxP sites, the offspring mice are expected to undergo sequence recombination between loxP sites mediated by Cre recombinase in alveolar type I cells, salivary gland alveolar cells, and gastrointestinal stem cells following Tamoxifen induction.

The TGA stop codon of the mouse Aire gene was replaced with P2A-CreERT2. When this strain is crossed with mice containing loxP sites, after induction with tamoxifen in the offspring mice, it is expected that Cre-recombinase-mediated sequence recombination between loxP sites will occur in medullary thymic epithelial cells (mTECs).

For the Kl model, the TGA stop codon will be replaced by P2A-Cre. A synonymous mutation p.R894=(CGG to CGC) and an additional mutation c.*3C>G in 3'UTR will also be introduced to prevent the binding and re-cutting of the sequence.

The TAG stop codon was replaced with "P2A-CreERT2" cassette. CreERT2 recombinase is expressed under the regulatory control of Ace2 gene elements. This model is a Tamoxifen-inducible Cre mouse, and when crossed with mice containing loxP sites, the offspring mice are expected to undergo sequence recombination between loxP sites mediated by Cre recombinase in Ace2-positive cells following Tamoxifen induction.

The TAA stop codon was replaced with the "P2A-EGFP-T2A-iCre" cassette. Cre recombinase and enhanced green fluorescent protein (EGFP) are expressed under the regulatory control of Alas2 gene elements. In addition to studies of Cre recombinase-mediated gene recombination, this model can also be used for EGFP fluorescent protein tracing studies.

For the Kl model, the TGA stop codon was replaced by the P2A-CreERT2 cassette, thus the expression of Cre will be under the control of the mouse Bcl6 gene regulatory element. When this strain is crossed with mice containing loxP sites, after the offspring mice are induced by tamoxifen, sequence recombination between the loxP sites mediated by Cre recombinase will occur in germinal center B cells and follicular helper T cells (TFH cells).