The Transferrin receptor (TFRC) gene encodes Transferrin Receptor 1 (TFR1), a protein that is expressed at low levels in most normal cells but shows increased expression in highly proliferative cells, such as basal epidermal cells, intestinal epithelium, and certain activated immune cells. Brain capillary endothelial cells, which constitute the blood-brain barrier (BBB), also express this receptor at high levels ^[1]. TFR1 plays a critical role in maintaining iron metabolism and homeostasis by facilitating receptor-mediated endocytosis of iron-bound transferrin (Tf) via Tf cycling, thereby promoting iron uptake ^[2]. Cellular iron deficiency can lead to apoptosis, while cellular transformation requires substantial iron to sustain proliferation, with iron overload contributing to tumor progression. The high expression of TFR1 in many tumors makes it a potential tumor marker, offering a target for therapies to inhibit tumor growth and metastasis ^[1]. Moreover, TFR1 is implicated in anemia and iron metabolism disorders. Studies have shown that elevated TFR1 expression in cardiomyocytes is associated with exacerbated inflammation in myocarditis patients ^[3]. Various clinical drugs targeting TFR1 are currently under development, including antisense oligonucleotides (ASOs), antibody-drug conjugates (ADCs), and antibody-oligonucleotide conjugates, applicable to diseases such as cancer, anemia, and neurodegenerative disorders. Research indicates that enhancing antibody transport across the blood-brain barrier via TFR1, by forming specific bispecific antibodies with anti-β-amyloid antibodies, can improve therapeutic outcomes in Alzheimer's patients ^[4-5]. As research progresses, TFR1 is expected to become an effective clinical target for multiple diseases and a synergistic target for drug delivery across the blood-brain barrier (BBB). Parkinson's disease (PD) is a neurodegenerative disease with a high prevalence mainly in the middle-aged and elderly population. It is the second most common neurodegenerative disease after Alzheimer's disease (AD). The main clinical symptoms include resting tremors, limb stiffness, bradykinesia, loss of voluntary movement, etc. The typical pathological process of PD is the formation of Lewy bodies (LB) in the central nervous system (CNS), which results in the gradual death and loss of dopaminergic neurons, leading to the disease ^[6-7]. The main components of Lewy bodies are insoluble aggregates of abnormal α-synuclein (α-syn), and the SNCA gene, which encodes α-synuclein, is one of the key causative genes in Parkinson's disease. Mutations in this gene cause overexpression of α-syn, leading to the formation of Lewy bodies, ultimately leading to PD ^[8]. In addition, SNCA mutations are also associated with diseases such as dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). B6-huTFRC/huSNCA(3'UTR) mice are a dual-gene humanized model generated by crossing B6-huTFRC mice (Catalog No.: C001860) with B6-hSNCA (3'UTR) mice (Catalog No.: C001698). This model can be used for research on neurodegenerative diseases such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), as well as iron metabolism disorders and tumorigenesis and development. It is also applicable for the development of TFRC/SNCA-targeted drugs.

Rett syndrome (RTT) is an X-linked dominant neurodevelopmental disorder that occurs predominantly in female infants and young children. The incidence is approximately 1 in 10,000–15,000 females. Clinical features include intellectual disability, loss of language function, stereotyped hand movements, and gait abnormalities. Affected children typically have a period of normal development followed by stagnation of head circumference growth at 6–18 months of age, and regression of acquired skills. Overt cognitive and motor impairments develop 1–2 years later. Mutations in the methyl-CpG-binding protein 2 (MECP2) gene account for >90% of RTT cases. MECP2 is a nuclear protein that binds to methylated DNA to regulate gene transcription. MECP2 duplications cause MECP2 duplication syndrome (MDS), while functional deficiency of MECP2 impairs the production of this nuclear protein, leading to central nervous system functional maturation disorders that affect learning and memory functions, resulting in RTT. Treatment for RTT focuses mainly on gene supplementation therapy based on adeno-associated virus (AAV) vectors. This involves delivering human MECP2 genes via AAV vectors to compensate for the deficiency of MECP2 genes in patients. However, the large size of the MECP2 gene exceeds the delivery capacity of most vectors, and over-expression of the MECP2 gene can also lead to serious neurological diseases. These limitations have hindered the development of this therapy. Therefore, DNA/RNA editing to repair MECP2 gene mutations and restore normal expression of MECP2 protein has received widespread attention. Currently, multiple research groups have used CRISPR-based gene editing technology to repair mutations in the MECP2 gene in induced pluripotent stem cells (iPSCs) or ex vivo patient cells ^[1-2]. Animal studies are an essential part of preclinical research. RTT therapies based on small nucleic acids, CRISPR gene editing technology, base editors, and RNA editing technology target the human MECP2 gene. Humanized mouse models can help advance gene therapy drug pipelines into clinical stages ^[3-4]. This strain is a humanized MECP2 gene mouse model that can be used for RTT research. Homozygous B6-hMECP2 mice are viable and fertile. Additionally, based on the independently developed TurboKnockout fusion BAC recombination technology, Cyagen can also generate hot mutation models based on this strain (B6-hMECP2*T158M, Catalog Number: C001569) and provide customized services for specific mutations to meet experimental needs in pharmacology and other RTT-related fields.