The mouse ob gene is located on chromosome 6, spanning approximately 650 kb, and consists of three exons separated by two introns. Several regulatory elements have been identified within the ob gene promoter region, including cyclic AMP (cAMP) and glucocorticoid response elements, as well as CCATT/enhancer and SP-1 binding sites.
The initial step in confirming the leptin receptor involved identifying and localizing leptin-binding sites. Louis conducted this investigation by incubating coronal brain subsections from mice with radiolabeled leptin ([125I]-leptin) to observe its binding to potential receptors. Tissue subsections were incubated with [125I]-leptin, and after washing, the distribution of signals was visualized through autoradiography, revealing significant binding in the lateral and third ventricles. To further trace the leptin receptor, researchers designed and constructed several leptin-alkaline phosphatase (AP) fusion proteins. The leptin gene sequence was inserted into expression vectors (APtag-2 and APtag-3), allowing the expressed fusion proteins to attach AP at different ends of leptin. Mouse brain tissue was then divided into four subsections, each stained for AP activity. Results showed pronounced staining in the choroid plexus, while surrounding brain tissues showed no staining, indicating that leptin receptor localization is in the choroid plexus.
Building on this, researchers employed an expression cloning strategy and functional screening to successfully isolate the leptin receptor (Ob-R) from the mouse choroid plexus. The isolated Ob-R protein contains a characteristic extracellular domain (816 amino acids), displaying conserved features of cytokine receptors, including cysteine-rich sequences and a Trp-Ser-X-Trp-Ser motif. The transmembrane domain comprises 23 amino acids, while the short intracellular domain, with only 34 amino acids, includes a Box 1 region that interacts with JAK kinases. Subsequent studies confirmed that the leptin receptor belongs to the class 1 cytokine receptor family.
Based on BioGPS searches and existing literature, the ob gene in mice is predominantly expressed in adipose tissue, both brown and white, as well as in the mammary gland under both lactating and non-lactating conditions. There is minimal expression observed in the ovary and eyecup.
Based on BioGPS data and literature, leptin receptors in mice are expressed across a wide range of tissues, highlighting leptin's diverse physiological roles. Notable expression is observed in the lung, placenta, uterus, ovary, bladder, epidermis, stomach, intestine, prostate, adrenal glands, and mammary gland, indicating leptin's involvement in reproductive, respiratory, and gastrointestinal functions. Additionally, leptin receptor expression in osteoblasts, bone marrow, bone, spleen, lymph nodes, and particularly high levels in lymphoid tissues, points to a significant role in immune regulation and bone metabolism. This broad expression pattern suggests the leptin receptor's role in mediating leptin’s systemic effects on energy homeostasis, immune function, and tissue-specific processes.