Several common diseases such as type II diabetes, hypertension, cardiovascular diseases, hyperlipidemia, and some cancers are associated with obesity. An abnormal increase in body fat relative to lean tissue mass has been used as an indicator of obesity. High fat diet, certain environmental factors, and genetic linkage are the primary causes of obesity. In order to understand the genetic basis of obesity, several monogenic murine obesity models have been characterized including obese (Ob), diabetes (db), fat (fat), agouti yellow (Ay), and tubby (tub). More recently, Tub, the human homolog of mouse Tub, TULP1 & TULP2 (for Tubby Like Proteins) and Agouti related protein (AGRP) have been cloned. The obesity associated with Ay mice may be due to ectopic expression of a secreted protein Agouti. Agouti protein (132 aa in human) is normally expressed in skin but its ubiquitous expression, such as in rare allele lethal yellow, causes yellow coat., linear growth, immune defects and obesity. Agouti is a paracrine-signaling molecule that affects pigmentation by inhibiting the melanocortin receptor 1 (MCR-1 and possibly MC2R and MC4R).

The Mahogany (mg) mutations suppress the effect of lethal yellow including obesity. The Mahogany locus does not suppress the obese phenotype of the MC4R null allele or those of monogenic obese models (Lepdb, tub, and Cpefat). However, mahogany can suppress diet-induced obesity. Mahogany (mg) gene, Mgca, encodes a 1428 aa single transmembrane protein that is expressed in many tissues including pigment cells and hypothalamus. The extracellular domain of the Mgca protein is the orthologue of human attractin, a circulating molecule produced by activated T-cells implicated in immune cell interaction. The short cytoplasmic tail contains a site that is conserved between C. elegans and mammals.

AGRP (132 aa in human, chromosome 16q21) is normally expressed in adrenal and hypothalamus. AGRP levels are increased several folds in ob/ob mice. AGRP is a strong antagonist of MC3R and MC4R. Ubiquitous expression of AGRP in transgenic mice causes obesity without altering skin pigmentation.

The fat phenotype is associated with caroboxypeptidase E (CPE), a prehomrone processing enzyme. Ob encodes a circulating factor (obese protein or leptin) that may function in sensing body fat and transmitting this information to brain. The db gene encodes the leptin/obese receptor. Tubby (tub) represents an autosomal recessive mutation. Homozygous tubby mice show an increased weight gain between 3-6 months. Maturity-onset obesity is also associated with the fat mouse. In contrast, obese and diabetes mice gain weight soon after birth. Therefore, fat and tubby phenotypes are a better model for human obesity.

Mouse Tubby encodes a protein of 505 aa that is devoid of any secreted or transmembrane domains. Mouse tubby is primarily expressed in hippocampus, hypothalamus, and cortex. TUB (561 aa, chromosome 11p15.4), a human homolg of mouse tubby, is widely expressed in several tissues (brain, testes, liver, heart small intestine, ovary, skeletal muscle, spinal cord and trachea). Mouse Tubby and human TUB differ in the first 148 aa and the rest of the proteins show 94% homology. TULP1 (542 aa, chromosome 6p21.3) is highly expressed retina. TULP2 (520 aa, chromosome 19q13.1) is expressed in testes. TUB is more closely related to TULP1 (90% identity) than TULP2 (66% identity). TULP1 and TULP2 share 63% identity. The functions of tub-family of proteins are not evident at present. However, a mutation in the highly conserved C-terminal protein of the tub gene leads to obesity, and cochlear and retinal degeneration.

ADI has produced highly specific antibodies for Tubby, Tub, TULP1, TULP2, Agouti and AGRP, and Mahogany. Specific antigenic peptides were carefully selected to avoid any crossreactivity among various proteins. Control peptides for each antibody are also available to confirm antibody specificity.