Biotechnology and Bioinformatics (1+1)

2.2.3.1. Growth hormone gene

Growth is a complex biological process involving genetic, hormonal, nutritional and environmental factors.

• ‘Growth hormone ’ (GH) is produced by the anterior lobe of the pituitary. It increases growth by stimulating appetite and improving the food conversion efficiency.
• GH is a protein hormone having a molecular weight of about 22 kilodaltons.
• Injection of recombinant bovine or chicken GH also caused significant increase in the growth rate in Coho salmon, Rainbow trout and some other fishes.
• However, it is difficult to practice this technique in cultured species of fishes because GH may get digested in the gut, if given through feed.
• Transgenic fish carrying GH gene will produce growth hormone endogenous ly by passing the necessity of exogenous hormone treatment.
• GH gene has been clone d in some fishes either from the genomic library or from the c DNA library .
• Zhu et al., in 1985 first reported the production of transgenic gold fish by microinjection of human growth hormone gene (hGH) which was linked with mouse metallothionein gene promoter (mMT).
• Growth hormone gene was subsequently transferred into several species of fishes including Loach, Common carp, Crucian carp, Atlantic salmon, Channel catfish, Medaka and Zebrafish.
• In late 1980s the gene construct s used for transgenic fish production were primarily from the non-piscine sources. Human, bovine or salmonid growth hormone gene fused with some viral gene promoter or mouse metallothionein gene promoter were used in these studies.
• Higher growth rate at the range of 10 to 80% was achieved by using these gene constructs.
• The studies conducted at Auburn University in transgenic common carp showed 20 to 40% increase in the growth rate. Similar studies conducted in Scotland have resulted in a test animal almost 11 times heavier than the normal one. Instead of normal size of 7 lbs, the genetically altered pacific salmon attained a weight of 80 lbs.
• In few cases, no difference was observed between the transgenic and their non-transgenic siblings.
• The transgenic Atlantic salmon produced by Devlin et al., (1994) carrying ‘all-fish gene’ showed dramatic improvement in growth.
• In India, transgenic fish research has been initiated in carps (National Institute of Immunology, New Delhi), tilapia, zebrafish, catfish, carp (Madurai Kamaraj University, Madurai) and catfish (Centre for Cellular and Molecular Biology, Hyderabad).