Preliminary characterisation of gonad inhibiting hormone (GIH) gene and its expression pattern during vitellogenesis in giant tiger shrimp, Penaeus monodon Fabricius, 1798

Abstract

Farming of giant tiger shrimp is one of the most important and relatively recent coastal food production sectors in India. Although great strides have been made in shrimp husbandry practices in growout systems, management of reproduction in captivity has not kept pace. Although several hormones are involved in crustacean reproduction, the inhibitory effect of gonad inhibiting hormone (GIH) is thought to be more intense than any other hormones. As an essential component of understanding the reproduction of Penaeus monodon, we characterised the expression pattern of GIH gene in the sinus gland in relation to the female gametogenic cycle. A 633 bp sequence was cloned from the eyestalk of P. monodon by RT PCR. The sequence comprises an open reading frame (ORF) of 291 bp that encodes a protein of 96 amino acids. The deduced protein was used to search the GenBank database using BlastP. Protein alignment with all known crustacean GIH revealed that homology of P. monodon GIH shares 61, 48, 46, 46 and 35% identity with Metapenaeus ensis, Nephrops norvegicus, Homarus americanus, Rimicaris kairei and Armadillidium vulgarae respectively. The RT PCR analysis shows that GIH mRNA is expressed mainly in the eyestalk of female. In order to find the expression profile of GIH during different reproductive cycle, P. monodon female was categorised into four major stages of maturation, using light microscopical observations as well as morphological characteristics. Eyestalk of all animals from different stages of maturation indicated that GIH is expressed in all stages of maturation, although the expression of GIH mRNA changes during different stages of vitellogenesis. In animals with immature ovary, the relative GIH mRNA level was found to be less, which peaked in previtellogenic phase and diminished in subsequent phases. Low GIH mRNA level during the immature (oogonial) phase is particularly intriguing and has application in the commercial aquaculture to select the brooders.