ABSTRACT
In a recent review of cell cycle regulation, it is indicated that mitotic and meiotic cell division are governed by several control mechanisms generally known as check points, whose main function is to ensure critical events in cell division such as DNA replication and chromosome segregation with high fidelity in the correct order and time. These checkpoints work as signal transudation pathways with their initiating signals, sensors, transducers and effectors (Elledge 1996). In meiotic cell cycle regulation, there are specific checkpoints. Two of them have been recently characterized at the molecular level. The most intriguing difference between meiotic and mitotic division with respect to cell cycle regulation is the ability of animal oocyte to arrest at a specific stage during maturation and maintain this block for a long time. It is established that meiotic block is due to the activity of a cytostatic factor (CSF) identified by Masui and Maskert (1971). Russo et al., (1998) have conducted in-depth studies of CSF mechanism mediated by protein kinase enzyme in acidian oocyte. Development of fish cell lines in vitro condition and its advantage for genetic improvement of aquaculture livestock's have been highlighted many a times. Hong et al., (1998) developed a feeder cell-free culture condition supporting the long-term growth of blastula-derived embryonic cells (ES) in the medeka. This has led to the establishment of several medaka ES-like cell lines. It was further investigated that medeka ES cells after an extended period of culture are able to produce chimeras with a higher efficiency. Besides transgenesis, efforts are being made to develop other methods for enhancing growth, reproduction rate, disease resistance and other features in many of the cultivated organisms of aquaculture importance. Counihan et al., (1998) did in-depth studies regarding molecular and cellular mechanism controlling growth in tropical abalone Haliotis asininia that grows faster compared to many other temperate species. The nucleotide sequence of the gene responsible for the faster growth of H. asinina was obtained using PCR amplification cloning and sequencing with a gene specific primer identical to that described for H. rufescens, Degnan (1997), which is also a fast-growing animal of temperate regions. Remarkable similarity has been observed in the nucleotide and amino acid sequences of growth factor genes of both species. Such findings may have wider applications to develop improved tracts of aquaculture livestock.
