Experimental models have allowed the identification of the diversity and the similarity in morphology and development across species. One example is the comparative analysis done to understand diversity. The physiology and development of vertebrates have been studied using fish such as zebrafish and medaka on account of the ease of usage and cost. These fish have also spawned studies of disease models such as bone defects, cardiovascular defects, blood disorders and even cancer, according to research published in the Journal of applied ichthyology in 2014. These disease models can be examined for the mechanisms along with possible therapeutic approaches. Using mutagens, genes that regulate the process of development have been identified whose similar counterparts have also been seen in other vertebrates!
Thus, we can see the utility of fish as model systems. Instead of using live animals, cell lines represent in vitro options to study biology, pathogenesis, carcinogenesis and toxicology. While several parts of fish have been used such as the liver, kidney and fin, gonads of marine fish have few takers.
Cell lines established from the gonads can allow studying the processes of gamete formation including spermatogenesis and oogenesis. Lower vertebrates have allowed the process of spermatogenesis to be studied in vitro using cultures. Examples include an early work published in 1997 in Development Growth & Differentiation that obtained fertile sperm from primary spermatocyte cultures of Oryzias latipes (medaka)! Another work published in the Proceedings of the National Academy of Sciences of the USA in 2004 reported that established cultures from medaka that recapitulated the process of sperm formation and could generate sperms.
In line with these studies, a team led by Zhang reported the primary culture from the testis of a fish called Cynoglossus semilaevis or the half-smooth tongue sole in The International Journal of Biological Sciences. This organism has been reported as an important commercial fish in Chinese aquaculture, according to Guo and colleagues in PLoS ONE (2017). It was also reported that this fish is important to study sex determination with the females showing ZW and males showing ZZ (ZW type sex-determination system). Some genetically female members can undergo sex reversal to become phenotypic males that can produce viable sperm to mate with phenotypic males.
The gonad was washed and minced and placed in MEM plus foetal bovine serum (FBS), basic fibroblast growth factor (bFGF) and 1000 U each of penicillin and streptomycin. Primary cultures were obtained after 2 weeks of incubation at 24 ℃. PCR analysis revealed that the cell line was male. The cells also expressed dmrt1: a marker of testicular cells. As host-pathogen interactions warrant detailed studies and systems, the culture was exposed to lymphocystis disease virus (LCDV) and turbot reddish body iridovirus (TRBIV). The susceptibility of the cells revealed that this culture can be used to assess viral interactions.
Thus, the establishment of primary culture from gonads not only serves as systems to assess the differentiation of gametes but also host-pathogen relationships. Fish primary cultures serve as invaluable tools in aquaculture, developmental studies, sex determination or in other words several facets of research.
Harris, M. P., Henke, K., Hawkins, M. B., & Witten, P. E. (2014). Fish is Fish: the use of experimental model species to reveal causes of skeletal diversity in evolution and disease. Zeitschrift fur angewandte Ichthyologie = Journal of applied ichthyology, 30(4), 616–629. doi:10.1111/jai.12533.
Sakai A, Tamura M, Matsumoto M. Establishment of in vitro spermatogenesis from spermatocytes in the medaka, Oryzias latipes. Development Growth & Differentiation. 1997;39:337-344.
Hong YH, Liu TM, Zhao HB. et al. Establishment of a normal medakafish spermatogonial cell line capable of sperm production in vitro. Proceedings of the National Academy of Sciences of the USA. 2004;101:8011-8016.
Zhang B, Wang X, Sha Z, Yang C, Liu S, Wang N, Chen SL. Establishment and Characterization of a Testicular Cell Line from the Half-Smooth Tongue Sole, Cynoglossus semilaevis. The International Journal of Biological Sciences 2011; 7(4):452-459. doi:10.7150/ijbs.7.452.
Guo H, Wei M, Liu Y, Zhu Y, Xu W, Meng L, et al. (2017) Molecular cloning and expression analysis of the aqp1aa gene in half-smooth tongue sole (Cynoglossus semilaevis). PLoS ONE 12(4): e0175033. https://doi.org/10.1371/journal.pone.0175033.