**7. Acknowledgement**

280 Current Frontiers in Cryobiology

Model organisms offer a platform to address biological issues of a broad range of interests with ease. An ideal platform must have specific traits allowing convenient manipulations in a manner beneficial to specific fields of study. Use of classical model organisms such as the house mouse *Mus musculus*, zebrafish *Danio rerio*, fruit fly *Drosophila melanogaster* and nematode *Caenorhabditis elegans* for studying physiology, genetics, genomics, behavior, human diseases and their treatments, etc is well established. These are attractive model organisms from their representative evolutionary position. They are relatively more readily available, tractable, small in body size, rapid in development and have short reproductive cycles. They are still popular models because of the establishment of transgenic technologies related to these animals (Fire, 1986; Gordon et al., 1980; Rubin & Spradling, 1982; Zelenin et al., 1991). Such genome manipulation technologies make reverse genetics possible, allowing

Knowledge gained on the above-mentioned classical models and other less popular model organisms has been expanding for the past few decades. Thorough comparative studies in various fields of research will benefit translational research and our understanding of the evolutionary tree of life. More interdisciplinary studies on model organisms representing animals in various branches of the phylogenetic tree will enhance our comparative study. Promising transgenic techniques have been recently established in respect of some of these animals, e.g., planaria *Girardia tigrina*, brine shrimp *Artemia sinica*, amphipod crustacean *Parhyale hawaiensis*, red flour beetle *Tribolium castaneum*, sea anemone *Nematostella vectensis*, Mollusk dwarf surfclam *Mulinia lateralis*, sea squirt *Ciona intestinalis*, channel catfish *Ictalurus punctatus*, frog *Xenopus laevis* and *Xenopus tropicalis*, chicken *Gallus gallus*, Japanese quail *Coturnix japonica*, goat *Capra hircus*, dog *Canis familiaris* and marmoset *Callithrix jacchus*, (Berghammer et al., 1999; Chang et al., 2011; Dunham et al., 2002; Gonzalez-Estevez et al., 2003; Hong et al., 2009; Houdebine, 2009; Huss et al., 2008; Lu et al. 1996; Macha et al., 1997; Mozdziak & Petitte 2004 ; Pavlopoulos and Averof, 2005; Renfer et al., 2010; Sasaki et al., 2009; Sasakura et al., 2007; Wheeler, 2003). The development of genome manipulation techniques for these emerging animal models will open the door to unlimited possibilities of

The cost of the knowledge explosion and scientific advancement will be the handling of an enormous number of transgenic strains generated. The cost of managing these invaluable resources can be a substantial burden on research laboratories or institutions world wide, which may impede further development. So far cryopreservation has been developed for embryos/larvae from non-classical model animals, including oyster *Crassostrea gigas*, hard clam *Meretrix lusoria*, sea urchin *Loxechinus albus*, amphioxus *Branchiotoma belcheri*, brine shrimp *Artimia franciscana*, euryhaline rotifer *Brachionus plicatilis* and marmoset *Callithrix jacchus*, etc. (Barros et al., 1997; Chao et al., 1997; Summers et al., 1987; Sun et al., 2007;

The experience in cryopreserving embryos from such a broad evolutionary range will benefit the development of cryopreservation techniques in other emerging model organisms. The parameters highlighted in this review represent some keys for developing an effective cryopreservation protocol for any organisms for experimental use. The thorough understanding of these parameters in different model systems, the optimization therein, and improved procedures to store transgenic strains will not only release the management stress caused by the need for keeping the live animals but also eliminate the risk of their being affected by disease outbreaks and genetic drifts. It has great practical

studies to be amendable for these model organisms.

Toleda & Kurokura, 1990; Yoshida et al., 2011).

*in vivo* investigations.

We would like to thank Miss Mandy Chan and Prof. Andrew L. Miller (HKUST) for contribution to the photograph of a zebrafish embryo in Figure 3C. FlyMove, an internet educational resource (Weigmann 2003), is acknowledged for the permission in reproducing an image of a fly embryo in Figure 3B. WHT is a postdoctoral fellow supported by HKUST postdoctoral fellowship. This work was conducted and supported by Research Grants Council (HKUST 660407 and 660508).
