Avian Genetic Resource Banking: Can Fish Embryos Yield Any Clues for Bird Embryos?

Cryopreservation and Laser Nanowarming of Zebrafish Embryos Followed by Hatching and Spawning

This study shows for the first time the ability to rewarm cryopreserved zebrafish embryos that grow into adult fish capable of breeding normally. The protocol employs a single injection of cryoprotective agents (CPAs) and gold nanorods (GNRs) into the yolk and immersion in a precooling bath to dehydrate the perivitelline space. Then embryos are encapsulated within CPA and GNR droplets, plunged into liquid nitrogen, cryogenically stabilized, and rewarmed by a laser pulse. Postlaser nanowarming, embryos (n = 282) exhibit intact structure by 1 h (40%), continued development after 3 h (22%), movement after 24 h (11%), hatching after 48 h (9%), and swimming after Day 5 (3%). Finally, from fish that survives till Day 5, two larvae are grown to adulthood and spawned, yielding survival comparable to an unfrozen control. Future efforts will focus on improving the survival to adulthood and developing methods to cryopreserve large numbers of embryos for research, aquaculture, and biodiversity preservation.

Microscopic Morphology and Apoptosis of Ovarian Tissue after Cryopreservation using a Vitrification Method in Post-Hatching Turkey Poults, Meleagris gallopavo

The objectives of this study were to examine morphological changes of oogonia and primordial follicles in the ovaries of turkey poults within the first week after hatching, and to evaluate the effect of cryopreservation on histology and apoptosis of these immature ovaries. Ovaries from poults at Day 1, Day 3, Day 5 and Day 7 post-hatch were cryopreserved using a modified vitrification method. The histology of oogonia and primordial follicles in fresh and cryopreserved tissue was assessed, and the apoptosis of tissue in different age groups was identified using a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The mean oogonium diameter in fresh tissue increased from 11.9±1.3 µm (Day 1) to 15.2±2.7 µm (Day 7) within the first week; however, oogonia in cryopreserved tissue from Day 3 and Day 7 ovaries were smaller than those in fresh tissue (P<0.05). Formation of primordial follicles was observed as early as Day 5. For Day 7 ovaries, follicles in cryopreserved tissue were smaller than those in fresh tissue; this was also true for oocyte diameter (P<0.05). Apoptosis was most frequent in Day 1 fresh tissue, which was reduced as the poults aged. The frequency of apoptosis in cryopreserved tissue was comparable among age groups. This study provides the first documentation of morphological changes in the turkey ovary within the first week post-hatching. Results suggest that oogonia and primordial follicles that are smaller in size could be more resistant to the damage caused by cryopreservation. Of the ages assessed in this study, it is concluded that 3 days of age appears optimal for recovery of donor ovaries for cryopreservation, taking the advance of reduced cryoinjury and ease of tissue handling at this age.

Genome resource banking of biomedically important laboratory animals

Genome resource banking is the systematic collection, storage, and redistribution of biomaterials in an organized, logistical, and secure manner. Genome cryobanks usually contain biomaterials and associated genomic information essential for progression of biomedicine, human health, and research. In that regard, appropriate genome cryobanks could provide essential biomaterials for both current and future research projects in the form of various cell types and tissues, including sperm, oocytes, embryos, embryonic or adult stem cells, induced pluripotent stem cells, and gonadal tissues. In addition to cryobanked germplasm, cryobanking of DNA, serum, blood products, and tissues from scientifically, economically, and ecologically important species has become a common practice. For revitalization of the whole organism, cryopreserved germplasm in conjunction with assisted reproductive technologies, offer a powerful approach for research model management, as well as assisting in animal production for agriculture, conservation, and human reproductive medicine. Recently, many developed and developing countries have allocated substantial resources to establish genome resources banks which are responsible for safeguarding scientifically, economically, and ecologically important wild type, mutant, and transgenic plants, fish, and local livestock breeds, as well as wildlife species. This review is dedicated to the memory of Dr. John K. Critser, who has made profound contributions to the science of cryobiology and establishment of genome research and resources centers for mice, rats, and swine. Emphasis will be given to application of genome resource banks to species with substantial contributions to the advancement of biomedicine and human health.

Current progress in oocyte and embryo cryopreservation by slow freezing and vitrification

Preservation of female genetics is currently done primarily by means of oocyte and embryo cryopreservation. The field has seen much progress during its four-decade history, progress driven predominantly by research in humans, cows, and mice. Two basic cryopreservation techniques rule the field – controlled-rate freezing, the first to be developed, and vitrification, which, in recent years, has gained a foothold. While much progress has been achieved in human medicine, the cattle industry, and in laboratory animals, this is far from being the case for most other mammals and even less so for other vertebrates. The major strides and obstacles in human and other vertebrate oocyte and embryo cryopreservation will be reviewed here.

Antifreeze protein gene expression in winter flounder pre-hatch embryos: implications for cryopreservation

Cryopreservation of fish embryos has proven to be an elusive goal. Two reasons for this lack of success are their high chilling sensitivity and the formation of ice crystals while in the frozen state or during the thawing process. Antifreeze proteins (AFP) that protect marine teleost fishes from freezing in subzero waters have been shown to be capable of inhibiting ice recrystallization and protecting cell membranes from cold induced damage. Therefore they have the potential to improve the success of embryo cryopreservation. A recent study demonstrated that vitrified winter flounder embryos continued to show developmental changes following thaw [V. Robles, E. Cabrita, G.L. Fletcher, M.A. Shears, M.J. King, M.P. Herráez, Vitrification assays with embryos from a cold tolerant sub-arctic fish species, Theriogenology 64 (2005) 1633-1646]. Since winter flounder produce AFP it was hypothesized that these proteins, if present in the embryos, could have contributed to this progressive step towards success. Winter flounder produce three species of type 1 AFP: a small liver type, a large "hyperactive" liver type and a skin type. This study was conducted to determine which, if any, of these AFP genes was being expressed in pre-hatch winter flounder embryos. There was no evidence of AFP activity in freshly fertilized embryos. However, low levels of AFP activity were found in embryos at 4, 8, and 11 days post-fertilization. Reverse transcriptase-polymerase chain reaction (RT-PCR) analyses of the AFP mRNA isolated from the embryos revealed the expression of seven different skin type AFP genes that translated into four distinct AFP. Neither of the liver type AFP genes was expressed in the embryos.