Genetic transformation of chickens using irradiated male gametes

Transgenesis in chickens

The application of transgenic technology to domestic poultry offers an alternative means to conventional practice for improvement of this highly productive agricultural species. The hen's reproductive system has unique characteristics which have imposed limitations on the use of established methods for artificial gene transfer. In this article, we review the various strategies that have been adopted to overcome the problem. Target sites for gene insertion include the fertilized ovum, the blastodermal embryo in the unincubated egg, and the primordial germ cells. Notable success in obtaining somatic and germline transformation has been achieved with the use of retroviral vectors to infect the blastodermal embryo. Current attempts to introduce DNA directly into the genome, without resort to pathogen-derived vectors, are discussed.

Production of transgenic birds

The avian embryo presents a tremendous challenge for those interested in accessing and manipulating the avian germ line. By far the most successful method of gene transfer is by retrovirus vector. The efficacy of retrovirus vectors has been demonstrated by germ line insertion of replication-competent retroviruses as well as the insertion of replication-defective retrovirus vectors carrying bacterial marker genes. Retroviral vectors have also been shown to be useful for the transfer and expression of genes in somatic cells. Further, germ line transgenesis has been reported in both the chicken and the Japanese quail. In addition, several alternative gene transfer methods are under development. These include transfection of avian sperm, development of germ line chimeras using primordial germ cells and blastodermal cells, and the development of embryonic stem cell lines. Potentially, basic research and the poultry industry will derive substantial benefit from this revolutionary technology.

Estimation of the quality of irradiated spermatozoa from cockerels using the classical method and zona-free hamster ova

1. The quality of gamma irradiated spermatozoa from cockerels was investigated by measuring motility, oxygen consumption and ability to penetrate zona-free hamster ova. 2. Doses of 750 Gy slightly reduced motility and oxygen consumption; however, irradiated spermatozoa penetrated on average 56% (minimum 33%) of hamster ova. 3. The zona-free hamster ova test may be useful for estimating avian sperm quality.

The improbability of irradiated spermatozoa as gene transfer vectors in chickens

It is concluded that chromatin fragments derived from irradiated chicken spermatozoa are not viable vectors for gene transfer. In three experiments conducted at sequential intervals over a period of 1 1/2 years, no marker traits were found in 1,065 G0 progeny from irradiated spermatozoa of Minnesota Dominant Marker males inseminated into recessive Rhode Island Red and White Leghorn females. The inability to secure transformants is ascribed to the following factors: a maximum of five and probably fewer potential vector fragments for each G0 progeny because of irradiation effect on spermatozoan ability to enter the germinal disc; uncertainty of DNA integrity from highly irradiated chromatin; no known mechanism for release of chromatin fragments from irradiated spermatozoa supernumerary pronuclei; and the uncertainty of selective integration into the zygotic nucleus.

Genetic differences in susceptibility to a mixture of avian infectious bronchitis virus and Escherichia coli

Two-week-old chickens of 9 inbred and partially inbred lines of chickens were challenged intranasally with a mixed infection consisting of a pool of virulent strains of infectious bronchitis virus and a pool of pathogenic strains of Escherichia coli. 2. Wide differences in mortality were observed in the different lines, ranging from 3% in a Brown Leghorn line to 87% in White Leghorn line 7(2). 3. Experiments involving challenge with E. coli alone or virus alone suggested that this variation reflected resistance to the virus rather than to E. coli. 4. Reciprocal F1 matings suggested these differences in mortality were not attributable to maternal effects and indicated that the inheritance of resistance was fully dominant. 5. The pattern of mortality in F2 and backcross progeny of matings was compatible with the inheritance of a dominant autosomal resistance gene and showed no evidence of association with the major histocompatibility complex.

Maintenance of foreign gene expression and independent chromosome fragments in adult transgenic rainbow trout and their offspring

Transgenic rainbow trout (RT) were generated in earlier experiments by an in vivo modification of the chromosome-mediated gene transfer technique. This involved fertilizing albino RT eggs with gamma-irradiated brook (speckled) trout (ST) sperm and then heat shocking the eggs to induce second polar body retention. Striped pigment patterns were stable in six mosaic individuals between the ages of 7 and 14 months. We estimated the total ST DNA contribution in adult transgenic fish using DNA dot blot analyses. An average of 7% ST DNA was obtained in analyses of 11 transgenic individuals. Nine of 55 transgenic individuals examined expressed a ST-specific isozyme in adulthood; some were mosaic for foreign gene expression. Variable numbers of autonomous chromosome fragments were maintained in 10 adult transgenic individuals examined. Five transgenic RT were backcrossed to albino RT. Chromosome fragments were inherited by 29 of 31 backcross embryos examined. Additional active nucleolar organizer regions (NORs) were present on some fragments and may also have been integrated into some host chromosomes. This method may have numerous applications for basic and applied genetic research in fish.