Upon photostimulation, restricted ovulator (RO) female chickens exhibit endogenous hyperlipidemia, develop atherosclerotic lesions, and generally fail to lay eggs. This phenotype results from a point mutation in the gene specifying the very low density lipoprotein receptor (VLDLR), whose protein product normally mediates the massive oocytic uptake of egg yolk precursors from the circulation. Taking advantage of the single base change in the mutant VLDLR allele, a PCR-based method for the rapid identification of RO chickens was developed at the Biocenter and University of Vienna, Austria. However, this procedure was incompletely validated because phenotypic data were not obtained and conventional progeny testing of sons and grandsons was not performed. Here, the assay validation was completed by providing plasma lipid concentrations, plasma very low density lipoprotein particle sizes, or egg production records of PCR-genotyped females and their brothers and sires to demonstrate that each bird's phenotypic traits substantiated their genotypic classification. Moreover, several methodological modifications resulted in improved chemical safety, speed, and cost of preparing and analyzing genomic DNA from chicken erythrocytes. Because the ovaries of mutant RO females generally contain numerous vitellogenic follicles in the absence of a functional oocyte plasma membrane VLDLR, the existence of an alternate system for the oocytic uptake of plasma very low density lipoprotein and vitellogenin is suggested, whereas a physiological explanation as to why some, but not all, mutant RO hens are able to ovulate and lay eggs is lacking.
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The authors thank Ken Wolber and Tom Heim for their excellent supervision of the birds and their progeny. Appreciation is also extended to Cansu Agca, Ryan Meunier, Mickey Latour, and Stacey Neuman for their technical assistance and to J. James Bitgood, University of Wisconsin, for providing hatching eggs that enabled us to establish the RO colony and for his helpful suggestions. This work was funded in part by a grant from Progen Biotechnik GmbH (Heidelberg, Germany).
- Point mutation
- Restricted ovulator chicken
- Very low density lipoprotein receptor