The numerous strategies for reproduction, sexual and asexual, that have evolved, suggest experimental designs for altering the reproduction of any particular species. The ability to culture and manipulate mammalian eggs and embryos in vitro provides the technological basis for experimentally altering the reproduction of mammals and can lead to the generation of new and useful genotypes. All of these advances, however, are restricted by our lack of understanding of the chromosomal mechanisms by which genes are regulated during the course of cell differentiation. An attractive hypothesis postulates that programs of gene regulation during development are based upon topographic interactions among chromosomes in the interphase nucleus and that these interactions in turn require an appropriate positioning of regulatory DNA throughout the genome.

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Gametogenesis, fertilization and early development.

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Production and reproductive performance of hexaparental and octaparental mice.

The production of hexaparental and octaparental mice following embryo aggregation is reported. These mice were progeny-tested to determine which cell components were contributing to gamete formation. One chimera (No. 15) was shown to be producing eggs from all three cell strains--white, yellow, and black. The other chimeras tested were not forming germ cells from all of the cell strains involved. The use of these animals for obtaining a minimum estimate of the number of cells giving rise to the embryo proper is discussed. The suggestion is made that multi-embryo aggregates may actually be developmentally different from normal sized embryos and this may result in modified mechanisms of cell recruitment.

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Human testis-specific lactate dehydrogenase-C promoter drives overexpression of mouse lactate dehydrogenase-1 cDNA in testes of transgenic mice.

The three isozymes of lactate dehydrogenase, each encoded by a separate gene, are developmentally regulated and differentially expressed in tissue-specific patterns. The lactate dehydrogenase-C (LDHC, mouse Ldh3) gene is temporally expressed exclusively in the germ line during spermatogenesis, whereas lactate dehydrogenase-A (LDHA, mouse Ldh1) and B (LDHB, mouse Ldh2) genes are active in somatic tissues. To determine, therefore, whether overexpression of Ldh1 would perturb spermatogenesis, we constructed a transgene in which a sequence from the promoter region of human LDHC was coupled with mouse Ldh1 cDNA. Among nine (three males, six females) founder lines that were identified as being transgenic for the construct, one male transmitted the gene through its germ line. Homo- and heterotetramers containing the LDH-A subunit were detected in homogenates of testes from transgenic animals. We conclude that the human LDHC promoter contains the necessary regulatory sequence(s) for specific expression of mouse Ldh1 as a transgene during spermatogenesis. The fertility of the founder animal was not impaired.

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