Molecular and genetic analysis of the gene encoding the A subunit of lactate dehydrogenase in the mouse

In higher vetebrates, the genes encoding the A and B subunits of lactate dehydrogenase (E.G. 1.1.1.27, LDH) show complex patterns of developmental and tissue-specific regulation.

In order to determine whether the genes encoding LDH in mammals are controlled by feedback regulation, a mouse stock, 46DFiOD, having a recessive lethal deletion of Ldh-1, the mouse gene encoding the LDH-A subunit, was identified in a screen of several presumptive deletion carriers affected at a closely linked marker, p, on mouse chromosome 7. Analysis of LDH activity in tissues of this stock provided no evidence for feedback regulation of mouse LDH genes.

A molecular analysis of Ldh-1 was initiated by using a partial LDH-A cDNA, obtained from Dr. Kenneth Fong, to isolate full-length LDH-A cDNA and genomic clones.

Cloning of expressed LDH-A genomic sequences was complicated by the presence of several LDH-A pseudogenes. A 14 kilobase pair (Kb) EcoRl restriction fragment having homology to mouse LDH-A cDNA was localized to mouse chromosome 7 using Southern analysis of DNA from a somatic-cell hybrid mapping panel. Southern analysis of DNA from offspring of a cross between 46DFiOD, the Ldh-1 deletion stock, and Mus spretus, a species having a polymorphism for the 14 Kb restriction fragment was used to further localize this fragment to the chromosomal region containing Ldh-1. Genomic clones containing that fragment were shown to direct the synthesis of mouse LDH-A following transfection into Chinese hamster cells.

Sequence analysis of a portion of the LDH-A genomic clone showed that Ldh-1 has a promoter region that is G-C rich, lacks TATAA and CAAT boxes, and contains consensus sequences for Spl binding and cAMP induction.

The 46DFiOD deletion was also characterized for the involvement of nearby markers using the 46DFiOD x Mus spretus offspring. Xld-1 and LHβ are not included in the chromosomal segment missing in 46DFiOD, while the Saa gene complex, and 24.2, a probe from a syntenic region of human chromosome 11, are included in that segment.