Marsupial and monotreme lactate dehydrogenase isozymes: Phylogeny, ontogeny, and homology eutherian mammals

Lactate dehydrogenase (LDH) isozymes have been examined from tissues of mammalian species representative of the five families of marsupials and of the monotremes. Immunochemical, molecular hybridization, and tissue distribution studies showed that three genes (A, B and C) are responsible for LDH synthesis giving rise to five major isozymes in most tissues (LDH's A₄, A₃B₁, A₂B₂, A₁B₃, and B₄) and an additional isozyme (LDH‐C₄) which is present only in mature testes. The LDH phenotypes of 93 erythrocyte samples from 31 marsupial and 2 monotreme species were analysed. Although the isozymic composition varied markedly within the marsupial families Macropodidae and Phalangeridae, the Dasyuridae showed remarkable uniformity, containing only LDH‐A₄. The two monotreme species analysed also exhibited this latter pheno‐type in their erythrocytes. Ontogenic studies of the LDH isozymes of pouch young from Macropus parryi (pretty‐face wallaby) showed changes similar to those reported for the developing mammalian fetus in utero. The immature pouch young exhibited similar tissue patterns of LDH isozymes which diverged during growth in the pouch thus reflecting differential genetic activity. A comparison of the relative maturity of the eutherian fetus with marsupial pouch young may be made. From these observations, it is concluded that a high degree of correlation exists among the properties of eutherian, marsupial, and monotreme LDH isozymes.