Cell membrane antigens serve as recognition codes for normal cell functions (substrate transport, cell-cell interaction, etc.). Changes in antigenfunction activity are associated with ontogeny and speciation. Some prenatal antigenic configurations are postulated to provide host protection during early development.The functional significance of ontogenetic changes observed in bovine fetal red cell antigens (Miller and Hubbert, '74) became more evident after integrating recent findings from diverse fields. A new understanding was gained of the importance of membrane antigens to cell membrane structure-function relationships as they relate to ontogeny. Although examples of development in cattle were used where possible, the observations were drawn from a much wider range of animal species, and consequently, the conclusions derived should be broadly applicable in developmental biology, including those concerning mechanisms beneficial or damaging to the host.Ontogeny of cellular function Wald ('63) commented that the Biogenetic Law refers to the history of past embryos, not past adults. He observed that organisms undergo great and sometimes abrupt chemical changes at various stages in their life cycles. All land vertebrates undergo embryogeny in water, and ordinarily metamorphic changes are completed before the animal migrates; i.e., metamorphoses are preparations for a new environment rather than responses to it. The prenatal mammal is typical of such development. Changes in animal heat production and biologic frequencies (heart and respiration rates), according to Kleiber's law, are correlated with change in body weight (McMahon, '73). Although these changes are marked during postnatal growth when cattle have a ten-fold increase in weight, such changes are even more spectacular during prenatal growth J. CELL. PHYSIOL., 84: 42-44 when fetal weight increases several thouMarkert ('68) listed the following differentiation-associated changes in cell characteristics: division rate, membrane adhesive properties (migration), and cellular metabolic patterns. Moog ('52) demonstrated that young embryonic tissue is enzymatically complex, that enzymogenesis proceeds at a differential rate (potentially more active early), and that enzyme accumulation is an aspect of functional differentiation. She predicted that, in regard to fetal preparation for later function: (1) different patterns of enzyme increase occur in different organs; (2) in the same organ, several function-associated enzymes will have similar patterns: and (3) enzyme accumulation will show a clear-cut relation to functional activity. The suggestion of Selander and Kaufman ('73) that greater enzymatic variability among species is a function of smaller size and limited mobility has a parallel in the fetus with its smaller size and restricted environment.Examples of these processes are found in the transition of red cells during bovine development. The activity of D-glucose-6-phosphate dehydrogenose (G6PD) was greater in red cells of bovine fetuses than adult...
