Transferrin was not required for the short-term survival of cultured chick retinal neurons. Both human and chick transferrin failed to enhance the in vitro survival of 8-or 11-day embryonic chick retinal neurons when cultured in a defined medium. Furthermore, maintenance of neurons in the presence of chick transferrin antibody did not alter in vitro survival. Retinal neurons, however, could bind and internalize human or chick transferrin when assayed for by fluorescence immunohistochemical techniques. Binding and internalization of chick transferrin appeared to be greater than human transferrin. Iron uptake was measured in cultures maintained in the absence of transferrin. After incubation with 59FeC13, iron uptake was 3.5 * 1.1 fmoleskell. The presence of chick transferrin antibody did not significantly alter the amount of iron uptake occurring in this assay. In a comparison of human and chick transferrin mediated iron uptake, chick transferrin was 50% more effective than human transferrin in transporting iron. This study demonstrates that cultured embryonic retinal neurons are not dependent on transferrin for survival or iron uptake, although they actively bind and internalize transferrin. Results also demonstrate that whereas cultured chick retinal neurons can bind and utilize human transferrin, they do so with less efficiency than chick tran sferri n.
The blood serum protein transferrin is known to be
In this laboratory, we have used a monolayer tissue important in iron binding, transport, and storage culture system of purified neurons from 8-day chick (Fletcher and Huehns, 1968;Aisen and Listowsky, 1980). neural retina to study CNS development in vitro (Hynd-However, recent reports have indicated that transferrin man and Adler, 1982a,b; Hyndman, 1984; Zeevalk and may play a broader role in cellular development and Hyndman, 1986). These cultures have been shown to be physiology. Transferrin is well known as a survival fac-virtually glial free (Hyndman and Lemmon, 1987). Neutor for cells maintained in vitro (Barnes and Sato, 1980). ronal development in these cultures continues along a It is a widely used ingredient of defined media for the predictable path (Hyndman and Adler, 198213; Zeevalk culture of CNS (Bottenstein et al., 1980; Cestelli et al., and Hyndman, 1986). We have observed that transferrin 1985; Weiss et al., 1986;Zeevalk and Hyndman, 1987). binding and iron accumulation in the retina is region-Transferrin may play a role in neuronal differentiation ally localized and that the pattern of transferrin binding and synaptogenesis (Mollgard et al., 1984) and has been changes as the neural retina matures (Zeevalk and suggested to function as a neuromodulator in the brain Hyndman, 1987). We have previously suggested (Zeevand in the regulation or maintenance of synaptic mem-alk and Hyndman, 1986) that retinal neurons could be branes (Mollgard et al., 1984;Hill et al., 1985, Zeevalk maintained in vitro in the absence of transferrin. In this and Hyndman, 1987). Transferrin or transferrin recep-study, the role of transferrin in in vitro neuronal surtors have been found in the mouse brain, rat brain, chick vival is investigated more thoroughly. Also examined brain, and chick retina (Toran-Allerand, 1980; Hill et are whether transferrin binds to and is internalized by al., 1985;Oh et al., 1986;Zeevalk and Hyndman, 1987). isolated retinal neurons (maintained in vitro in the ab-Some laboratories have found that transferrin was not sence of transferrin) and if iron uptake can occur in the required for the survival of all neurons in culture (Ska-absence of exogenously supplied transfenin. Furtherper et al., 1984;Aizenman et al., 1986). There have been more, since human transferrin is commonly used by suggestions that neuronal dependence on transferrin many laboratories as a media supplement for the culturwas developmentally regulated, being required only in more mature neurons (Selak et al., 1983;Aizenman et al., 1986). Therefore, the role of transferrin in neuronal