Ontogeny of alpha-foetoprotein in human foetal brain

Trajectories and phenotypes with estrogen exposures across the lifespan: What does Goldilocks have to do with it?

This article is part of a Special Issue "Estradiol and cognition". Estrogens impact the organization and activation of the mammalian brain in both sexes, with sex-specific critical windows. Throughout the female lifespan estrogens activate brain substrates previously organized by estrogens, and estrogens can induce non-transient brain and behavior changes into adulthood. Therefore, from early life through the transition to reproductive senescence and beyond, estrogens are potent modulators of the brain and behavior. Organizational, reorganizational, and activational hormone events likely impact the trajectory of brain profiles during aging. A "brain profile," or quantitative brain measurement for research purposes, is typically a snapshot in time, but in life a brain profile is anything but static--it is in flux, variable, and dynamic. Akin to this, the only thing continuous and consistent about hormone exposures across a female's lifespan is that they are noncontinuous and inconsistent, building and rebuilding on past exposures to create a present brain and behavioral landscape. Thus, hormone variation is especially rich in females, and is likely the destiny for maximal responsiveness in the female brain. The magnitude and direction of estrogenic effects on the brain and its functions depend on a myriad of factors; a "Goldilocks" phenomenon exists for estrogens, whereby if the timing, dose, and regimen for an individual are just right, markedly efficacious effects present. Data indicate that exogenously-administered estrogens can bestow beneficial cognitive effects in some circumstances, especially when initiated in a window of opportunity such as the menopause transition. Could it be that the age-related reduction in efficacy of estrogens reflects the closure of a late-in-life critical window occurring around the menopause transition? Information from classic and contemporary works studying organizational/activational estrogen actions, in combination with acknowledging the tendency for maximal responsiveness to cyclicity, will elucidate ways to extend sensitivity and efficacy into post-menopause.

Estradiol stimulates progenitor cell division in the ventricular and subventricular zones of the embryonic neocortex

Two distinct populations of cerebral cortical progenitor cells that generate neurons during embryogenesis have been identified: radial glial cells and intermediate progenitor cells. Despite advances in our understanding of progenitor cell populations, we know relatively little about factors that regulate their proliferative behaviour. 17-beta-Estradiol (E2) is present in the adult and developing mammalian brain, and plays an important role in central nervous system processes such as neuronal differentiation, survival and plasticity. E2 also stimulates neurogenesis in the adult dentate gyrus. We examined the role of E2 during embryonic cortical neurogenesis through immunohistochemistry, in situ hybridization, functional enzyme assay, organotypic culture and in utero administration of estradiol-blocking agents in mice. We show that aromatase, the E2 synthesizing enzyme, is present in the embryonic neocortex, that estrogen receptor-alpha is present in progenitor cells during cortical neurogenesis, that in vitro E2 administration rapidly promotes proliferation, and that in utero blockade of estrogen receptors decreases proliferation of embryonic cortical progenitor cells. Furthermore, the E2 inhibitor alpha-fetoprotein is expressed at high levels by radial glial cells but at lower levels by intermediate progenitor cells, suggesting that E2 differentially influences the proliferation of these cortical progenitor cell types. These findings demonstrate a new functional role for E2 as a proliferative agent during critical stages of cerebral cortex development.

Alpha-fetoprotein in human fetal cerebrospinal fluid

Alpha-fetoprotein (AFP) is a fetal glycoprotein. It has been ascribed a regulatory function of growth factor responses and immune functions. The concentrations of AFP and albumin (ALB) are highly variable in fetal serum and CSF and change with gestational age. The AFP index=[AFP(CSF)/AFP(SERUM)]/[ALB(CSF)/ALB(SERUM)] was determined in six normal fetuses at gestational age 17-23 weeks and found to be independent of gestational age and close to unity, mean 0.90+/-0.11 (S.D.). The ratio of CSF-serum concentrations of AFP and ALB both decreased significantly (p<0.05) with gestational age. The mean fraction of AFP being non-reactive with concanavalin A was 1.7% in serum and 1.9% in CSF, suggesting a common hepatic origin of AFP in both compartments. In conclusion, the concentration of AFP in CSF seems to be determined largely by the serum-CSF concentration gradient in normal fetuses. This finding, combined with the remarkable constancy of the AFP index compared to the highly variable absolute concentrations of AFP in both serum and CSF should make the AFP index the marker of choice when analyzing for intrathecal AFP synthesis during development and in pathological conditions.

alpha-Fetoprotein and albumin gene expression in brain and other tissues of fetal and adult rats

Quantitative measurement of messenger RNA (mRNA) for alpha-fetoprotein (AFP) and albumin in developing rat liver and in different fetal and adult tissues reveals a close correlation between the previously determined rate of protein synthesis and mRNA levels. mRNA for AFP and albumin exists in fetal intestine, lung, liver and kidney whereas there are no such transcripts in fetal brain or heart. There are no mRNA transcripts for AFP in any adult organs other than the liver. The lack of mRNA AFP in fetal brain tissue indicates that the AFP found in fetal brain cells is absorbed from the serum. This finding supports the hypothesis that AFP may serve as a carrier protein to deliver bound molecules, such as non-esterified fatty acids, to brain cells at a specific time during development.

Alpha-fetoprotein favours accumulation of estrone but not arachidonic acid into the fetal and new-born rat brain

Tritriated estrone or arachidonic acid, two high affinity ligands for rat alpha-fetoprotein (AFP), were injected into adult, pregnant or newborn Sprague Dawley rats in order to evaluate their possible transfer into the brain. This study shows that the developing brain accumulates the estrogen but not the fatty acid, suggesting that the uptake of AFP by the developing brain is a mechanism for transporting estrogens, but not fatty acids.

Immunohistochemical identification of some plasma proteins in human embryonic and fetal forebrain with particular reference to the development of the neocortex

The histogenesis of the cerebral neocortex has been studied in human embryos and fetuses from the ventricular zone stage at 9-10 mm crown-rump length (CRL) to the well-developed neocortex at 210 mm CRL. The initial proliferation of the neuroepithelial cells in the ventricular zone stage was followed by a stage characterized by a ventricular zone covered by a primordial plexiform layer; the subventricular zone then arose before the cortical plate was formed within the primordial plexiform layer, thus dividing it into an outer marginal zone and an inner subplate zone; finally the intermediate zone appeared between the subventricular and subplate zones. The distribution of cells containing albumin, alpha-fetoprotein, transferrin, prealbumin, IgG and alpha 1-antitrypsin in the cerebral vesicle and developing neocortex was investigated by the indirect immunoperoxidase technique. Alpha-fetoprotein found in the cells of the ventricular zone was the most widespread and prominent of the plasma proteins examined in the early embryos. The cerebral vesicle was negative for all other plasma proteins investigated at this stage. By 15 and 16 mm CRL, a few cells in the ventricular zone were positive for albumin and transferrin whereas AFP exhibited a distribution similar to that of the 9 mm embryo. By 20-25 mm CRL, albumin and AFP had a similar distribution in the telencephalic wall. At 40-150 mm CRL a positive staining reaction for AFP, albumin, prealbumin and transferrin was predominant in the outer half of cortical plate. At 150-170 mm CRL only cells in the inner half exhibited positive staining and at 210 mm CRL the staining reactions were negative. The cells containing plasma proteins did not belong to a single cell line or type; thus plasma proteins were detected primarily in different types of neurons but also in glial cells. Staining with polyvalent antiserum indicated that the same cells may be positive for more than one plasma protein. Positive staining reactions were also observed in or along fiber systems. It is proposed that cells initially take up plasma protein from the CSF and migrate with it towards the cortical plate. After a certain period they lose their plasma protein but when the neuronal cells which represent the majority of the positively stained cells have reached their final position in the cortical plate they commence plasma protein synthesis which continues for a short period during which the neurons establish their pattern of connectivity.

Isolation, characterization, and synthesis of alpha-fetoprotein from neonatal rat brain

Monospecific anti-rat serum alpha-fetoprotein (AFP) IgG was coupled to cyanogen bromide-activated Sepharose-4B (4.5 mg/ml packed volume of gel) to yield an immunoaffinity matrix. The immunoaffinity column was used to isolate AFP from feto-neonatal rat brain. The purified AFP was immunologically and electrophoretically similar to serum AFP. It yielded a single band with a molecular weight of 70,000 on sodium dodecyl sulphate polyacrylamide gel electrophoresis. Polyacrylamide gel electrophoresis of the protein under nondenaturing conditions yielded two charge variants of AFP, reminiscent of AFP from feto-neonatal rat serum. The AFP was observed to bind estradiol with Ka = 5.8 X 10(8) M -1 and 1.3 X 10(8) M -1 by dextran-coated charcoal adsorption and Sephadex gel filtration techniques, respectively. Newborn rat brain cells linearly incorporated [14C]leucine into immunoprecipitable AFP during 6 h in culture. It is, therefore, concluded that feto-neonatal rat brain contains AFP similar to that present in fetal serum and that it may arise in brain as a result of its in situ synthesis.

Changes in alpha-fetoprotein and albumin synthesis rates and their levels during fetal and neonatal development of rat brain

An attempt was made to find a correlation between AFP and albumin levels in brain and their rates of synthesis in the brain cells during maturation of rat brain. Levels of alpha-fetoprotein (AFP) and albumin in the developing brain were studied by rocket immunoassay. Rate of synthesis of AFP and albumin in brain cell cultures, established from rat brain at various stages of development, were determined by incorporation of [14C]leucine into immuno-precipitable intracellular AFP and albumin. AFP and albumin levels in brain as well as rates of their synthesis by brain cells in culture registered a continuous decline during development. Synthesis of AFP and albumin in the brain is switched off after first week of postnatal life with a concomitant disappearance of these proteins from the brain. Levels of AFP and albumin in brain correlated well with rates of their synthesis by brain cells in vitro at any specific stage of brain maturation implying that levels of AFP and albumin in brain are regulated by controlling rates of their synthesis in the maturing brain cells.

Synthesis and secretion of alpha-fetoprotein and albumin by newborn rat brain cells in culture

Brain cells of newborn rat were found to synthesize and secrete alpha-fetoprotein (AFP) and albumin in short-term culture. Synthesis of AFP and albumin was demonstrated by time-related linear incorporation of [14C]leucine into immunoprecipitable AFP and albumin by brain cells from newborn rat during 6 h incubation of the cultures. Newly synthesized labeled AFP and albumin were also accumulated (secreted) linearly as a function of incubation period. Cycloheximide could inhibit this incorporation of [14C]leucine into immunoprecipitable AFP and albumin. Synthesis of AFP and albumin accounted for 11-13% and 5-6% respectively, while their secretion into the culture medium was about 27-30% and 11-13% respectively of the total proteins synthesized and secreted by brain cells of newborn rat. Rate of AFP synthesis was about 2-fold greater than that of albumin. AFP and albumin secreted by brain cells displayed a complete immunological identity with, and electrophoretic mobilities similar to, the serum AFP and albumin. Molecular weights of AFP and albumin secreted by brain cells were also similar to their corresponding serum proteins. AFP was identified as the only active estradiol binding protein secreted by newborn rat brain cells in culture. Our studies suggest that albumin and estrophilic AFP originate in the developing rat brain in situ by intracellular synthesis.

Regional differences in intraneuronal localization of alpha-fetoprotein in developing mouse brain

Estrogen receptor-containing regions of limbic, hypothalamic and amygdaloid areas of the developing mouse brain exhibited little or no intraneuronal immunofluorescence reactivity for AFP in comparison with the bright fluorescence of adjacent regions. These regional differences in the topographic distribution of intraneuronal AFP may represent intrinsic differences in the uptake, turnover or immunoreactivity of the internalized protein, perhaps related to estrogen metabolism by such neurons.

Intraneuronal alpha-fetoprotein and albumin are not synthesized locally in developing brain

Alpha-Fetoprotein and albumin are found intraneuronally in developing mammalian brains. To investigate whether this results from local biosynthesis, the existence of the corresponding brain messenger RNAs and the ability of brain cultures to synthesize these proteins were studied in the mouse. The findings show that neither the proteins nor the mRNAs coding for them are made in sufficient quantities to account for the material detected immunologically, supporting an extracellular origin.

Human fetal brain antigen expression common to tumors of neuroectodermal tissue origin

The antigenic relationship between human tumors of neuroectodermal origin and fetal brain were further investigated by characterization of two hybridoma antibodies derived from a fusion of P3-NS1/1-Ag 4-1 (NSI) myeloma cells and splenocytes hyperimmunized to second trimester human fetal brain homogenate. Monoclonal antibodies (MAs) 1H8cl 2 and 1H8cl 3 were analyzed by cell surface radioimmunoassay (CS-RIA), quantitative absorption, indirect immunofluorescence, and peroxidase-antiperoxidase (PAP) immunohistology. MA 1H8cl 3 is the more broadly reactive, binding to 9/14 glioblastoma (GBM), 2/3 neuroblastoma, 1/2 melanoma, and 1 medulloblastoma cell line(s) by CS-RIA analysis, and to 12/15 GBM, fetal brain, spleen, and liver, and adult spleen by PAP analysis. MA 1H8cl 2 is more restricted, binding to 7/14 GBM, 2/3 neuroblastoma, 1 medulloblastoma, and 2/3 fetal skin fibroblast cell line(s) by CS-RIA, and to 9/15 GBM and fetal brain and spleen by PAP analysis. Control non-central nervous system tumors and normal adult tissue including brain, thymus, lymph node, liver, kidney, lung, skin, and pancreas, were unreactive with both 1H8cl 2 and 1H8cl 3 by CS-RIA, PAP, and absorption analysis. The data presented here establish the unique nature of the detected antigenic specificities as compared to previously described oncofetal and onconeural antigens, and define two immune reagents which are operationally specific for tumors of neuroectodermal origin within the adult central nervous system.

Characterization, origin and evolution of alpha-fetoprotein and albumin in postnatal rat brain

1. The levels of AFP and albumin in rat brain at birth were 77 and 340 micrograms per g of tissue, respectively. These levels quickly dropped with age. AFP was undetectable in 20 days brain extracts whereas 30 micrograms of albumin per g of brain were still measured. 2. AFP from brain and serum were identical by immunodiffusion, electrophoresis and immuno-affinoelectrophoresis with free Concanavalin A. 3. No in vitro synthesis of AFP and albumin in the postnatal brain was observed. However, the total amount of AFP in the developing rat brain increases from birth to 4-5 days post-partum.

Ontogeny and distribution of alpha-fetoprotein in feto-neonatal rat brain

Maximal level of alpha-fetoprotein (AFP) recorded in fetal rat brain on day 18 of gestation declined progressively with development to low level at day 7 after parturition. Different regions of brain contained AFP in the following order: olfactory greater than cerebrum greater than cerebellum, remaining portion. Developmental profiles of AFP in discrete regions of feto-neonatal rat brain were similar and reflected the ontogeny of the protein in whole brain.