The E3 ubiquitin ligase SMURF1 regulates cell-fate specification and outflow tract septation during mammalian heart development.

Smad ubiquitin regulatory factor 1 (SMURF1) is a HECT-type E3 ubiquitin ligase that plays a critical role in vertebrate development by regulating planar cell polarity (PCP) signaling and convergent extension (CE). Here we show that SMURF1 is involved in mammalian heart development. We find that SMURF1 is highly expressed in outflow tract cushion mesenchyme and Smurf1-/- mouse embryos show delayed outflow tract septation. SMURF1 is expressed in smooth muscle cells of the coronary arteries and great vessels. Thickness of the aortic smooth muscle cell layer is reduced in Smurf1-/- mouse embryos. We show that SMURF1 is a negative regulator of cardiomyogenesis and a positive regulator of smooth muscle cell and cardiac fibroblast differentiation, indicating that SMURF1 is important for cell-type specification during heart development. Finally, we provide evidence that SMURF1 localizes at the primary cilium where it may regulate bone morphogenetic protein (BMP) signaling, which controls the initial phase of cardiomyocyte differentiation. In summary, our results demonstrate that SMURF1 is a critical regulator of outflow tract septation and cell-type specification during heart development, and that these effects may in part be mediated via control of cilium-associated BMP signaling.

Proteolytic processing of anti-Müllerian hormone differs between human fetal testes and adult ovaries.

From early embryonic life, anti-Müllerian hormone (AMH) is produced by Sertoli cells and is essential for male sex differentiation. In females, AMH is produced by immature granulosa cells (GCs) but a definitive function in females is uncertain. We have assessed the cellular localization and specificity of a panel of five novel high-affinity AMH monoclonal antibodies. Two recognize the mature C-terminal form of AMH, whereas three recognize the active pro-mature form of AMH in human tissue. The antibodies were tested on fetal male testicular and mesonephric tissue aged 8-19 weeks post conception (pc), fetal male serum aged 16-26 weeks pc and human immature GCs by immunofluorescence, immunohistochemistry, ELISA and western blotting. The active pro-mature forms of AMH were expressed in both Sertoli cells from human fetal testis and human immature GCs. In contrast, the mature C-terminal form of AMH was hardly detected in Sertoli cells, but was readily detected in GCs. This particular form was also located to the nucleus in GCs, whereas the other investigated AMH forms remained in the cytoplasm. Interestingly, the distribution of the AMH forms in the fetal serum of boys showed that the fraction of inactive precursor AMH only accounted for 4.5% ± 0.6 (mean ± SD) of the total AMH measured, and the remaining AMH was the active pro-mature form. Furthermore, western blot analysis demonstrated a number of previously unrecognized molecular forms of AMH. The present findings suggest that processing of AMH is a tightly regulated process, which is likely to be important for the function of AMH and which differs between the two sexes.

SPARC/osteonectin, an endogenous mechanism for targeting albumin to the blood-cerebrospinal fluid interface during brain development.

Specialized populations of choroid plexus epithelial cells have previously been shown to be responsible for the transfer of individual plasma proteins from blood to the cerebrospinal fluid (CSF), contributing to their characteristically high concentrations in CSF of the developing brain. The mechanism of this protein transfer remains elusive. Using a marsupial, Monodelphis domestica, we demonstrate that the albumin-binding protein SPARC (osteonectin/BM-40/culture-shock protein) is present in a subset of choroid plexus epithelial cells from its first appearance, throughout development, and into adulthood. The synthesis of SPARC by the lateral ventricular plexus was confirmed with real-time PCR. The expression level of SPARC was higher in plexuses of younger than older animals. Western blot analysis of the gene product confirmed the quantitative PCR results. The co-localization of SPARC and albumin shown by immunocytochemistry and its cellular location indicate that this glycoprotein may act as a recognition site for albumin. In addition, the numbers of SPARC-immunopositive cells and its expression were responsive to experimental changes of albumin concentration in the blood. It is suggested that SPARC may be one of the molecules that govern the uptake and delivery of proteins from blood to the CSF. The results also confirm that protein transfer across the blood-CSF barrier is developmentally and physiologically regulated.

No evidence for the presence of oogonia in the human ovary after their final clearance during the first two years of life.

BACKGROUND: Conflicting results of studies on mouse and human have either verified or refuted the presence of oogonia/primordial germ cells in the post-natal ovary. The aim of this study was to trace whether oogonia recognized by immunohistochemical methods in the first trimester human ovary were present also in peri- and post-natal ovaries. METHODS: For this study, 82 human ovaries were collected: 25 from embryos from 5 to 10 weeks post conception (wpc), 2 at 18 wpc, 32 from 32 wpc to 2 years and 23 from 2 to 32 years. Of these, 80 ovaries were fixed and paraffin-embedded and 2 (8 year-old) ovaries were processed for plastic sections. Serial sections were prepared for immunohistochemical detection of markers for oogonia: tyrosine kinase receptor for stem cell factor (SCF)(C-KIT), stage-specific embryonic antigen-4 (SSEA4), homeobox gene transcription factor (NANOG), octamer binding transcription factor 4 (OCT4) and melanoma antigen-4 (Mage-A4), while noting that C-KIT also stains diplotene oocytes. RESULTS: Almost all oogonia exclusively stained for SSEA4, NANOG, OCT4 and C-KIT, whereas MAGE-A4 only stained a small fraction. At birth only a few oogonia were stained. These disappeared before 2 years, leaving only diplotene oocytes stained for C-KIT. From 18 wpc to 2 years, the medulla contained conglomerates of healthy and degenerating oogonia and small follicles, waste baskets (WBs) and oogonia enclosed in growing follicles (FWB). Medulla of older ovaries contained groups of primordial, healthy follicles. CONCLUSIONS: We found no evidence for the presence of oogonia in the human ovary after their final clearing during the first 2 years. We suggest that perinatal medullary WB and FWB give rise to the groups of small, healthy follicles in the medulla.

In human granulosa cells from small antral follicles, androgen receptor mRNA and androgen levels in follicular fluid correlate with FSH receptor mRNA.

Human small antral follicles (diameter 3-9 mm) were obtained from ovaries surgically removed for fertility preservation. From the individual aspirated follicles, granulosa cells and the corresponding follicular fluid were isolated in 64 follicles, of which 55 were available for mRNA analysis (24 women). Expressions of androgen receptor (AR) mRNA levels in granulosa cells, and of androstenedione and testosterone in follicular fluid, were correlated to the expression of the FSH receptor (FSHR), LH receptor (LHR), CYP19 and anti-Müllerian Hormone-receptor II (AMHRII) mRNA in the granulosa cells and to the follicular fluid concentrations of AMH, inhibin-B, progesterone and estradiol. AR mRNA expression in granulosa cells and the follicular fluid content of androgens both showed a highly significant positive association with the expression of FSHR mRNA in granulosa cells. AR mRNA expression also correlated significantly with the expression of AMHRII, but did not correlate with any of the hormones in the follicular fluid. These data demonstrate an intimate association between AR expression in immature granulosa cells, and the expression of FSHR in normal small human antral follicles and between the follicular fluid levels of androgen and FSHR expression. This suggests that follicular sensitivity towards FSH stimulation may be augmented by stimulation of androgens via the AR.

Human primordial germ cells migrate along nerve fibers and Schwann cells from the dorsal hind gut mesentery to the gonadal ridge.

The aim of this study was to investigate the spatiotemporal development of autonomic nerve fibers and primordial germ cells (PGCs) along their migratory route from the dorsal mesentery to the gonadal ridges in human embryos using immunohistochemical markers and electron microscopy. Autonomic nerve fibers in the dorsal mesentery, the pre-aortic and para-aortic plexuses and in the gonadal ridge were stained for beta III tubulin, neuron specific enolase and the glia fibrillary acidic protein. Electron microscopy demonstrated the presence of neurofilaments and neurotubules in these nerve fibers and their intimate contact with PGCs. PGCs expressed GAGE, MAGE-A4, OCT4 and c-Kit. Serial paraffin sections showed that most PGCs were located inside bundles of autonomic nerve fibers with the majority adjacent to the most peripheral fibers (close to Schwann cells). We also show that both nerve fibers and PGCs arrive at the gonadal ridge between 29 and 33 days pc. In conclusion, our data suggest that PGCs in human embryos preferentially migrate along autonomic nerve fibers from the dorsal mesentery to the developing gonad where they are delivered via a fine nerve plexus.

Cryopreservation of intact testicular tissue from boys with cryptorchidism.

BACKGROUND: Boys with cryptorchidism often face fertility problems in adult life despite having orchiopexy performed at a very young age. During this operation, a biopsy of the testis is normally taken in order to evaluate their infertility potential and the presence of malignant cells. This study evaluated the morphology and functional capacity of cryopreserved testes biopsies and their possible use in fertility preservation. METHODS: Biopsies from 11 testes (eight boys) were obtained. Each biopsy was subdivided into six pieces and two pieces were frozen in each of two different cryoprotectants. One fresh and two cryopreserved pieces were cultured for 2 weeks. All pieces were prepared for histology. Used culture media were analysed for testosterone and inhibin B concentrations. RESULTS: The morphology of the fresh and frozen-thawed samples was similar, with well-preserved seminiferous tubules and interstitial cells. A similar picture appeared after 2 weeks of culture, but a few of the cultured biopsies contained small necrotic areas. The presence of spermatogonia was verified by c-kit-positive immunostaining. Production of testosterone and inhibin B (ng/mm(3) testis tissue) in the frozen-thawed pieces was on average similar to that of the fresh samples. CONCLUSIONS: Intact testicular tissue from young boys with non-descended testes tolerates cryopreservation with surviving spermatogonia and without significant loss of the ability to produce testis-specific hormones in vitro. It may be an option to freeze part of the testis biopsy, which is routinely removed during the operation for cryptorchidism, for fertility preservation in adult life.

Aquaporin-1 in the choroid plexuses of developing mammalian brain.

The normal brain develops within a well-controlled stable internal "milieu" protected by specialised mechanisms referred to collectively as blood-brain barriers. A fundamental feature of this environment is the control of water flow in and out of the developing brain. Because of limited vascularisation of the immature brain, choroid plexuses, via the cerebrospinal fluid, have been proposed as the main route of fluid exchange between the blood and brain interfaces. We describe the temporal expression and appearance of aquaporin-1 (AQP1) which is important for water transfer across adult choroid plexuses. AQP1 expression was studied in rat embryos using real time reverse transcription/polymerase chain reaction. mRNA for AQP1 was present in rat brain at embryonic day 12 (E12) one day before the protein was detectable in the fourth ventricular choroid plexus (the first plexus to appear); its relative levels increased at E13-E14 when more AQP1-immunoreactive cells appeared in all plexuses. The presence of AQP1 was determined immunocytochemically in five different mammalian species (rat, mouse, human, sheep and opossum) in all four choroid plexuses from their earliest appearance. In all five species studied, the appearance of AQP1 immunoreactivity followed the same developmental sequence: the fourth, lateral and, finally, third ventricular choroid plexus. The stage of choroid plexus development when AQP1 was first detected in all five species and in all four choroid plexuses corresponded to the transition between Stages I and II. The cellular localisation of AQP1 in all choroid plexuses, as soon as it was detectable, had the characteristic apical membrane distribution previously described in the adult; a basolateral membrane localisation was also observed.

Rat fetuin: distribution of protein and mRNA in embryonic and neonatal rat tissues.

Fetuin is a serum protein widely distributed in the animal kingdom and found in all mammalian species so far investigated. It is mainly a fetal protein, in the sense that the highest concentrations are found in serum and body fluids of embryos and fetuses. In order to elucidate possible biological functions of fetuin, we have studied its synthesis and distribution during the prenatal development of the rat with immunohistochemistry and in situ hybridization. We have isolated fetuin from rat serum and produced an antibody against this protein. In situ hybridization was performed using a 375-nucleotides-long digoxigenin-labeled riboprobe. Fetuin was unevenly distributed in all organ systems during development, with the most pronounced expression at E 10Fetuin is a serum protein widely distributed in the animal kingdom and found in all mammalian species so far investigated. It is mainly a fetal protein, in the sense that the highest concentrations are found in serum and body fluids of embryos and fetuses. In order to elucidate possible biological functions of fetuin, we have studied its synthesis and distribution during the prenatal development of the rat with immunohistochemistry and in situ hybridization. We have isolated fetuin from rat serum and produced an antibody against this protein. In situ hybridization was performed using a 375-nucleotides-long digoxigenin-labeled riboprobe. Fetuin was unevenly distributed in all organ systems during development, with the most pronounced expression at E16-E18. Fetuin expression was present in germinal cell populations, e.g., in the basal layer in the skin, in the germinal cell populations in the brain anlage and the gonads, and it was heavily expressed in the fetal hemopoietic liver. Furthermore, fetuin was expressed in the gastrointestinal epithelium prior to the development of glands and crypts. Fetuin was widely distributed in mesenchymal derived tissues, e.g., bone and muscle. In the developing kidney fetuin was heavily expressed is both mesenchymal condensations and glomerular anlages. Thus, fetuin was located in cells or structures undergoing differentiation and transformation. As fetuin has been shown previously to interfere with hormone signaling of transforming growth factor-beta, insulin and hepatocyte-growth factor, fetuin might be involved in cell differentiation and tissue transformation during the initial histogenesis, i.e., the time period in which cellular phenotypic characteristics are established.

The multidrug-resistance P-glycoprotein (Pgp, MDR1) is an early marker of blood-brain barrier development in the microvessels of the developing human brain.

The multidrug-resistance P-glycoprotein (Pgp) was initially identified as an energy-dependent proton pump, which transports a variety of non-related compounds out of chemotherapy-resistant cancer cells. Molecular biological investigations using knockout mice for the mouse homologue of the human Pgp showed that these mice partially lack a functioning blood-brain barrier, indicating that Pgp has an important role in the blood-brain barrier as its normal function. The presence of Pgp expression in formalin-fixed and wax-processed tissue sections can be assessed using the monoclonal antibody, JSB-1. Since no data on the developmental expression of Pgp are available, we stained a developmental series of human brain sections with JSB-1. Our results indicate that Pgp expression in endothelia of brain microvessels occurs regularly in embryos of about 30-mm crown-rump length (CRL). Strong reactivity is seen in blood vessels of fetuses from 123-mm CRL. There is also reactivity in pial blood vessels but not in choroid plexus blood vessels known to be without a blood-brain barrier. Pgp expression is therefore an early marker of the blood-brain barrier in the developing human brain.

Intercellular barriers to and transcellular transfer of albumin in the fetal sheep brain.

The nature of the barriers that keep proteins out of the developing brain has been studied in tissues obtained from fetal sheep in experiments conducted under controlled physiological conditions. In anaesthetised pregnant ewes, 60 day gestation fetuses (term is 150 days) were exposed to human albumin injected intravenously for periods up to 6 h. The immunocytochemical distribution of exogenous human albumin was compared with that of endogenous sheep albumin at both the light and electron-microscopical level. Immunogold labelling of ultracryosections suggests that a tubulocisternal endoplasmic reticulum system in immature choroid-plexus epithelial cells is the route by which albumin crosses from blood to cerebrospinal fluid (CSF) in the developing brain. The integrity of the blood-brain barrier, the blood-cerebrospinal fluid barrier and the cerebrospinal fluid-brain barrier to protein, was confirmed. In addition, at the outer surface of the developing brain there also appears to be a restriction on the passage of albumin from CSF into the brain. These observations support earlier proposals that the immature brain develops within an internal environment from which proteins in plasma and CSF are largely excluded.

Ontogenetic development of diffusional restriction to protein at the pial surface of the rat brain: an electron microscopical study.

Blood-brain, blood-CSF and ventricular CSF-brain barriers to protein are present very early in brain development. In order to determine whether the outer pial surface of the brain also restricts free penetration of macromolecules, the dorso-lateral part of the sensorimotor cortex from rats at embryonic day 12 (E12), 14, 16, and 18, the day of birth (P0), and adult rat, was studied by electron microscopical techniques. Potassium ferrocyanide, Ruthenium Red and immunogold labelling of endogenous albumin were used to investigate junctional structures and the sites of restriction to albumin diffusion. At E12, large fenestrated sinusoids were present in the pia-arachnoid and the brain surface was formed by an incomplete layer of neuroepithelial and presumptive radial glial end feet, but capillaries in the pia-arachnoid showed no fenestrations at E14 or later. From E14, we observed the progressive appearance of distinct junctional structures between the glial end feet which, to our knowledge, have not been described before. Analysis of albumin distribution from E16 to P0 suggests that the junctions may contribute to restriction of diffusion between the subarachnoid space and the brain extracellular fluid. The restriction to the penetration of protein at both the pial and the ependymal surfaces may ensure the isolation of the neural environment during a critical phase in development of the nervous system. The changes in the structure of the junctions between E12 and P0 suggests a transitional series of embryonic junctional types, which eventually give way to the mature junctions of the adult. Parallels between the embryonic glial junctions and junctions described in adult invertebrate brain, suggest some interesting parallels in junctional development in phylogeny and ontogeny.

Synaptogenesis in the neocortical anlage and early developing neocortex of rat embryos.

The recent finding of synapses in Monodelphis domestica (South American grey short-tailed opossum) before the establishment of the cortical plate raises the question of whether this finding is species-specific. Therefore, the establishment of the first synapses in the developing neocortex has been studied in the sensorimotor cortex of rat fetuses with a gestational age ranging from embryonic day 12 (E12) to birth. At E14, we found well-defined synapses with postsynaptic thickening and containing several vesicles in the presynaptic element in the primordial plexiform layer, before the appearance of the cortical plate. The postsynaptic elements were probably dendrites of Cajal-Retzius cells in the primordial plexiform layer and/or differentiating dendrites of presumptive cortical plate neurons. At E16, in addition to the presence of axodendritic and very few axosomatic synapses in the marginal and the subplate zones, synapses of both types were present within the cortical plate. Thus, this paper provides evidence for the presence of synapses in the developing rat brain both at an earlier stage and with a wider distribution than previously reported.

Expression and distribution of fetuin in the developing sheep fetus.

Tissue distribution and developmental expression of fetuin were studied in the sheep fetus from embryonic day (E) 30 to adult (gestational period is 150 days). The presence of fetuin was demonstrated immunocytochemically using anti-fetuin antibodies; in situ hybridisation using short anti-sense oligonucleotide probes labelled with digoxigenin was used to study the ability of the developing tissue to synthesise fetuin, and reverse transcription-polymerase chain reaction (RT-PCR) was used to estimate the level of fetuin mRNA in selected tissues. Tissue distribution of fetuin was widespread in the younger fetuses (E30 to E40). The most prominent presence due to in situ synthesis was demonstrated in the liver, central nervous system (CNS) including anterior horn cells, dorsal root ganglia and in skeletal muscle cells. Other developing tissues and organs that showed evidence of fetuin synthesis and presence of the protein included mesenchyme, kidney, adrenal, developing bone, gut, lung and heart. In the immature liver (E30-40) there was a strong signal for fetuin mRNA in hepatocytes and also in numerous haemopoietic cells; the proportion of these latter cells that was positive for fetuin mRNA increased between E30 and E40. Only some hepatocytes and a proportion of the haemopoietic stem cells were immunoreactive for fetuin itself at E30-40; immunoreactive hepatocytes were more frequently observed in the more mature outer regions of the developing liver. Lung and gut contained scattered fetuin-positive epithelial cells, especially at E30; a weak fetuin mRNA signal could be detected above background in many of these cells up to E40, but not at E60-E115 or in the adult. Particularly at E30 to E40, mesenchymal tissue both within organs such as the gut and lung and around forming bone and skeletal muscle contained cells that were positive for fetuin mRNA. Mesenchyme at these ages was also very strongly stained for fetuin protein, much of which may reflect fetuin in tissue extracellular spaces and be derived from the high concentration in plasma. By E80 fetuin mRNA was mainly present in the liver and the CNS; staining of the muscle tissue was becoming less pronounced. However in developing bone tissue, staining of chondrocytes for fetuin mRNA was still prominent in older (E80) fetuses; there was also fetuin protein staining of chondrocytes at the growing surfaces of bones and in bone marrow at this age. In the adult, weak immunocytochemical staining for fetuin itself was present in hepatocytes, but the mRNA signal was barely above the threshold limit of detection.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of spinal cord in the isolated CNS of a neonatal mammal (the opossum Monodelphis domestica) maintained in longterm culture.

The CNS of the newly born opossum removed in its entirety survives and maintains its electrical excitability in suitable culture media for up to ten days at 25 degrees C. The structure of the developing neonatal spinal cord has been studied in the intact animal and in the cultured CNS. The differentiation and survival of individual cells and subcellular structures were followed at the light and electron microscopic level. The expression of cell markers in neuronal and glial cells was studied immunocytochemically using commercially available antibodies. Both mono- and polyclonal antibodies raised against antigens from several other species cross-reacted with Monodelphis antigens. The spinal cord of preparations removed from three-day-old-animals showed many neuron specific enolase-positive large neurons in the ventral horn as well as vimentin- and glial fibrillary acidic protein-positive radial glial cells and numerous small diameter unmyelinated axons, abundant dendrites and synaptic structures. From post natal day 5 to post natal day 8 continued differentiation of neurons and differentiation of radial glial cells into astrocytes were apparent. Radial glial fibres and astrocytes reacted positively to antibodies against glial fibrillary acidic protein. Myelin had not appeared at 8 days. A comparison of material obtained from postnatal day 3-postnatal day 4 preparations fixed immediately after dissection and from postnatal day 3-postnatal day 4 preparations fixed after 5 days in culture showed growth with continued mitotic activity of the neuroepithelial cells and further neuronal and glial maturation in the spinal cord especially in the more rostral end. In successful experiments in vitro, the preservation of individual cells, organelles, membranes and synapses was similar in the freshly dissected and cultured preparations apart from a distinct loss of the youngest and some of the oldest neurons in the spinal cord. Also the main fibre tracts (dorsal, lateral and ventromedial funiculus) survived. Virtually all preparations that had not been damaged or injured showed these results. Possible reasons for the death or survival of individual neuronal or glial cell populations in these preparations are discussed.

An immunocytochemical study of the innervation of developing human fetal teeth using protein gene product 9.5 (PGP 9.5).

Developing teeth of 32 human fetuses (crown-rump length 11-205 mm) were examined immunohistochemically by antisera to protein gene product 9.5 (PGP 9.5) in an attempt to shed light upon the possible role of innervation in odontogenesis. As a control for the specificity of PGP 9.5 as a neuronal marker, the results were verified by immunocytochemical co-localization in peripheral nerves of neurone-specific enolase, neurofilaments and S-100 protein. The dental follicle received the first nerve fibres in the early cap stage. At this stage, fibroblasts differentiated in the presence of nerve fibres and formed the dental follicle surrounding the developing tooth. In the dental papilla, however, no fibres were demonstrated until the dentine and enamel matrices had formed, about half of the present height of the tooth germ. Most nerve fibres were localized in the basal part of the papilla until the last stage examined and usually followed the blood vessels of the papilla. Thus the effect of innervation on tooth development may be associated with the development of the dental follicle. A novel finding was that functional odontoblasts were not only positive for S-100 but also for PGP 9.5, indicating their neural crest origin.

Immunocytochemical demonstration of nerve growth factor receptor (NGF-R) in developing human fetal teeth.

Evidence is accumulating that nerve growth factor receptor (NGF-R or p75NGFR) can mediate cell growth and differentiation of non-neuronal cells. NGF-R expression was studied in developing teeth of human embryos and fetuses between the 6th and 18th weeks of gestation, using a monoclonal mouse-anti-human NGF-R antibody. In contrast to earlier findings in rodents, the NGF-R expression of the human dental papilla was found to be transient. NGF-R was present in the condensing ecto-mesenchymal cells of the dental papilla in the early cap stage tooth germ. In later developmental stages, a shift of the NGF-R expression from the papilla to the cytoplasmic membrane of the inner enamel epithelium (IEE) was demonstrated. As in rodent odontogenesis, the NGF-R immunoreactivity of the IEE remained until the odontoblasts started secretion of predentinal matrix in the late bell state. The mitotic activity in the IEE was detected by an antibody against proliferating cell nuclear antigen (PCNA) and showed that the NGF-R expression of the IEE decreased as the cell proliferation ceased. We propose that NGF-R may, be involved in differential and/or proliferative events of human odontogenesis.

A sensitive post-DAB enhancement technique for demonstration of iron in the central nervous system.

A technique is described for enhancing the reaction product of the staining reaction for iron in paraffin-embedded tissue from central nervous system (CNS). After amplification of the Prussian Blue staining reaction with 3,3'-diaminobenzidine (DAB), the reaction product was further intensified using a stepwise treatment with silver methenamine, gold chloride and uranyl nitrate (post-DAB treatment). Following the Prussian Blue-DAB staining reaction, iron was seen only in glial cells and choroid plexus epithelial cells, whereas the post-DAB treatment revealed that neurons and endothelial cells of the brain capillaries were also positively stained. The post-DAB treatment resulted additionally in an increased intensity of the reaction product within choroid plexus epithelial cells compared to that obtained in sections subjected only to the Prussian Blue-DAB reaction. The reliability of the method was evaluated using liver sections as positive controls. Furthermore the higher sensitivity of the method was assessed using nitrocellulose filters containing serially diluted iron-saturated transferrin. The post-DAB method is simple and can easily be applied to formalin- or glutaraldehyde fixed, paraffin-embedded nervous and non-nervous tissue.

Synthesis of the foetal protein fetuin by early developing neurons in the immature neocortex.

The presence of the foetal protein fetuin has previously been demonstrated by immunocytochemistry to be specifically confined to the primordial plexiform layer, the early cortical plate and subplate zone cells in the developing neocortex of a number of species. In order to investigate its origin there, we have applied in situ hybridization in paraffin sections of Bouin's fixed foetal sheep brain, using a short anti-sense oligonucleotide probe. The distribution of fetuin mRNA has been compared with that of the protein by using anti-fetuin antibodies and immunocytochemistry. This allowed us to confirm that fetuin is synthesised initially in cells of the primordial plexiform layer and subsequently cortical plate and subplate cells. On the other hand, cells in the ventricular zone that are fetuin (protein) positive do not contain detectable fetuin mRNA. The time course of fetuin mRNA expression in the developing neocortex follows closely the previously described pattern of fetuin (protein) distribution in the sheep brain, apart from its absence from the ventricular zone where its origin is probably by uptake from cerebrospinal fluid.