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 non-ciliated (NC) cells of the bovine oviduct epithelium, have been shown to release embryotrophic substances to the oviduct lumen. The aim of the present study was to investigate the ultrastructure, focusing on aspects of the secretory machinery, of NC cells in different segments of the oviduct during and after transoviduct migration of zygotes and embryos. Dairy heifers (n = 8) were superovulated with an ECG/cloprostenol regimen, and the time of ovulation was estimated by ultrasound scanning. Samples from the infundibulum, ampulla, isthmus and uterotubal-junction of the oviduct were surgically collected from animals at 19-96 h and 7 1/2-8 1/2 days after ovulation and processed for transmission electron microscopy, following standard procedures. The NC cells contained characteristic membrane-bound secretory granules composed of a lamellar cortex encaging an amorphous medulla. The two components could still be recognized during extrusion of the granule content into the oviduct lumen by exocytosis. During granulogenesis, small maturing granules without the lamellar structure were observed, but distinct condensing vacuoles were absent. An abundance of granules was found in the early versus the late group. In both groups the uterotubual junction was almost free of granules. This segment, on the contrary, was characterized by the presence of primary and secondary lysosome-like bodies. In the early group the intracellular location of the granules varied between oviduct segments.(ABSTRACT TRUNCATED AT 250 WORDS)

The distribution of the neural cell adhesion molecule (NCAM) and Thy-1 in the olfactory mucosa and olfactory bulb, the eye and the inner ear was examined with immunocytochemistry in mouse embryos from embryonic day 12 (E 12) to embryonic day 19 (E 19). In general, neurons are completely outlined with NCAM, whereas Thy-1 outlines only dendrites and axons. A variable cytoplasmic staining for Thy-1 is present in the perikarya. Neurons directly associated with special sense organs express NCAM and Thy-1 already from the earliest stage and throughout the period investigated, apart from the olfactory neurons in which Thy-1 disappears at E 19. The mitral cells in the olfactory bulb show Thy-1 but no NCAM reactivity. In the eye, lens fibers express Thy-1 and the pigmented layer expresses NCAM; neither of the two molecules can be detected at E 19. In the inner ear, hair cells express NCAM at E 19. Based on the distribution during the developmental period studied and on the cellular localisation of reaction products, it is suggested that the NCAM adhesion function could be of a more general nature by keeping appropriate cell membranes in close contact and thereby allowing more specific molecular interactions to take place. Thy-1, which is located on dendrites and axons, could be such a specific factor and function as recognition molecule in the developing nervous system.

ContentsPre-implantation bovine development is characterized by a sequential activation of genes in the embryo. The first, second and third embryonic cell cycles, i.e. the one-, two-and four-cell stages, are characterized by a low rate of transcription, while a burst of transcription is seen during the fourth cell cycle, i.e. the eight-cell stage. Also during the fourth cell cycle, nucleolar function is re-established by activation of the rRNA genes. The associated process of nucleologenesis is, from an ultrastructural point of view, a reversal of the nucleolar deactivation seen in the oocyte, which occurs at the completion of the oocyte growth phase. During the first, second and third embryonic cell cycles, attempts are apparently made to re-establish nucleolar function as the nucleolar assembly within cach of these cycles proceeds to a certain but still transcriptionally inactive stage.

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