Stage-specific localization of cytoskeletal actin mRNA in murine seminiferous tubules and intestinal epithelia as demonstrated by in-situ hybridization

Isolation of the rat spermatid manchette and its perinuclear ring

The manchette is a transient structure that develops during spermiogenesis. It consists of three components: a perinuclear ring, a microtubule mantle inserted in the ring, and dense plaques attached at the distal end of the mantle. A procedure has been developed for the fractionation of intact manchettes from rat spermatids. Each fractionation step was monitored by indirect immunofluorescence using an antibody to unmodified alpha-tubulin. Indirect immunofluorescence and electron microscopy demonstrate that fractionated manchettes are relatively intact. A thermocleavage step was used to sever the microtubule mantle from the perinuclear ring. Microtubules of the mantle collected in a stabilizing buffer containing Taxol formed long bundles of side-by-side aligned microtubules. The perinuclear ring sample consisted of circular-shaped units of different diameter with truncated microtubules still attached to the ring, a property that enabled the initial recognition of the rings by alpha-tubulin antibody staining. Indirect immunofluorescence and immunoblotting experiments using isoform-specific antibodies to alpha-tubulins show that the manchette contains acetylated, tyrosinated, glutamylated alpha-tubulin and an alpha-3/7 tubulin isoform. The same alpha-tubulin isoforms were observed in the axoneme of the sperm tail. Two-dimensional polyacrylamide gel electrophoresis fractionation maps of silver-stained proteins of the intact manchette show four predominant proteins: alpha- and beta-tubulins, beta-actin, vimentin, and a 62-kDa protein. The latter persisted in thermocleaved perinuclear ring samples. Results of this study indicate that the newly developed procedure for the fractionation of manchettes will facilitate a direct characterization of posttranslationally modified tubulin variants, microtubule-associatedproteins, and the components of the perinuclear ring of this largely neglected structure of the spermiogenic process.

Asymmetrical localization of mRNAs in enterocytes of human jejunum

Intracellular localization of specific mRNAs is known to be a mechanism for targeting proteins to specific sites within the cell. Previous studies from this laboratory have demonstrated co-localization of mRNAs and proteins for a number of genes in absorptive enterocytes of fetal rat intestine. The present study was undertaken to examine in human enterocytes the intracellular localization patterns of mRNAs for the microvillous membrane proteins lactase-phlorizin hydrolase (LPH), sucrase-isomaltase (SI), and intestinal alkaline phosphatase (IAP), and the cytoskeletal protein beta-actin. In sections of human jejunum, mRNAs were localized by in situ hybridization using digoxigenin-labeled anti-sense RNA probes. Both LPH and SI mRNAs were localized to the apical region of villous enterocytes, whereas IAP and beta-actin mRNAs were detected both apically and basally relative to the nucleus. Therefore, in contrast to LPH, SI, and beta-actin mRNAs, which co-localize with their encoded proteins, that of IAP is present in the basal region of the cell where IAP protein has not directly been demonstrated to be present. Absorptive enterocytes from humans possess the mechanisms for intracellular mRNA localization, but not all mRNAs co-localize with their encoded proteins.

Alterations of antioxidant enzyme expression in response to hydrogen peroxide

The effect of hydrogen peroxide (H2O2) on the expression of different antioxidant enzymes was investigated in primary rat hepatocytes and the rat hepatoma H4IIE cell line. Catalase mRNA expression and enzyme activity decreased during rat hepatocyte culture. Exposure of hepatocytes to H2O2 prevented this decrease in catalase mRNA expression, catalase expression was induced 2-fold. MnSOD message levels showed a peak after 12 h of culture and MnSOD enzyme activity increased similarly. MnSOD mRNA expression was also induced after exposure to H2O2. Cu/ZnSOD mRNA expression remained constant during culturing and was not affected by H2O2 treatment. In confluent hepatoma H4IIE cells catalase mRNA expression was lower than in early hepatocyte cultures and could be induced 2-fold upon treatment with H2O2. Actinomycin D alone caused the same amount of induction of catalase mRNA in rat hepatocytes as in combination with H2O2. Exposure of hepatocytes to cycloheximide did not influence the induction of catalase mRNA by H2O2. In rat hepatoma H4IIE cells the induction of catalase mRNA by H2O2 was prevented by the addition of actinomycin D or cycloheximide. Although induction of catalase mRNA by H2O2 was found in rat hepatocytes and H4IIE cells, gene expression of catalase does not appear to be regulated in both cell types in the same manner.

CP beta3, a novel isoform of an actin-binding protein, is a component of the cytoskeletal calyx of the mammalian sperm head

In the mammalian sperm head, the nucleus is tightly associated with the calyx, a cell type-specific cytoskeletal structure. Previously, we have identified and characterized some basic proteins such as calicin and cylicins I and II as major calyx components of bovine and human spermatids and spermatozoa. Surprisingly we have now discovered another calyx constituent which by amino acid sequencing and cDNA cloning was recognized as a novel isoform of the widespread beta subunit of the heterodimeric actin-binding "capping protein" (CP). This polypeptide, CP beta3, of sperm calices, is identical with the beta2 subunit present in diverse somatic cell types, except that it shows an amino-terminal extension of 29 amino acids and its mRNA is detected only in testis and, albeit in trace amounts, brain. This CP beta3 mRNA contains the additional sequence, encoded by exon 1 of the gene, which is missing in beta2 mRNAs. Antibodies specific for the beta3 amino-terminal addition have been used to identify the protein by immunoblotting and to localize it to the calyx structure by immunofluorescence microscopy. We conclude that in spermiogenesis the transcription of the gene encoding the beta1, beta2, and beta3 CP subunits is regulated specifically to include exon 1 and to give rise to the testis isoform CP beta3, which is integrated into the calyx structure of the forming sperm head. This surprising finding of an actin-binding protein isoform in an insoluble cytoskeletal structure is discussed in relation to the demonstrated roles of actin and certain actin-binding proteins, such as Limulus alpha-scruin, in spermiogenesis and spermatozoa.

Analysis of connexin43 gene expression induced by retinoic acid in F9 teratocarcinoma cells

All-trans retinoic acid (10(-7) M) induces cell-cell communication and expression of the gap junction protein connexin43 in mouse F9 teratocarcinoma cells. Northern blot analysis revealed an increase of connexin43 mRNA after treatment with retinoic acid, accompanied by an increase of the mRNA of collagen IV, a differentiation marker. To address the question at what level gene expression is enhanced by retinoic acid, nuclear run-on experiments were carried out. There was no detectable change in the level of newly transcribed connexin43 mRNA. Therefore, we postulate a post-transcriptional mechanism responsible for the regulation of connexin43 mRNA levels by retinoic acid.

Loss of heterozygosity at the NAD(P)H: quinone oxidoreductase locus associated with increased resistance against mitomycin C in a human bladder carcinoma cell line

The human bladder carcinoma cell line RT112 and the mitomycin C-resistant cell line RT112MMC, derived from RT112 cells, were examined for their expression of NAD(P)H:quinone oxidoreductase (NQOR) and glutathione S-transferases (GSTs). RT112 cells were 40-fold more sensitive towards mitomycin C than RT112MMC cells. The NQOR mRNA level in RT112MMC cells was decreased to 15% as compared to RT112 cells. NQOR enzyme activity was 391 +/- 140 mU/mg protein in RT112 cells, whereas NQOR activity in RT112MMC cells was not measurable. As shown by a fast PCR-based assay and DNA-sequencing, the cell line RT112 is heterozygous, whereas RT112MMC is homozygous for a null allele of the NQOR gene without enzymatic activity. Accordingly, both wild-type and null allele mRNAs were present in RT112 cells, whereas only null allele mRNA was found in RT112MMC. The lack of NQOR enzyme activity in RT112MMC cells was thus associated with loss of heterozygosity at the NQOR locus. By a PCR-RFLP assay, three kidney carcinoma patients without measurable NQOR enzyme activity were shown to be homozygous for the null allele. The PCR assay described here is useful for examination of large numbers of samples. The relative amount of GST-Pi mRNA was decreased by 30% in RT112MMC as compared to RT112, contributing to a diminished level of GST enzyme activity, using CDNB as a substrate, from 95 +/- 62 mU/mg protein in RT112 to 26 +/- 6 mU/mg protein in RT112MMC.

Increase of beta-actin mRNA upon hypotonic perfusion of perfused rat liver

beta-Actin mRNA levels in livers exposed to hypotonic perfusion (from 305 to 225 mosmol/l) for one hour are increased 2-fold relative to albumin mRNA. Like albumin, glyceraldehyde-3-phosphate dehydrogenase and tyrosine aminotransferase mRNAs remain at the levels observed under normotonic conditions. The increase in beta-actin mRNA is interpreted as a cytoskeletal response due to cell swelling.

Distribution of actin-filament bundles in myoid cells, Sertoli cells, and tunica albuginea of rat and mouse testes

Frozen sections of the rat and mouse testes were stained with either FITC-phalloidin or NBD-phallacidin and viewed with conventional fluorescence and confocal laser microscopes in order to demonstrate the arrangement of actin-filament bundles in myoid cells, Sertoli cells and tunica albuginea. Myoid cells are rich in actin-filament bundles crossing at right angles. These bundles running in different directions can also be visualized by means of electron microscopy. Nerve fibers occur in the vicinity of myoid cells, suggesting a neural control of the cell. At Sertoli cell junctions actin filaments occur at the circumference of the cell, where they show a honeycomb pattern. The ratio of the number of Sertoli cells per myoid cell can be calculated by means of confocal microscopy; this technique may provide a new parameter for determining spermatogenic activity. In the tunica albuginea of the juvenile mouse testis, actin filaments are arranged in an alternate fashion.

Developmental changes of expression of non-muscle (beta and gamma) actin mRNAs in the central nervous system studied by in situ hybridization

In situ hybridization of mRNAs for beta- and gamma-cytoplasmic non-muscle actin in the mouse central nervous system revealed their differential expression correlating with the developmental stages. Most intense expression of both isoactin mRNAs at the specific postnatal developmental stage was observed in pyramidal cells of cerebral cortex. Purkinje cells of the cerebellar cortex and facial motor neurons.