Molecular cloning of cDNA to mRNA for a cerebellar spot 35 protein

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Supralinear Ca2+ signaling by cooperative and mobile Ca2+ buffering in Purkinje neurons

Endogenous high-affinity Ca2+ buffering and its roles were investigated in mouse cerebellar Purkinje cells with the use of a low-affinity Ca2+ indicator and a high-affinity caged Ca2+ compound. Increases in the cytosolic Ca2+ concentration ([Ca2+]i) were markedly facilitated during repetitive depolarization, resulting in the generation of steep micromolar Ca2+ gradients along dendrites. Such supralinear Ca2+ responses were attributed to the saturation of a large concentration (0.36 mM) of a mobile, high-affinity (dissociation constant, 0.37 microM) Ca2+ buffer with cooperative Ca2+ binding sites, resembling calbindin-D28K, and to an immobile, low-affinity Ca2+ buffer. These data suggest that the high-affinity Ca2+ buffer operates as the neuronal computational element that enables efficient coincidence detection of the Ca2+ signal and that facilitates spatiotemporal integration of the Ca2+ signal at submicromolar [Ca2+]i.

Expressions of a calcium-binding protein (spot35/calbindin-D28K) in mouse olfactory cells: possible relationship to neuronal differentiation

We used immunohistochemistry to investigate the expression of spot35/calbindin-D28k (calbindin) in mouse olfactory epithelium during development. Cell stages of immunopositive olfactory cells were determined by comparing the levels of proliferating cell nuclear antigen (PCNA). Calbindin-positive cells were abundant in the middle layer of the epithelium of animals before 2 weeks of age and gradually diminished during development. Only low levels were detectable near the basement membrane in the adult. Changes of calbindin-positive cells in terms of number and distribution were apparently compatible with localization changes of premature olfactory cells. PCNA overlapped calbindin in the nasal mucosa at lower magnifications on stained serial sections and immunohistochemical double staining revealed that calbindin-immunoreactive cells were located mainly just above PCNA-immunoreactive cells in the basal layer of the epithelium. This indicated that calbindin is expressed postmitotically in immature olfactory cells and is lost by mature cells. These findings suggest that calbindin might support the maturation of the olfactory cells, such as the projection of the neuronal processes, by stabilizing intracellular calcium ions in immature cells.

The POU domain transcription factor Brn-2 is required for the determination of specific neuronal lineages in the hypothalamus of the mouse

We generated mice carrying a loss-of-function mutation in Brn-2, a gene encoding a nervous system specific POU transcription factor, by gene targeting in embryonic stem cells. In homozygous mutant embryos, migratory precursor cells for neurons of the paraventricular nuclei (PVN) and the supraoptic nuclei (SO) of the hypothalamus die at approximately E12.5. All homozygous mutants suffered mortality within 10 days after birth, possibly because of a complete deficiency of these neurons in the hypothalamus. Although neither developmental nor histological abnormalities were observed in heterozygous mice, the levels of expression of vasopressin and oxytocin in the hypothalamus of these animals were half these of wild-type mice. These results strongly suggest that Brn-2 plays an essential role in the determination and development of the PVN and SO neuronal lineages in the hypothalamus.

The effect of castration on tumor growth rate and cell kinetics in hormone sensitive and hormone insensitive rat prostatic adenocarcinomas

Cell kinetics were measured in vivo in four experimental rat prostatic adenocarcinomas grown in normal or castrated rats. The aim was to investigate the effect of castration on growth rate and cell kinetics in hormone sensitive and hormone insensitive prostatic carcinomas. We used two anaplastic, hormone insensitive, fast growing tumors (Dunning R-3327-AT1 H and E), as well as two well differentiated, hormone sensitive, slow growing tumors (R-3327-H and R-3327-PAP). DNA ploidy, S-phase transit time (Ts), the labeling index (LI) and potential doubling time (Tpot) was determined by dual parameter flow cytometry, after in-vivo labeling, using bromodeoxyuridine (BUdR) and the tumor doubling time (DT) was determined from growth curves. After castration DT in the hormone sensitive H-subline changed from 21.7 days to 82.0 days, and in the PAP-subline from 22.2 days to 33.2 days. No significant changes in Tpot were observed. In the anaplastic tumors no differences in neither DT nor Tpot were seen. The cell loss factor (CLF) was relatively low in the two anaplastic tumors (0.55-0.59) compared to the well differentiated tumors. The CLF was unaffected by castration in the poorly differentiated tumors, whereas it increased significantly (from 0.75 to 0.92, P = 0.005) after castration in the H-tumor, and showed a non-significant increase in the PAP-tumor. This implies that the decrease in tumor growth in the hormone sensitive tumors is due to an increase in cell death, not a decrease in cell proliferation. These data indicate that CLF is the dominating factor in the reduced growth following androgen ablation in an androgen sensitive tumor. This study suggests that Tpot might be an additional predictor of a tumors proliferating rate and it may provide important information of the human prostatic cancer.

A new soluble brain-specific protein: identification and partial purification

A new soluble 170-kDa protein (BP170) was found to be present exclusively in the brain of all the vertebrates that we studied by Western immunoblotting. It was not detected in peripheral rat tissues, including heart, kidney, liver, spleen, lung, muscle, adrenal, intestinal mucosa, sciatic nerve, or pituitary. In rat brain, its regional distribution was found to be heterogeneous, with its highest concentration in the cerebrum and its lowest in the hypothalamus, and 89% of it was in the post-microsomal fraction. BP170 constitutes at least 0.05% of the total brain cytosol proteins. Its level increases during development, being the lowest at 5 days and the highest at 90 days postnatal. BP170 is a single-chain polypeptide. It could be partially purified by precipitation with polyethylene glycol followed by column chromatography on Q Sepharose. Although BP170 was identified by an antiserum against puromycin-sensitive aminopeptidase (PSA), the two proteins differ in molecular weight, chromatographic properties, regional and subcellular distribution, developmental changes, immunoreactivity, and enzyme activity. Self-incubation or trypsin treatment of the partially purified BP170 generates no PSA activity, indicating that BP170 is not a PSA precursor. Furthermore, BP170 is neither an inhibitor nor an activator of PSA. Our data suggest that BP170 is a novel brain-specific protein not previously described.

Gene expression in cells of the central nervous system

This review summarized a part of our studies over a long period of time, relating them to the literature on the same topics. We aimed our research toward an understanding of the genetic origin of brain specific proteins, identified by B. W. Moore and of the high complexity of the nucleotide sequence of brain mRNA, originally investigated by W. E. Hahn, but have not completely achieved the projected goal. According to our studies, the reason for the high complexity in the RNA of brain nuclei might be the high complexity in neuronal nuclear RNA as described in the Introduction. Although one possible explanation is that it results from the summation of RNA complexities of several neuronal types, our saturation hybridization study with RNA from the isolated nuclei of granule cells showed an equally high sequence complexity as that of brain. It is likely that this type of neuron also contains numerous rare proteins and peptides, perhaps as many as 20,000 species which were not detectable even by two-dimensional PAGE. I was possible to gain insight into the reasons for the high sequence complexity of brain RNA by cloning the cDNA and genomic DNA of the brain-specific proteins as described in the previous sections. These data provided evidence for the long 3'-noncoding regions in the cDNA of the brain-specific proteins which caused the mRNA of brain to be larger than that from other tissues. During isolation of such large mRNAs, a molecule might be split into a 3'-poly(A)+RNA and 5'-poly(A)-RNA. In the studies on genomic DNA, genes with multiple transcription initiation sites were found in brain, such as CCK, CNP and MAG, in addition to NSE which was a housekeeping gene, and this may contribute to the high sequence complexity of brain RNA. Our studies also indicated the presence of genes with alternative splicing in brain, such as those for CNP, MAG and NGF, suggesting a further basis for greater RNA nucleotide sequence complexity. It is noteworthy that alternative splicing of the genes for MBP and PLP also produced multiple mRNAs. Such a mechanism may be a general characteristic of the genes for the myelin-specific proteins produced by oligodendrocytes. In considering the high nucleotide sequence complexity, it is interesting that MAG and S-100 beta genes etc. possess two additional sites for poly(A).(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of gene expression of calbindin in the brain of adult rats

Localization of gene expression of calbindin, a cytosolic calcium-binding protein, was examined throughout the adult rat brain by in situ hybridization with cDNA probes. The gene was expressed most intensely in the Purkinje cells in the cerebellum, intensely in the granule cells of the dentate gyrus, and moderately in the inferior olivary nucleus, in the nuclei of the trapezoid body, in the medial part of the lateral habenular nuclei, entorhinal cortex and in the mammillary nuclei. In addition, weak expression of the gene was widespread in the forebrain and brainstem gray matter, and also in small cells in the spinal posterior horn as well as the ependymal cells. The widespread and heterogeneous expression of the gene in the brain suggests that calbindin is differentially involved in calcium-regulated phenomena in different neurons.

Transient appearance of Ca-binding protein (spot 35-calbindin) in bronchial epithelial cells, thyroid parafollicular cells and thymic epithelial cells during the development of rats

Tracheobronchial epithelium, thyroid organ, thymus, of the developing rats were examined by immunohistochemistry using anti-spot 35 calbindin-antiserum. At E 14, weak to moderate immunoreactivity for spot 35-calbindin was detected in the airway epithelia of the distal half of the trachea and the extrapulmonary bronchus. The immunoreactive cells increased in intensity at E 16-E 21, but decreased markedly after birth. These cells were non-ciliated cells and comprised a majority of the epithelial cells especially in the ventral/cartilaginous portion of the airway. They were characterized by microvilli, vacuoles, granular and agranular endoplasmic reticulum. Typical ciliated cells, which were much less numerous than the immunopositive non-ciliated cells, were immunonegative. In thyroid gland, calbindin-immunoreactive cells first appeared at E 18. They increased in number at E 20-P 1 and decreased gradually after P 7. These cells were the parafollicular cells characterized by numerous secretory granules and situated in close proximity to the basal surface of the follicular cells. In the thymus, immunoreactive cells appeared in the thymic medulla at E 20. They increased in number at P 1, but decreased gradually after P 7. They were stellate in shape and had vesicles, vacuoles, intermediate filaments and represented a subpopulation of thymic reticular epithelial cells. Such a transient appearance of spot 35-calbindin in these cells suggests that this protein may be involved in the regulation of differentiation or may be involved in the process of secretion during the limited developmental period.

In situ hybridization histochemistry of Spot 35 protein, a calcium-binding protein, in the rat brain

Using in situ hybridization, we analyzed the localization of mRNA for Spot 35 protein (Spot 35), a calcium-binding protein of the EF-hand type, in the rat cerebellum at various developmental stages. A cDNA fragment corresponding to part of the 3'-noncoding region was 35S-labeled and used as a hybridization probe. Autoradiographic signals for Spot 35 mRNA were detected in all the Purkinje cells, but not in any other neurons or glial cells in the adult rat cerebellum. There was no significant difference in signal intensity among individual cells. The signals were observed exclusively in Purkinje cell bodies, but not in their processes, in striking contrast to previous immunohistochemical studies in which Spot 35 protein was demonstrated in both cell bodies and processes. In the time-course study, signals for Spot 35 mRNA were detected in Purkinje cell bodies weakly at embryonic day 19, thereafter more intensely at more developed stages and most intensely at postnatal days 30 and 60 (adulthood). The signal intensities of individual cells were similar at each of these developmental stages except for the very early stages at which signals were weak and slightly variable among cells. These findings, especially that of the characteristic coordinated expression of Spot 35 mRNA at given stages, should prove useful in studies of degenerative diseases in the cerebellum in experimental animals and man. A weak expression of Spot 35 mRNA in some of non-Purkinje cells was also noted.

Transient expression of a calcium-binding protein (spot 35-calbindin) and its mRNA in the immature pituicytes of embryonic rats

Spot 35 protein is a Ca-binding protein originating from the rat cerebellum; it is now referred to spot 35-calbindin. This protein is expressed in immature pituicytes of the neurohypophyseal anlage in the E11-E18 rat embryo. The gene expression of spot 35-calbindin was detected by in-situ hybridization analysis only at stage E11-E12. Profiles of spot 35-positive nerve fibers of a neurosecretory nature were found in anlage at stage E16. At this stage, some immature pituicytes are partially immunopositive for spot 35-calbindin only in their peripheral cytoplasm; others are immunonegative. At birth and thereafter through adulthood, abundant nerve fibers are the sole structures immunoreactive for spot 35-calbindin; all the pituicytes are immunonegative, resulting in a light-microscopic appearance of numerous immunonegative round profiles, corresponding to pituicytes, and capillaries embedded in the granularly immunostained neurohypophysis. The present findings suggest that, during specific embryonic stages, immature pituicytes exert some as yet unidentified roles related to Ca-mediated functions involving the expression of spot 35-calbindin.

Transient appearance of immunoreactivity for Ca-binding protein (spot 35-calbindin) in small principal neurons in the superior cervical ganglion of pre-weanling rats

Immunoreactivity for rat cerebellar calbindin, termed spot 35-calbindin, is transiently expressed largely in numerous small principal neurons of the superior cervical ganglion in pre-weanling rats and disappears by the fourth postnatal week. Preganglionic denervation results in a slower rate of disappearance of the immunoreactivity in ganglion neurons. This finding suggests that small principal neurons in the superior cervical ganglion may exert some yet to be determined Ca-mediated functions that are not shared with larger neurons at the pre-weanling stage.

Synaptic receptors and intracellular signal transduction in the cerebellum

Glutamate receptor subtypes mediating excitatory synaptic neurotransmission in the cerebellar cortex are briefly reviewed from molecular biological, electrophysiological and pharmacological points of view. In particular, molecular biological findings of a novel family of AMPA-selective glutamate receptors are introduced, and the pharmacological and electrophysiological properties and the identity of cerebellar N-methyl-D-aspartate-sensitive receptors probably existing on Purkinje cells are discussed in comparison with well-established cerebral NMDA receptors. As possible intracellular mechanisms of the long-term depression of parallel fiber-Purkinje cell neurotransmission, the perspective of the roles of novel messengers, nitric oxide and arachidonic acid, is particularly commented based on recent information about cerebral long-term events. The specificity and possible independence of cerebellar excitatory amino acid receptors and linked intracellular second messengers are also suggested, taking the highly active guanylate cyclase system in Purkinje cells and other cerebellum-specific proteins into consideration.

Calbindin immunoreactivity in sensory and autonomic ganglia in the guinea pig

Immunoreactivity (IR) for the calcium binding protein, calbindin, was localized in sensory ganglia (nodose, trigeminal and dorsal root), in parasympathetic ganglia (otic and sphenopalatine) in sympathetic chain ganglia and in sympathetic pre-vertebral ganglia of guinea pig. In sensory ganglia, fine nerve fibres with calbindin-IR surrounded the majority of cell bodies, a low proportion of which were themselves reactive. In cranial parasympathetic and in sympathetic chain ganglia, a small proportion of nerve cells was surrounded with baskets of calbindin-IR nerve fibres, but very few cell bodies were reactive. In prevertebral sympathetic ganglia, dense networks of terminals surrounded many cell bodies, but few somata were themselves reactive. In the coeliac and inferior mesenteric ganglia, the calbindin-IR nerve fibres surrounded somatostatin-IR cell bodies, but not those with neuropeptide Y-IR. It is concluded that specific subgroups of peripheral autonomic and sensory neurones have calbindin-IR.

Ontogenic changes in expression of neuron-specific enolase (NSE) and its mRNA in the Purkinje cells of the rat cerebellum: immunohistochemical and in situ hybridization study

In the postnatal development of rats, neuron-specific enolase (NSE)-immunoreactivity first appeared in the Purkinje cells at postnatal day 3 (P3) and elevated strikingly at P9 when almost all the Purkinje cell somata and dendrites exhibited the intense immunoreactivity. In situ hybridization signals for NSE-mRNA also increased markedly in the Purkinje cell somata from P3 to P9. These results indicate that the NSE synthesis is transiently enhanced in the Purkinje cells from P3 to P9 at the transcriptional level. At P11 and thereafter NSE-immunoreactive Purkinje cells decreased in number, and no significant immunoreaction was detected in their somata and dendrites in the adulthood, whereas distinct immunoreactivity for NSE was still detected in the Purkinje cell axons until the adult stage. However, the signals for NSE-mRNA were still localized in the Purkinje cell somata after P11 until the adult. The possible involvement of the negative translational control and/or the axoplasmic transport of NSE was briefly discussed to explain this discrepancy between NSE-immunoreactivity and its mRNA expression in the Purkinje cells in the late postnatal development.

Expression of immunoreactivity for Ca-binding protein, spot 35 in the interstitial cell of the rat pineal organ

In the rat pineal organ numerous stellate cells exhibited intense immunoreactivity for calcium-binding spot 35 protein. Because of their peculiar shape and ultrastructure, identical to those of intrapineal S-100-immunoreactive cells, the spot 35-immunoreactive stellate cells were identified as the interstitial cells. The comparison of the morphology and population density of spot 35-, S-100-, and GFAP (glial fibrillar acidic protein)-immunoreactive cells, suggests that spot 35-immunoreactive cells represent a major subpopulation of the interstitial cells, all of which are S-100-immunoreactive and generally considered to be of glial nature, while GFAP-immunoreactive cells represent a minor subpopulation of the interstitial cells located in the proximal part close to the pineal stalk. This is the first report describing the occurrence of the calcium-binding protein in cells of glial nature.

Isolation, partial amino acid sequence, and immunohistochemical localization of a brain-specific calcium-binding protein

A calcium-binding protein (protein 10) having a molecular mass of 29 kDa and an isoelectric point of 5.3 was purified from guinea pig brain. The amino acid sequence of fragments from proteolytic digestion of protein 10 revealed an 86% sequence identity with a calcium-binding protein (calretinin) found in chicken retina. Polyclonal antibodies against protein 10 revealed a specific distribution of this protein within sensory neurons of auditory, visual, olfactory, nociceptive, and gustatory systems as well as other discrete neuronal circuits in rat and guinea pig brain, whereas no specific label was observed in any of several peripheral tissues examined.

Cloning and analysis of calbindin-D28K cDNA and its expression in the central nervous system

The vitamin D-dependent calcium-binding protein (CaBP), calbindin-D28K (CaBP28K), is present in the central nervous system (CNS), the sensory system, and kidneys of mammals and birds. Recent studies have indicated that several other CaBPs of very similar Mrs are also present in the CNS. This study was carried out to establish the relationship between CaBP28K and other CaBP, particularly spot 35, to provide a basis for further studies on the tissue-specific regulation and distribution of CaBP28K. A cloned pC28 cDNA was isolated from a rat brain expression library using synthetic oligodeoxyribonucleotides (oligos) complementary to rat spot-35 mRNA. This pC28 cDNA had an open reading frame (ORF) of 783 nucleotides (nt) coding for a 261-aa, 30-kDa protein. There was 100% homology between the pC28 sequence and that of the CaBP28K isolated from rat brain cDNA library using a chicken intestinal CaBP28K probe (Hunziker and Schrickel, 1988). Thus the aa and nt sequences of rat CaBP28K and spot 35 are identical. Primer extension studies and Northern analyses show that the major species of CaBP28K mRNA contains a 5'-untranslated region of 132 nt, a coding region of 261 codons and a 3'-untranslated region of 804 nt without the poly(A) tail. The rat CaBP28K probe hybridizes to one major RNA species (1.9 kb) and two minor ones (2.8 and 3.2 kb) in the cerebellum, hippocampus, retina and kidney. This distribution correlates well with the distribution of CaBP28K itself in these organs. Comparison of the genomic organization of the CaBP28K gene with that of other members of the 'EF-hand' CaBP family emphasizes that the CaBP28K gene diverged from the others at the first duplication of the gene encoding one CaBP domain. All the members of the 'EF-hand' gene CaBP family evolved by exon shuffling and specific genomic rearrangements.

Developmental and regional changes of mRNA for a cerebellar protein (spot 35) in the rat brain

Spot 35 protein is a cerebellar Ca-binding protein. Because Southern blot analysis showed evidence for the nucleotide sequence of spot 35 protein cDNA in the rat genome, we applied cDNA to quantitate the mRNA of rat spot 35 protein. The size of this mRNA was about 1,900 nucleotides in length, and that of mRNA from bovine cerebellum was larger. We also examined the developmental changes and regional distribution of spot 35 protein mRNA in rat brains by dot-blot analysis using cDNA as a probe. During postnatal days 1-20, a rapid increase of mRNA levels was observed. Further, the level of mRNA for spot 35 protein was found in the cerebellum and was negligible in the cerebral cortex, striatum, and hippocampus.