Expression of occ1 mRNA in the visual cortex during postnatal development in macaques

Relationships among the hippocampus, dentate gyrus, mammillary body, fornix, and anterior commissure from a viewpoint of elements

To elucidate the relationships among the brain regions belonging to the limbic system, the authors investigated the relationships among the hippocampus, dentate gyrus, mammillary body, and fornix, using the anterior commissure as a control, from a viewpoint of elements. After ordinary dissections at Nara Medical University were finished, the hippocampi, dentate gyri, mammillary bodies, fornices, and anterior commissures were resected from identical cerebra of the subjects. The subjects consisted of 23 men and 23 women, ranging in age from 70 to 101 years (average age = 83.5 ± 7.5 years). After ashing with nitric acid and perchloric acid, element contents were determined by inductively coupled plasma-atomic emission spectrometry. With regard to seven elements of Ca, P, S, Mg, Zn, Fe, and Na, it was examined whether there were significant correlations among the hippocampus, dentate gyrus, mammillary body, fornix, and anterior commissure. It was found that there were extremely or very significant direct correlations among all of the five brain regions of the hippocampus, dentate gyrus, mammillary body, fornix, and anterior commissure in the P content. Likewise, with regard to the Fe content, there were significant direct correlations among the four brain regions belonging to the limbic system, except for the anterior commissure. In both the Ca and Zn contents, there were extremely or very significant direct correlations among the hippocampus, dentate gyrus, and mammillary body of the gray matter.

Prefrontal-enriched SLIT1 expression in Old World monkey cortex established during the postnatal development

To elucidate the molecular basis of the specialization of cortical architectures, we searched for genes differentially expressed among neocortical areas of Old World monkeys by restriction landmark cDNA scanning . We found that mRNA of SLIT1, an axon guidance molecule, was enriched in the prefrontal cortex but with developmentally related changes. In situ hybridization analysis revealed that SLIT1 mRNA was mainly distributed in the middle layers of most cortical areas, robustly in the prefrontal cortex and faintly in primary sensory areas. The lowest expression was in the primary visual area. Analyses of other SLIT (SLIT2 and SLIT3) mRNAs showed preferential expression in the prefrontal cortex with a distinct laminar pattern. By contrast, the receptor Roundabout (ROBO1 and ROBO2) mRNAs were widely distributed throughout the cortex. Perinatally, SLIT1 mRNA was abundantly expressed in the cortex with modest area specificity. Downregulation of expression initially occurred in early sensory areas around postnatal day 60 and followed in the association areas. The prefrontal area-enriched SLIT1 mRNA expression results from a relatively greater attenuation of this expression in the other areas. These results suggest that its role is altered postnatally and that this is particularly important for prefrontal connectivity in the Old World monkey cortex.

DIP2 disco-interacting protein 2 homolog A (Drosophila) is a candidate receptor for follistatin-related protein/follistatin-like 1--analysis of their binding with TGF-β superfamily proteins

Follistatin-related protein (FRP)/follistatin-like 1 (FSTL1) is a member of the follistatin protein family, all of which share a characteristic structure unit found in follistatin, called the FS domain. Developmental studies have suggested that FRP regulates organ tissue formation in embryos. Immunological studies showed that FRP modifies joint inflammation in arthritic disease, and modulates allograft tolerance. However, the principle physiological function of FRP is currently unknown. To address this issue, we cloned four FRP-associated proteins using a two-hybrid cloning method: disco-interacting protein 2 homolog A from Drosophila (DIP2A), CD14, glypican 1 and titin. Only DIP2A was expected to be a membrane receptor protein with intracellular regions. Over-expression of FLAG epitope-tagged DIP2A augmented the suppressive effect of FRP on FBJ murine osteosarcoma viral oncogene homolog (FOS) expression, and the Fab fragment of IgG to FLAG blocked this effect. Knockdown of Dip2a leaded to Fos gene up-regulation, and this was not affected by exogenous FRP. These in vitro experiments confirmed that DIP2A could be a cell-surface receptor protein and mediate a FOS down-regulation signal of FRP. Moreover, molecular interaction analyses using Biacore demonstrated that FRP bound to DIP2A and CD14, and also with proteins of the TGF-β superfamily, i.e. activin, TGF-β, bone morphogenetic protein 2/4 (BMP-2/4), their receptors and follistatin. FRP binding to DIP2A was blocked by CD14, follistatin, activin and BMP-2. FRP blocked the ligand-receptor binding of activin and BMP-2, but integrated itself with that of BMP-4. This multi-specific binding may reflect the broad physiological activity of FRP.

The expression pattern of Follistatin-like 1 in mouse central nervous system development

Follistatin-like 1 (Fstl1), also named TSC-36 (TGF-beta-stimulated clone 36), was first cloned from the mouse osteoblastic MC3T3-E1 cell line and can be up-regulated by TGF-beta. To better study the function of Fstl1 during the development of the mouse central nervous system (CNS), we examined Fstl1 expression in the developing mouse CNS, in detail, by in situ hybridization. Our results show that Fstl1 is strongly expressed in the telencephalon, diencephalon, brainstem, limbic system and spinal cord. In the telencephalon, Fstl1 positive cells are mainly located in the ventricular zone (VZ) and the subventricular zone (SVZ); a relatively weak signal was observed in layers II and III of the neocortex at postnatal stages. Fstl1 expression is robust in the developing hippocampus and persists to P20. In the developing diencephalon and hindbrain, abundant Fstl1 signals were also detected in nuclei including the medial habenular nucleus, the medial dorsal nucleus, the cochlear nuclei and so on. In addition, a strong expression of Fstl1 was detected in the thalamencephalic signal center, as well as in the olfactory cortex from E14.5 to P0. Meanwhile, Fstl1 was expressed in the septal area and the cingulate gyrus of the limbic system after birth. A high level of expression was also observed in the ventral horn of the spinal cord. These results indicate that Fstl1 may play an important role during CNS development in the mouse.

Neocortical areas, layers, connections, and gene expression

Cortical patterns of gene expression provide a new approach to long standing issues of lamination, and area identity and formation. In this review, we summarize recent findings where molecular biological techniques have revealed a small number of area-specific genes in the nonhuman primate cortex. One of these (occ1) is strongly expressed in primary visual cortex and is associated with thalamocortical connections. Another gene, RBP, is more strongly expressed in association areas. It is not clear whether RBP might be linked with any particular connectional system, but several possibilities are raised. We also discuss possible roles of area-specific genes in postnatal development, and conclude with a brief sketch of future directions.

Activity-dependent Expression of occ1 in Excitatory Neurons Is a Characteristic Feature of the Primate Visual Cortex

occ1 is a gene whose expression is particularly abundant in neurons in the macaque primary visual cortex (V1). In the present study, we report that the expression of occ1 mRNA in the macaque neocortex can be classified into two modes. The first mode is associated with excitatory neurons distributed in the major thalamocortical recipient layers that exhibit strong cytochrome oxidase activity. This is highly prominent in V1. The second mode is associated with parvalbumin-positive GABAergic interneurons and is distributed across the macaque neocortex. In V1, monocular deprivation showed that occ1 mRNA expression in excitatory neurons was markedly dependent on afferent activity, whereas that in GABAergic interneurons was not. Cross-species comparison showed specific differences in expression. In marmosets, a strong expression was observed in V1 similarly to macaques. The occ1 mRNA expression, however, was generally weak in the mouse neocortex. In rabbit and ferret cortices, the strong expression was observed only in GABAergic interneurons. We conclude that activity-dependent occ1 mRNA expression in the excitatory neurons of V1 was caused by a novel mechanism acquired by primates after their separation from other lineages.

Occ1 mRNA expression reveals a characteristic feature in the hippocampal CA2 field of adult macaques

The gene occ1 is preferentially expressed in the primary visual cortex in an activity-dependent and developmentally regulated manner. In this report, we show the characteristic distribution of occ1 transcripts in the CA2 subfield of the hippocampal formation in adult monkeys. occ1 mRNA signals were observed selectively in the pyramidal cell layer of CA2. In addition to these signals, a relatively sparse distribution of occ1 was found in the stratum oriens and, occasionally, in the outermost regions of the pyramidal cell layers of both CA1 and CA2. A few labeled cells were detected in CA3. The elevated expression of occ1 in the CA2 subfield provides a new approach for investigating the function of this subregion, whose role has still not been well clarified.