Intracortical regionality represented by specific transcription for a novel protein, latexin

Origin and development of the claustrum in rhesus macaque

Understanding the claustrum's functions has recently progressed thanks to new anatomical and behavioral studies in rodents, which suggest that it plays an important role in attention, salience detection, slow-wave generation, and neocortical network synchronization. Nevertheless, knowledge about the origin and development of the claustrum, especially in primates, is still limited. Here, we show that neurons of rhesus macaque claustrum primordium are generated between embryonic day E48 and E55 and express some neocortical molecular markers, such as NR4A2, SATB2, and SOX5. However, in the early stages, it lacks TBR1 expression, which separates it from other surrounding telencephalic structures. We also found that two waves of neurogenesis (E48 and E55) in the claustrum, corresponding to the birthdates of layers 6 and 5 of the insular cortex, establish a "core" and "shell" cytoarchitecture, which is potentially a basis for differential circuit formation and could influence information processing underlying higher cognitive functions of the claustrum. In addition, parvalbumin-positive interneurons are the dominant interneuron type in the claustrum in fetal macaque, and their maturation is independent of that in the overlaying neocortex. Finally, our study reveals that the claustrum is likely not a continuance of subplate neurons of the insular cortex, but an independent pallial region, suggesting its potentially unique role in cognitive control.

Differential distribution of inhibitory neuron types in subregions of claustrum and dorsal endopiriform nucleus of the short-tailed fruit bat

Few brain regions have such wide-ranging inputs and outputs as the claustrum does, and fewer have posed equivalent challenges in defining their structural boundaries. We studied the distributions of three calcium-binding proteins-calretinin, parvalbumin, and calbindin-in the claustrum and dorsal endopiriform nucleus of the fruit bat, Carollia perspicillata. The proportionately large sizes of claustrum and dorsal endopiriform nucleus in Carollia brain afford unique access to these structures' intrinsic anatomy. Latexin immunoreactivity permits a separation of claustrum into core and shell subregions and an equivalent separation of dorsal endopiriform nucleus. Using latexin labeling, we found that the claustral shell in Carollia brain can be further subdivided into at least four distinct subregions. Calretinin and parvalbumin immunoreactivity reinforced the boundaries of the claustral core and its shell subregions with diametrically opposite distribution patterns. Calretinin, parvalbumin, and calbindin all colocalized with GAD67, indicating that these proteins label inhibitory neurons in both claustrum and dorsal endopiriform nucleus. Calretinin, however, also colocalized with latexin in a subset of neurons. Confocal microscopy revealed appositions that suggest synaptic contacts between cells labeled for each of the three calcium-binding proteins and latexin-immunoreactive somata in claustrum and dorsal endopiriform nucleus. Our results indicate significant subregional differences in the intrinsic inhibitory connectivity within and between claustrum and dorsal endopiriform nucleus. We conclude that the claustrum is structurally more complex than previously appreciated and that claustral and dorsal endopiriform nucleus subregions are differentially modulated by multiple inhibitory systems. These findings can also account for the excitability differences between claustrum and dorsal endopiriform nucleus described previously.

Bone Microenvironment Changes in Latexin Expression Promote Chemoresistance

Although docetaxel is the standard of care for advanced prostate cancer, most patients develop resistance to docetaxel. Therefore, elucidating the mechanism that underlies resistance to docetaxel is critical to enhance therapeutic intervention. Mining cDNA microarray from the PC-3 prostate cancer cell line and its docetaxel-resistant derivative (PC3-TxR) revealed decreased latexin (LXN) expression in the resistant cells. LXN expression was inversely correlated with taxane resistance in a panel of prostate cancer cell lines. LXN knockdown conferred docetaxel resistance to prostate cancer cells in vitro and in vivo, whereas LXN overexpression reduced docetaxel resistance in several prostate cancer cell lines. A mouse model of prostate cancer demonstrated that prostate cancer cells developed resistance to docetaxel in the bone microenvironment, but not the soft tissue microenvironment. This was associated with decreased LXN expression in prostate cancer cells in the bone microenvironment compared with the soft tissue microenvironment. It was identified that bone stromal cells decreased LXN expression through methylation and induced chemoresistance in prostate cancer in vitro These findings reveal that a subset of prostate cancer develops docetaxel resistance through loss of LXN expression associated with methylation and that the bone microenvironment promotes this drug resistance phenotype.Implications: This study suggests that the LXN pathway should be further explored as a viable target for preventing or reversing taxane resistance in prostate cancer. Mol Cancer Res; 15(4); 457-66. ©2017 AACR.

Latexin inhibits the proliferation of CD133+ miapaca-2 pancreatic cancer stem-like cells

Background

An increasing number of evidence suggests that pancreatic cancer contains cancer stem cells (CSCs), which may be relevant to the resistance of chemotherapy. Latexin (Lxn) is a negative regulator of stem cell proliferation and we investigate the effects of Lxn on CD133+ pancreatic cancer stem-like cells.

Methods

CD133+ miapaca-2 cells, a human pancreatic carcinoma cell line, were isolated and sorted by magnetic activated cell sorting and flow cytometry. The capacity for self-renewal, proliferation, and tumorigenicity of CD133+ miapaca-2 cells was determined by the floating spheres test and tumor xenograft assays. Protein and mRNA expression of Lxn in CD133+ and CD133- miapaca-2 cells were detected by Western blotting and qRT-PCR, respectively. After CD133+ miapaca-2 cells were treated with Lxn in serum-free medium (SFM), cell proliferation was assayed with a Cell Counting Kit 8 (CCK-8) and apoptosis was analyzed by flow cytometry. The protein and mRNA expression levels of Bcl-2, bax, and c-myc were also analyzed.

Results

We successfully isolated CD133+ miapaca-2 cells that exhibited the capacity for self-renewal in SFM, a proliferation potential in DMEM supplemented with FBS, and high tumorigenicity in nude mice. Lxn protein and mRNA expression levels in CD133+ miapaca-2 cells were significantly lower than those in CD133- cells. Lxn-treated CD133+ miapaca-2 cells exhibited increased apoptosis and low proliferation activity, down-regulation of Bcl-2 and c-myc expression, and up-regulation of Bax expression in a dose-dependent manner.

Conclusions

Lxn induces apoptosis and inhibits the proliferation of CD133+ miapaca-2 cells. These changes are associated with down-regulation of Bcl-2 and c-myc and up-regulation of Bax.

Clinical implications of AGBL2 expression and its inhibitor latexin in breast cancer

Background

We investigated the expression status of AGBL2 and its inhibitor latexin in breast cancer stem cells and its clinical implications in order to lay a foundation for managing breast cancer.

Methods

CD44+/CD24- tumor cells (CSC) from clinical specimens were sorted using flow cytometry. AGBL2 expression status was detected in CSC and 126 breast cancer specimens by western blot and immunohistochemistry staining. The relationship between the AGBL2 protein and clinicopathological parameters and prognosis was subsequently determined.

Result

As a result, CSC are more likely to generate new tumors in mice and cell microspheres that are deficient in non-obese diabetic/severe combined immunodeficiency mice (NOD/SCID) compared to the control group. The AGBL2 protein was expressed higher in CSC induced to epithelial to mesenchymal transition (EMT) when compared to the control cells, and was found to be related to CSC chemotherapy resistance. After Spearman regression correlation analysis, AGBL2 was observed to be related to clinical stage, histological stage, and lymph node metastasis. In the Cox regression test, the AGBL2 protein was detected as an independent prognostic factor. Through immunoprecipitation, AGBL2 and latexin could form immune complexes.

Conclusions

These results demonstrate that AGBL2 is a latexin-interacting protein that regulates the tubulin tyrosination cycle and is a potential target for intervention.

Latexin exhibits tumor suppressor potential in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary cancer of the liver and latexin is downregulated in several types of human cancer. However, latexin expression in HCC remains unknown. mRNA expression of latexin in HCC samples and HCC-derived cell lines was detected by semi‑quantitative PCR and real-time PCR, while protein expression was assessed by immunohistochemistry. The role of latexin in the regulation of the proliferation of HCC-derived cells was investigated both in vitro and in vivo. Flow cytometry was used to differentiate cell cycle distribution in SK-hep-1 and YY-8103. In a total of 60 paired HCC specimens, compared with adjacent non-cancer tissues, latexin mRNA was downregulated in 42 specimens. Immunohistochemical analysis showed a significant reduction in latexin expression in HCC compared to control tissues. Overexpression of latexin inhibited SK-hep-1 and HepG2 cellular colony formation and tumor growth. Conversely, YY‑8103 and Focus cells transfected with shRNA enhanced colony formation and tumor growth. Latexin overexpression promoted cell cycle arrest in the G0/G1 phase in SK-hep-1 and silencing of latexin promoted the cell cycle transition from G0/G1 phase to S phase in YY-8103. The cyclin-dependent kinase inhibitors (CDKIs) (p21Cip1, p27Kip1, p15INK4B), cyclin D1 and cyclin E were shown to be differentially expressed in latexin-overexpressed cells and latexin-silenced cells. These results indicated that latexin may be an effective target for gene therapy.

Retinoic acid represses invasion and stem cell phenotype by induction of the metastasis suppressors RARRES1 and LXN

The mouse haematopoietic stem cell (SC) regulator Latexin (LXN) is the only known homologue of the retinoic acid receptor responder 1 (RARRES1) gene. Both genes lie adjacent on chromosome 3 and differ mostly by the presence of a transmembrane domain in RARRES1. Despite their homology, it is not known whether they possess similar regulatory mechanisms, cellular localization and function. Here, we identified RARRES1 and LXN as highly significantly downregulated genes in human prostate SCs, whose expression was induced by the pro-differentiation agent all-trans retinoic acid (atRA). AtRA induced expression in the most differentiated cells compared with the SC fraction, suggesting that this subpopulation was less responsive to atRA. Small interfering RNA suppression of RARRES1 and LXN enhanced the SC properties of primary prostate cultures, as shown by a significant increase in their colony-forming ability. Expression of both RARRES1 and LXN was co-ordinately repressed by DNA methylation in prostate cancer cell lines and inhibition of RARRES1 and LXN increased the invasive capacity of primary prostate cultures, which also fully rescued an inhibitory effect induced by atRA. Moreover, we showed that RARRES1 and LXN reside within different sub-cellular compartments, providing evidence that RARRES1 is not a plasma membrane protein as previously supposed but is located primarily in the endoplasmic reticulum; whereas LXN was detected in the nucleus of prostate epithelial cells. Thus, LXN and RARRES1 are potential tumour suppressor genes, which are co-ordinately regulated, SC-silenced genes functioning to suppress invasion and colony-forming ability of prostate cancer cells; yet the proteins reside within different sub-cellular compartments.

The hematopoietic stem cell regulatory gene latexin has tumor-suppressive properties in malignant melanoma

Despite recent advancements in therapy, melanoma still remains a highly lethal skin cancer. A better understanding of the genetic and epigenetic changes responsible for melanoma formation and progression could result in development of more effective treatments. Advanced melanomas are known to exhibit widespread promoter region CpG island methylation leading to inactivation of key tumor suppressor genes. Meta-analyses of relevant microarray data sets revealed the hematopoietic stem cell regulator gene Latexin (LXN) to be commonly down regulated in approximately 50% of melanomas. The CpG island in the promoter region of LXN was almost universally hypermethylated in melanoma cell lines and tumors and treatment of the cell lines with the demethylating drug, 5-Aza-2-deoxycytidine, resulted in increased LXN expression. In this paper, we demonstrate that exogenous expression of LXN in melanoma cell lines results in a significant inhibition of tumor cell proliferation. In addition, we show that the increased expression of LXN in these lines correlates with reduction in expression levels of stem cell transcription factors OCT4, NANOG, SOX2, KLF4 and MYCN indicating that LXN may exert its tumor suppressive function by altering the stem cell like properties of melanoma cells.

Pallio-pallial tangential migrations and growth signaling: new scenario for cortical evolution?

Observations accruing in recent years imply that the areal patterning and size dimensioning of the mammalian neocortex are influenced by diverse sets of tangentially migrating glutamatergic neurons that invade the cortical plate and, in so doing, modify the properties of the neopallial proliferative compartments. This developmental scenario sheds new light upon the old issue of how the mammalian neocortex evolved its more complex structure from nonmammalian antecedent forms. In reviewing these novelties, I first point out the topological position of the neopallial island as a central component of the pallium in all gnathostomes, surrounded by a ring of prospective allocortical pallial regions and a more distant set of peripheral neighboring forebrain areas. Early patterning arises from the periphery via passive planar signaling. This process probably establishes the pallium field and its basic island plus allocortical ring organization, as well as a rough prepatterning of some regional subareas. Afterwards, patterning and modulated growth are also actively influenced by the convergence of separate streams of tangentially migrating subpial cells (partly peripheral and partly allocortical in origin) which collectively form the Cajal-Retzius neuronal population in layer I. Effects of these cells include the inside-out stratification of the cortical plate and they may also contribute to the evolutionary emergence of the 6-layered neocortical structure. The most recent addition to our knowledge of pallio-pallial migrations is the existence of a subsequent deep tangential migration of ventropallial cells into the neopallial primordium, whose signaling influence upon local progenitors magnifies the cortex population by 20%. These glutamatergic cells dispersedly invade the entire cortex but largely die postnatally. The crucial implications of these data for comparative thinking on mammalian neocortex evolution and interpretation of potential homologs in sauropsids are explored. Finally, a new conjecture regarding a possible role of the hitherto disregarded lateral pallium is advanced.

Nerve injury evoked loss of latexin expression in spinal cord neurons contributes to the development of neuropathic pain

Nerve injury leads to sensitization mechanisms in the peripheral and central nervous system which involve transcriptional and post-transcriptional modifications in sensory nerves. To assess protein regulations in the spinal cord after injury of the sciatic nerve in the Spared Nerve Injury model (SNI) we performed a proteomic analysis using 2D-difference gel electrophoresis (DIGE) technology. Among approximately 2300 protein spots separated on each gel we detected 55 significantly regulated proteins after SNI whereof 41 were successfully identified by MALDI-TOF MS. Out of the proteins which were regulated in the DIGE analyses after SNI we focused on the carboxypeptidase A inhibitor latexin because protease dysfunctions contribute to the development of neuropathic pain. Latexin protein expression was reduced after SNI which could be confirmed by Western Blot analysis, quantitative RT-PCR and in-situ hybridisation. The decrease of latexin was associated with an increase of the activity of carboxypeptidase A indicating that the balance between latexin and carboxypeptidase A was impaired in the spinal cord after peripheral nerve injury due to a loss of latexin expression in spinal cord neurons. This may contribute to the development of cold allodynia because normalization of neuronal latexin expression in the spinal cord by AAV-mediated latexin transduction or administration of a small molecule carboxypeptidase A inhibitor significantly reduced acetone-evoked nociceptive behavior after SNI. Our results show the usefulness of proteomics as a screening tool to identify novel mechanisms of nerve injury evoked hypernociception and suggest that carboxypeptidase A inhibition might be useful to reduce cold allodynia.

Latexin expression is downregulated in human gastric carcinomas and exhibits tumor suppressor potential

Background

Latexin, also known as endogenous carboxypeptidase inhibitor (CPI), has been found to inhibit mouse stem cell populations and lymphoma cell proliferation, demonstrating its potential role as a tumor suppressor. Our previous study also suggested a correlation between latexin expression and malignant transformation of immortalized human gastric epithelial cells. Here, we examined latexin expression in human gastric carcinomas and investigated the effect of differential latexin expression on proliferation of gastric cancer cells in vitro and in vivo.

Methods

Monoclonal antibody against human latexin was prepared and immunohistochemical analysis was performed to detect latexin expression in 41 paired gastric carcinomas and adjacent normal control tissues. Human gastric cancer cells MGC803 (latexin negative) stably transfected with LXN gene and BGC823 cells (latexin positive) stably transfected with antisense LXN gene were established for anchorage-dependent colony formation assay and tumorigenesis assay in nude mice. Differentially expressed genes in response to exogeneous latexin expression were screened using microarray analysis and identified by RT-PCR. Bisulfite sequencing was performed to analyze the correlation of the methylation status of LXN promoter with latexin expression in cell lines.

Results

Immunohistochemical analysis showed significantly reduced latexin expression in gastric carcinomas (6/41, 14.6%) compared to control tissues (31/41, 75.6%) (P < 0.05). Overexpression of LXN gene in MGC803 cells inhibited colony formation and tumor growth in nude mice. Conversely, BGC823 cells transfected with antisense LXN gene exhibited enhanced tumor growth and colony formation. Additionally, several tumor related genes, including Maspin, WFDC1, SLPI, S100P, and PDGFRB, were shown to be differentially expressed in MGC803 cells in response to latexin expression. Differential expression of Maspin and S100P was also identified in BGC823 cells while latexin expression was downregulated. Further bisulfite sequencing of the LXN gene promoter indicated CpG hypermethylation was correlated with silencing of latexin expression in human cells.

Conclusions

Latexin expression was reduced in human gastric cancers compared with their normal control tissues. The cellular and molecular evidences demonstrated the inhibitory effect of latexin in human gastric cancer cell growth and tumorigenicity. These results strongly suggest the possible involvement of latexin expression in tumor suppression.

Tumor suppressor RARRES1 interacts with cytoplasmic carboxypeptidase AGBL2 to regulate the α-tubulin tyrosination cycle

Even though it is among the most commonly methylated loci in multiple cancers, the retinoic acid-induced tumor suppressor retinoic acid receptor responder 1 (RARRES1) has no known function. We now show that RARRES1 is lost in many cancer cells, particularly those with a mesenchymal phenotype, and is a transmembrane carboxypeptidase inhibitor that interacts with ATP/GTP binding protein-like 2 (AGBL2), a cytoplasmic carboxypeptidase. Knockdown of AGBL2 results in a failure of the cell to detyrosinate the C-terminal EEY region of α-tubulin and indicates that it is a candidate for the long sought-after tubulin tyrosine carboxypeptidase important in the regulation of microtubule dynamics. In contrast, knockdown of RARRES1 increases the level of detyrosinated α-tubulin consistent with a role as the cognate inhibitor of AGBL2. We conclude that RARRES1, its interacting partners AGBL2, Eg5/KIF11, another EEY-bearing protein (EB1), and the microtubule tyrosination cycle are important in tumorigenesis and identify a novel area for therapeutic intervention.

Quality control and monitoring for the isolation process of mesenchymal stem cells and their differentiation into osteoblasts

We developed a method of quality control and monitoring for the isolation of mesenchymal stem cells (MSCs) from bone marrow and their differentiation into osteoblasts. After dividing the cell culture process into five groups based on cell types such as MSCs and osteoblasts, we used microarray analysis to select genes with expression profiles characteristic of each group and quantitative polymerase chain reaction for confirming the expression profiles of these genes. Comparing multiple gene expression profiles per cell from quantitative polymerase chain reaction permitted us to distinguish (1) different groups of cell culture including MSCs and osteoblasts; (2) MSCs that had differentiated cells other than osteoblasts such as chondroblasts, adipocytes, or skin-derived fibroblasts; and (3) desirable MSCs from undesirable MSCs occurring under different culture conditions. These findings suggest that it is possible to standardize MSCs and osteoblasts on the basis of multiple gene expression profiles and to check the quality of these cells. We believe that our methods can be applied to cells cultured for transplants.

Polymorphism of the ovocalyxin-32 gene and its association with egg production traits in the chicken

We performed candidate gene analysis to identify SNP in the chicken ovocalyxin-32 (OCX-32) gene in the F(2) resource population, to develop a PCR-RFLP method for genotyping and to evaluate the associations of the gene polymorphism with egg production traits. The F(2) resource population-comprising 272 chickens-was obtained by crossing White Leghorn (WL) males and Rhode Island Red (RIR) females. They were measured for egg production traits and used for candidate gene analysis. Among parental individuals of the F(2) population, 2 novel nonsynonymous polymorphisms (c.267T>G and c.494A>C) and 1 known nonsynonymous polymorphism (c.381G>C) in the coding sequences of the chicken OCX-32 gene were detected. The PCR-RFLP method was used for screening the chickens of the F(2) population. In parental populations, genotype c.267T>G and c.494A>C were segregated within WL and RIR breeds, respectively, but genotype c.381G>C was breed-specific SNP between WL and RIR breeds. A total of 4 haplotypes were constructed based on the 3 SNP in parental populations, and there was no recombination between c.267T>G and c.494A>C. There was a significant association (P < 0.05) between the OCX-32 gene SNP and egg production traits, but there was no significant association between the haplotypes of the OCX-32 gene and egg production traits in the F(2) population. In the present study, there was the most significant association between c.381G>C of the OCX-32 gene and rate of egg production. The current study is the first step to confirm the relationship between OCX-32 gene polymorphisms and egg production traits.

Localization of latexin-immunoreactive neurons in the adult cat cerebral cortex and claustrum/endopiriform formation

The distribution of neurons that are immunoreactive to latexin, which is an endogenous inhibitor of the A/B subfamily of metallocarboxypeptidases, was investigated in the adult cat telencephalon. Latexin-immunoreactive neurons were distributed in the lower layers of the neocortex and adjacent ventral mesocortex, as well as in the claustrum/endopiriform formation. There were marked regional and laminar differences in density and distribution of latexin-immunoreactive neurons in the cerebral cortex. The density followed a roughly lateral-to-medial decreasing gradient: it was high in lateral cortical regions, which included the insular, second somatosensory, and anterior sylvian areas, and in the temporal auditory field; moderate in laterodorsal cortical regions, which included the primary and second auditory fields; and low in dorsal cortical regions, which included visual areas 18 and 19. Latexin-immunoreactive neurons were absent in medial cortical regions, which included the motor, premotor, prefrontal, prelimbic, cingulate, and retrosplenial areas. The lateral-to-medial gradient was apparent even within a single cytoarchitectonic area in certain cortical regions. The allocortex was devoid of latexin-immunoreactive neurons, with the exception of the anteroventral part of the dentate gyrus. The majority of cortical latexin-immunoreactive neurons were localized in layers V and VI and appeared to correspond to the "modified pyramidal cells in the infragranular layers." The remaining latexin-immunoreactive neurons were localized in layer IV, as well as in lower layer III and in the white matter. There were no latexin-immunoreactive neurons from layer I through upper layer III. Latexin-immunoreactive neurons were present in telencephalic structures outside the cerebral cortex, with particularly high density in the claustrum/endopiriform formation. All these features, with the exception of that detected in the archicortex, are compatible with the features observed previously in the rat telencephalon. The similar pattern of distribution of latexin-immunoreactive neurons in several mammalian species from different orders suggests that latexin plays an important role in a specific cortical network.

Molecular contributions to cerebral cortical specification

Evidence is accumulating that decisions of cell fate and commitment to specific regional phenotypes in the cerebral cortex occur through cell interactions that likely begin early in development, perhaps in the proliferative zone. We have focused on the development of the limbic cortex in rats, which includes areas involved in both cognitive and autonomic functions and is marked by expression of the limbic system-associated membrane protein. Transplantation studies show that precursor cells are sensitive to environmental cues which can control expression of area-specific phenotypes, including limbic system-associated protein synthesis and connectivity patterns, but early postmitotic neurons faithfully express traits based on their origin in the donor. We have studied this sensitive period of decision making in vitro. Molecules from the epidermal growth factor family influence dramatically the fate of precursor cells, but only in the presence of matrix molecules. In vivo, both the epidermal growth factor receptor and collagen type IV are expressed in the progenitor cell pool indicating that they can directly affect the initial decisions in differentiation. We suggest that early patterns of gene expression, influenced by environmental cues, are likely to provide a specific framework for subsequent decisions that lead to establishing cortical areas.

Reduced pain sensitivity in mice lacking latexin, an inhibitor of metallocarboxypeptidases

Latexin, the endogenous protein inhibitor of the A/B subfamily of metallocarboxypeptidases, is expressed in small nociceptive neurons in sensory ganglia and in a subset of neurons in the telencephalon. In this study, we generated latexin-deficient mice that exhibited increased tail-flick latency compared to wild-type animals upon noxious heat stimulation. The reduced pain sensitivity in the mutants was rescued by the systemic administration of a plant carboxypeptidase inhibitor that inhibits the A/B subfamily of metallocarboxypeptidases. These findings suggest that latexin is involved in the transmission of pain.

Structure of human carboxypeptidase A4 with its endogenous protein inhibitor, latexin

The only endogenous protein inhibitor known for metallocarboxypeptidases (MCPs) is latexin, a 25-kDa protein discovered in the rat brain. Latexin, alias endogenous carboxypeptidase inhibitor, inhibits human CPA4 (hCPA4), whose expression is induced in prostate cancer cells after treatment with histone deacetylase inhibitors. hCPA4 is a member of the A/B subfamily of MCPs and displays the characteristic alpha/beta-hydrolase fold. Human latexin consists of two topologically equivalent subdomains, reminiscent of cystatins, consisting of an alpha-helix enveloped by a curved beta-sheet. These subdomains are packed against each other through the helices and linked by a connecting segment encompassing a third alpha-helix. The enzyme is bound at the interface of these subdomains. The complex occludes a large contact surface but makes rather few contacts, despite a nanomolar inhibition constant. This low specificity explains the flexibility of latexin in inhibiting all vertebrate A/B MCPs tested, even across species barriers. In contrast, modeling studies reveal why the N/E subfamily of MCPs and invertebrate A/B MCPs are not inhibited. Major differences in the loop segments shaping the border of the funnel-like access to the protease active site impede complex formation with latexin. Several sequences ascribable to diverse tissues and organs have been identified in vertebrate genomes as being highly similar to latexin. They are proposed to constitute the latexin family of potential inhibitors. Because they are ubiquitous, latexins could represent for vertebrate A/B MCPs the counterparts of tissue inhibitors of metalloproteases for matrix metalloproteinases.

Chemically defined feedback connections from infragranular layers of sensory association cortices in the rat

The primary visual (V1), auditory (AI), and somatosensory (SI) cortices are reciprocally connected with their respective sensory association cortices. In the rat, we have previously demonstrated that some of the connections arising from the secondary somatosensory (SII) and parietal insular (PA) cortices and terminating in the SI, are characterized by the expression of latexin, a candidate protein of carboxypeptidase A inhibitor. Here, by using retrograde tracing and latexin-immunohistochemistry, we show that latexin-expressing neurons in other association cortices of different sensory modalities also contribute to the feedback projections to the corresponding primary sensory cortices. These are the lateral part of the secondary visual cortex (V2L), temporal association cortex, and the dorsal and ventral (AIIv) parts of the secondary auditory belt cortex. Within sublayer VIa of the V2L, AIIv and SII, the majority of the V1-, AI- and SI-projecting neurons respectively, are latexin-immunopositive. In contrast to feedback connections, far fewer latexin-expressing neurons participate in callosal or intrahemispheric feedforward connections. The latexin-expressing neurons constitute a virtually completely different population from corticothalamic neurons within the infragranular layers. Given that latexin might participate in the modulation of neuronal activity by controlling the protease activity, latexin-expressing feedback pathways would play a unique role in the modulation of sensory perception.

Distinct neuronal populations specified to form corticocortical and corticothalamic projections from layer VI of developing cerebral cortex

Layer VI of the cerebral cortex contains heterogeneous populations of pyramidal neurons whose axons project either cortically or subcortically. It has been shown that a subset of layer VI neurons expressing latexin projects ipsilaterally to other cortical areas but does not contribute to the corticothalamic projections. Taking advantage of the connectional specificity of latexin-expressing neurons, we here determine whether corticocortical and corticothalamic neurons are generated at different times, and at which stage the connectional distinction develops in corticogenesis. Our experimental findings indicate that: (1) thalamic-projecting neurons in layer VI of the rat secondary somatosensory cortex (SII) are born at embryonic day 14 or before while latexin-expressing neurons in the same layer are generated at embryonic day 15 or later; (2) axonal invasion by SII neurons into ipsilateral cortical areas and into the posterior dorsal thalamus mainly takes place early in the postnatal period; (3) latexin-expressing neurons never project toward the dorsal thalamus in normal development; (4) presumptive latexin-expressing neurons in the neonatal SII are able to grow into a cortical slice in vitro, but do not invade a thalamic slice even transiently; (5) thalamic-projecting neurons, on the other hand, fail to simultaneously establish connections with a cortical slice. Taken together, our findings suggest that the time frame in which presumptive corticocortical and corticothalamic neurons are generated differs, and that the two populations are restricted in connectional fate potential by the perinatal period prior to target innervation.

Cloning, tissue expression pattern and genomic organization of latexin, a human homologue of rat carboxypeptidase A inhibitor

Latexin, a carboxypeptidase A inhibitor, is expressed in a cell type-specific manner in both central and peripheral nervous systems in the rat. It is used as a molecular marker for the regional specification of the neocortex. In this study, a cDNA was isolated from a human fetal brain cDNA library. The cDNA (LXN) contains an open reading frame encoding 222 amino acids. The comparison between the deduced amino acid sequences of LXN and latexins of rat and mouse revealed high sequence identity (84.2 and 84.7%, respectively). Northern blot analysis showed that LXN was expressed as a transcript of 1.3 kb in 15 out of 16 tissues examined, except in peripheral blood leukocyte. The expression levels were high in heart, prostate, ovary, kidney, pancreas, and colon, moderate or low in other tissues including brain. It is noteworthy that the tissue distribution of human LXN differs greatly to that of its homologue in the model animal, rat latexin. In addition, the LXN gene contains at least 6 exons and spans 5.9 kb according to the genomic sequence of the clone RP11-79M21 and the gap sequence cloned in this paper. LXN was assigned to 3q25-q26.2 according to the position of the marker SHGC-35682 found adjacent to LXN gene.

Ovocalyxin-32, a novel chicken eggshell matrix protein. isolation, amino acid sequencing, cloning, and immunocytochemical localization

The eggshell is a highly ordered structure resulting from the deposition of calcium carbonate concomitantly with an organic matrix upon the eggshell membranes. Mineralization takes place in an acellular uterine fluid, which contains the ionic and matrix precursors of the eggshell. We have identified a novel 32-kDa protein, ovocalyxin-32, which is expressed at high levels in the uterine and isthmus regions of the oviduct, and concentrated in the eggshell. Sequencing of peptides derived from the purified protein allowed expressed sequence tag sequences to be identified that were assembled to yield a full-length composite sequence whose conceptual translation product contained the complete amino acid sequence of ovocalyxin-32. Data base searches revealed that ovocalyxin-32 has limited identity (32%) to two unrelated proteins: latexin, a carboxypeptidase inhibitor expressed in the rat cerebral cortex and mast cells, and a skin protein, which is encoded by a retinoic acid receptor-responsive gene, TIG1. High level expression of ovocalyxin-32 was limited to the isthmus and uterus tissue, where immunocytochemistry at the light and electron microscope levels demonstrated that ovocalyxin-32 is secreted by surface epithelial cells. In the eggshell, ovocalyxin-32 localizes to the outer palisade layer, the vertical crystal layer, and the cuticle of the eggshell, in agreement with its demonstration by Western blotting at high levels in the uterine fluid during the termination phase of eggshell formation. Ovocalyxin-32 is therefore identified as a novel protein synthesized in the distal oviduct where hen eggshell formation occurs.

A membrane-associated progesterone-binding protein, 25-Dx, is regulated by progesterone in brain regions involved in female reproductive behaviors

The ventromedial hypothalamus (VMH) plays a central role in the regulation of the female reproductive behavior lordosis, a behavior dependent upon the sequential activation of receptors for the ovarian steroid hormones estradiol (E) and progesterone (P). These receptors function as transcription factors to alter the expression of target genes. To discover behaviorally relevant genes targeted by E and P in the VMH, we used the differential display PCR to identify messenger RNAs that are differentially expressed in the hypothalamus of ovariectomized (ovx) rats treated with E alone compared with ovariectomized rats treated with E and P. We show here that one interesting mRNA within the hypothalamus that is repressed by P after E priming encodes the protein 25-Dx, the rat homolog of the human membrane-associated P-binding protein Hpr6.6. Neurons in the brain containing the highest levels of 25-Dx are located in several nuclei of the basal forebrain, including the VMH. 25-Dx expression is also higher in the hypothalamus of female P receptor "knockout" mice than in their wild-type littermates. These findings suggest a mechanism in which the activation of nuclear P receptor represses expression of a membrane P receptor, 25-Dx, during lordosis facilitation.

Genomic organization and regulatory elements of the rat latexin gene, which is expressed in a cell type-specific manner in both central and peripheral nervous systems

Latexin, a carboxypeptidase A inhibitor, is expressed in a cell type-specific manner in both central and peripheral nervous systems in the rat. In the neocortex, a specific subpopulation of neurons in layers V and VI expresses latexin. In the primary sensory ganglia, the expression is restricted to smaller diameter neurons. As a first step to clarify regulatory mechanisms underlying cell type-specific expression of latexin, we have determined the organization of the rat latexin gene and analyzed its regulatory elements. The latexin gene spans approximately 5.8 kb, and consists of six exons and five introns. Three transcription initiation sites were mapped. The upstream region lacks typical TATA or CAAT boxes but has several GC-rich sites. To assess promoter activity, the luciferase reporter gene fused to the 5'-flanking region (6.4 kb) of the latexin gene was transiently transfected into several cell lines. Luciferase activity was 2-8 times higher in latexin-expressing cells (PC12) than non-expressing cells (NS20 and L6). Deletion analysis with PC12 cells revealed that a core promoter is located between nucleotide positions -261 and -201 relative to the A of the initiation codon. Nerve growth factor (NGF)-responsive element(s) is located between positions -518 and -262, in which AP-1, AP-2 and NF-kappaB binding sites are found. Furthermore, we demonstrate that a 1.3 kb genomic fragment containing the first intron has transcriptional enhancing activity in PC12 cells. These results suggest that up and downstream regulatory elements are involved in the control of cell type-specific expression of latexin.

Cerebral cortical specification by early potential restriction of progenitor cells and later phenotype control of postmitotic neurons

Neurons expressing latexin, a carboxypeptidase A inhibitor, are restricted to lateral areas in the cerebral cortex of adult and early postnatal rats. To address the precise timing of cortical regional specification at the cellular level, we monitored latexin expression in developing cortical cells under specific conditions in vitro. Individual cortical cells were labeled with 5-bromo-2′-deoxyuridine in vivo, dissociated and exposed to a defined new environment in a monolayer or a reaggregated-cell culture system. While a substantial fraction of early progenitor cells derived from the lateral cerebral wall became latexin-expressing neurons in both systems, far fewer progenitors from dorsal cortex did so under the same environmental conditions, indicating early establishment of cortical regional specification at the progenitor cell level. Furthermore, it was shown that the probability for postmitotic cells within lateral cortex to become latexin-expressing neurons was influenced by temporally regulated regional environmental signals. These findings suggest that developing cortical cells are progressively specified for a regional molecular phenotype during both their proliferative and postmitotic periods.

Area- and lamina-specific organization of a neuronal subpopulation defined by expression of latexin in the rat cerebral cortex

The aim of the present study was to investigate the density, laminar distribution, size, morphology, and neurotransmitter phenotype of rat cortical neurons expressing latexin, an inhibitor of carboxypeptidase A. Immunohistochemical analyses established that latexin-immunoreactive neurons are restricted essentially to the infragranular layers of lateral cortical areas in the rat. The overall density, laminar or sublaminar localization, and cell size distribution of latexin-positive neurons differed substantially across cytoarchitectonic areas within lateral cortex. Numerous latexin-positive neurons had the morphology of modified pyramidal cells especially of layer VI. The vast majority of latexin-positive neurons were glutamate-immunoreactive in the six lateral neocortical areas examined, while neurons immunoreactive for both latexin and GABA were virtually absent. Thus the majority of latexin-positive neurons are likely to be excitatory projection neurons. The area- and lamina-specific distribution of the latexin-expressing subpopulation of glutamate-immunoreactive neurons is a distinctive feature that may contribute to the functional specialization of the lateral cortical areas.

Membrane-associated molecules guide limbic and nonlimbic thalamocortical projections

Membrane-associated signals expressed in restricted domains of the developing cerebral cortex may mediate axon target recognition during the establishment of thalamocortical projections, which form in a highly precise manner during development. To test this hypothesis, we first analyzed the outgrowth of thalamic explants from limbic and nonlimbic nuclei on membrane substrates prepared from limbic cortex and neocortex. The results show that different thalamic fiber populations are able to discriminate between membrane substrates prepared from target and nontarget cortical regions. A candidate molecule that could mediate selective choice in the thalamocortical system is the limbic system-associated membrane protein (LAMP), which is an early marker of cortical and subcortical limbic regions (Pimenta et al.,1995) that can promote outgrowth of limbic axons. Limbic thalamic and cortical axons showed preferences for recombinant LAMP (rLAMP) in a stripe assay. Incubation of cortical membranes with an antibody against LAMP prevented the ability of limbic thalamic fibers to distinguish between membranes from limbic cortex and neocortex. Strikingly, nonlimbic thalamic fibers also responded to LAMP, but in contrast to limbic thalamic fibers, rLAMP inhibited branch formation and acted as a repulsive axonal guidance signal for nonlimbic thalamic axons. The present studies indicate that LAMP fulfills a role as a selective guidance cue in the developing thalamocortical system.

Latexin expression in smaller diameter primary sensory neurons in the rat

Most of the smaller diameter neurons of dorsal root and trigeminal ganglia in adult rats expressed latexin, which has the inhibitor activity of carboxypeptidase A. Most of the dorsal root ganglion (DRG) neurons containing either calcitonin gene-related peptide (CGRP), substance P (SP) or somatostatin (SST) coexpressed latexin. Latexin was widely distributed in the cytoplasm of the cell body and in axonal fibers of cultured DRG neurons which were sensitive to capsaicin. In addition, latexin-immunoreactivity was observed throughout lamina II of the spinal cord in normal animals, but was lost following sciatic nerve-axotomy, suggesting the presence of latexin-immunoreactive axonal fibers and/or terminals from DRG neurons. Immunoelectron microscopy indeed revealed latexin-immunoreactive axonal terminals and thinly myelinated and unmyelinated axonal fibers within the dorsal horn. These observations suggest that latexin may be involved in nociceptive information transmission or its modulation.

Early patterning of the rat cerebral wall for regional organization of a neuronal population expressing latexin

The exact timing of regional patterning in the developing cerebral cortex and other telencephalic structures remains to be elucidated. In the present study, we addressed this issue by comparing the distribution and density of neuronal population expressing latexin in the adult rat telencephalon, with the regional pattern in the fetal cerebral wall as to the potential to generate latexin-expressing neurons. Immunohistochemical analyses on adult animals have shown that latexin-expressing neurons are restricted to a lateral cortical field, within which they are most abundant at the middle level, decreasing in number rostrally and caudally. Substantial numbers of latexin-immunopositive neurons were recorded in the claustrum and endopiriform nuclei, both of which are located from rostral to middle level in the lateral telencephalon. By examining the number and density of latexin-immunopositive neurons in organotypic slice cultures from various portions of the developing rat cerebral wall, it has been shown that the regional pattern within the early cerebral wall as to the potential to generate latexin-expressing neurons matches well the distribution and density of latexin-expressing neurons in the adult telencephalon. Thus, in cultures derived from either embryonic day 13 or 16 fetuses, latexin-immunopositive neurons appeared most prominently in those from rostral-to-middle portions of the lateral cerebral wall, decreasing in number rostrally and caudally. In cultures from the dorsal cerebral wall, the number was generally very low. In light of our previous finding that most prospective latexin-expressing neurons are still dividing at embryonic day 13, it can be concluded that some kind of pattern formation event occurs within the early cerebral wall even prior to the genesis of the postmitotic neurons that would be later allocated in a region-specific manner.

Early molecular specification in the hippocampal rudiment: isolation of genes expressed in a region-specific manner in the embryonic telencephalon

During development, the structure of the telencephalon is dramatically transformed by region-specific proliferation and differentiation of neuroepithelial cells. To understand mechanisms of morphogenesis in the telencephalon, a search was made for genes expressed in a region-specific manner in the dorsal telencephalon of embryonic rats. Dorso-lateral and dorso-medial portions of the telencephalon were taken from rat fetuses on embryonic day (E) 13. Genes expressed in each portion were compared by a modified differential display method. Among more than 4000 cDNA fragments, four fragments termed M1, M1', M2 and M3 were found only after amplification of cDNAs derived from the dorso-medial portion of the telencephalon. Nucleotide sequence and Northern blot analyses showed that M1 and M1' were identical and that M2 and M3 were related genes. In situ hybridization revealed that M1 was expressed in a restricted portion of the hippocampal rudiment with a sharp boundary. M2 and M3 were expressed in the hippocampal rudiment with a more diffuse boundary than that of M1. Expression of M2 and M3 was also found in the most anterior part of the medial diencephalon with a caudal extension along the dorsal midline. These results suggest that at least two types of molecular specification occur in the dorso-medial telencephalon, contributing to the construction of the hippocampal elements during early stages of development.

Patterning and specification of the cerebral cortex

Regionalization of the cerebral cortex occurs during development by the formation of anatomically and functionally discrete areas of the brain. Descriptive evidence based on expression of molecules and structural features suggests that an early parcelation of the cerebral wall may occur during fetal development. Experimental strategies using tissue transplants and cell culture models have explored the nature of the timing of areal specification. New signaling systems displaying the sensitivity of precursor cells to environmental cues that define the fate of neurons destined for specific areas of the cortex have been discovered. Studies in the field now suggest mechanisms of regulating cell phenotype in the cortex that are common to all parts of the neuraxis.

Schizophrenia, the heteromodal association neocortex and development: potential for a neurogenetic approach

The heteromodal association neocortex is believed to be a major site of involvement in schizophrenia. This system includes the prefrontal cortex and portions of the superior temporal and inferior parietal cortices, which are linked in cognitive networks observing complex executive functions. The heteromodal cortex is highly elaborated in humans and is believed to continue to develop past birth. The neuropathology of schizophrenia is likely to be heterogeneous and appears to involve developmental abnormalities, with a prominent genetic component. However, the genes involved in the development of the neocortex, and particularly the heteromodal cortex, are not well understood. A candidate-gene approach to schizophrenia using techniques of differential expression might now be feasible and could illuminate the basic neurobiology of the heteromodal cortical network.

T-brain-1: a homolog of Brachyury whose expression defines molecularly distinct domains within the cerebral cortex

The mechanisms that regulate regional specification and evolution of the cerebral cortex are obscure. To this end, we have identified and characterized a novel murine and human gene encoding a putative transcription factor related to the Brachyury (T) gene that is expressed only in postmitotic cells. T-brain-1 (Tbr-1) mRNA is largely restricted to the cerebral cortex, where during embryogenesis it distinguishes domains that we propose may give rise to paleocortex, limbic cortex, and neocortex. Tbr-1 and Id-2 expression in the neocortex have discontinuities that define molecularly distinct neocortical areas. Tbr-1 expression is analyzed in the context of the prosomeric model. Topological maps are proposed for the organization of the dorsal telencephalon.

Regulation of regional differences in the differentiation of cerebral cortical neurons by EGF family-matrix interactions

Both lineage-based and epigenetic regulation have been postulated as mechanisms to control the formation of discrete areas in the cerebral cortex, but specific genes or signaling pathways that may be involved have yet to be defined. In this paper, we examine whether progenitors, isolated from the cerebral wall prior to neurogenesis, can respond to exogenous cues by adopting a region-specific phenotype. The expression of the limbic system-associated membrane protein (LAMP), a neuron-specific marker of limbic cortical areas, was monitored in cultured neurons arising from precursors harvested from presumptive perirhinal (limbic) and sensorimotor (nonlimbic) zones at embryonic day 12 in the rat. Neuronal phenotype in all cultures was identified by expression of microtubule-associated protein-2 (MAP2). On a substrate of poly-lysine, over 80% of the precursors from the limbic area that differentiate into neurons express a LAMP+ phenotype. Approximately 20% of the neurons generated from precursors of the sensorimotor region become LAMP+. However, modification of the microenvironment had a significant effect on the differentiation of the sensorimotor precursors. When the nonlimbic precursors are grown on Matrigel, there is a 2-fold increase in the number of MAP2+/LAMP+ double-labeled neurons. Dissection of the Matrigel components reveals that in combination with growth factor-deficient Matrigel or collagen type IV, epidermal growth factor and transforming growth factor-alpha increase LAMP expression in the sensorimotor population. Delaying the addition of growth factor until after most cell division had ceased failed to increase the number of LAMP+ neurons. Another growth factor in Matrigel, platelet-derived growth factor, does not produce the same effect. Our results indicate that local signals can regulate the differentiation of cortical progenitors, providing a potential mechanism for establishing an early commitment to specific regional phenotypes in the developing cerebral wall that relate to future functional domains in the cortex.

Latexin: a molecular marker for regional specification in the neocortex

It largely remains to be elucidated how the mammalian neocortex is regionally specified during development. In an attempt to obtain molecular markers in the neocortex, we have generated a monoclonal antibody PC3.1 which recognizes a subset of neurons located in lateral, but not dorsal, neocortical areas. The antigen is a novel class of protein, named latexin, having a molecular weight of 29,000. Our in vitro studies have revealed that the neocortical regional specification for the production of latexin-positive neurons occurs very early prior to thalamocortical interactions and the completion of neurogenesis, indicating that elements intrinsic to the neocortex play important roles in the neocortical specification. Furthermore, our recent analyses have suggested that this regional specification is attributable, at least in part, to an early restriction of developmental potential in neocortical progenitor cells to become latexin-positive neurons.