The role of Zic genes in neural development

EphB2 induces proliferation and promotes a neuronal fate in adult subventricular neural precursor cells

The subventricular germinal zone (SVZ) retains an active population of stem cells and neural precursor cells throughout adulthood. EphrinB signaling mediates angiogenesis and vasculogenesis in the developing and adult brain. Recent studies indicate that molecules involved in angiogenesis often influence neurogenesis as well. However, little work has been done considering a role for EphB2/EphrinB in adult neural precursor cells. We therefore examined whether the EphB2 receptor tyrosine kinase could directly effect proliferation of SVZ neural precursors and/or direct the cell fate of SVZ cells in vitro. Here, we found that clustered EphB2 increased bromodeoxyuridine (BrdU) incorporation and proliferation of SVZ neurosphere cultures. Immunostaining and RT-PCR analysis for beta-tubulin III (Tuj1) and GFAP indicated 4-day treatment with EphB2 promoted a neuronal phenotype, suggesting that the EphB2 receptor might also direct SVZ cell fate. EphB2 transiently down-regulated SVZ cell mRNA of Notch1 and Zic1, genes that regulate neurogenesis and neuronal differentiation. Notch1 has been implicated in apoptosis of neural precursors, however, a cell viability assay revealed no statistical difference between EphB2-treated and control cultures. When SVZ neurospheres were cultured upon Matrigel, EphB2 attenuated radial migration of SVZ cells in vitro. These results demonstrate that EphB2/EphrinB signaling directly induces SVZ proliferation, decreases migration, and promotes a neuronal fate of SVZ neural precursors independent of cell survival.

Ci-Tbx6b and Ci-Tbx6c are key mediators of the maternal effect gene Ci-macho1 in muscle cell differentiation in Ciona intestinalis embryos

Maternally deposited mRNA encoding the Zic family zinc-finger protein Ci-macho1 is a determinant responsible for muscle cell differentiation in Ciona intestinalis embryos. In a previous study, we identified possible Ci-macho1 downstream genes, which include seven transcription factor genes and seven signaling molecule genes (Yagi, K., Satoh, N., Satou, Y., 2004. Identification of downstream genes of the ascidian muscle determinant gene Ci-macho1. Dev. Biol. 274, 478-489), suggesting complex Ci-macho1 downstream cascades. Here, we show that of the Ci-macho1 downstream genes, only Ci-Tbx6b and Ci-Tbx6c promote ectopic differentiation of muscle cells when misexpressed in non-muscle blastomeres. Overexpression of Ci-Tbx6b or Ci-Tbx6c in Ci-macho1 knockdown embryos is able to compensate for the functional loss of Ci-macho1 and promote differentiation of muscle cells. In addition, we show that knockdown of each of Ci-Tbx6b or Ci-Tbx6c suppresses the initiation of muscle protein gene expression, and both gene products appear to recognize a similar binding sequence. However, later expression of muscle protein genes at the tailbud stage is only reduced in Ci-Tbx6b knockdown embryos and undisturbed in Ci-Tbx6c knockdown embryos. Although ectopic expression or knockdown of Ci-ZicL alone does not affect muscle cell differentiation, simultaneous knockdown of Ci-Tbx6b, Ci-Tbx6c, and Ci-ZicL completely abolishes muscle cell differentiation, as in the case of knockdown of Ci-macho1 and Ci-ZicL. These results strongly suggest that muscle cell differentiation in Ciona embryos is controlled by four key factors: maternal macho1 and zygotic Tbx6b, Tbx6c, and ZicL. The two T-box genes are primary mediators of macho1 function, and cooperation between the zygotically expressed transcription factors is indispensable for muscle cell differentiation in Ciona embryos.

Frequency of SOX Group B (SOX1, 2, 3) and ZIC2 antibodies in Turkish patients with small cell lung carcinoma and their correlation with clinical parameters

BACKGROUND

Expression of neuroectodermal markers is a key feature of small cell lung carcinoma (SCLC). Although immune responses against a number of these proteins have been associated with paraneoplastic neuronal disease (PND), most patients with SCLC have anti-neuroectodermal antibodies in the absence of PND. Whether these immune responses affect the clinical outcome in SCLC is critical in understanding the potential value of these proteins as cancer vaccine targets as well as in the pathogenesis of PND.

METHODS

The authors investigated the frequency of immunoglobulin G autoantibodies against Sry-like high-mobility group box (SOX)1, 2, 3 and Zinc-finger gene of the cerebellum (ZIC)2 proteins in stored serum samples from 90 patients utilizing the lambda-phage plaque assay. Data obtained from patient records were utilized to measure clinical correlates of seroreactivity.

RESULTS

Antibodies to SOX1 were present in 28% of patients and another 28% had anti-ZIC2 antibodies, classifying these as some of the most frequent antibody responses observed in SCLC. None had autoimmune paraneoplastic disease. Antibody titers were frequently as high as > or = 1:10(6) and were stable for < or = 6 months after diagnosis. Seroreactivity against either SOX1 or ZIC2 correlated with younger age, lower lactate dehydrogenase levels, and better response to initial therapy.

CONCLUSIONS

The frequent and stable presence of SOX Group B and/or ZIC2 antibodies in SCLC, but not in healthy individuals examined, indicates they are serological markers of SCLC. However, the correlation between known clinical parameters of less aggressive disease and seroreactivity suggests that these antibodies are indicators of better prognosis in SCLC and warrants further studies to clarify the nature of the underlying immune responses.

Identification of downstream genes of the ascidian muscle determinant gene Ci-macho1

Autonomous differentiation of primary muscle cells in ascidian embryos is triggered by a maternal determinant recently identified as the macho-1 gene. macho-1 encodes a transcription factor of the Zic family with five C2H2 zinc-finger motifs. In the present study, we firstly performed a screen, using a quantitative PCR method, of genes encoding transcription factors and components in major signaling pathways to identify those regulated downstream of Ci-macho1 in early embryos of Ciona intestinalis. The amount of transcripts for a total of 64 genes was altered at the 32-cell stage depending on the Ci-macho1 activity level. Whole-mount in situ hybridization assays revealed that the alteration of expression for at least 13 of them was adequately visualized to confirm the results of quantitative PCR. Second, we determined a possible binding sequence of Ciona macho1. macho1 recombinant proteins of both C. intestinalis and Ciona savignyi recognized a sequence, 5'-GCCCCCCGCTG-3', that resembles the mammalian Zic binding site. In addition, most of the genes identified as potential Ci-macho1 downstream genes, in particular Ci-Tbx6b and Ci-snail, possessed plausible Ci-macho1-binding sequences in their 5' upstream region, suggesting their direct activation by Ci-macho1. Furthermore, some of the genes including three Wnt genes noted in the quantitative analyses implied that Ci-macho1 is involved in the differentiation of endoderm and mesenchyme via intracellular communications.

Molecular properties of Zic4 and Zic5 proteins: functional diversity within Zic family

The Zic-family proteins control various developmental processes. Previous studies have shown that Zic1, Zic2, and Zic3 can act as transcriptional regulators, and that their functions are repressed by I-mfa, which has been identified as a repressor for basic helix-loop-helix-type transcriptional factors. Here, we investigated the molecular properties of the Zic4 and Zic5 proteins. Zic4/Zic5 showed DNA-binding activity to the Gli-binding sequence, similar to Zic1/Zic2/Zic3 proteins. However, Zic4/Zic5 did not exhibit any significant transcriptional activation ability nor they bind to I-mfa differently from Zic1/Zic2/Zic3. The nuclear localization of Zic4/Zic5 was not affected by the presence of the I-mfa protein, whereas the Zic1/Zic2/Zic3 proteins were translocated to the cytoplasmic compartment in the presence of I-mfa. The difference may be attributable to the dissimilarity of the N-terminal region between the Zic1/Zic2/Zic3 and Zic4/Zic5 proteins, since the binding of the Zic1/Zic2/Zic3 proteins to I-mfa occurs through their N-terminal regions.

Mouse Zic5 deficiency results in neural tube defects and hypoplasia of cephalic neural crest derivatives

Zic family genes encode zinc finger proteins, which are homologues of the Drosophila pair-rule gene odd-paired. In the present study, we characterized the fifth member of the mouse Zic family gene, mouse Zic5. Zic5 is located near Zic2, which is responsible for human brain malformation syndrome (holoprosencephaly, or HPE). In embryonic stages, Zic5 was expressed in dorsal part of neural tissues and limbs. Expression of Zic5 overlapped with those of other Zic genes, most closely with Zic2, but was not identical. Targeted disruption of Zic5 resulted in insufficient neural tube closure at the rostral end, similar to that seen in Zic2 mutant mice. In addition, the Zic5-deficient mice exhibited malformation of neural-crest-derived facial bones, especially the mandible, which had not been observed in other Zic family mutants. During the embryonic stages, there were delays in the development of the first branchial arch and extension of the trigeminal and facial nerves. Neural crest marker staining revealed fewer neural crest cells in the dorsal cephalic region of the mutant embryos without significant changes in their migration. When mouse Zic5 was overexpressed in Xenopus embryos, expression of a neural crest marker was enhanced. These findings suggested that Zic5 is involved in the generation of neural crest tissue in mouse development. ZIC5 is also located close to ZIC2 in humans, and deletions of 13q32, where ZIC2 is located, lead to congenital brain and digit malformations known as the "13q32 deletion syndrome". Based on both their similar expression pattern in mouse embryos and the malformations observed in Zic5-deficient mutant mice, human ZIC5 might be involved in the deletion syndrome.