The KANNO blood group system

The KANNO blood group system (International Society of Blood Transfusion [ISBT] 037) includes one high-prevalence antigen, KANNO1, across ethnic groups. Sporadic KANNO1- cases among East and South Asians are theoretically estimated by the DNA database library. Anti-KANNO1 has been found most often among Japanese women with current or prior pregnancy. Thus far, there are no reported cases of hemolytic transfusion reaction or hemolytic disease of the fetus and newborn due to anti-KANNO1.

The many faces of Sox2 function in neural crest development

Neural crest (NC) cells give rise to a wide variety of cell types and tissues, such as neurons and glial cells in the peripheral nervous system. Sox2, which encodes an HMG-box transcription factor, is known to mediate pluripotency of primordial germ cells and embryonic stem (ES)/induced pluripotent stem (iPS) cells, and to regulate central nervous system development. Previous studies have revealed that Sox2 is also an important regulator of NC development. This review summarizes the well-established inhibitory roles of Sox2 in NC formation and subsequent neuronal differentiation of NC-derived cells. This review also covers recent studies suggesting additional roles for Sox2 in early NC development, neurogenesis, and glial differentiation of NC-derived cells.

The absence of SOX2 in the anterior foregut alters the esophagus into trachea and bronchi in both epithelial and mesenchymal components

In the anterior foregut (AFG) of mouse embryos, the transcription factor SOX2 is expressed in the epithelia of the esophagus and proximal branches of respiratory organs comprising the trachea and bronchi, whereas NKX2.1 is expressed only in the epithelia of respiratory organs. Previous studies using hypomorphic Sox2 alleles have indicated that reduced SOX2 expression causes the esophageal epithelium to display some respiratory organ characteristics. In the present study, we produced mouse embryos with AFG-specific SOX2 deficiency. In the absence of SOX2 expression, a single NKX2.1-expressing epithelial tube connected the pharynx and the stomach, and a pair of bronchi developed in the middle of the tube. Expression patterns of NKX2.1 and SOX9 revealed that the anterior and posterior halves of SOX2-deficient AFG epithelial tubes assumed the characteristics of the trachea and bronchus, respectively. In addition, we found that mesenchymal tissues surrounding the SOX2-deficient NKX2.1-expressing epithelial tube changed to those surrounding the trachea and bronchi in the anterior and posterior halves, as indicated by the arrangement of smooth muscle cells and SOX9-expressing cells and by the expression of Wnt4 (esophagus specific), Tbx4 (respiratory organ specific), and Hoxb6 (distal bronchus specific). The impact of mesenchyme-derived signaling on the early stage of AFG epithelial specification has been indicated. Our study demonstrated an opposite trend where epithelial tissue specification causes concordant changes in mesenchymal tissues, indicating a reciprocity of epithelial-mesenchymal interactions.

Sox2 gene regulation via the D1 enhancer in embryonic neural tube and neural crest by the combined action of SOX2 and ZIC2

The transcription factor (TF) SOX2 regulates various stem cells and tissue progenitors via functional interactions with cell type-specific partner TFs that co-bind to enhancer sequences. Neural progenitors are the major embryonic tissues where SOX2 assumes central regulatory roles. In order to characterize the partner TFs of SOX2 in neural progenitors, we investigated the regulation of the D1 enhancer of the Sox2 gene, which is activated in the embryonic neural tube (NT) and neural crest (NC), using chicken embryo electroporation. We identified essential TF binding sites for a SOX, and two ZIC TFs in the activation of the D1 enhancer. By comparison of dorso-ventral and antero-posterior patterns of D1 enhancer activation, and the effect of mutations on the enhancer activation patterns with TF expression patterns, we determined SOX2 and ZIC2 as the major D1 enhancer-activating TFs. Binding of these TFs to the D1 enhancer sequence was confirmed by chromatin immunoprecipitation analysis. The combination of SOX2 and ZIC2 TFs activated the enhancer in both the NT and NC. These results indicate that SOX2 and ZIC2, which have been known to play major regulatory roles in neural progenitors, do functionally cooperate. In addition, the recently demonstrated SOX2 expression during the NC development is accounted for at least partly by the D1 enhancer activity. Deletion of the D1 enhancer sequence from the mouse genome, however, did not affect the mouse development, indicating functional redundancies of other enhancers.

Nodal paralogues underlie distinct mechanisms for visceral left-right asymmetry in reptiles and mammals

Unidirectional fluid flow generated by motile cilia at the left-right organizer (LRO) breaks left-right (L-R) symmetry during early embryogenesis in mouse, frog and zebrafish. The chick embryo, however, does not require motile cilia for L-R symmetry breaking. The diversity of mechanisms for L-R symmetry breaking among vertebrates and the trigger for such symmetry breaking in non-mammalian amniotes have remained unknown. Here we examined how L-R asymmetry is established in two reptiles, Madagascar ground gecko and Chinese softshell turtle. Both of these reptiles appear to lack motile cilia at the LRO. The expression of the Nodal gene at the LRO in the reptilian embryos was found to be asymmetric, in contrast to that in vertebrates such as mouse that are dependent on cilia for L-R patterning. Two paralogues of the Nodal gene derived from an ancient gene duplication are retained and expressed differentially in cilia-dependent and cilia-independent vertebrates. The expression of these two Nodal paralogues is similarly controlled in the lateral plate mesoderm but regulated differently at the LRO. Our in-depth analysis of reptilian embryos thus suggests that mammals and non-mammalian amniotes deploy distinct strategies dependent on different Nodal paralogues for rendering Nodal activity asymmetric at the LRO.

The B allele with a 5·8 kb deletion in intron 1 of the ABO gene is the major allele in Japanese individuals with Bm and A1 Bm phenotypes

B_m and A₁ B_m phenotypes are the most frequent ABO variants in the Japanese population. The B antigen on B_m red blood cells is only detectable by adsorption and elution tests, and plasma B-transferase activity is usually detected at half or less levels compared with that of common B. Recently, a B allele lacking an erythroid cell-specific transcription enhancer in intron 1 of the ABO gene was identified from individuals with B_m and A₁ B_m phenotypes, which could explain the unique serologic properties of B_m . In the Japanese Red Cross Society, eight Blood Centers tested blood samples from donors throughout Japan and collected blood samples from 888 B_m and 415 A₁ B_m individuals. DNA analysis revealed that 1300 of 1303 (99·77%) individuals had the B allele with a 5·8 kb deletion (c.28 + 5110_10889del), which included the enhancer element.

Silent KEL alleles identified from Japanese individuals with the Ko phenotype

BACKGROUND AND OBJECTIVE

The rare K_o phenotype lacks all 36 antigens in the Kell blood system. The molecular basis of the K_o phenotype has been investigated, and more than 40 silent KEL alleles are reported by many investigators. The majority of silent alleles are the KEL*02 background. Here, we report molecular genetic analysis of the KEL gene in Japanese individuals with the K_o phenotype.

MATERIALS AND METHODS

The K_o phenotype was screened from Japanese blood donors for several years using monoclonal anti-Ku or anti-K14 by an automated blood grouping system PK7300. Kell-related antigens were typed by standard tube tests. Genomic DNA was extracted from the blood samples, and KEL gene was analysed by polymerase chain reaction (PCR) and Sanger sequencing.

RESULTS

We collected 35 K_o blood samples with K-k-, Kp(a-b-), Js(a-b-) and K14-. PCR and sequence analysis revealed that 11 individuals were homozygous for a mutant KEL allele with a c.299G>C (p.Cys100Ser) mutation (rs. 200268316). Three individuals were homozygous for the KEL*02N.24 allele that is c.715G>T (p.Glu239*), and one individual was homozygous for the KEL*02N.40 allele that is c.1474C>T (p.Arg492*). Five individuals were homozygous for novel KEL alleles with single-nucleotide mutations, four individuals had a c.2175delC (p.Pro725 fs*43), and one individual had a c.328delA (p.Arg110 fs*79). The remaining 15 individuals were compound heterozygous, and eight new alleles were identified from them.

CONCLUSIONS

We identified three known and ten new silent KEL alleles from Japanese individuals with the K_o phenotype. The KEL allele with the c.299G>C (p.Cys100Ser) mutation was the most frequent.

Regulation of trunk neural crest delamination by δEF1 and Sip1 in the chicken embryo

The vertebrate Zfhx1 transcription factor family comprises δEF1 and Sip1, which bind to CACCT-containing sequences and act as transcriptional repressors. It has been a longstanding question whether these transcription factors share the same regulatory functions in vivo. It has been shown that neural crest (NC) delamination depends on the Sip1 activity at the cranial level in mouse and chicken embryos, and it remained unclear how NC delamination is regulated at the trunk level. We observed that the expression of δEF1 and Sip1 overlaps in many tissues in chicken embryos, including NC cells at the trunk level. To clarify the above questions, we separately knocked down δEF1 and Sip1 or in combination in NC cells by electroporation of vectors expressing short hairpin RNAs (shRNAs) against respective mRNAs on the dorsal side of neural tubes that generate NC cells. In all cases, the migrating NC cell population was significantly reduced, paralleled by the decreased expression of δEF1 or Sip1 targeted by shRNAs. Expression of Sox10, the major transcription factor that regulates NC development, was also decreased by the shRNAs against δEF1 or Sip1. We conclude that the trunk NC delamination is regulated by both δEF1 and Sip1 in an analogous manner, and that these transcription factors can share equivalent regulatory functions in embryonic tissues.

Presence of nucleotide substitutions in the ABO promoter in individuals with phenotypes A3 and B3

Recently, the involvement of mutation and deletion of transcription regulatory elements in the Bm , Am , A3 and B3 phenotypes has been reported. In the present study, we carried out genetic analysis of individuals with A3 and B3 using peptide nucleic acid-clamping PCR to exclude amplification of O alleles. Two single-point mutations, -76G>C and -68G>T, were found in the ABO promoter on the A-allele in three A3 individuals and on the B allele in a B3 individual, respectively. Transient transfection of luciferase reporter plasmids carrying the same mutations into K562 cells revealed decreased luciferase activity in comparison with that carrying the wild-type promoter. These observations suggest that the mutations downregulate the promoter activity, leading to reduction in A- or B-antigen expression on red blood cells in individuals with the A3 and B3 phenotypes.

Blood group B gene is barely expressed in in vitro erythroid culture of Bm-derived CD34+ cells without an erythroid cell-specific regulatory element

BACKGROUND AND OBJECTIVES

Previously, a weak phenotype Am or Bm was assumed to be caused by a reduction of A or B gene expression in bone marrow cells, but not in mucus-secreting cells. However, ABO expression has not been examined in erythroid progenitor cells of Am or Bm individuals.

MATERIALS AND METHODS

We carried out in vitro erythroid differentiation of CD34(+) cells from peripheral blood of a Bm individual harbouring a 3.0-kb deletion including an erythroid cell-specific regulatory element, named the +5.8-kb site, in intron 1 of the human ABO blood group gene.

RESULTS

During the in vitro differentiation of CD34(+) cells from this Bm individual into erythroid cells, B-antigens were not detectable on the cultured cells by flow cytometric analysis, and allele-specific RT-PCR consistently detected the transcripts from the O allele, but not from the B allele. Moreover, chromatin immunoprecipitation assay demonstrated that both RUNX1 and GATA-2 or GATA-1 were bound to the +5.8-kb site in cultured erythroid cells expressing ABO.

CONCLUSION

It is likely that the +5.8-kb site enhances transcription from the ABO promoter in erythroid cells through binding of RUNX1 and GATA-2 or GATA-1.

Production of human monoclonal anti-Jk3, recognising an epitope including the Jk(a) /Jk(b) polymorphic site of the Kidd glycoprotein

BACKGROUND AND OBJECTIVES

The Kidd blood group system consists of polymorphic antigens, Jk(a) (JK1) and Jk(b) (JK2), and a high-incidence antigen, Jk3. Anti-Jk3 is often observed in immunised Jk(a-b-) individuals. In this study, we aimed to establish a human hybridoma cell line secreting monoclonal anti-Jk3 (HIRO-294).

MATERIALS AND METHODS

Peripheral blood lymphocytes of a Filipino woman with the Jk(a-b-) phenotype having anti-Jk3 were transformed with Epstein-Barr virus and then hybridised with the myeloma cell line JMS-3 using the polyethylene glycol (PEG) method. The reactivity and specificity of the anti-Jk3 were examined by serology and flow cytometry.

RESULTS

Four hybridoma clones secreting anti-Jk3 were established and the antibody from one of these clones, HIRO-294, was examined. The reactivity of HIRO-294 was positive with 227 Jk(a+b-) red blood cells (RBCs), 298 Jk(a-b+) RBCs, and 1043 Jk(a+b+) RBCs, but was negative with 21 Jk(a-b-) RBCs. Eluates from Jk(a+b-) RBCs and Jk(a-b+) RBCs sensitised with the anti-Jk3 were cross-reacted with Jk(a-b+) RBCs and Jk(a+b-) RBCs, respectively. The reactivity of HIRO-294 was enhanced by the treatment of RBCs with ficin, trypsin, pronase and α-chymotrypsin, but was not changed by their treatment with neuraminidase, dithiothreitol and ethylenediaminetetraacetic acid (EDTA) glycine acid (GA). The RBCs sensitised by the anti-Jk3 were not agglutinated with the commercial reagents of anti-Jk(a) and anti-Jk(b) by saline test, whereas the nonsensitised RBCs or those sensitised by monoclonal anti-D [HIRO-3, immunoglobulin G (IgG) class] were agglutinated with those reagents.

CONCLUSIONS

We established a human hybridoma cell line secreting monoclonal anti-Jk3 (HIRO-294). This antibody had unique specificity, recognising the Kidd glycoprotein including the Jk(a) /Jk(b) polymorphic site.

JK null alleles identified from Japanese individuals with Jk(a−b−) phenotype

The Kidd blood group system consists of three common phenotypes: Jk(a+b−), Jk(a−b+) and Jk(a+b+), and one rare phenotype, Jk(a−b−). Jka/Jkb polymorphism is associated with c.838G>A (p.Asp280Asn) in exon 9 of the JK (SLC14A1) gene, and the corresponding alleles are named JK*01 and JK*02. The rare phenotype Jk(a−b−) was first found in a Filipina of Spanish and Chinese ancestry, and to date, several JK null alleles responsible for the Jk(a−b−) phenotype have been reported. We report seven novel JK null alleles, 4 with a JK*01 background and 3 with a JK*02 background, identified from Jk(a−b−) Japanese.

Deletion of the RUNX1 binding site in the erythroid cell-specific regulatory element of the ABO gene in two individuals with the Am phenotype

BACKGROUND AND OBJECTIVES

An erythroid cell-specific regulatory element, referred to as the +5·8-kb site, had been identified in the first intron of the human ABO blood group gene. Subsequent studies revealed that either a 5·8-kb deletion including the +5·8-kb site or disruption of a GATA factor binding motif at the site was present in all Bm and ABm individuals examined. We investigated the molecular mechanism of the Am phenotype, which is analogous to the Bm phenotype.

MATERIALS AND METHODS

Genomic DNAs were prepared from peripheral blood of two Am individuals, and the nucleotide sequences were investigated using PCR and direct sequencing. Electrophoretic mobility shift assay (EMSA) and promoter assay with K562 cells were carried out.

RESULTS

A novel 23-bp nucleotide deletion was found at the +5·8-kb site in both individuals. EMSAs demonstrated binding of the transcription factor RUNX1 to the nucleotides within the deletion. Promoter assays showed that the deletion reduced the transcriptional activity of the +5·8-kb site.

CONCLUSION

Deletion of the 23-bp nucleotides including the RUNX1 binding site decreases transcription of the A allele, resulting in the reduction in A antigen expression in the Am phenotype.

The prosensory function of Sox2 in the chicken inner ear relies on the direct regulation of Atoh1

The proneural gene Atoh1 is crucial for the development of inner ear hair cells and it requires the function of the transcription factor Sox2 through yet unknown mechanisms. In the present work, we used the chicken embryo and HEK293T cells to explore the regulation of Atoh1 by Sox2. The results show that hair cells derive from Sox2-positive otic progenitors and that Sox2 directly activates Atoh1 through a transcriptional activator function that requires the integrity of Sox2 DNA binding domain. Atoh1 activation depends on Sox transcription factor binding sites (SoxTFBS) present in the Atoh1 3′ enhancer where Sox2 directly binds, as shown by site directed mutagenesis and chromatin immunoprecipitation (ChIP). In the inner ear, Atoh1 enhancer activity is detected in the neurosensory domain and it depends on Sox2. Dominant negative competition (Sox2HMG-Engrailed) and mutation of the SoxTFBS abolish the reporter activity in vivo. Moreover, ChIP assay in isolated otic vesicles shows that Sox2 is bound to the Atoh1 enhancer in vivo. However, besides activating Atoh1, Sox2 also promotes the expression of Atoh1 negative regulators and the temporal profile of Atoh1 activation by Sox2 is transient suggesting that Sox2 triggers an incoherent feed-forward loop. These results provide a mechanism for the prosensory function of Sox2 in the inner ear. We suggest that sensory competence is established early in otic development through the activation of Atoh1 by Sox2, however, hair cell differentiation is prevented until later stages by the parallel activation of negative regulators of Atoh1 function.

The Pou5f1/Pou3f-dependent but SoxB-independent regulation of conserved enhancer N2 initiates Sox2 expression during epiblast to neural plate stages in vertebrates

The transcription factor Sox2 is a core component of the pluripotency control circuits in the early embryo, and later controls many aspects of neural development. Here, we demonstrate that Sox2 expression in the epiblast (mouse blastoderm) and anterior neural plate (ANP) is determined by the upstream enhancer N2. The mouse enhancer N2 exhibits strong activity in mouse ES cells, epiblast and ANP, and is regulated correctly in chicken and zebrafish embryos. Targeted deletion of this enhancer in mouse embryos caused a large reduction of Sox2 expression to 10% of that of wild-type levels in epiblast and ANP. However, this was tolerated by mouse embryo, probably due to functional compensation by Sox3. The activity of enhancer N2 depends on phylogenetically conserved bipartite POU factor-binding motifs in a 73-bp core sequence that function synergistically, but this activation does not involve Sox2. The major POU factor expressed at the epiblastic stage is Pou5f1 (Oct3/4), while those in the anterior neural plate are Pou3f factors (Oct6, Brn2 etc.). These factors are gradually exchanged during the transition from epiblast to ANP stages in mouse embryos and epiblast stem cells (EpiSC). Consistently, enhancer N2 activity changes from full Pou5f1 dependence to Pou3f dependence during the development of neural plate cells (NPC) from EpiSC, as assessed by specific POU factor knockdown in these cells. Zebrafish mutant embryos completely devoid of Pou5f1 activity failed to activate enhancer N2 and to express Sox2 in the blastoderm and ANP, and these defects were rescued by exogenous supply of pou5f1. Previously, Pou5f1-Sox2 synergism-dependent Sox2 activation through enhancer SRR2 in ES cells has been highlighted, but this mechanism is limited to ES cells and amniotes. In contrast, the enhancer N2-mediated, POU factor-dependent activation of Sox2, without involvement of Sox2, is a phylogenetically conserved core mechanism that functions in gene regulatory networks at early embryonic stages.

A new blood group system, RHAG: three antigens resulting from amino acid substitutions in the Rh-associated glycoprotein

BACKGROUND AND OBJECTIVES

Rh-associated glycoprotein (RhAG) is closely associated with the Rh proteins in the red cell membrane. Two high frequency antigens (Duclos and DSLK) and one low frequency antigen (Ol(a)) have serological characteristics suggestive of expression on RhAG.

MATERIALS AND METHODS

RHAG was sequenced from the DNA of one Duclos-negative, one DSLK-negative, and two Ol(a+) individuals. Recombinant protein was expressed in HEK 293 cells. Protein models with RhAG subunits were constructed.

RESULTS

The original Duclos-negative patient was homozygous for RHAG 316C>G, encoding Gln106Glu. HEK 293 cells expressing Gln106Glu mutant RhAG did not react with anti-Duclos. An individual with DSLK-negative red cells was homozygous for 490A>C, encoding Lys164Gln. Two Ol(a+) members of the original Norwegian family were heterozygous for 680C>T, encoding Ser227Leu. A Japanese donor with Rh(mod) phenotype had Ol(a+) red cells and was homozygous for 680C>T.

CONCLUSION

The three red cell antigens encoded by RHAG form the RHAG blood group system: Duclos is RHAG1 (030001); Ol(a) is RHAG2 (030002); and DSLK is provisionally RHAG3 (030003).

Evolution of non-coding regulatory sequences involved in the developmental process: reflection of differential employment of paralogous genes as highlighted by Sox2 and group B1 Sox genes

In higher vertebrates, the expression of Sox2, a group B1 Sox gene, is the hallmark of neural primordial cell state during the developmental processes from embryo to adult. Sox2 is regulated by the combined action of many enhancers with distinct spatio-temporal specificities. DNA sequences for these enhancers are conserved in a wide range of vertebrate species, corresponding to a majority of highly conserved non-coding sequences surrounding the Sox2 gene, corroborating the notion that the conservation of non-coding sequences mirrors their functional importance. Among the Sox2 enhancers, N-1 and N-2 are activated the earliest in embryogenesis and regulate Sox2 in posterior and anterior neural plates, respectively. These enhancers differ in their evolutionary history: the sequence and activity of enhancer N-2 is conserved in all vertebrate species, while enhancer N-1 is fully conserved only in amniotes. In teleost embryos, Sox19a/b play the major pan-neural role among the group B1 Sox paralogues, while strong Sox2 expression is limited to the anterior neural plate, reflecting the absence of posterior CNS-dedicated enhancers, including N-1. In Xenopus, neurally expressed SoxD is the orthologue of Sox19, but Sox3 appears to dominate other B1 paralogues. In amniotes, however, Sox19 has lost its group B1 Sox function and transforms into group G Sox15 (neofunctionalization), and Sox2 assumes the dominant position by gaining enhancer N-1 and other enhancers for posterior CNS. Thus, the gain and loss of specific enhancer elements during the evolutionary process reflects the change in functional assignment of particular paralogous genes, while overall regulatory functions attributed to the gene family are maintained.

Anteroventrally localized activity in the optic vesicle plays a crucial role in the optic development

The vertebrate eye develops from the optic vesicle (OV), a laterally protrusive structure of the forebrain, by a coordinated interaction with surrounding tissues. The OV then invaginates to form an optic cup, and the lens placode develops to the lens vesicle at the same time. These aspects in the early stage characterize vertebrate eye formation and are controlled by appropriate dorsal-ventral coordination. In the present study, we performed surgical manipulation in the chick OV to remove either the dorsal or ventral half and examined the development of the remaining OV. The results show that the dorsal and ventral halves of the OV have a clearly different developmental pattern. When the dorsal half was removed, the remaining ventral OV developed into an entire eye, while the dorsal OV developed to a pigmented vesicle consisting of retinal pigmented epithelium alone. These results indicate that the ventral part of the OV retains the potency to develop the entire eye structure and plays an essential role in proper eye development. In subsequent manipulations of early chick embryos, it was found that only the anterior ventral quadrant of the OV has the potential to develop the entire eye and that no other part of the OV has a similar activity. Fgf8 expression was localized in this portion and no Fgf8 expression was observed within the OV when the ventral OV was removed. These results suggest that the anterior ventral portion of the OV plays a crucial role in the proper development of the eye, possibly generating the dorsal-ventral gradients of signal proteins within the eye primordium.

Nuclear RNA export factor 7 is localized in processing bodies and neuronal RNA granules through interactions with shuttling hnRNPs

The nuclear RNA export factor (NXF) family proteins have been implicated in various aspects of post-transcriptional gene expression. This study shows that mouse NXF7 exhibits heterologous localization, i.e. NXF7 associates with translating ribosomes, stress granules (SGs) and processing bodies (P-bodies), the latter two of which are believed to be cytoplasmic sites of storage, degradation and/or sorting of mRNAs. By yeast two-hybrid screening, a series of heterogeneous nuclear ribonucleoproteins (hnRNPs) were identified as possible binding partners for NXF7. Among them, hnRNP A3, which is believed to be involved in translational control and/or cytoplasmic localization of certain mRNAs, formed a stable complex with NXF7 in vitro. Although hnRNP A3 was not associated with translating ribosomes, it was co-localized with NXF7 in P-bodies. After exposing to oxidative stress, NXF7 trans-localized to SGs, whereas hnRNP A3 did not. In differentiated neuroblastoma Neuro2a cells, NXF7 was co-localized with hnRNP A3 in cell body and neurites. The amino terminal half of NXF7, which was required for stable complex formation with hnRNP A3, coincided with the region required for localization in both P-bodies and neuronal RNA granules. These findings suggest that NXF7 plays a role in sorting, transport and/or storage of mRNAs through interactions with hnRNP A3.

PAX6 and SOX2-dependent regulation of the Sox2 enhancer N-3 involved in embryonic visual system development

Sox2 is universally expressed in the neural and placodal primordia in early stage embryos, and this expression depends on various phylogenetically conserved enhancers having different regional and temporal specificities. The enhancer N-3 was identified as a regulator of the Sox2 gene active in the diencephalon, optic vesicle, and after the contact of the vesicle with the ectoderm, in the lens placodal surface area, suggesting its involvement in embryonic visual system development. A 36-bp minimal essential core sequence was defined in the 568-bp-long enhancer N-3, which in a tetrameric form emulates the original enhancer activity. The core sequence comprises a SOX-binding sequence and a non-canonical PAX6 (Paired domain) binding sequence, and is activated by the synergistic action of SOX2 and PAX6 in transfected cells. The SOX and PAX6 binding sequences of the N-3 core are arranged with the same orientation and spacing as the DC5 sequence of the delta-crystallin enhancer previously demonstrated to be cooperatively bound by SOX2 and PAX6. The N-3 core sequence was also bound by these factors in a cooperative fashion, but with a higher threshold of these factors' levels than DC5, and the enhancer effect of the tetrameric sequence activated by exogenous SOX2 and PAX6 was less pronounced than that of DC5. The observations suggest that gene activation mechanisms that depend on the cooperative interaction of SOX2 and PAX6 but with different thresholds of the factor levels are crucial for the regulation of visual system development.

Identification of a prosencephalic-specific enhancer of SALL1: comparative genomic approach using the chick embryo

Comparative genomics is a promising approach for identifying regulatory elements governing the unique spatio-temporal expression patterns of morphogenetic genes. Conserved noncoding genomic sequences are candidate regulatory elements. Here we performed a survey for conserved noncoding elements (CNE) nested within the SALL1 gene; mutations in this gene result in the Townes-Brocks syndrome. A comparison of the genomic sequence between humans and chicken revealed five CNE. Genomic fragments corresponding to each CNE were inserted into reporter cassettes consisting of eGFP cDNA and a minimal promoter. These constructs were electroporated into chick embryos during gastrula, neurula, and pharyngula stages. Among the five CNE that were examined, one 443 bp CNE exhibited tissue-specific enhancer activity. At the neurula stage, the eGFP signal was visualized in the prosencephalon. At the pharyngula stage, the eGFP signal was confined within the anterior neural ridge, which represents one of the morphogenetic centers regulating the patterning of the anterior neural plate. This report identifies, for the first time, an enhancer element of SALL1.

Comparative genomic and expression analysis of group B1soxgenes in zebrafish indicates their diversification during vertebrate evolution

Group B1 Sox genes encode HMG domain transcription factors that play major roles in neural development. We have identified six zebrafish B1 sox genes, which include pan-vertebrate sox1a/b, sox2, and sox3, and also fish-specific sox19a/b. SOX19A/B proteins show a transcriptional activation potential that is similar to other B1 SOX proteins. The expression of sox19a and sox3 begins at approximately the 1,000-cell stage during embryogenesis and becomes confined to the future ectoderm by the shield stage. This is reminiscent of the epiblastic expression of Sox2 and/or Sox3 in amniotes. As development progresses, these six B1 sox genes display unique expression patterns that overlap distinctly from one region to another. sox19a expression is widespread in the early neuroectoderm, resembling pan-neural Sox2 expression in amniotes, whereas zebrafish sox2 shows anterior-restricted expression. Comparative genomics suggests that sox19a/b and mammalian Sox15 (group G) have an orthologous relationship and that the B1/G Sox genes arose from a common ancestral gene through two rounds of genome duplication. It seems likely, therefore, that each B1/G Sox gene has gained a distinct expression profile and function during vertebrate evolution.

Convergence of Wnt and FGF signals in the genesis of posterior neural plate through activation of the Sox2 enhancer N-1

The expression of the transcription factor gene Sox2 precisely marks the neural plate in various vertebrate species. We previously showed that the Sox2 expression prevailing in the neural plate of chicken embryos is actually regulated by the coordination of five phylogenetically conserved enhancers having discrete regional coverage, among which the 420-bp long enhancer N-1, active in the node-proximal region, is probably involved directly in the genesis of the posterior neural plate. We investigated the signaling systems regulating this enhancer, first identifying the 56-bp N-1 core enhancer (N-1c), which in a trimeric form recapitulates the activity of the enhancer N-1. Mutational analysis identified five blocks, A to E, that regulate the enhancer N-1c. Functional analysis of these blocks indicated that Wnt and FGF signals synergistically activate the enhancer through Blocks A-B, bound by Lef1, and Block D, respectively. Fgf8b and Wnt8c expressed in the organizer-primitive streak region account for the activity in the embryo. Block E is essential for the repression of the enhancer N-1c activity in the mesendodermal precursors. The enhancer N-1c is not affected by BMP signals. Thus, Wnt and FGF signals converge to activate Sox2 expression through the enhancer N-1c, revealing the direct involvement of the Wnt signal in the initiation of neural plate development.

Multiple N-cadherin enhancers identified by systematic functional screening indicate its Group B1 SOX-dependent regulation in neural and placodal development

Neural plate and sensory placodes share the expression of N-cadherin and Group B1 Sox genes, represented by Sox2. A 219-kb region of the chicken genome centered by the N-cadherin gene was scanned for neural and placodal enhancers. Random subfragments of 4.5 kb average length were prepared and inserted into tkEGFP reporter vector to construct a library with threefold coverage of the region. Each clone was then transfected into N-cadherin-positive (lens, retina and forebrain) or -negative embryonic cells, or electroporated into early chicken embryos to examine enhancer activity. Enhancers 1-4 active in the CNS/placode derivatives and non-specific Enhancer 5 were identified by transfection, while electroporation of early embryos confirmed enhancers 2-4 as having activity in the early CNS and/or sensory placodes but with unique spatiotemporal specificities. Enhancers 2-4 are dependent on SOX-binding sites, and misexpression of Group B1 Sox genes in the head ectoderm caused ectopic development of placodes expressing N-cadherin, indicating the involvement of Group B1 Sox functions in N-cadherin regulation. Enhancers 1, 2 and 4 correspond to sequence blocks conserved between the chicken and mammalian genomes, but enhancers 3 and 5 are unique to the chicken.

Interplay of Pax6 and SOX2 in lens development as a paradigm of genetic switch mechanisms for cell differentiation

When the cloning era arrived, our first target for cloning was the delta1-crystallin gene of the chicken, the lens-specific gene expressed earliest following lens induction. We have investigated the regulation of this gene with the idea that the mechanism of its activation must reflect that of lens differentiation per se. We here summarize the investigation carried out in our group along this line over the past 20 years. The delta1-crystallin gene is regulated by an enhancer in the third intron, and the specificity of this regulation is governed by a DNA region (called DC5) of only 30 bp DNA bound by two transcription factors. These factors have been identified as SOX1/2/3 (Group B1 SOX proteins, SOX2 being the major player) and Pax6, and have been shown to bind cooperatively to DC5 and form a ternary complex having a robust potency for transcriptional activation. In the embryo, Pax6 is widely expressed in the head ectoderm before the lens is formed, and as the optic vesicle comes into contact with the ectoderm, SOX2/3 expression is induced in the contacted area of the ectoderm, thereby allowing Pax6 and SOX2/3 to meet in the same cell nucleus, where they can then activate a battery of genes for early lens development including delta1-crystallin. Thus, the cooperative action of Pax6 and SOX2 initiates lens differentiation. More broadly, SOX1/2/3 interact with various partner transcription factors, and participate in defining distinct cell states that depend on the partner factors: Pax6 for lens differentiation, Oct3/4 for establishing the epiblast/ES cell state, and Brn2 for the neural primordia. Thus, the regulation of SOX2 (and SOX1/3) and its partner factors, exemplified by Pax6, determines the spatio-temporal order of the occurrence of cell differentiation.

Efficient identification of regulatory sequences in the chicken genome by a powerful combination of embryo electroporation and genome comparison

Recently expanded knowledge of gene regulation clearly indicates that the regulatory sequences of a gene, usually identified as enhancers, are widely distributed in the gene locus, revising the classical view that they are clustered in the vicinity of genes. To identify regulatory sequences for Sox2 expression governing early neurogenesis, we scanned the 50-kb region of the chicken Sox2 locus for enhancer activity utilizing embryo electroporation, resulting in identification of a number of enhancers scattered throughout the analyzed genomic span. The 'pan-neural' Sox2 expression in early embryos is actually brought about by the composite activities of five separate enhancers with distinct spatio-temporal specificities. These and other functionally defined enhancers exactly correspond to extragenic sequence blocks that are conspicuously conserved between the chicken and mammalian genomes and that are embedded in sequences with a wide range of sequence conservation between humans and mice. The sequences conserved between amniotes and teleosts correspond to subregions of the enhancer subsets which presumably represent core motifs of the enhancers, and the limited conservation partly reflects divergent expression patterns of the gene. The phylogenic distance between the chicken and mammals appears optimal for identifying a battery of genetic regulatory elements as conserved sequence blocks, and chicken embryo electroporation facilitates functional characterization of these elements.

Gene arrangement at the Rhesus blood group locus of chimpanzees detected by fiber-FISH

The Rhesus (Rh) blood group system in humans is encoded by two genes with high sequence homology. These two genes, namely, RHCE and RHD, have been implied to be duplicated during evolution. However, the genomic organization of Rh genes in chimpanzees and other nonhuman primates has not been precisely studied. We analyzed the arrangement of the Rh genes of chimpanzees (Pan troglodytes) by two-color fluorescence in situ hybridization on chromatin DNA fibers (fiber-FISH) using two genomic DNA probes that respectively contain introns 3 and 7 of human RH genes. Among the five chimpanzees studied, three were found to be homozygous for the two-Rh-gene type, in an arrangement of Rh (5'-->3') - Rh (3'<--5'). Although a similar gene arrangement can be detected in the RH gene locus of typical Rh-positive humans, the distance between the two genes in chimpanzees was about 50 kb longer than that in humans. The remaining two chimpanzees were homozygous for a four-Rh-gene type, in an arrangement of Rh (5'-->3') - Rh (3'<--5') - Rh (3'<--5') - Rh (3'<--5') within a region spanning about 300 kb. This four-Rh-gene type has not been detected in humans. Further analysis of other great apes showed different gene arrangements: a bonobo was homozygous for the three-Rh-gene type; a gorilla was heterozygous for the one-Rh- and two-Rh-gene types; an orangutan was homozygous for the one-Rh-gene type. Our findings on the intra- and interspecific genomic variations in the Rh gene locus in Hominoids would shed further light on reconstructing the genomic pathways of Rh gene duplication during evolution.

Chromosome assignment of eight SOX family genes in chicken

Chromosome locations of the eight SOX family genes, SOX1, SOX2, SOX3, SOX5, SOX9, SOX10, SOX14 and SOX21, were determined in the chicken by fluorescence in situ hybridization. The SOX1 and SOX21 genes were localized to chicken chromosome 1q3.1-->q3.2, SOX5 to chromosome 1p1.6-->p1.4, SOX10 to chromosome 1p1.6, and SOX3 to chromosome 4p1.2-->p1.1. The SOX2 and SOX14 genes were shown to be linked to chromosome 9 using two-colored FISH and chromosome painting, and the SOX9 gene was assigned to a pair of microchromosomes. These results suggest that these SOX genes form at least three clusters on chicken chromosomes. The seven SOX genes, SOX1, SOX2, SOX3, SOX5, SOX10, SOX14 and SOX21 were localized to chromosome segments with homologies to human chromosomes, indicating that the chromosome locations of SOX family genes are highly conserved between chicken and human.