DNA-binding specificity of the S8 homeodomain

Identification of a fish short-chain dehydrogenase/reductase associated with bone metabolism

Although human and mouse genetics have largely contributed to the better understanding of the mechanisms underlying skeletogenesis, much more remains to be uncovered. In this regard alternative and complementary systems have been sought and cell systems capable of in vitro calcification have been developed to study the mechanisms underlying bone formation. In gilthead seabream (Sparus aurata), a gene coding for an unknown protein that is strongly up-regulated during extracellular matrix (ECM) mineralization of a pre-osteoblast cell line was recently identified as a potentially important player in bone formation. In silico analysis of the deduced protein revealed the presence of domains typical of short-chain dehydrogenase/reductases (SDR). Closely related to carbonyl reductase 1, seabream protein belongs to a novel subfamily of SDR proteins with no orthologs in mammals. Analysis of gene expression by qPCR confirmed the strong up-regulation of sdr-like expression during in vitro mineralization but also revealed high expression levels in calcified tissues. A possible role for Sdr-like in osteoblast and bone metabolism was further evidenced through (i) the localization by in situ hybridization of sdr-like transcript in pre-osteoblasts of the operculum and (ii) the regulation of sdr-like gene transcription by Runx2 and retinoic acid receptor, two regulators of osteoblast differentiation and mineralization. Expression data also indicated a role for Sdr-like in gastrointestinal tract homeostasis and during gilthead seabream development at gastrulation and metamorphosis. This study reports a new subfamily of short-chain dehydrogenases/reductases in vertebrates and, for the first time, provides evidence of a role for SDRs in bone metabolism, osteoblast differentiation and/or tissue mineralization.

TdIF1 recognizes a specific DNA sequence through its Helix-Turn-Helix and AT-hook motifs to regulate gene transcription

TdIF1 was originally identified as a protein that directly binds to DNA polymerase TdT. TdIF1 is also thought to function in transcription regulation, because it binds directly to the transcriptional factor TReP-132, and to histone deacetylases HDAC1 and HDAC2. Here we show that TdIF1 recognizes a specific DNA sequence and regulates gene transcription. By constructing TdIF1 mutants, we identify amino acid residues essential for its interaction with DNA. An in vitro DNA selection assay, SELEX, reveals that TdIF1 preferentially binds to the sequence 5′-GNTGCATG-3′ following an AT-tract, through its Helix-Turn-Helix and AT-hook motifs. We show that four repeats of this recognition sequence allow TdIF1 to regulate gene transcription in a plasmid-based luciferase reporter assay. We demonstrate that TdIF1 associates with the RAB20 promoter, and RAB20 gene transcription is reduced in TdIF1-knocked-down cells, suggesting that TdIF1 stimulates RAB20 gene transcription.

Analysis on DNA sequence of goat RFRP gene and its possible association with average daily sunshine duration

Goat RFRP gene was cloned and its mutations were detected in thirteen goat breeds whose reproductive seasonality and litter size were different. Then sequence characteristics were analyzed and association analyses were performed to reveal the relationships between mutations of RFRP gene and average daily sunshine duration, reproductive seasonality as well as litter size in goats. A 4,862 bp DNA fragment of goat RFRP gene was obtained and the complete CDS of 591 bp encodes 196 amino acids, having high homology with that of other mammals. The protein was predicted to be a secreted protein with a signal peptide of 21 amino acids. Moreover, two mutations (A712G, T1493C) in 5' regulatory region and one mutation (A3438T) in exon 2 were detected. The test of genotype distribution in six selective goat breeds showed that there was no uniform significant association between the three polymorphisms and seasonal reproduction. The association just existed in some goat breeds for each locus. Interestingly, however, there was a strong positive correlation (r = 0.830, P = 0.003) between the G allele frequency of the A712G locus and average daily sunshine duration in ten local goat breeds, suggesting that RFRP gene has undergone a selective pressure in sunshine duration and may have indirect relationship with reproductive seasonality in goats. Additionally, no significant difference was found in litter size between genotypes in prolific Jining Grey goats.

Promoter analysis of ventricular myosin heavy chain (vmhc) in zebrafish embryos

In zebrafish, ventricular myosin heavy chain (vmhc) gene is initially expressed at the anterior lateral mesoderm and thereafter its expression is restricted to the cardiac ventricle. The transcriptional control mechanisms in regulating chamber-specific expression of myosin heavy chains are not well defined. We isolated and analyzed zebrafish vmhc upstream region to examine the spatial and temporal regulation of vmhc using transgenic and transient expression techniques. Promoter deletion analyses defined a basal promoter region sufficient to drive vmhc expression in the ventricle and an upstream fragment necessary for repressing ectopic vmhc expression in the atrium. The transcriptional mechanism that prevents vmhc expression in the atrium is mediated through Nkx2.5 binding elements (NKE). We have further discovered that paired-related homeobox transcriptional factor 2 (Prx2/S8)-like binding elements are required for promoting vmhc expression, and Prrx1b, a Prx-related homeobox protein, participates in the regulation of vmhc expression with other transcriptional factors.

Dimeric PROP1 binding to diverse palindromic TAAT sequences promotes its transcriptional activity

Mutations in the Prop1 gene are responsible for murine Ames dwarfism and human combined pituitary hormone deficiency with hypogonadism. Recently, we reported that PROP1 is a possible transcription factor for gonadotropin subunit genes through plural cis-acting sites composed of AT-rich sequences containing a TAAT motif which differs from its consensus binding sequence known as PRDQ9 (TAATTGAATTA). This study aimed to verify the binding specificity and sequence of PROP1 by applying the method of SELEX (Systematic Evolution of Ligands by EXponential enrichment), EMSA (electrophoretic mobility shift assay) and transient transfection assay. SELEX, after 5, 7 and 9 generations of selection using a random sequence library, showed that nucleotides containing one or two TAAT motifs were accumulated and accounted for 98.5% at the 9th generation. Aligned sequences and EMSA demonstrated that PROP1 binds preferentially to 11 nucleotides composed of an inverted TAAT motif separated by 3 nucleotides with variation in the half site of palindromic TAAT motifs and with preferential requirement of T at the nucleotide number 5 immediately 3' to a TAAT motif. Transient transfection assay demonstrated first that dimeric binding of PROP1 to an inverted TAAT motif and its cognates resulted in transcriptional activation, whereas monomeric binding of PROP1 to a single TAAT motif and an inverted ATTA motif did not mediate activation. Thus, this study demonstrated that dimeric binding of PROP1 is able to recognize diverse palindromic TAAT sequences separated by 3 nucleotides and to exhibit its transcriptional activity.

Molecular cloning of paired related homeobox 2 (prx2) as a novel pituitary transcription factor

This study aimed to identify protein(s) that bind(s) to the highly AT-rich sequence of porcine Fshb promoter region -852/-746 (named Fd2) by the Yeast One-Hybrid Cloning System and finally a paired related homeodomain transcription factor, Prx2, known as a key factor for skeletogenesis was cloned. RT-PCR analysis of fetal and postnatal porcine pituitaries demonstrated that Prx2 starts to be expressed at around fetal days 40-50 just before the beginning of Lhb-expression and that the level of Prx2 increases after birth. Immunohistochemical analysis of the prepubertal porcine pituitary revealed that some Prx2-positive cells overlap some Lh beta-positive cells. Transient transfection assay using non-pituitary CHO cells and pituitary tumor-derived LbetaT2 cells revealed that Prx2 plays a cell-type dependent role in modulation of the Fshb promoter, showing stimulation in CHO cells and repression in LbetaT2 cells via the regions of Fd2 and -596/-239. The binding ability of Prx2 to the regions of Fd2 and -596/-239 was confirmed by electrophoretic mobility shift assay. DNase I footprinting revealed that broad regions of Fd2 were bound by Prx2 and that -596/-239 contained seven Prx2-binding sites. The SELEX method using a random N15-mer oligonucleotide pool demonstrated that Prx2 monomer binds to a TAATT motif, which is present in Fd2 and -596/-239. However, the binding of Prx2 to TAATT with a single molecule and its inverted repeat with two molecules could not induce transcriptional activation, indicating that the Prx2-dependent transcriptional modulation demonstrated in cultured cells is not introduced by Prx2 alone. Thus, this study demonstrated for the first time that Prx2 is expressed in the pituitary gland and at least in a part of gonadotropes in which Prx2 may play a role in repression of the Fshb gene.

A homeodomain-zinc finger protein, ZFHX4, is expressed in neuronal differentiation manner and suppressed in muscle differentiation manner

Human ZFHX4 has recently been shown to be a candidate gene for congenital bilateral isolated ptosis. Here, we report molecular cloning of the human ZFHX4 cDNA and genomic organization of this gene. Human ZFHX4 is about 180 kb long, containing 12 exons that encodes a 3599-amino acid protein carrying four homeodomains and 22 zinc fingers. The 11th exon is 3.2 kb in length and encodes all the four homeodomains together with four of the 22 zinc fingers. ZFHX4 is 90% homologous to mouse Zfhx4, 52% to human ATBF1A and 24% to Drosophila ZFH-2. ZFHX4 was mapped to human chromosome 8q13.3-q21.11 by fluorescence in situ hybridization using BAC clone RP11-48D4 as a probe. RT-PCR analysis showed that ZFHX4 transcripts were expressed in adult human brain, liver and muscle. This, together with the finding that Zfhx4 was expressed transiently in differentiating P19 embryonal carcinoma cells and C2C12 myoblasts, suggests that ZFHX4/Zfhx4 is involved in neural and muscle differentiation.

DNA Binding Domains and Nuclear Localization Signal of LEDGF: Contribution of two Helix-Turn-Helix (HTH)-like Domains and a Stretch of 58 Amino Acids of the N-terminal to the Trans-activation Potential of LEDGF

Lens epithelium derived growth factor (LEDGF), a nuclear protein, plays a role in regulating the transcription of stress-associated genes such as heat shock proteins by binding to consensus core DNA sequences nAGGn or nGAAn or their repeats, and in doing so helps to provide cyto-protection. However, additional information is required to identify the specific structural features of LEDGF involved in gene transcription. Here we have investigated the functional domains activating and repressing DNA-binding modules, by using a DNA binding assay and trans-activation experiments performed by analyzing proteins prepared from deletion constructs. The results disclosed the DNA-binding domain of N-terminal LEDGF mapped between amino acid residues 5 and 62, a 58 amino acid residue stretch PWWP domain which binds to stress response elements (STRE; A/TGGGGA/T). C-terminal LEDGF contains activation domains, an extensive loop-region (aa 418-530) with two helix-turn-helix (HTH)-like domains, and binds to a heat shock element (HSE; nGAAn). A trans-activation assay using Hsp27 promoter revealed that both HTH domains contribute in a cooperative manner to the trans-activation potential of LEDGF. Interestingly, removal of N-terminal LEDGF (aa 1-187) significantly enhances the gene activation potential of C-terminal LEDGF (aa 199-530); thus the N-terminal domain (aa 5-62), exhibits auto-transcriptional repression activity. It appears that this domain is involved in stabilizing the LEDGF-DNA binding complex. Collectively, our results demonstrate that LEDGF contains three DNA-binding domains, which regulate gene expression depending on cellular microenvironment and thus modify the physiology of cells to maintain cellular homeostasis.

A phylogenetically conserved cis-regulatory module in the Msx2 promoter is sufficient for BMP-dependent transcription in murine and Drosophila embryos

To understand the actions of morphogens, it is crucial to determine how they elicit different transcriptional responses in different cell types. Here, we identify a BMP-responsive enhancer of Msx2, an immediate early target of bone morphogenetic protein (BMP) signaling. We show that the BMP-responsive region of Msx2 consists of a core element, required generally for BMP-dependent expression, and ancillary elements that mediate signaling in diverse developmental settings. Analysis of the core element identified two classes of functional sites: GCCG sequences related to the consensus binding site of Mad/Smad-related BMP signal transducers; and a single TTAATT sequence, matching the consensus site for Antennapedia superclass homeodomain proteins. Chromatin immunoprecipitation and mutagenesis experiments indicate that the GCCG sites are direct targets of BMP restricted Smads. Intriguingly, however, these sites are not sufficient for BMP responsiveness in mouse embryos; the TTAATT sequence is also required. DNA sequence comparisons reveal this element is highly conserved in Msx2 promoters from mammalian orders but is not detectable in other vertebrates or non-vertebrates. Despite this lack of conservation outside mammals, the Msx2 BMP-responsive element serves as an accurate readout of Dpp signaling in a distantly related bilaterian - Drosophila. Strikingly, in Drosophila embryos, as in mice, both TTAATT and GCCG sequences are required for Dpp responsiveness, showing that a common cis-regulatory apparatus can mediate the transcriptional activation of BMP-regulated genes in widely divergent bilaterians.

Multiple signaling pathways and a selector protein sequentially regulate Drosophila wing development

Drosophila wing development is a useful model to study organogenesis, which requires the input of selector genes that specify the identity of various morphogenetic fields (Weatherbee, S. D. and Carroll, S. B. (1999) Cell 97, 283-286) and cell signaling molecules. In order to understand how the integration of multiple signaling pathways and selector proteins can be achieved during wing development, we studied the regulatory network that controls the expression of Serrate (Ser), a ligand for the Notch (N) signaling pathway, which is essential for the development of the Drosophila wing, as well as vertebrate limbs. Here, we show that a 794 bp cis-regulatory element located in the 3' region of the Ser gene can recapitulate the dynamic patterns of endogenous Ser expression during wing development. Using this enhancer element, we demonstrate that Apterous (Ap, a selector protein), and the Notch and Wingless (Wg) signaling pathways, can sequentially control wing development through direct regulation of Ser expression in early, mid and late third instar stages, respectively. In addition, we show that later Ser expression in the presumptive vein cells is controlled by the Egfr pathway. Thus, a cis-regulatory element is sequentially regulated by multiple signaling pathways and a selector protein during Drosophila wing development. Such a mechanism is possibly conserved in the appendage outgrowth of other arthropods and vertebrates.

Expression of alternatively spliced isoforms of human Sp7 in osteoblast-like cells

BACKGROUND

Osteogenic and chondrocytic differentiation involves a cascade of coordinated transcription factor gene expression that regulates proliferation and matrix protein formation in a defined temporo-spatial manner. Bone morphogenetic protein-2 induces expression of the murine Osterix/Specificity protein-7 (Sp7) transcription factor that is required for osteoblast differentiation and bone formation. Regulation of its expression may prove useful for mediating skeletal repair.

RESULTS

Sp7, the human homologue of the mouse Osterix gene, maps to 12q13.13, close to Sp1 and homeobox gene cluster-C. The first two exons of the 3-exon gene are alternatively spliced, encoding a 431-residue long protein isoform and an amino-terminus truncated 413-residue short protein isoform. The human Sp7 protein is a member of the Sp family having 78% identity with Sp1 in the three, Cys2-His2 type, DNA-binding zinc-fingers, but there is little homology elsewhere. The Sp7 mRNA was expressed in human foetal osteoblasts and craniofacial osteoblasts, chondrocytes and the osteosarcoma cell lines HOS and MG63, but was not detected in adult femoral osteoblasts. Generally, the expression of the short (or beta) protein isoform of Sp7 was much higher than the long (or alpha) protein isoform. No expression of either isoform was found in a panel of other cell types. However, in tissues, low levels of Sp7 were detected in testis, heart, brain, placenta, lung, pancreas, ovary and spleen.

CONCLUSIONS

Sp7 expression in humans is largely confined to osteoblasts and chondrocytes, both of which differentiate from the mesenchymal lineage. Of the two protein isoforms, the short isoform is most abundant.

GeneChip microarrays facilitate identification of Protease Nexin-1 as a target gene of the Prx2 (S8) homeoprotein

The paired-related homeobox genes, Prx1 and Prx2, are important for normal skeletal and cardiovascular development as well as adult vascular remodeling. The identification and characterization of Prx downstream targets is crucial to understanding their function in normal developmental processes and congenital malformations. To identify Prx2 regulated genes, stably transfected NIH3T3 clones expressing Prx2 sense or antisense transcripts were generated. Expression profiles initially were established for two of the clones using Affymetrix GeneChip arrays. Over 6,400 genes were screened by the microarray approach, and approximately 500 genes differed in expression by a factor of two or more. Fifteen genes were chosen for further analysis. RT-PCR of the two transfectants used in the GeneChip analysis demonstrated that five out of the 15 genes were differentially expressed. However, after screening additional stable transfectant clones only one of the 15 genes, Protease Nexin-1 (PN-1), was differentially expressed. Subsequent Northern blot, RT-PCR, and further GeneChip analysis of additional stable transfectants confirmed that PN-1 expression is increased at least fivefold when Prx2 is overexpressed. It was demonstrated that Prx2 directly regulates PN-1 because (1) Prx2 binds to a cis element in the PN-1 promoter in vitro, and (2) Prx2 regulates the PN-1 promoter in transient transfection assays. The GeneChip analysis generated a prioritized list of other potential targets. The utility and limitations of cell culture models combined with microarray analysis for elucidating complex regulatory cascades are discussed.

Organic anion and cation transporters occur in pairs of similar and similarly expressed genes

Organic anion and cation transporters (OATs, OCTs, OCTNs, and ORCTLs), transmembrane proteins essential to renal xenobiotic excretion, are encoded by a group of related genes. As yet there have been no studies of the transcriptional regulation of this important gene family. While such studies have traditionally been labor-intensive, comparative genomics approaches are now available that have proven reliable guides to critical regulatory elements. We report here the genomic sequencing of murine OAT1 (the cDNA of which was originally cloned by us as NKT) and OAT3 (Roct), and derivation of phylogenetic footprints (evolutionarily conserved non-coding sequences) by comparison to the human genome. We find binding sites within these footprints for several transcription factors implicated in kidney development, including PAX1, PBX, WT1, and HNF1. Additionally, we note that OATs and OCTs occur in the human and mouse genomes as tightly linked pairs (OAT1 and OAT3, UST3 and OAT5, OAT4 and URAT1/RST, OCT1 and 2, OCTN1 and 2, ORCTL3 and 4) that are also close phylogenetic relations, with Flipt1 and 2, and OAT2 the only unpaired family members. Finally, we find that pair-members have similar tissue distributions, suggesting that the pairing might exist to facilitate the co-regulation of the genes within each pair.

Adhesion, migration, transcriptional, interferon-inducible, and other signaling molecules newly implicated in cancer susceptibility and resistance of JB6 cells by cDNA microarray analyses

Relative expression levels of 9500 genes were determined by cDNA microarray analyses in mouse skin JB6 cells susceptible (P+) and resistant (P-) to 12-O-tetradecanoyl phorbol-13 acetate (TPA)-induced neoplastic transformation. Seventy-four genes in 6 functional classes were differentially expressed: (I) extracellular matrix (ECM) and basement membrane (BM) proteins (20 genes). P+ cells express higher levels than P- cells of several collagens and proteases, and lower levels of protease inhibitors. Multiple genes encoding adhesion molecules are expressed preferentially in P- cells, including six genes implicated in axon guidance and adhesion. (II) Cytoskeletal proteins (13 genes). These include actin isoforms and regulatory proteins, almost all preferentially expressed in P- cells. (III) Signal transduction proteins (12 genes). Among these are Ras-GTPase activating protein (Ras-GAP), the deleted in oral cancer-1 and SLIT2 tumor suppressors, and connexin 43 (Cx43) gap junctional protein, all expressed preferentially in P- cells. (IV) Interferon-inducible proteins (3 genes). These include interferon-inducible protein (IFI)-16, an Sp1 transcriptional regulator expressed preferentially in P- cells. (V) Other transcription factors (4 genes). Paired related homeobox gene 2 (Prx2)/S8 homeobox, and retinoic acid (RA)-regulated nur77 and cellular retinoic acid-binding protein II (CRABPII) transcription factors are expressed preferentially in P- cells. The RIN-ZF Sp-transcriptional suppressor exhibits preferential P+ expression. (VI) Genes of unknown functions (22 sequences). Numerous mesenchymal markers are expressed in both cell types. Data for multiple genes were confirmed by real-time PCR. Overall, 26 genes were newly implicated in cancer. Detailed analyses of the functions of the genes and their interrelationships provided converging evidence for their possible roles in implementing genetic programs mediating cancer susceptibility and resistance. These results, in conjunction with cell wounding and phalloidin staining data, indicated that concerted genetic programs were implemented that were conducive to cell adhesion and tumor suppression in P- cells and that favored matrix turnover, cell motility, and abrogation of tumor suppression in P+ cells. Such genetic programs may in part be orchestrated by Sp-, RA-, and Hox-transcriptional regulatory pathways implicated in this study.

A novel muscle-specific enhancer identified within the deletion overlap region of two XLDC patients lacking muscle exon 1 of the human dystrophin gene

Previous studies point to the involvement of several discrete transcriptional enhancers in the modulation of dystrophin gene expression in skeletal and cardiac muscle. Analysis of deletion breakpoints in two X-linked dilated cardiomyopathy patients with mutations that remove muscle exon 1 identified a 3.2-kb deletion overlap region (XLDC3.2) between -1199 and +2057 bp predicted to contain regulatory elements essential for dystrophin gene expression in cardiac muscle. A novel-sequence-based search strategy was used to identify a 543-bp region downstream of muscle exon 1 rich in cardiac-specific transcriptional elements. Designated dystrophin muscle enhancer 2 (DME2), this candidate enhancer was seen to function in a position- and orientation-independent manner in muscle cell lines but not in fibroblasts. As only modest activity was observed in primary neonatal rat cardiomyocytes, DME2 is thought to play a role in dystrophin gene regulation at later stages of cardiac muscle development.

CL-46, a novel collectin highly expressed in bovine thymus and liver

Collectins are oligomeric molecules with C-type lectin domains attached to collagen-like regions via alpha-helical neck regions. They bind nonself glycoconjugates on the surface of microorganisms and inhibit infection by direct neutralization, agglutination, or opsonization. During the characterization of the gene encoding bovine CL-43 (43-kDa collectin), we identified a novel collectin-gene. We report the cloning and partial characterization of the novel collectin CL-46. The mRNA comprises 1188 nucleotides encoding a protein of 371 aa with an included leader peptide of 20 residues. CL-46 has two cysteine residues in the N-terminal segment, a potential N-glycosylation site in the collagen region, and an extended hydrophilic loop close to the binding site of the carbohydrate recognition domain. It is expressed in the thymus, liver, mammary gland, and tissues of the digestive system. Recombinant CL-46 corresponding to the alpha-helical neck region and the C-type lectin domain binds preferential N-acetyl-D-glucoseamine and N-acetyl-D-mannoseamine. The gene encoding CL-46 spans approximately 10 kb and consists of eight exons, with high structural resemblance to the gene encoding human surfactant protein D. It is located on the bovine chromosome 28 at position q1.8 together with the gene encoding conglutinin and CL-43. Several potential thymus-related cis-regulatory elements were identified in the 5'-upstream sequence, indicating that the expression in thymus may be modulated by signals involved in T cell development.

Characterization and expression analyses of the mouse Wiskott-Aldrich syndrome protein (WASP) family member Wave1/Scar

Characterization of multiprotein complexes involved in actin remodeling and cytoskeleton reorganization is essential to understand the basic mechanisms of cell motility and migration. To identify proteins implicated in these processes, we have isolated the mouse Wave1/Scar gene, a member of the Wiskott-Aldrich syndrome protein (WASP) family. The mouse Wave1 gene was physically localized on chromosome 10 and spans over 12 Kb comprising eight exons and seven introns. The mouse Wave1 complementary DNA encodes a predicted 559 amino acid protein, with a SCAR homology domain, a basic domain, a proline-rich region, a WASP homology domain and an acidic domain conserved in the orthologous proteins. The Wave1 transcription initiation site was mapped 210 base pairs upstream of the ATG translational start site. The presumptive proximal promoter contains putative consensus binding sites for E2 basic helix-loop-helix transcription factors, hepatocyte nuclear factor-3beta, S8 homeodomain protein, zinc finger transcription factor MZF-1, and an interferon-stimulated response element. Northern analysis demonstrated a strong expression of a unique approximately 2.6 Kb Wave1 transcript in brain tissue, and in situ hybridization showed restricted expression to Purkinje cells from the cerebellum and pyramidal cells from the hippocampus. Characterization and expression analyses of the murine Wave1 gene provide the basis toward functional studies in mouse models of the role of Wave1 in neuronal cytoskeleton organization.

The KLHL1-antisense transcript ( KLHL1AS) is evolutionarily conserved

Spinocerebellar ataxia type 8 (SCA8) is caused by a CTG expansion in an untranslated, endogenous antisense RNA that overlaps the Kelch-like 1 ( KLHL1) gene. The normal function of this transcript is currently unknown. We have now identified the promoter region for the KLHL1-antisense ( KLHL1AS) RNA and report that a Klhl1as transcript is present in the mouse as well. Human and mouse KLHL1AS are transcribed from homologous promoter regions in the first intron of KLHL1 and extend through the transcription and translation start sites as well as the first splice donor sequence of KLHL1. We found that the mouse Klhl1as RNA is not spliced and terminates in a polyadenylation site in the Klhl1 promoter region, whereas both the present and previous work show that human KLHL1AS is highly variably spliced into processed transcripts that contain up to six exons. Mouse Klhl1as transcript was detected in RNA isolated from the cerebellum and from total adult brain and total fetal tissue, and at a low level in testis and ovary. Similarly, human KLHL1AS is expressed in various brain tissues, including the cerebellum, the tissue most affected by SCA8, and was detected at low levels in testis and kidney. The evolutionary conservation of this antisense/sense transcriptional organization strongly indicates that KLHL1AS transcripts play a significant biological role in both human and mouse, presumably as a regulator of KLHL1 expression.

Comparative genomics of the SOX9 region in human and Fugu rubripes: conservation of short regulatory sequence elements within large intergenic regions

Campomelic dysplasia (CD), a human skeletal malformation syndrome with XY sex reversal, is caused by heterozygous mutations in and around the gene SOX9. SOX9 has an extended 5' control region, as indicated by CD translocation breakpoints scattered over 1 Mb proximal to SOX9 and by expression data from mice transgenic for human SOX9-spanning yeast artificial chromosomes. To identify long-range regulatory elements within the SOX9 5' control region, we compared approximately 3.7 Mb and 195 kb of sequence around human and Fugu rubripes SOX9, respectively. We identified only seven and five protein-coding genes in the human and F. rubripes sequences, respectively. Four of the F. rubripes genes have been mapped in humans; all reside on chromosome 17 but show extensive intrachromosomal gene shuffling compared with the gene order in F. rubripes. In both species, very large intergenic distances separate SOX9 from its directly flanking genes: 2 Mb and 500 kb on either side of SOX9 in humans, and 68 and 97 kb on either side of SOX9 in F. rubripes. Comparative sequence analysis of the intergenic regions revealed five conserved elements, E1-E5, up to 290 kb 5' to human SOX9 and up to 18 kb 5' to F. rubripes SOX9, and three such elements, E6-E8, 3' to SOX9. Where available, mouse sequences confirm conservation of the elements. From the yeast artificial chromosome transgenic data, elements E3-E5 are candidate enhancers for SOX9 expression in limb and vertebral column, and 8 of 10 CD translocation breakpoints separate these elements from SOX9.

Genomic organization and expression of the human tumorous imaginal disc (TID1) gene

Human Tid-1, the human homologue of the Drosophila tumor suppressor lethal (2) tumorous imaginal discs, l(2) tid gene product, is a member of the DNAJ family of proteins which serve as co-chaperones to Hsp70 proteins. Here we report the cloning and characterization of the genomic structure of the human TID1 gene (hTID1), which is located on chromosome 16p13.3. hTID1 is approximately 34 kb and is composed of 12 exons. Exon sizes vary from 64 to 232 nucleotides, with the exception of exon 12 corresponding to the 3' untranslated region of hTID1, which extends over 1.1 kb. S1 nuclease protection assays and primer extension experiments indicate a putative transcriptional start site 21 nucleotides upstream of the initiating methionine. The presumptive promoter is characterized by the lack of TATA and CAAT motifs, and a high G+C content. The 5' flanking region contains several consensus binding sites for transcription factors that regulate gene expression during tissue and organ development, such as myeloid zinc finger (MZF1), Ikaros 2 and homeodomain proteins, as well as factors implicated in cell growth and survival responses, including AP-1, PEA3, E2F and NF-kB. Three alternatively spliced variants of hTID1 are expressed in a tissue and cell-type specific manner in many of the human tissues examined. The existence of these forms needs to be considered in efforts aimed at identifying mutations in the hTID1 gene.

Protein-binding elements in the proximal parotid secretory protein gene enhancer essential for salivary-gland-specific expression

The murine parotid secretory protein (PSP) gene is expressed at high levels in the parotid gland and at lower levels in the sublingual gland. A proximal enhancer core necessary for tissue-specific expression was identified previously, and it was demonstrated that one element, parotid gland element I (PGE I), exhibited specific binding of parotid gland nuclear proteins. In the present study, we demonstrate that a related adjacent element, PGE II, which binds nuclear proteins in a much less tissue-restricted manner, is able to compete with PGE I for binding of parotid-gland-specific factors. The functional significance of PGE I and PGE II was examined in transgenic mice. Deletion of PGE II reduced transgene expression only in the parotid gland, whereas deletion of PGE I appeared to reduce expression in both of the PSP-expressing salivary glands. Combined deletion of PGE I and PGE II reduced expression below the limit of detection. Thus PGE I and PGE II are functionally important salivary-gland-specific binding elements that are necessary for the salivary-gland-specific expression of a PSP minigene in transgenic mice.

The identification of Prx1 transcription regulatory domains provides a mechanism for unequal compensation by the Prx1 and Prx2 loci

Transcription regulatory domains of the Prx1a and Prx1b homeoproteins were analyzed in transient transfection assays using artificial promoters as well as an established downstream target promoter (tenascin-c). Activation and repression domains were detected in their common amino end. In the carboxyl end of Prx1a an activation domain and an inhibition/masking region (OAR domain) were detected. The Prx1b isoform, generated by alternative splicing, does not contain these carboxyl activation or inhibition domains. Instead, the data demonstrate that the carboxyl tail of Prx1b contains a potent repressor region. This difference in the carboxyl tail accounts for a 45-fold difference observed in transcription regulatory activity between Prx1a and Prx1b. The data also support the likelihood that this difference between Prx1a and Prx1b is higher in the presence of still undetermined cofactors. DNA binding affinities of Prx1a, Prx1b, and a series of truncation mutants were also examined. The carboxyl tail of Prx1a, which inhibited transcription activation in the transfection assays, also inhibited DNA binding. These differences in biochemical function between Prx1a and Prx1b, as well as the recently described activities of Prx2, provide a mechanism for the unequal compensation between the Prx1 and Prx2 loci.

Transcriptional Activation of β-Tropomyosin Mediated by Serum Response Factor and a Novel Barx Homologue, Barx1b, in Smooth Muscle Cells

Tropomyosin (TM) is a regulatory protein of actomyosin system. Muscle type-specific expression of TM isoforms is generated from different genes and by alternative splicing. beta-TM isoforms in chicken skeletal and smooth muscles are encoded by a single gene and transcribed from the same promoter. We previously reported a smooth muscle cell (SMC) phenotype-dependent change in beta-TM expression (Kashiwada, K., Nishida, W., Hayashi, K., Ozawa, K., Yamanaka, Y., Saga, H., Yamashita, T., Tohyama, M., Shimada, S., Sato, K., and Sobue, K. (1997) J. Biol. Chem. 272, 15396-15404), and identified beta-TM as an SMC-differentiation marker. Here, we characterized the transcriptional machinery of the beta-TM gene in SMCs. Promoter and gel mobility shift analyses revealed an obligatory role for serum response factor and its interaction with the CArG box sequence in the SMC-specific transcription of the beta-TM gene in differentiated SMCs. We further isolated a novel homologue of the Barx homeoprotein family, Barx1b, from chicken gizzard. Barx1b was exclusively localized to SMCs of the upper digestive organs and their attached arteries and to craniofacial structures. Serum response factor and Barx1b bound each other directly, coordinately transactivated the beta-TM gene in differentiated SMCs and heterologous cells, and formed a ternary complex with a CArG probe. Taken together, these results suggest that SRF and Barx1b are coordinately involved in the SMC-specific transcription of the beta-TM gene in the upper digestive organs and their attached arteries.

Identification of domains mediating transcription activation, repression, and inhibition in the paired-related homeobox protein, Prx2 (S8)

Despite the growing information concerning the developmental importance of the Prx2 protein, the structural determinants of Prx2 function are poorly understood. To gain insight into the transcription regulatory regions of the Prx2 protein, we generated a series of truncation mutants. Both the Prx2 response element (PRE) and a portion of the tenascin promoter, a downstream target of Prx2, were used as reporters in transient transfection assays. This analysis showed that a conserved domain (PRX), found in both Prx1 and Prx2, activated transcription in NIH 3T3 cells. This PRX domain, as well as other functional regions of Prx2, demonstrated both cell-specific and promoter-dependent transcriptional regulation. A second important region, the OAR (aristaless) domain, which is conserved among 35 Paired-type homeodomain proteins, was observed to inhibit transcription. Deletion of this element resulted in a 20-fold increase of transcription from the tenascin reporter in NIH 3T3 cells but not in C2C12 cells. The OAR domain did not function as a repressor in chimeric fusions with the Gal4 DNA binding domain in either cell type, characterizing it as an inhibitor instead of a repressor. These results give insight into the function of the Prx2 transcription factor while establishing the framework for comparison with the two isoforms of Prx1.

Tenascin-C in development and disease: gene regulation and cell function

Tenascin-C (TN-C) is a modular and multifunctional extracellular matrix (ECM) glycoprotein that is exquisitely regulated during embryonic development and in adult tissue remodeling. TN-C gene transcription is controlled by intracellular signals that are generated by multiple soluble factors, integrins and mechanical forces. These external cues are interpreted by particular DNA control elements that interact with different classes of transcription factors to activate or repress TN-C expression in a cell type- and differentiation-dependent fashion. Among the transcriptional regulators of the TN-C gene that have been identified, the homeobox family of proteins has emerged as a major player. Downstream from TN-C, intracellular signals that are relayed via specific cell surface receptors often impart contrary cellular functions, even within the same cell type. A key to understanding this behavior may lie in the dual ability of TN-C-enriched extracellular matrices to generate intracellular signals, and to define unique cellular morphologies that modulate these signal transduction pathways. Thus, despite the contention that TN-C null mice appear to develop and act normally, TN-C biology continues to provide a wealth of information regarding the complex nature of the ECM in development and disease.

Molecular characterization of the TrkA/NGF receptor minimal enhancer reveals regulation by multiple cis elements to drive embryonic neuron expression

Neural development relies on stringent regulation of key genes that mediate specialized function. TrkA is primarily expressed in neural crest-derived sensory and sympathetic neurons where it transmits critical survival information. We have identified a 457 base pair sequence upstream of the murine first TrkA coding exon that is conserved in human and in chick, and is sufficient for expression in the correct cells with appropriate timing. Mutation analysis of consensus transcription factor binding domains within the minimal enhancer reveals a complex positive regulation that includes sites required for global expression and sites that are specifically required for DRG, trigeminal or sympathetic expression. These results provide a foundation for identification of the transcriptional machinery that specifies neurotrophin receptor expression.

Sequence analyses of the olfactory receptor gene cluster mOR37 on mouse chromosome 4

The olfactory receptor multigene family is organized in clusters spread throughout the genome. In the present study, we have sequenced two subregions of the mOR37 gene cluster on mouse chromosome 4. The resulting 100 kb of sequence revealed seven odorant receptor coding regions and one gene fragment. Sequence analyses reveal that the mOR37 gene cluster may represent a rather ancient cluster. The mOR37 genes exhibit a complex intron/exon structure, and some appear to be differentially spliced. All genes in the cluster share conserved sequence motifs 5' of their putative initial exons, which represent potential binding sites for transcription factors. The clustered organization and conserved sequence motifs suggest common expression control mechanisms for these genes.

The tenascin family of ECM glycoproteins: structure, function, and regulation during embryonic development and tissue remodeling

The determination of animal form depends on the coordination of events that lead to the morphological patterning of cells. This epigenetic view of development suggests that embryonic structures arise as a consequence of environmental influences acting on the properties of cells, rather than an unfolding of a completely genetically specified and preexisting invisible pattern. Specialized cells of developing multicellular organisms are surrounded by a complex extracellular matrix (ECM), comprised largely of different collagens, proteoglycans, and glycoproteins. This ECM is a substrate for tissue morphogenesis, lends support and flexibility to mature tissues, and acts as an epigenetic informational entity in the sense that it transduces and integrates intracellular signals via distinct cell surface receptors. Consequently, ECM-receptor interactions have a profound influence on major cellular programs including growth, differentiation, migration, and survival. In contrast to many other ECM proteins, the tenascin (TN) family of glycoproteins (TN-C, TN-R, TN-W, TN-X, and TN-Y) display highly restricted and dynamic patterns of expression in the embryo, particularly during neural development, skeletogenesis, and vasculogenesis. These molecules are reexpressed in the adult during normal processes such as wound healing, nerve regeneration, and tissue involution, and in pathological states including vascular disease, tumorigenesis, and metastasis. In concert with a multitude of associated ECM proteins and cell surface receptors that include members of the integrin family, TN proteins impart contrary cellular functions, depending on their mode of presentation (i.e., soluble or substrate-bound) and the cell types and differentiation states of the target tissues. Expression of tenascins is regulated by a variety of growth factors, cytokines, vasoactive peptides, ECM proteins, and biomechanical factors. The signals generated by these factors converge on particular combinations of cis-regulatory elements within the recently identified TN gene promoters via specific transcriptional activators or repressors. Additional complexity in regulating TN gene expression is achieved through alternative splicing, resulting in variants of TN polypeptides that exhibit different combinations of functional protein domains. In this review, we discuss some of the recent advances in TN biology that provide insights into the complex way in which the ECM is regulated and how it functions to regulate tissue morphogenesis and gene expression.

Structure of the mouse metalloprotease meprin beta gene (Mep1b): alternative splicing in cancer cells

The mouse meprin beta gene encodes an integral membrane protease that is expressed in a tissue-specific manner in embryonic and adult epithelial cells, and in carcinoma cells. The meprin beta mRNA in the embryo, kidney and intestinal cells is 2.5kb, whereas the isoform in carcinoma cells (beta' mRNA) is 2.7kb. The work herein was initiated to explore the molecular mechanism responsible for the different isoforms. Overlapping fragments containing the Mep1b gene were obtained from a yeast artificial chromosome clone using polymerase chain reactions. The gene spans approximately 40kb and consists of 18 exons and 17 introns. The first three exons are unique to the 5' end of beta' mRNA; the next two exons correspond to the 5' end of beta mRNA. The rest of the exons (13 total) encode the regions common to both beta and beta' messages. In conjunction with the cDNA sequences, the gene structure establishes that alternative splicing of 5' exons is responsible for the generation of the mRNA isoforms. The DNA regions between beta'- and beta-specific exons and upstream of the first beta' exon have been completely sequenced to identify potential regulatory elements for beta and beta' transcription. There is significant homology between the two regions, indicating that a duplication event occurred during evolution of the Mep1b gene. Potential promoter elements and transcription factor-binding sites were identified from comparisons to sequences in the databanks. This is the first gene structure that has been completed for meprin subunits from all species. The work elucidates molecular mechanisms that regulate differential expression of the Mep1b gene.

Both PCE-1/RX and OTX/CRX interactions are necessary for photoreceptor-specific gene expression

RX, a homeodomain-containing protein essential for proper eye development (Mathers, P. H. Grinberg, A., Mahon, K. A., and Jamrich, M. (1997) Nature 387, 603-607), binds to the photoreceptor conserved element-1 (PCE-1/Ret 1) in the photoreceptor cell-specific arrestin promoter and stimulates gene expression. RX is found in many retinal cell types including photoreceptor cells. Another homeodomain-containing protein, CRX, which binds to the OTX element to stimulate promoter activity, is found exclusively in photoreceptor cells (Chen, S., Wang, Q. L., Nie, Z., Sun, H., Lennon, G., Copeland, N. G., Gillbert, D. J. Jenkins, N. A., and Zack, D. J. (1997) Neuron 19, 1017-1030; Furukawa, T., Morrow, E. M., and Cepko, C. L. (1997) Cell 91, 531-541). Binding assay and cell culture studies indicate that both PCE-1 and OTX elements and at least two different regulatory factors RX and CRX are necessary for high level, photoreceptor cell-restricted gene expression. Thus, photoreceptor specificity can be achieved by multiple promoter elements interacting with a combination of both photoreceptor-specific regulatory factors and factors present in closely related cell lineages.

The gene structure and organization of mouse PG-Lb, a small chondroitin/dermatan sulphate proteoglycan

PG-Lb was originally characterized as a small chondroitin/dermatan sulphate proteoglycan expressed preferentially in the zones of flattened chondrocytes in developing chick limb cartilage. The occurrence of this proteoglycan in mammalian cartilage has been shown by the isolation of a cDNA clone from mouse cartilage cDNA library [Kurita, Shinomura,Ujita, Zako, Kida, Iwata and Kimata (1996) Biochem. J. 318, 909-914]. To understand the regulation mechanisms for such a unique expression, we have investigated a genomic DNA structure of the PG-Lb gene. The gene is composed of seven exons and six introns spanning more than 50 kb. The leucine-rich repeats are encoded from exon V to exon VII. The transcription initiation site has been determined by rapid amplification of the cDNA ends ('5'-RACE'). The possible TATA box was detected about 90 bp upstream of the adenosine residue that was numbered as position +1. Further analyses of 1.5 kb of the 5' flanking region and 2.2 kb of the first intron have revealed several potential binding motifs for transcription factors such as Sox 5 and 9. The presence of those sequences in the PG-Lb gene was discussed in relation to the unique expression of this proteoglycan. The chromosomal localization of the murine PG-Lb gene was determined to be on the mouse chromosome 10 by the fluorescence-in-situ-hybridization ('FISH') method.

Characterization of the 5' flanking region of the Xenopus laevis transforming growth factor-beta 5 (TGF-beta 5) gene

Transforming growth factors-beta are potent regulators of cellular proliferation, differentiation and morphogenesis. 2.41 kb of the 5' flanking region of the transforming growth factor-beta 5 (TGF-beta 5) gene has been isolated from a Xenopus laevis genomic library and sequenced. The transcription start site of this gene was determined by 5' RACE method. Promoter activity was demonstrated by transient transfection experiments using luciferase reporter gene constructs in XTC cells. A number of putative recognition sites for transcription factors were found in the 5' flanking region of the TGF-beta 5 gene.

Organization of the chick CDC37 gene

CDC37 and the chaperone protein, Hsp90, form a complex that binds to several kinases, resulting in stabilization and promotion of their activity. CDC37 also binds DNA and glycosaminoglycans in a sequence-specific manner. In this study, we further characterize chick CDC37 and examine the organization of the CDC37 gene. Chick CDC37 is a approximately 50-kDa protein encoded by an mRNA of approximately 1.7 kilobases. The CDC37 gene is approximately 8.5 kilobases and contains 8 exons and 7 introns of various sizes. The presumptive promoter and 5'-flanking regions contain an E2 box and consensus binding sites for SP1, for the S8 homeodomain protein, and for two zinc finger clusters within the myeloid progenitor transcription factor, MZF1. Particularly striking is a approximately 470-base pair region composed of a highly repetitive 10-11-base pair sequence, (T/C)gCTAT(A/G)GGG(A/T) (where g represents the additional G present in the 11-base pair sequence). This region includes 15 copies of the sequence, TATGGGGA, which conforms to the DNA consensus sequence recognized by one of the zinc finger clusters in MZF1. These findings emphasize the potential importance of CDC37 in regulation of cellular behavior during tissue development and reorganization.

Cloning and expression pattern of Xenopus prx-1 (Xprx-1) during embryonic development

Homeobox genes are expressed both temporally and spatially during vertebrate development, and regulate the tissue-specific expression of other genes. A Xenopus paired-related homeobox- 1 (Xprx-1) cDNA was cloned. Xprx-1 had a paired-related homeodomain, but did not contain a paired-box. The sequence of Xprx-1 had a high level of homology with K-2(mouse) and Prx-1 (chicken), thus Xprx-1 is assumed to be the Xenopus homolog of these genes. Xprx-1 transcripts were maternally restricted, in Xenopus embryos, and a decrease in the late blastula stage was followed by an increase in zygotic transcripts after gastrulation. The transcripts were localized to the animal hemisphere of the late blastula and were concentrated in the branchial arches of the tail-bud stage embryo. In animal cap experiments, Activin A dose-dependently induced Xprx-1 gene expression. These results suggest that Xprx-1 plays a role in early Xenopus development similar to other species.

The mouse homeobox gene, Gbx2: genomic organization and expression in pluripotent cells in vitro and in vivo

The Gbx2 homeodomain is widely conserved in metazoans. We investigated the mouse Gbx2 locus by isolation and characterization of genomic clones and by physical localization to the genome. The Gbx2 gene contained a single intron that separated the proposed functional protein domains. This organization was conserved with human GBX2. Physical localization of Gbx2 to Chromosome 1C5-E1 indicated that the genomic relationship between the linked Gbx2 and En1 genes differs between mouse and human, making it unlikely to be of functional significance. We also extended the known expression pattern of Gbx2 beyond the gastrulation stage embryo and the developing CNS to pluripotent cells in vitro and in vivo. Gbx2 expression was demonstrated in undifferentiated embryonic stem cells but was downregulated in differentiated cell populations. In the embryo, Gbx2 expression was detected before primitive streak formation, in the inner cell mass of the preimplantation embryo. Gbx2 is therefore a candidate control gene for cell pluripotency and differentiation in the embryo.

Kinetics of binding of Antp homeodomain to DNA analyzed by measurements of surface plasmon resonance

The kinetics of binding of the Antp homeodomain to three kinds of DNA fragment were analyzed by measurements of surface plasmon resonance at various temperatures. Non-specific and specific binding of the homeodomain to DNA was examined. In the case of non-specific binding, the association rate constant (k(ass)) was estimated to be 1.41-2.62 x 10(5) M(-1) s(-1) and the dissociation rate constant (k(diss)) was 1.36-3.10 x 10(-2) s(-1), thus, the dissociation constant (KD) was 0.847-1.72 x 10(-7) M. The association seemed to be driven by entropy. In the case of specific binding, by contrast, the enthalpy term seemed to contribute more to the binding than did the entropy term. The k(ass) was 2.04-2.59 x 10(5) M(-1) s(-1) and the k(diss) was 0.759-1.16 x 10(-3) s(-1), thus, the KD was 2.93-5.69 X 10(-9) M. These values were measured under the condition of 150 mM NaCl. Both interactions were strongly dependent on the concentration of NaCl. The KD at 50 mM NaCl became several tens of times smaller than those at 150 mM. Possible reasons for the differences between non-specific and specific interactions are discussed.

Genomic imprinting of the human serotonin-receptor (HTR2) gene involved in development of retinoblastoma

Epidemiological and genetic studies of retinoblastoma (RB) suggested that imprinted genes might be genetically linked to the RB gene. In this study, we found that the human serotonin-receptor, HTR2, gene, which had been mapped nearby the RB gene on chromosome 13, was expressed only in human fibroblasts with a maternal allele and not in cells without a maternal allele. The 5' genomic region of the human HTR2 gene was cloned by PCR-mediated method. Only the 5' region of the gene was methylated in cells with the maternal gene, and it was not methylated in cells without the maternal gene. A polymorphism of PvuII site of the gene was also found and useful for the segregation analysis in a family of a RB patient and for analysis of loss of heterozygosity on chromosome 13 in tumor and its parental origin. These results suggest that the human HTR2 gene might be affected by genomic imprinting and that exclusive expression of the maternal HTR2 gene may be associated with the delayed occurrence of RB, which had lost the maternal chromosome 13.

Conservation and diversification in homeodomain-DNA interactions: a comparative genetic analysis

Nearly all metazoan homeodomains (HDs) possess DNA binding targets that are related by the presence of a TAAT sequence. We use an in vitro genetic DNA binding site selection assay to refine our understanding of the amino acid determinants for the recognition of the TAAT site. Superimposed upon the conserved ability of metazoan HDs to recognize a TAAT core is a difference in their preference for the bases that lie immediately 3' to it. Amino acid position 50 of the HD has been shown to discriminate among these base pairs, and structural studies have suggested that water-mediated hydrogen bonds and van der Waals contacts underlie for this ability. Here, we show that each of six amino acids tested at position 50 can confer a distinct DNA binding specificity.

Expression patterns of the paired-related homeobox genes MHox/Prx1 and S8/Prx2 suggest roles in development of the heart and the forebrain

Prx1 and Prx2 (previously called MHox and S8, respectively) are the members of a small subfamily of vertebrate homeobox genes expressed during embryogenesis from gastrulation onwards. We directly compared the expression domains of the Prx genes in detail in mouse and in addition some aspects of these patterns in chicken. In addition to the superficially similar expression patterns of Prx1 and Prx2 in cranial mesenchyme, limb buds, axial mesoderm, and branchial arches and their derivatives, we detect major differences at many sites particularly in heart and brain. Our analysis indicated in several cases a correlation with regions developing into connective tissues. From at least day 8.5, Prx-1 expression was observed in the heart, initially in the endocardial cushions and later in the developing semilunar and atrioventricular valves. Prx2 develops early on a diffuse myocardial expression pattern and is later higher expressed in the ventricular septum and in particular in the ductus arteriosus. Prx2 is never expressed in the brain, whereas Prx1 is expressed, from at least day 9.5 onwards, in a unique distinct domain in the ventral part of the hypothalamus, as well as in a broader region of the telencephalon.