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Homeobox genes encode transcription factors that are widely known to control developmental processes. This is also the case in the pineal gland, a neuroendocrine brain structure devoted to nighttime synthesis of the hormone melatonin. Thus, in accordance with high prenatal gene expression, knockout studies have identified a specific set of homeobox genes that are essential for development of the pineal gland. However, as a special feature of the pineal gland, homeobox gene expression persists into adulthood, and gene product abundance exhibits 24 h circadian rhythms. Recent lines of evidence show that some homeobox genes even control expression of enzymes catalyzing melatonin synthesis. We here review current knowledge of homeobox genes in the rodent pineal gland and suggest a model for dual functions of homeobox gene-encoded transcription factors in developmental and circadian mature neuroendocrine function., Homeobox genes encode transcription factors that are widely known to control developmental processes. This is also the case in the pineal gland, a neuroendocrine brain structure devoted to nighttime synthesis of the hormone melatonin. Thus, in accordance with high prenatal gene expression, knockout studies have identified a specific set of homeobox genes that are essential for development of the pineal gland. However, as a special feature of the pineal gland, homeobox gene expression persists into adulthood, and gene product abundance exhibits 24 h circadian rhythms. Recent lines of evidence show that some homeobox genes even control expression of enzymes catalyzing melatonin synthesis. We here review current knowledge of homeobox genes in the rodent pineal gland and suggest a model for dual functions of homeobox gene-encoded transcription factors in developmental and circadian mature neuroendocrine function.

Homeobox genes encode transcription factors that are widely known to control developmental processes. This is also the case in the pineal gland, a neuroendocrine brain structure devoted to nighttime synthesis of the hormone melatonin. Thus, in accordance with high prenatal gene expression, knockout studies have identified a specific set of homeobox genes that are essential for development of the pineal gland. However, as a special feature of the pineal gland, homeobox gene expression persists into adulthood, and gene product abundance exhibits 24 h circadian rhythms. Recent lines of evidence show that some homeobox genes even control expression of enzymes catalyzing melatonin synthesis. We here review current knowledge of homeobox genes in the rodent pineal gland and suggest a model for dual functions of homeobox gene-encoded transcription factors in developmental and circadian mature neuroendocrine function., Homeobox genes encode transcription factors that are widely known to control developmental processes. This is also the case in the pineal gland, a neuroendocrine brain structure devoted to nighttime synthesis of the hormone melatonin. Thus, in accordance with high prenatal gene expression, knockout studies have identified a specific set of homeobox genes that are essential for development of the pineal gland. However, as a special feature of the pineal gland, homeobox gene expression persists into adulthood, and gene product abundance exhibits 24 h circadian rhythms. Recent lines of evidence show that some homeobox genes even control expression of enzymes catalyzing melatonin synthesis. We here review current knowledge of homeobox genes in the rodent pineal gland and suggest a model for dual functions of homeobox gene-encoded transcription factors in developmental and circadian mature neuroendocrine function.

Spermatogonial stem cells (SSCs) are essential for male fertility. Here, we report that mouse SSC generation is driven by a transcription factor (TF) cascade controlled by the homeobox protein, RHOX10, which acts by driving the differentiation of SSC precursors called pro-spermatogonia (ProSG). We identify genes regulated by RHOX10 in ProSG in vivo and define direct RHOX10-target genes using several approaches, including a rapid temporal induction assay: iSLAMseq. Together, these approaches identify temporal waves of RHOX10 direct targets, as well as RHOX10 secondary-target genes. Many of the RHOX10-regulated genes encode proteins with known roles in SSCs. Using an in vitro ProSG differentiation assay, we find that RHOX10 promotes mouse ProSG differentiation through a conserved transcriptional cascade involving the key germ-cell TFs DMRT1 and ZBTB16. Our study gives important insights into germ cell development and provides a blueprint for how to define TF cascades.

The Ventx genes are a family of non-clustered homeobox transcription factors that confer a ventral phenotype on mesodermal cells in the developing embryo. Ventx genes are conserved in vertebrates but have been lost in rodents. Studies in Xenopus have proposed Ventx as a transcriptional repressor during early mammalian embryo development. Although not much is known about the expression of this gene in humans, studies have shown that VENTX promotes myeloid differentiation in the human haematopoietic system and it is expressed in some acute myeloid leukaemias, including those with a RUNX1-ETO translocation. To further explore its function during mesoderm patterning and differentiation, we used a human pluripotent stem cell (hPSC) reporter line in which a GFP reporter marked the expression of VENTX. Surprisingly, differentiation studies revealed that early expression of VENTX identified a subset of early primordial germ cells (PGCs). Following these results, we used a double reporter hPSC line in which a mCHERRY reporter marked the pluripotency gene OCT4 and a third line in which the homeodomain of VENTX was deleted, creating a VENTX functional knockout. Human PSCs from the double reporter line and VENTX knockout line were differentiated into VENTX expressing PGC-like cells (PGCLCs). Transcriptional profiling of GFP-expressing cells from both cell lines confirmed expression of early PGC associated genes, including BLIMP1, PRDM14, SOX17 and TFA2PC. Examination of the RNA-sequencing data confirmed that VENTX is expressed in a subset of human PGCLCs, however it did not reveal significant transcriptional consequences when VENTX was deleted. These results suggest that VENTX is not required for early human PGC ontogeny, but does not exclude a role later in human PGC development. We also used a doxycycline (DOX) inducible VENTX expression system to investigate the role of VENTX during haematopoietic development. We found that VENTX overexpression in hPSC impaired mesoderm form

The presence of fibroids and endometrial polyps is associated with reduced endometrial receptivity and subsequent fertility outcomes. The following review explores the molecular mechanisms behind reduced endometrial receptivity, with a focus upon homebox genes, basic transcription element binding proteins, transforming growth factor beta-3, and bone morphogenetic protein 2. A better understanding of these processes is essential for future targeted therapy.Copyright © 2017 Wichtig Publishing.

The presence of fibroids and endometrial polyps is associated with reduced endometrial receptivity and subsequent fertility outcomes. The following review explores the molecular mechanisms behind reduced endometrial receptivity, with a focus upon homebox genes, basic transcription element binding proteins, transforming growth factor beta-3, and bone morphogenetic protein 2. A better understanding of these processes is essential for future targeted therapy.Copyright © 2017 Wichtig Publishing.

Las alteraciones del desarrollo embriológico de la dentición provocan anomalías y displasias dentarias. Los factores etiopatogénicos implicados en las alteraciones del desarrollo dentario son básicamente dos: genéticos y ambientales. Según la fase del desarrollo en que afecten al órgano del esmalte y a los tejidos dentarios, aparecerán diferentes anomalías y/o displasias dentales. El control genético del desarrollo dentario se lleva a cabo mediante dos procesos: a) control de la histogénesis del esmalte y la dentina, y b) la especificación del tipo, tamaño y posición de cada diente. La mutación de los genes implicados en la amelogénesis (AMELX, ENAM, MMP20 y KLK4) o en la dentinogénesis (DSPP) produce alteraciones del desarrollo dentario aisladas o no sindrómicas. Por el contrario, las mutaciones de los genes reguladores morfogenéticos involucrados en la determinación de la posición y el desarrollo precoz de los órganos dentarios (genes homeobox), además de alterar la morfodiferenciación dentaria, tienen efectos pleiotrópicos y afectan a otros órganos, provocando síndromes hereditarios en los que uno de sus rasgos es la alteración dentaria. En este artículo se revisan las principales anomalías y displasias dentarias de causa genético-hereditaria., Alterations of the embryologic development of the dentition cause dental anomalies and dysplasias. The causing factors involved in the disturbances of tooth development are basically two: genetic and environmental factors. Depending on the phase of tooth development when the factors act, they will appear different dental anomalies and dysplasias. Genetic control of tooth development is carried out through two processes: a) control of amelogenesis and dentinogenesis,and b) the specification of the type, size and position of each tooth. Mutation of genes involved in amelogenesis (AMELX, ENAM, MMP20 and KLK4) and dentinogenesis (DSPP) produces non-syndromic alterations of tooth development. On the contrary, mutations in morphogenetic regulatory genes involved in determining the position and the early development of the teeth (homeobox genes), not only alter teeth morpho differentiation, but also have pleiotropic effects affecting other organs, causing hereditary syndromes in which one of its features is the presence of dental abnormalities. Dental anomalies and dysplasias of genetic origin are reviewed in this article.

[EN] Plant leaves, simple or compound, initiate as peg-like structures from the peripheral zone of the shoot apical meristem, which requires class I KNOTTED-LIKE HOMEOBOXI (KNOXI) transcription factors to maintain its activity. The MYB domain protein encoded by the ASYMMETRIC LEAVES1/ROUGH SHEATH2/PHANTASTICA (ARP) gene, together with other factors, excludes KNOXI gene expression from incipient leaf primordia to initiate leaves and specify leaf adaxial identity. However, the regulatory relationship between ARP and KNOXI is more complex in compound-leafed species. Here, we investigated the role of ARP and KNOXI genes in compound leaf development in Medicago truncatula. We show that the M. truncatula phantastica mutant exhibited severe compound leaf defects, including curling and deep serration of leaf margins, shortened petioles, increased rachises, petioles acquiring motor organ characteristics, and ectopic development of petiolules. On the other hand, the M. truncatula brevipedicellus mutant did not exhibit visible compound leaf defects. Our analyses show that the altered petiole development requires ectopic expression of ELONGATED PETIOLULE1, which encodes a lateral organ boundary domain protein, and that the distal margin serration requires the auxin efflux protein M. truncatula PIN-FORMED10 in the M. truncatula phantastica mutant.

In Arabidopsis thaliana, the phytohormone auxin is an important patterning agent during embryogenesis and post-embryonic development, exerting effects through transcriptional regulation. The main determinants of the transcriptional auxin response machinery are AUXIN RESPONSE FACTOR (ARF) transcription factors and AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) inhibitors. Although members of these two protein families are major developmental regulators, the transcriptional regulation of the genes encoding them has not been well explored. For example, apart from auxin-linked regulatory inputs, factors regulating the expression of the AUX/IAA BODENLOS (BDL)/IAA12 are not known. Here, it was shown that the HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP) transcription factor HOMEOBOX PROTEIN 5 (HB5) negatively regulates BDL expression, which may contribute to the spatial control of BDL expression. As such, HB5 and probably other class I HD-ZIP proteins, appear to modulate BDL-dependent auxin response.

In Arabidopsis thaliana, the phytohormone auxin is an important patterning agent during embryogenesis and post-embryonic development, exerting effects through transcriptional regulation. The main determinants of the transcriptional auxin response machinery are AUXIN RESPONSE FACTOR (ARF) transcription factors and AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) inhibitors. Although members of these two protein families are major developmental regulators, the transcriptional regulation of the genes encoding them has not been well explored. For example, apart from auxin-linked regulatory inputs, factors regulating the expression of the AUX/IAA BODENLOS (BDL)/IAA12 are not known. Here, it was shown that the HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP) transcription factor HOMEOBOX PROTEIN 5 (HB5) negatively regulates BDL expression, which may contribute to the spatial control of BDL expression. As such, HB5 and probably other class I HD-ZIP proteins, appear to modulate BDL-dependent auxin response.

Lateral organ distribution at the shoot apical meristem defines specific and robust phyllotaxis patterns that have intrigued biologists and mathematicians for centuries. In silico studies have revealed that this self-organizing process can be recapitulated by modeling the polar transport of the phytohormone auxin. Phyllotactic patterns change between species and developmental stages, but the processes behind these variations have remained unknown. Here we use regional complementation experiments to reveal that phyllotactic switches in Arabidopsis shoots can be mediated by PLETHORA-dependent control of local auxin biosynthesis.

Ovarian cancer is the leading cause of death from gynecologic cancers in the developed world. We have previously identified a homeobox gene, Six1, which is overexpressed in ovarian cancers as compared to normal ovarian surface epithelium. Overexpression of six1 is associated with resistance to Tumor Necrosis Factor-related Apoptosis Inducing Ligand (TRAIL) based therapies. We have discovered elevated Six1 is associated with tumor formation in mice and that the TRAIL decoy receptor DcR2 is overexpressed when Six1 is overexpressed. However, knockdown of DcR2 does not restore TRAIL sensitivity to Six1 overexpressing tumors, implying additional mechanisms. On-going studies are evaluating the mechanism and significance of the findings on the way to designing new treatments for ovarian cancer., The original document contains color images.

In higher vertebrates, from amphibians to humans, epidemial maturation is a conserved developmental process. Using adult epidemial tissue and an established keratinocyte cell line, the mouse Nkx-2.3 homeobox gene was demonstrated, for the first time, to be expressed in mouse epidermal keratinocytes. Under the normal culture condition, the spontaneous aggregation phenomenon, a common initiation step of ES cell differentiation, and the induction of mouse adult K1 keratin, a marker of mature epidermal keratinocytes, were both observed in vitro when the Xenopus Nkx-2.3 gene was stably transfected into a mouse pluripotent P19 EC cell line. The induction of mouse K1 keratin by using its Xenopus orthologous gene in the mouse P19 cell implies that Nkx-2.3 may play a conserved role in the epidermal maturation of the mouse, as it does in that of the frog (Ma, 2004). However, the CAT assay study on frog adult keratin promoter could not find the induction of adult keratin. This implies there might not be a direct activation of its promoter.

Homeobox genes function as master regulators in embryonic morphogenesis. We hypothesized that homeobox genes are essential to maintain tissue- or organ-specificity even in adult body and that the dysregulated expression of homeobox genes results in tumor development and progression. To better understand the roles of homeobox genes in development and progression of esophageal cancer, we analyzed the expression patterns of 39 HOX genes and 4 ParaHOX (CDX1, CDX2, CDX4 and PDX1) genes in esophageal squamous cell carcinoma (ESCC) and normal esophageal mucosa tissues. A total of 48 primary ESCC tissues and 7 normal esophageal mucosa tissues were resected from patients who underwent radical surgery without any preoperative chemotherapy or radiotherapy. The expression of HOX and ParaHOX genes were analyzed by a quantitative real-time RT-PCR method and immunohistochemistry. The expression levels of 24 HOX genes, CDX1, CDX2 and PDX1 were significantly higher in ESCC compared to normal mucosa (p<0.01, Mann-Whitney U test). The Immunohistochemical study revealed that HOXA5 and D9 proteins were more cytoplasmic in ESCC than normal mucosa cells. Our data indicate that the disordered expression of HOX and ParaHOX genes are involved in the development of ESCC or its malignancy.

Homeobox genes function as master regulators in embryonic morphogenesis. We hypothesized that homeobox genes are essential to maintain tissue- or organ-specificity even in adult body and that the dysregulated expression of homeobox genes results in tumor development and progression. To better understand the roles of homeobox genes in development and progression of esophageal cancer, we analyzed the expression patterns of 39 HOX genes and 4 ParaHOX (CDX1, CDX2, CDX4 and PDX1) genes in esophageal squamous cell carcinoma (ESCC) and normal esophageal mucosa tissues. A total of 48 primary ESCC tissues and 7 normal esophageal mucosa tissues were resected from patients who underwent radical surgery without any preoperative chemotherapy or radiotherapy. The expression of HOX and ParaHOX genes were analyzed by a quantitative real-time RT-PCR method and immunohistochemistry. The expression levels of 24 HOX genes, CDX1, CDX2 and PDX1 were significantly higher in ESCC compared to normal mucosa (p<0.01, Mann-Whitney U test). The Immunohistochemical study revealed that HOXA5 and D9 proteins were more cytoplasmic in ESCC than normal mucosa cells. Our data indicate that the disordered expression of HOX and ParaHOX genes are involved in the development of ESCC or its malignancy.

We hypothesized that the disordered tissue architecture in cancer results from the steps that the cells execute the program designed during ontogeny in a spatiotemporally inappropriate manner. HOX genes are known as master regulators of embryonic morphogenesis, and encode transcription factors which regulate the transcription of the downstream genes to realize the program of body plan. In this study, we quantified the expression levels of 39 HOX genes in 41 human non-small cell lung cancer (non-SCLC) and non-cancerous lung tissues by a comprehensive analysis system based on the realtime RT-PCR method. We found that the expression levels of HOXA1, A5, A10 and C6 in squamous cell carcinoma tissues (and HOXA5 and A10 in adenocarcinoma tissues) were significantly higher than those in the non-cancerous tissues. Comparison of HOX gene expressions between adenocarcinoma and squamous cell carcinoma tissues showed higher expressions of HOXA1, D9, D10 and D11 in squamous cell carcinoma tissues than in adenocarcinoma tissues. Immunohistochemical analysis revealed that HOXA5 and A10 proteins were localized in the cytoplasm of tumor cells in both adenocarcinoma and squamous cell carcinoma tissues. These results suggest that the disordered patterns of HOX gene expressions were involved in not only the development of non-SCLC but also histological diversity such as adenocarcinoma and squamous cell carcinoma.

We hypothesized that the disordered tissue architecture in cancer results from the steps that the cells execute the program designed during ontogeny in a spatiotemporally inappropriate manner. HOX genes are known as master regulators of embryonic morphogenesis, and encode transcription factors which regulate the transcription of the downstream genes to realize the program of body plan. In this study, we quantified the expression levels of 39 HOX genes in 41 human non-small cell lung cancer (non-SCLC) and non-cancerous lung tissues by a comprehensive analysis system based on the realtime RT-PCR method. We found that the expression levels of HOXA1, A5, A10 and C6 in squamous cell carcinoma tissues (and HOXA5 and A10 in adenocarcinoma tissues) were significantly higher than those in the non-cancerous tissues. Comparison of HOX gene expressions between adenocarcinoma and squamous cell carcinoma tissues showed higher expressions of HOXA1, D9, D10 and D11 in squamous cell carcinoma tissues than in adenocarcinoma tissues. Immunohistochemical analysis revealed that HOXA5 and A10 proteins were localized in the cytoplasm of tumor cells in both adenocarcinoma and squamous cell carcinoma tissues. These results suggest that the disordered patterns of HOX gene expressions were involved in not only the development of non-SCLC but also histological diversity such as adenocarcinoma and squamous cell carcinoma.

We hypothesized that the disordered tissue architecture in cancer results from the steps that the cells execute the program designed during ontogeny in a spatiotemporally inappropriate manner. HOX genes are known as master regulators of embryonic morphogenesis, and encode transcription factors which regulate the transcription of the downstream genes to realize the program of body plan. In this study, we quantified the expression levels of 39 HOX genes in 41 human non-small cell lung cancer (non-SCLC) and non-cancerous lung tissues by a comprehensive analysis system based on the realtime RT-PCR method. We found that the expression levels of HOXA1, A5, A10 and C6 in squamous cell carcinoma tissues (and HOXA5 and A10 in adenocarcinoma tissues) were significantly higher than those in the non-cancerous tissues. Comparison of HOX gene expressions between adenocarcinoma and squamous cell carcinoma tissues showed higher expressions of HOXA1, D9, D10 and D11 in squamous cell carcinoma tissues than in adenocarcinoma tissues. Immunohistochemical analysis revealed that HOXA5 and A10 proteins were localized in the cytoplasm of tumor cells in both adenocarcinoma and squamous cell carcinoma tissues. These results suggest that the disordered patterns of HOX gene expressions were involved in not only the development of non-SCLC but also histological diversity such as adenocarcinoma and squamous cell carcinoma.

Members of the homeodomain leucine zipper (HDZip) family of transcription factors are present in a wide range of plants, from mosses to higher plants, but not in other eukaryotes. The HDZip genes act in developmental processes, including vascular tissue and trichome development, and several of them have been suggested to be involved in the mediation of external signals to regulate plant growth. The Arabidopsis ( Arabidopsis thaliana) genome contains 47 HDZip genes, which, based on sequence criteria, have been grouped into four different classes: HDZip I to IV. In this article, we present an overview of the class I HDZip genes in Arabidopsis. We describe their expression patterns, transcriptional regulation properties, duplication history, and phylogeny. The phylogeny of HDZip class I genes is supported by data on the duplication history of the genes, as well as the intron/exon patterning of the HDZip-encoding motifs. The HDZip class I genes were found to be widely expressed and partly to have overlapping expression patterns at the organ level. Further, abscisic acid or water deficit treatments and different light conditions affected the transcript levels of a majority of the HDZip I genes. Within the gene family, our data show examples of closely related HDZip genes with similarities in the function of the gene product, but a divergence in expression pattern. In addition, six HDZip class I proteins tested were found to be activators of gene expression. In conclusion, several HDZip I genes appear to regulate similar cellular processes, although in different organs or tissues and in response to different environmental signals.

There are 42 members of the homeodomain-leucine zipper (HDZip) family of transcription factors in Arabidopsis thaliana. This thesis focuses on the functional analysis of one member of this family, ATHB16, and on the biochemical properties of HDZip proteins. To assess the function of the ATHB16 gene, the expression of ATHB16 was altered in transgenic Arabidopsis plants by using sense and antisense RNA constructs under the control of the 35S promoter. The reciprocal phenotypic effects associated with elevated and reduced levels of ATHB16 expression suggested that, in wild-type plants, ATHB16 acts as a mediator of blue and red light effects on the regulation of plant growth and the timing of the floral transition. In wild-type Arabidopsis, expression of ATHB16 is high in leaves, intermediate in adult roots and inflorescences, and low in stems and siliques. The expression of ATHB16 in the root is markedly increased in response to exogenous abscisic acid (ABA) treatment, but is reduced in the ABA response mutants abil and abi2, suggesting that ATHB16 may be involved in ABA signal transduction. This hypothesis was corroborated by observations of alterations in sensitivity to ABA inhibition of root growth in seedlings of a T-DNA insertion mutant of ATHB16 and of transgenic plants with elevated ATHB16 levels. HDZip proteins bind DNA as dimers. DNA-binding studies showed that different HDZip proteins interact with very similar target sequences in vitro and that they selectively form heterodimers with each other. For example, it was demonstrated that ATHB16 can heterodimerize with ATHB6 and ATHB7 in yeast and with ATHB5 in vitro, suggesting that ATHB16 may interact with other HDZip proteins in Arabidopsis. This interaction may have functional significance, since it may provide a mechanism for the plant to integrate different input signals, like light of different spectral qualities and water availability in the regulation of its growth.

There are 42 members of the homeodomain-leucine zipper (HDZip) family of transcription factors in Arabidopsis thaliana. This thesis focuses on the functional analysis of one member of this family, ATHB16, and on the biochemical properties of HDZip proteins. To assess the function of the ATHB16 gene, the expression of ATHB16 was altered in transgenic Arabidopsis plants by using sense and antisense RNA constructs under the control of the 35S promoter. The reciprocal phenotypic effects associated with elevated and reduced levels of ATHB16 expression suggested that, in wild-type plants, ATHB16 acts as a mediator of blue and red light effects on the regulation of plant growth and the timing of the floral transition. In wild-type Arabidopsis, expression of ATHB16 is high in leaves, intermediate in adult roots and inflorescences, and low in stems and siliques. The expression of ATHB16 in the root is markedly increased in response to exogenous abscisic acid (ABA) treatment, but is reduced in the ABA response mutants abil and abi2, suggesting that ATHB16 may be involved in ABA signal transduction. This hypothesis was corroborated by observations of alterations in sensitivity to ABA inhibition of root growth in seedlings of a T-DNA insertion mutant of ATHB16 and of transgenic plants with elevated ATHB16 levels. HDZip proteins bind DNA as dimers. DNA-binding studies showed that different HDZip proteins interact with very similar target sequences in vitro and that they selectively form heterodimers with each other. For example, it was demonstrated that ATHB16 can heterodimerize with ATHB6 and ATHB7 in yeast and with ATHB5 in vitro, suggesting that ATHB16 may interact with other HDZip proteins in Arabidopsis. This interaction may have functional significance, since it may provide a mechanism for the plant to integrate different input signals, like light of different spectral qualities and water availability in the regulation of its growth.

There are 42 members of the homeodomain-leucine zipper (HDZip) family of transcription factors in Arabidopsis thaliana. This thesis focuses on the functional analysis of one member of this family, ATHB16, and on the biochemical properties of HDZip proteins. To assess the function of the ATHB16 gene, the expression of ATHB16 was altered in transgenic Arabidopsis plants by using sense and antisense RNA constructs under the control of the 35S promoter. The reciprocal phenotypic effects associated with elevated and reduced levels of ATHB16 expression suggested that, in wild-type plants, ATHB16 acts as a mediator of blue and red light effects on the regulation of plant growth and the timing of the floral transition. In wild-type Arabidopsis, expression of ATHB16 is high in leaves, intermediate in adult roots and inflorescences, and low in stems and siliques. The expression of ATHB16 in the root is markedly increased in response to exogenous abscisic acid (ABA) treatment, but is reduced in the ABA response mutants abil and abi2, suggesting that ATHB16 may be involved in ABA signal transduction. This hypothesis was corroborated by observations of alterations in sensitivity to ABA inhibition of root growth in seedlings of a T-DNA insertion mutant of ATHB16 and of transgenic plants with elevated ATHB16 levels. HDZip proteins bind DNA as dimers. DNA-binding studies showed that different HDZip proteins interact with very similar target sequences in vitro and that they selectively form heterodimers with each other. For example, it was demonstrated that ATHB16 can heterodimerize with ATHB6 and ATHB7 in yeast and with ATHB5 in vitro, suggesting that ATHB16 may interact with other HDZip proteins in Arabidopsis. This interaction may have functional significance, since it may provide a mechanism for the plant to integrate different input signals, like light of different spectral qualities and water availability in the regulation of its growth.

There are 42 members of the homeodomain-leucine zipper (HDZip) family of transcription factors in Arabidopsis thaliana. This thesis focuses on the functional analysis of one member of this family, ATHB16, and on the biochemical properties of HDZip proteins. To assess the function of the ATHB16 gene, the expression of ATHB16 was altered in transgenic Arabidopsis plants by using sense and antisense RNA constructs under the control of the 35S promoter. The reciprocal phenotypic effects associated with elevated and reduced levels of ATHB16 expression suggested that, in wild-type plants, ATHB16 acts as a mediator of blue and red light effects on the regulation of plant growth and the timing of the floral transition. In wild-type Arabidopsis, expression of ATHB16 is high in leaves, intermediate in adult roots and inflorescences, and low in stems and siliques. The expression of ATHB16 in the root is markedly increased in response to exogenous abscisic acid (ABA) treatment, but is reduced in the ABA response mutants abil and abi2, suggesting that ATHB16 may be involved in ABA signal transduction. This hypothesis was corroborated by observations of alterations in sensitivity to ABA inhibition of root growth in seedlings of a T-DNA insertion mutant of ATHB16 and of transgenic plants with elevated ATHB16 levels. HDZip proteins bind DNA as dimers. DNA-binding studies showed that different HDZip proteins interact with very similar target sequences in vitro and that they selectively form heterodimers with each other. For example, it was demonstrated that ATHB16 can heterodimerize with ATHB6 and ATHB7 in yeast and with ATHB5 in vitro, suggesting that ATHB16 may interact with other HDZip proteins in Arabidopsis. This interaction may have functional significance, since it may provide a mechanism for the plant to integrate different input signals, like light of different spectral qualities and water availability in the regulation of its growth.

We have isolated and characterized a novel human homeobox gene designated Mix. 1 homeobox (Xenopus laevis)-like gene 2 (MIXL2), as a gene that contains a repetitive element in its 3 UTR (MER22). The MIXL2 gene encodes a predicted 232 amino acid open reading frame, which contains a highly conserved mix. 1-like homeobox and an acidic motif Radiation hybrid mapping and Fluorescence in situ hybridization localize the MIXL2 gene to human chromosome 1q32-41, a region of gain in breast tumors. Consistent with these cytogenetic findings we detected allelic imbalance for loci flanking MIXL2 in 14/25 primary breast tumors. Additionally, a search of the human dbEST database suggested a highly restricted expression as we detected only three EST clones (one each from normal germinal center B cell, undifferentiated germ cell tumor, and infiltrating ductal carcinoma of the breast). These findings suggest MT)(L2 may play a role in development and mammary carcinogenesis.

The products of homeobox genes are DNAbinding transcription factors. However, little is known about downstream genes whose activities are regulated directly or indirectly by the homeobox genes. In the current study, we tested a differential display (DD) method using the tissue of a knockout mouse in order to identify the downstream genes of a homeobox gene Msx1 systematically. Our previous in situ hybridization analysis of a Msx1 deficient mouse showed that Msx1 induced by epithelial bone morphogenetic protein 4 (BMP4) and fibroblast growth factors (FGFs) induces Bmp4, the HMG box gene Lef1, and the heparan sulfate proteoglycan syndecan-1 in the tooth mesenchyme. Although it is a very powerful approach for identifying downstream genes of a homeobox gene to test whether the candidate gene's expression is affected in the knockout mouse, this approach is not directly applicable to the identification of unknown genes downstream of Msx1. In the current study, we performed DD using total RNA from E14.5 Msx1 mutant mandibles and were able to obtain four novel downstream genes of Msx1 from 20 cDNA clones verified by Northern blot hybridization and semiquantitative RT-PCR. Despite several problems inherent to this method, we concluded that DD analysis using the tissue of a knockout mouse is a useful systematic approach for the identification of downstream genes of a homeobox gene.

The products of homeobox genes are DNAbinding transcription factors. However, little is known about downstream genes whose activities are regulated directly or indirectly by the homeobox genes. In the current study, we tested a differential display (DD) method using the tissue of a knockout mouse in order to identify the downstream genes of a homeobox gene Msx1 systematically. Our previous in situ hybridization analysis of a Msx1 deficient mouse showed that Msx1 induced by epithelial bone morphogenetic protein 4 (BMP4) and fibroblast growth factors (FGFs) induces Bmp4, the HMG box gene Lef1, and the heparan sulfate proteoglycan syndecan-1 in the tooth mesenchyme. Although it is a very powerful approach for identifying downstream genes of a homeobox gene to test whether the candidate gene's expression is affected in the knockout mouse, this approach is not directly applicable to the identification of unknown genes downstream of Msx1. In the current study, we performed DD using total RNA from E14.5 Msx1 mutant mandibles and were able to obtain four novel downstream genes of Msx1 from 20 cDNA clones verified by Northern blot hybridization and semiquantitative RT-PCR. Despite several problems inherent to this method, we concluded that DD analysis using the tissue of a knockout mouse is a useful systematic approach for the identification of downstream genes of a homeobox gene., departmental bulletin paper

Gax is a homeobox-containing gene that has been detected in adult cardiovascular tissues and exhibits a growth arrest–specific pattern of expression in cultured vascular myocytes. To study the regulation of gax during development, we performed immunohistochemistry and in situ hybridization on mouse embryos. Gax was present in mesodermally and, as with other homeobox genes, neuroectodermally derived tissues. Early mesodermal protein expression was limited to the lateral plate and somitic mesoderm. Gax in the cardiac muscle lineage exhibited a biphasic pattern of expression. Expression was prominent in the heart tube of the earliest cardiomyocytes and remained prominent through the looping stage (day 12.5 post coitum [pc]) but fell below the threshold of detection in atria and ventricles by day 13.5 pc. At day 15.5 pc, Gax protein was again detectable but restricted to cells within the compact layer of the ventricular myocardium. Gax expression was also noted in smooth muscle cells as early as day 9.5 pc. In the skeletal muscle lineage, Gax protein was expressed at the onset of somitogenesis before the expression of the myogenic basic helix-loop-helix and MEF2/RSRF family proteins. Subsequently, it was noted at day 9.5 pc in premyogenic cells migrating into head, trunk, and limb buds. Gax was detected in myotomes, premuscle masses, and mature muscle groups. These data suggest an important developmental role for Gax in all muscle lineages.