Sox18 expression in blood vessels and feather buds during chicken embryogenesis

Genome-Wide Selective Signatures Reveal Candidate Genes Associated with Hair Follicle Development and Wool Shedding in Sheep

Hair follicle development and wool shedding in sheep are poorly understood. This study investigated the population structures and genetic differences between sheep with different wool types to identify candidate genes related to these traits. We used Illumina ovine SNP 50K chip genotyping data of 795 sheep populations comprising 27 breeds with two wool types, measuring the population differentiation index (Fst), nucleotide diversity (θπ ratio), and extended haplotype homozygosity among populations (XP-EHH) to detect the selective signatures of hair sheep and fine-wool sheep. The top 5% of the Fst and θπ ratio values, and values of XP-EHH < −2 were considered strongly selected SNP sites. Annotation showed that the PRX, SOX18, TGM3, and TCF3 genes related to hair follicle development and wool shedding were strongly selected. Our results indicated that these methods identified important genes related to hair follicle formation, epidermal differentiation, and hair follicle stem cell development, and provide a meaningful reference for further study on the molecular mechanisms of economically important traits in sheep.

Understanding vascular development

The vasculature of an organism has the daunting task of connecting all the organ systems to nourish tissue and sustain life. This complex network of vessels and associated cells must maintain blood flow, but constantly adapt to acute and chronic changes within tissues. While the vasculature has been studied for over a century, we are just beginning to understand the processes that regulate its formation and how genetic hierarchies are influenced by mechanical and metabolic cues to refine vessel structure and optimize efficiency. As we gain insights into the developmental mechanisms, it is clear that the processes that regulate blood vessel development can also enable the adult to adapt to changes in tissues that can be elicited by exercise, aging, injury, or pathology. Thus, research in vessel development has provided tremendous insights into therapies for vascular diseases and disorders, cancer interventions, wound repair and tissue engineering, and in turn, these models have clearly impacted our understanding of development. Here we provide an overview of the development of the vascular system, highlighting several areas of active investigation and key questions that remain to be answered.

The transcription factor SOX18 regulates the expression of matrix metalloproteinase 7 and guidance molecules in human endothelial cells

Background

Mutations in the transcription factor SOX18 are responsible for specific cardiovascular defects in humans and mice. In order to gain insight into the molecular basis of its action, we identified target genes of SOX18 and analyzed one, MMP7, in detail.

Methodology/Principal Findings

SOX18 was expressed in HUVEC using a recombinant adenoviral vector and the altered gene expression profile was analyzed using microarrays. Expression of several regulated candidate SOX18 target genes was verified by real-time PCR. Knock-down of SOX18 using RNA interference was then used to confirm the effect of the transcription factor on selected genes that included the guidance molecules ephrin B2 and semaphorin 3G. One gene, MMP7, was chosen for further analysis, including detailed promoter studies using reporter gene assays, electrophoretic mobility shift analysis and chromatin-immunoprecipitation, revealing that it responds directly to SOX18. Immunohistochemical analysis demonstrated the co-expression of SOX18 and MMP7 in blood vessels of human skin.

Conclusions/Significance

The identification of MMP7 as a direct SOX18 target gene as well as other potential candidates including guidance molecules provides a molecular basis for the proposed function of this transcription factor in the regulation of vessel formation.

Sox9, more than a marker of the outer root sheath: spatiotemporal expression pattern during human cutaneous embryogenesis

BACKGROUND

The sex-determining gene Sox9 was recently unexpectedly found to have an essential role in outer root sheath differentiation. It was also characterized as a general marker of basal cell carcinoma. Herein, we describe its spatiotemporal expression pattern outside the hair follicle during human cutaneous embryogenesis.

METHODS

We examined immunohistochemically samples from embryonic and fetal human skin for the expression of SOX9 using standard techniques. For comparison reasons, we also included scalp skin from adults.

RESULTS

SOX9 is expressed in the developing nail organ, eccrine glands, blood vessels and melanocytes/melanoblasts. In the nail organ, the nail bed but not the nail matrix was immunoreactive for SOX9. In plantar skin, SOX9 specifically labels the evolving eccrine glands but not the interfollicular keratinocytes.

CONCLUSIONS

The distinctive expression pattern of SOX9 during human cutaneous embryogenesis indicates a key role in skin homeostasis that includes but goes beyond its role in outer root sheath differentiation. Studying immunohistochemical markers in developing human skin has the potential to further our understanding of adult skin physiology and to deepen our concepts especially of the histogenesis of adnexal tumors (including those of the nail unit) and the relationship of the various adnexal structures to each other.

Vascular defects in a mouse model of hypotrichosis-lymphedema-telangiectasia syndrome indicate a role for SOX18 in blood vessel maturation

Mutations in the transcription factor gene SOX18 cause vascular, lymphatic and hair follicle defects in humans with dominant and recessive forms of hypotrichosis-lymphedema-telangiectasia (HLT) syndrome. Here, we clarify the role of SOX18 in the vascular dysfunction in HLT by ultrastructural, immunofluorescence, molecular and functional analysis of vascular anomalies in embryos of the naturally occurring Sox18-mutant mouse strain ragged-opossum (Ra(Op)). Early genesis and patterning of vasculature was unimpaired in Ra(Op) embryos, but surface capillaries became enlarged from 12.5 dpc and embryos developed massive surface hemorrhage by 14.5 dpc. Large focal breaches in the endothelial barrier were observed, in addition to endothelial hyperplasia associated with impaired pericyte recruitment to the microvasculature. Expression of the genes encoding the endothelial factors MMP7, IL7R and N-cadherin was reduced in Ra(Op) embryos, suggesting that these are downstream targets of SOX18. Together, our results indicate that vascular anomalies in HLT arise from defects in regulation of genes required for the acquisition of structural integrity during microvascular maturation.

A novel 9-amino-acid transactivation domain in the C-terminal part of Sox18

Sox transcription factors are members of the Sry-related protein family that play multiple roles mainly during development. Sox18 has been implicated in the development of hair follicles as well as the blood and lymphatic vasculature, due to the identification of mutations that result in the ragged phenotype in mice, and in the hypotrichosis lymphedema telangiectasia syndrome in humans. Sox18 consists of an N-terminal high-mobility group DNA binding and a central transactivation domain, followed by a C-terminal region of unknown function. We show here that this C-terminal domain consists of three blocks that are highly conserved within a subgroup of the Sox family, and that the central so-called charged block comprises an additional strong transactivating domain. This activity can be pinpointed to a recently described 9aa transactivation motif that mediates the interaction with the transcriptional cofactor TAF9. These result can explain previously controversial data on the functional consequences of Sox18 mutations in mice and humans.

Redundant roles of Sox17 and Sox18 in postnatal angiogenesis in mice

Sox7, Sox17 and Sox18 constitute group F of the Sox family of HMG box transcription factor genes. Dominant-negative mutations in Sox18 underlie the cardiovascular defects observed in ragged mutant mice. By contrast, Sox18(-/-) mice are viable and fertile, and display no appreciable anomaly in their vasculature, suggesting functional compensation by the two other SoxF genes. Here, we provide direct evidence for redundant function of Sox17 and Sox18 in postnatal neovascularization by generating Sox17(+/-) -Sox18(-/-) double mutant mice. Whereas Sox18(-/-) and Sox17(+/-) -Sox18(+/-) mice showed no vascular defects, approximately half of the Sox17(+/-) -Sox18(-/-) pups died before postnatal day 21 (P21). They showed reduced neovascularization in the liver sinusoids and kidney outer medulla vasa recta at P7, which most likely caused the ischemic necrosis observed by P14 in hepatocytes and renal tubular epithelia. Those that survived to adulthood showed similar, but milder, vascular anomalies in both liver and kidney, and females were infertile with varying degrees of vascular abnormalities in the reproductive organs. These anomalies corresponded with sites of expression of Sox7 and Sox17 in the developing postnatal vasculature. In vitro angiogenesis assays, using primary endothelial cells isolated from the P7 livers, showed that the Sox17(+/-) -Sox18(-/-) endothelial cells were defective in endothelial sprouting and remodeling of the vasculature in a phenotype-dependent manner. Therefore, our findings indicate that Sox17 and Sox18, and possibly all three SoxF genes, are cooperatively involved in mammalian vascular development.

Transcription Factor SOX18 Is Expressed in Human Coronary Atherosclerotic Lesions and Regulates DNA Synthesis and Vascular Cell Growth

OBJECTIVE

SOX18, a member of the SOX gene family (SRY-like 3-hydroxy-3-methylglutaryl box gene), is a transcription factor expressed in the development of blood vessels during embryogenesis. We analyzed SOX18 expression in human coronary atherosclerotic lesions and investigated its potential function in vascular cells.

METHODS AND RESULTS

In advanced human coronary atherosclerotic lesions, SOX18 immunostaining was localized in endothelial cells (on the luminal surface, in vasa vasorum, and in intimal neovessels) and in vascular smooth muscle cells (VSMCs) scattered in the intima, colocalizing with proliferating cell nuclear antigen. In cell cultures, SOX18 was mainly localized in subconfluent and denuded areas. Significant SOX18 mRNA levels (by Northern blot analysis and reverse transcription-polymerase chain reaction) were detected in cell cultures from human umbilical vein endothelial cells and human VSMCs. Antisense SOX18 inhibited DNA synthesis ([3H]thymidine incorporation) and vascular cell growth. Antisense SOX18 also significantly reduced VSMC regrowth after injury in an in vitro model of wound repair.

CONCLUSIONS

Our results indicate that SOX18 is involved in vascular cell growth and suggest that this transcription factor may play a role in atherosclerosis.

Conservation of Sox4 gene structure and expression during chicken embryogenesis

While mutations in Sox4, a member of the SRY-like HMG box gene family, have been associated with a variety of human disorders and embryonic defects in the mouse, the structure and developmental expression of Sox4 in the avian embryo has not been described. We have isolated and characterized the chicken Sox4 gene. The chicken Sox4 gene shows a high degree of sequence homology with the mouse and human Sox4 genes, particularly in the HMG-like DNA binding domain and at the carboxy terminus. Furthermore, our in situ hybridization studies document an expression pattern during embryonic development that is very similar to that described for the mouse, particularly with regards to expression in the developing heart. However, abundant expression was also detected in tissues of neural crest origin including pharyngeal arch and craniofacial mesoderm, supporting a potential primary role in neural crest cardiac pathology previously detected in Sox4 mutant mice. Furthermore, a reciprocal pattern of Sox4 and Sox11 expression in the developing neural tube was detected in the chicken compared to that seen in the mouse. These studies suggest that Sox4 plays an important and conserved role in the embryonic development of these structures in the chicken as well as in the mouse and lay the foundation for future studies of the role of Sox4 during critical events of organogenesis.

Sox18 mutations in the ragged mouse alleles ragged-like and opossum

The ragged (Ra) spontaneous mouse mutant is characterised by abnormalities in its coat and cardiovascular system. Four alleles are known and we have previously described mutations in the transcription factor gene Sox18 in the Ra and Ra(J) alleles. We report here Sox18 mutations in the remaining two ragged alleles, opossum (Ra(op)) and ragged-like (Ragl). The single-base deletions cause a C-terminal frameshift, abolishing transcriptional trans-activation and impairing interaction with the partner protein MEF2C. The nature of these mutations, together with the near-normal phenotype of Sox18-null mice, suggests that the ragged mutant SOX18 proteins act in a dominant-negative fashion. The four ragged mutants represent an allelic series that reveal SOX18 structure-function relationships and implicate related SOX proteins in cardiovascular and hair follicle development.

Matching SOX: partner proteins and co-factors of the SOX family of transcriptional regulators

SOX transcription factors perform a remarkable variety of important roles in vertebrate development, either activating or repressing specific target genes through interaction with different partner proteins. Surprisingly, these interactions are often mediated by the conserved, DNA-binding HMG domain, raising questions as to how each factor's specificity is generated. We propose a model whereby non-HMG domains may influence partner protein selection and/or binding stability.