Biomedical subjects

David G Jackson

Publications and source records attributed to David G Jackson.

At least 37 records · Page 2Linked to original sources

PubMed2004

Structure of the regulatory hyaluronan binding domain in the inflammatory leukocyte homing receptor CD44.

Adhesive interactions involving CD44, the cell surface receptor for hyaluronan, underlie fundamental processes such as inflammatory leukocyte homing and tumor metastasis. Regulation of such events is critical and appears to be effected by changes in CD44 N-glycosylation that switch the receptor "on" or "off" under appropriate circumstances. How altered glycosylation influences binding of hyaluronan to the lectin-like Link module in CD44 is unclear, although evidence suggests additional flanking sequences peculiar to CD44 may be involved. Here we show using X-ray crystallography and NMR spectroscopy that these sequences form a lobular extension to the Link module, creating an enlarged HA binding domain and a formerly unidentified protein fold. Moreover, the disposition of key N-glycosylation sites reveals how specific sugar chains could alter both the affinity and avidity of CD44 HA binding. Our results provide the necessary structural framework for understanding the diverse functions of CD44 and developing novel therapeutic strategies.

Amino Acid Sequence↗

PubMed2004

PDGF-BB induces intratumoral lymphangiogenesis and promotes lymphatic metastasis.

Cancer metastases are commonly found in the lymphatic system. Like tumor blood angiogenesis, stimulation of tumor lymphangiogenesis may require the interplay of several tumor-derived growth factors. Here we report that members of the PDGF family act as lymphangiogenic factors. In vitro, PDGF-BB stimulated MAP kinase activity and cell motility of isolated lymphatic endothelial cells. In vivo, PDGF-BB potently induced growth of lymphatic vessels. Expression of PDGF-BB in murine fibrosarcoma cells induced tumor lymphangiogenesis, leading to enhanced metastasis in lymph nodes. These data demonstrate that PDGF-BB is an important growth factor contributing to lymphatic metastasis. Thus, blockage of PDGF-induced lymphangiogenesis may provide a novel approach for prevention and treatment of lymphatic metastasis.

Animals↗

PubMed2004

Dynamic populations of dendritic cell-specific ICAM-3 grabbing nonintegrin-positive immature dendritic cells and liver/lymph node-specific ICAM-3 grabbing nonintegrin-positive endothelial cells in the outer zones of the paracortex of human lymph nodes.

In the paracortex of lymph nodes, cellular immune responses are generated against antigens captured in peripheral tissues by dendritic cells (DCs). DC-SIGN (dendritic cell-specific ICAM-3 grabbing nonintegrin), a C-type lectin exclusively expressed by DCs, functions as an antigen receptor as well as an adhesion receptor. A functional homologue of DC-SIGN, L-SIGN (liver/lymph node-SIGN, also called DC-SIGN-related), is expressed by liver sinus endothelial cells. In lymph nodes, both DC-SIGN and L-SIGN are expressed. In this study, we analyzed the distribution of these two SIGN molecules in detail in both normal and immunoreactive lymph nodes. DC-SIGN is expressed by mature DCs in paracortical areas and in addition by DCs with an immature phenotype in the outer zones of the paracortex. L-SIGN expression was also detected in the outer zones on sinus endothelial cells characterized by their expression of the lymphatic endothelial markers LYVE-1 and CLEVER-1. During both cellular and humoral immune responses changes in the amount of DC-SIGN+ immature and mature DCs and L-SIGN+ endothelial cells were observed, indicating that the influx or proliferation of these cells is dynamically regulated.

Antigens, CD↗

PubMed2004

Lymph and blood vessel architecture in benign and malignant prostatic tissue: lack of lymphangiogenesis in prostate carcinoma assessed with novel lymphatic marker lymphatic vessel endothelial hyaluronan receptor (LYVE-1).

PURPOSE: Due to the lack of specific markers the analysis of lymphatic vessel density (LVD) has been almost impossible in the past. We report the novel specific marker for lymphatic endothelium, lymphatic vessel endothelial hyaluronan receptor (LYVE-1), in prostatic, benign prostatic hyperplasia (BPH) and prostate cancer (PCa) tissue. Normal blood vessels were additionally quantified in BPH and PCa. MATERIALS AND METHODS: LYVE-1 lymphatics (LVD) and CD34 blood vessels were assessed in 20 paraffin sections of BPH and 50 of PCa tissue by immunohistochemistry in a standardized experimental setting. The regions of PCa, periphery of the tumor and nontumorous regions of the PCa specimens, and BPH tissue were evaluated. Double staining was done (LYVE-1/CD34). Acquired data were interrelated and compared to the pathological parameters of the specimens. RESULTS: Double staining revealed numerous CD34 blood vessels but only a few LYVE-1 lymphatic vessels in BPH and PCa sections. Mean LVD +/- SD was distinctly lower (0.55 +/- 0.93) in PCa tissue than in tumor periphery (2.45 +/- 1.93) and nontumorous (3.16 +/- 2.23) tissue (p <0.0001). Maximum LVD was observed in BPH (7.17 +/- 3.61), which differed markedly from nontumorous areas of PCa specimens (p <0.001). In contrast to LVD, significantly more blood vessels were found in PCa (116.00 +/- 39.25) than in BPH (60.30 +/- 19.34) tissue (p <0.001). CONCLUSIONS: LYVE-1 is a specific lymphatic endothelial marker in benign and malignant prostate tissues. It is a useful new marker for the investigation of lymphatics. To our knowledge we report the immunohistochemical visualization and quantification of lymphatic vessels in prostatic tissue for the first time. In contrast to the stimulated angiogenesis of blood vessels in PCa, the destruction of lymphatic vessels occurs rather than lymphangiogenesis.

Antigens, CD34↗

PubMed2004

Feline lymphangiosarcoma--definitive identification using a lymphatic vascular marker.

Three cases of feline exudative dermatitis associated with lymphangiosarcoma are described. The animals, an 11-year-old, neutered male and two 10-year-old, neutered female short hair European cats, presented with a 2-month history of transparent liquid oozing from the skin of the groin and caudal abdomen. On physical examination the neutered male cat and one of the females were slightly depressed and showed loss of weight. Skin lesions were similar in all cats and characterized by the presence of alopecia and moist dermatitis in the ventral abdomen, groin and inner thigh. The hair at the periphery appeared matted by the fluid. In all three cases, histopathological examination of skin biopsies from the abdomen identified poorly defined neoplasia involving dermis and subcutis, characterized by proliferation of spindle cells aligned along pre-existing collagen bundles. The dissection of collagen bundles gave rise to irregular shaped anastomosing, often blind-ending vascular channels and trabeculae. Vascular spaces were mostly optically empty. These histological features were strongly suggestive of lymphangiosarcoma. Neoplastic cells were positive for the blood vascular marker Von Willebrand factor, and a lymphatic vascular marker LYVE-1 (Lymphatic Vessel Endothelial receptor - 1), demonstrating the mixed vascular origin of the tumour. Ultrastructural findings confirmed the final diagnosis of lymphangiosarcoma.

Abdomen↗

PubMed2003

Vascular endothelial growth factor C is required for sprouting of the first lymphatic vessels from embryonic veins.

Lymphatic vessels are essential for immune surveillance, tissue fluid homeostasis and fat absorption. Defects in lymphatic vessel formation or function cause lymphedema. Here we show that the vascular endothelial growth factor C (VEGF-C) is required for the initial steps in lymphatic development. In Vegfc-/- mice, endothelial cells commit to the lymphatic lineage but do not sprout to form lymph vessels. Sprouting was rescued by VEGF-C and VEGF-D but not by VEGF, indicating VEGF receptor 3 specificity. The lack of lymphatic vessels resulted in prenatal death due to fluid accumulation in tissues, and Vegfc+/- mice developed cutaneous lymphatic hypoplasia and lymphedema. Our results indicate that VEGF-C is the paracrine factor essential for lymphangiogenesis, and show that both Vegfc alleles are required for normal lymphatic development.

Animals↗

PubMed2003

Regulation of blood and lymphatic vascular separation by signaling proteins SLP-76 and Syk.

Lymphatic vessels develop from specialized endothelial cells in preexisting blood vessels, but the molecular signals that regulate this separation are unknown. Here we identify a failure to separate emerging lymphatic vessels from blood vessels in mice lacking the hematopoietic signaling protein SLP-76 or Syk. Blood-lymphatic connections lead to embryonic hemorrhage and arteriovenous shunting. Expression of slp-76 could not be detected in endothelial cells, and blood-filled lymphatics also arose in wild-type mice reconstituted with SLP-76-deficient bone marrow. These studies reveal a hematopoietic signaling pathway required for separation of the two major vascular networks in mammals.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Intratumoral lymphatics and lymph node metastases in papillary thyroid carcinoma.

OBJECTIVE: To examine the relationship between lymphatic vessel density and clinical and pathological variables in patients with well-differentiated papillary thyroid carcinoma. SUBJECTS: Clinical information was retrieved on 109 previously untreated patients with well-differentiated papillary thyroid carcinoma treated with total thyroidectomy and postoperative iodine I 131 ablation. Median follow-up was 38 months. DESIGN: Archived tissue specimens were sectioned and stained with hematoxylin-eosin and anti-LYVE-1 antibody, a highly specific marker for lymphatic endothelium. The size of the tumor and its multifocality were noted and lymphatic vessel density was measured by means of Chalkley point counting. RESULTS: Numerous intratumoral lymphatics were seen in papillary thyroid carcinoma. There was a highly significant association between the presence of intratumoral lymphatics and the presence of neck node metastases (P<.001). There was also a significant association with male sex (P =.03) and the presence of multifocal disease (P =.05). The presence of intratumoral lymphatics remained significantly associated with the presence of nodal metastases at presentation (P =.003) on multivariate analysis. Intratumoral lymphatics were not a significant predictor of tumor recurrence (P =.42, log-rank test). CONCLUSIONS: The development of intratumoral lymphatics in well-differentiated papillary thyroid carcinoma appears to be associated with the spread of tumor to regional lymph nodes. The antimetastatic potential of targeting these lymphatics may be of potential therapeutic benefit in the future.

Carcinoma, Papillary↗

PubMed2003

Absence of lymphangiogenesis and intratumoural lymph vessels in human metastatic breast cancer.

Early metastasis to lymph nodes is a frequent complication in human breast cancer. However, the extent to which this depends on lymphangiogenesis or on invasion of existing lymph vessels remains controversial. Although proliferating intratumoural lymphatics that promote nodal metastasis have been demonstrated in experimental breast tumours overexpressing VEGF-C, it has yet to be determined whether the same phenomena occur in spontaneous human breast cancers. To address this important issue, the present study investigated the lymphatics in primary human breast carcinoma (75 cases of invasive ductal and lobular breast cancer) by quantitative immunohistochemical staining for the lymphatic endothelial hyaluronan receptor LYVE-1, the blood vascular marker CD34, and the nuclear proliferation marker pKi67. None of the breast carcinomas was found to contain dividing lymph vessels, even in areas of active haemangiogenesis. Furthermore, the majority of non-dividing lymph vessels were confined to the tumour periphery where their incidence was low and unrelated to tumour size, grade or nodal status; rather, their density was inversely correlated with tumour aggressiveness as assessed by macrophage density (p = 0.009), and blood microvessel density (p = 0.05, Spearman Rank), as well as with distance from the tumour edge. Finally, a proportion of the peritumoural lymphatics contained tumour emboli associated with hyaluronan, indicating a possible role for LYVE-1/hyaluronan interactions in lymphatic invasion or metastasis. These results suggest that naturally occurring breast carcinomas invade and destroy lymph vessels rather than promoting their proliferation; that breast tumour lymphangiogenesis may not always occur at physiological VEGF-C levels; and that nodal metastasis can proceed via pre-existing lymphatics.

Adult↗

PubMed2003

Expression of vascular endothelial growth factor (VEGF)-C and VEGF-D, and their receptor VEGFR-3, during different stages of cervical carcinogenesis.

Cervical carcinogenesis has well-defined stages of disease progression including three grades of pre-invasive lesions--cervical intraepithelial neoplasia grades 1-3 (CIN 1-3)--and invasive cervical cancer. However, the biological properties of CIN lesions prone to develop invasive disease are not well defined. Recent observations suggest that early invasive disease spreads to regional lymph nodes in several tumour types and that growth factors (VEGF-C and VEGF-D) involved in new lymphatic vessel formation may play a crucial role in this process. The present study has assessed the expression of VEGF-C and VEGF-D, and their receptor VEGFR-3, in 152 cervical lesions (33 CIN 1, 33 CIN 2, 37 CIN 3, and 49 squamous cell carcinomas) to determine whether expression of lymphangiogenic factors occurs prior to invasion. The presence of lymphatic vessels was determined using LYVE-1 and podoplanin staining, as well as double immunostaining for LYVE-1/CD34 and podoplanin/CD34. In situ hybridization was performed to determine VEGFR-3 mRNA expression. A significant positive correlation was found between VEGF-C, VEGF-D, and VEGFR-3 expression through the different stages of cervical carcinogenesis. Significant differences in protein expression for VEGF-C, VEGF-D, and VEGFR-3 were found between CIN 1-2 and CIN 3 (p<0.001 for all), but not between CIN 3 and cervical cancer. More than 50% of the CIN 3 lesions showed moderate to strong staining for VEGF-C and VEGF-D, whereas most of the early pre-cancerous lesions (CIN 1 and 2) were negative. In cervical cancer, similar observations to those in CIN 3 were found. VEGFR-3 mRNA expression was found in the cytoplasm of epithelial neoplastic cells and VEGFR3 protein expression was found in more than 50% of CIN 3 lesions and cervical cancers, compared with 15% in CIN 1 and 2. These findings suggest an autocrine growth stimulation pattern via VEGFR-3. Adjacent CIN 3 was present in nine cervical cancers and displayed strong expression for VEGF-C, VEGF-D, and VEGFR-3. These results suggest that in cervical carcinogenesis a switch to the lymphangiogenic phenotype may occur at the stage of CIN 3.

Adolescent↗

PubMed2003

Tumor lymphangiogenesis: a novel prognostic indicator for cutaneous melanoma metastasis and survival.

Malignant melanomas of the skin are distinguished by their propensity for early metastatic spread via lymphatic vessels to regional lymph nodes, and lymph node metastasis is a major determinant for the staging and clinical management of melanoma. However, the importance of tumor-induced lymphangiogenesis for lymphatic melanoma spread has remained unclear. We investigated whether tumor lymphangiogenesis occurs in human malignant melanomas of the skin and whether the extent of tumor lymphangiogenesis may be related to the risk for lymph node metastasis and to patient survival, using double immunostains for the novel lymphatic endothelial marker LYVE-1 and for the panvascular marker CD31. Tumor samples were obtained from clinically and histologically closely matched cases of primary melanomas with early lymph node metastasis (n = 18) and from nonmetastatic melanomas (n = 19). Hot spots of proliferating intratumoral and peritumoral lymphatic vessels were detected in a large number of melanomas. The incidence of intratumoral lymphatics was significantly higher in metastatic melanomas and correlated with poor disease-free survival. Metastatic melanomas had significantly more and larger tumor-associated lymphatic vessels, and a relative lymphatic vessel area of >1.5% was significantly associated with poor disease-free and overall survival. In contrast, no differences in the density of tumor-associated blood vessels were found. Vascular endothelial growth factor and vascular endothelial growth factor-C expression was equally detected in a minority of cases in both groups. Our results reveal tumor lymphangiogenesis as a novel prognostic indicator for the risk of lymph node metastasis in cutaneous melanoma.

Adult↗

PubMed2003

The lymphatics revisited: new perspectives from the hyaluronan receptor LYVE-1.

The lymphatic vasculature forms a second circulatory system that drains extracellular fluid from the tissues and provides an exclusive environment in which immune cells can encounter and respond to foreign antigen. Although equally important for the functioning of both the cardiovascular and immune systems, there is only a rudimentary knowledge of the molecular biology of lymphatics, owing to longstanding difficulties in identifying and isolating lymphatic endothelial cells. Recently, however, a number of interesting molecules have been identified that may be exploited as markers for lymphatic endothelium, including the hyaluronan receptor LYVE-1, the subject of this review. This article considers the biology of LYVE-1 and outlines how recent research into this molecule is providing new insights into the nature of lymphatics and their role in tumor metastasis.

Glycoproteins↗

PubMed2003

VEGF-C gene therapy augments postnatal lymphangiogenesis and ameliorates secondary lymphedema.

Although lymphedema is a common clinical condition, treatment for this disabling condition remains limited and largely ineffective. Recently, it has been reported that overexpression of VEGF-C correlates with increased lymphatic vessel growth (lymphangiogenesis). However, the effect of VEGF-C-induced lymphangiogenesis on lymphedema has yet to be demonstrated. Here we investigated the impact of local transfer of naked plasmid DNA encoding human VEGF-C (phVEGF-C) on two animal models of lymphedema: one in the rabbit ear and the other in the mouse tail. In a rabbit model, following local phVEGF-C gene transfer, VEGFR-3 expression was significantly increased. This gene transfer led to a decrease in thickness and volume of lymphedema, improvement of lymphatic function demonstrated by serial lymphoscintigraphy, and finally, attenuation of the fibrofatty changes of the skin, the final consequences of lymphedema. The favorable effect of phVEGF-C on lymphedema was reconfirmed in a mouse tail model. Immunohistochemical analysis using lymphatic-specific markers: VEGFR-3, lymphatic endothelial hyaluronan receptor-1, together with the proliferation marker Ki-67 Ab revealed that phVEGF-C transfection potently induced new lymphatic vessel growth. This study, we believe for the first time, documents that gene transfer of phVEGF-C resolves lymphedema through direct augmentation of lymphangiogenesis. This novel therapeutic strategy may merit clinical investigation in patients with lymphedema.

Amino Acid Sequence↗

PubMed2003

Independent prognostic impact of lymphatic vessel density and presence of low-grade lymphangiogenesis in cutaneous melanoma.

The aim of this study was to determine lymphatic vessel density (LVD) in a series of nodular melanoma and correlate the findings with the expression of several angiogenic factors, including vascular endothelial growth factor-C, basic fibroblast growth factor (bFGF), patient survival, and clinico-pathologic data. Patients with nodular melanoma and complete follow-up information were included. Lymphatic vessels were immunostained with the LYVE-1 and Podoplanin antibodies, and LVD was evaluated in both intra- and peri-tumoral (LVDpt) areas. Median LVD was 6.3 and 12.5 vessels/mm(2) in intra- and peri-tumoral areas, and coexpression of LYVE-1 and Ki-67/MIB-1 in lymphatic endothelial cells within the tumor was demonstrated, indicating active but low-grade lymphangiogenesis. Increased LVDpt was significantly associated with localization on the extremities (P = 0.005), decreased tumor thickness (P = 0.036), absence of vascular invasion (P = 0.004), brisk lymphocytic infiltration (P = 0.018), low proliferative rate by Ki-67 (P = 0.011), increased bFGF expression in tumor cells (P = 0.01) as well as in endothelial cells (P = 0.008), and decreased tumor cell expression of Ephrin-A1 (P = 0.009). Decreased LVD in intra-tumoral areas and LVDpt both predicted improved survival rates in multivariate analyses (for LVDpt, Hazard ratio: 2.1, P = 0.009). We found that decreased LVD was present in thicker and more proliferative tumors (Ki-67) and that increased LVD was significantly associated with improved patient survival in multivariate analysis. In addition, our data suggest the presence of low-grade intra-tumoral lymphangiogenesis in melanoma and a stimulating role of bFGF in lymphangiogenesis.

Cell Division↗

PubMed2002

Spontaneous hematogenous and lymphatic metastasis, but not primary tumor growth or angiogenesis, is diminished in fibrinogen-deficient mice.

Previous studies of tumor cell-associated procoagulants and fibrinolytic factors have strongly suggested that local thrombin and plasmin generation may be important in tumor growth and dissemination. Given that one central target of both of these serine proteases is fibrin(ogen), a logical extension of this hypothesis is that local fibrin deposition and dissolution may be key determinants of tumor progression. In this paper, the role of fibrin(ogen) and its degradation products in the growth and spontaneous metastasis of Lewis lung carcinoma was directly examined by comparative studies of control and fibrinogen-deficient mice. Fibrinogen deficiency was found to have no effect on the time required for the formation of palpable tumors, tumor angiogenesis, overall tumor architecture, or primary (s.c.) or secondary (pulmonary) tumor growth. However, fibrinogen deficiency markedly reduced the incidence of spontaneous macroscopic metastases in the lung and regional lymph nodes, a process that occurred relatively late in tumor development. Furthermore, a significant quantitative reduction in pulmonary micrometastases was observed in fibrinogen-deficient mice. Quantitative analyses of pulmonary micrometastases in primary tumor-bearing mice indicated that spontaneous showering of tumor cell emboli into the lung was robust, regardless of animal genotype. Hence, our results suggest fibrin(ogen) plays an important role in spontaneous metastasis, facilitating the stable adhesion and/or survival of metastatic emboli after tumor cell intravasation. These studies suggest that therapeutic strategies focusing on hemostatic factors may be effective in controlling solid tumor metastasis, particularly if used for the treatment of micrometastatic disease.

Animals↗

PubMed2002

Thrombospondin-1 selectively inhibits early-stage carcinogenesis and angiogenesis but not tumor lymphangiogenesis and lymphatic metastasis in transgenic mice.

The roles played by the endogenous angiogenesis inhibitor thrombospondin-1 (TSP-1) in the early stages of multi-step carcinogenesis and in the control of hematogenous versus lymphatic metastasis are unknown. To investigate these issues we compared tumor development in normal mice and in transgenic mice with targeted overexpression of TSP-1 in the epidermis following a standard two-step chemical skin carcinogenesis regimen. Overexpression of TSP-1 resulted in delayed and reduced development of premalignant epithelial hyperplasias, but did not inhibit the malignant conversion to squamous cell carcinomas. TSP-1 overexpression also suppressed tumor angiogenesis and distant organ metastasis, but failed to inhibit tumor-associated lymphangiogenesis or lymphatic tumor spread to regional lymph nodes. Concomitant with these results, we found that the endothelial TSP-1 receptor CD36 was mostly absent from cutaneous lymphatic vessels. Our findings indicate the potential use of TSP-1 for the prevention of premalignant stages of tumorigenesis and are likely to have implications for the further development of anti-angiogenic cancer therapies.

Animals↗

PubMed2002

VEGF-C induced lymphangiogenesis is associated with lymph node metastasis in orthotopic MCF-7 tumors.

The spread of cancer cells to regional lymph nodes through the lymphatic system is the first step in the dissemination of breast cancer. In several human cancers including those of the breast and prostate, the expression of vascular endothelial growth factor C (VEGF-C) is associated with lymph node metastasis. Our study was undertaken to evaluate the effect of VEGF-C on metastasis of poorly invasive, estrogen dependent human MCF-7 breast cancer cells. MCF-7 breast cancer cells transfected with VEGF-C (MCF-7-VEGF-C) were grown as tumors in the mammary fat pads of nude mice implanted with subcutaneous estrogen pellets. Tumor lymphangiogenesis and lymph node metastasis were studied immunohistochemically using antibodies against lymphatic vessel hyaluronan receptor -1 (LYVE-1), VEGF receptor-3 (VEGFR-3), PECAM-1, pan-cytokeratin and estrogen dependent pS2 protein. Overexpression of VEGF-C in transfected MCF-7 cells stimulated in vivo tumor growth in xenotransplanted mice without affecting estrogen responsiveness. The resulting tumors metastasized to the regional lymph nodes in 75% (in 6 mice out of 8, Experiment I) and in 62% (in 5 mice out of 8, Experiment II) of mice bearing orthotopic tumors formed by MCF-7-VEGF-C cells whereas no metastases were observed in mice bearing tumors of control vector-transfected MCF-7 cells (MCF-7-Mock). The density of intratumoral and peritumoral lymphatic vessels was increased in tumors derived from MCF-7-VEGF-C cells but not MCF-7-Mock cells. Taken together, our results show that VEGF-C overexpression stimulates tumor lymphangiogenesis and induces normally poorly metastatic estrogen-dependent MCF-7 tumors to disseminate to local lymph nodes. These data suggest that VEGF-C has an important role in lymph node metastasis of breast cancer even at its hormone-dependent early stage.

Animals↗

PubMed2002

An essential role for Prox1 in the induction of the lymphatic endothelial cell phenotype.

The process of angiogenesis has been well documented, but little is known about the biology of lymphatic endothelial cells and the molecular mechanisms controlling lymphangiogenesis. The homeobox gene Prox1 is expressed in a subpopulation of endothelial cells that, after budding from veins, gives rise to the mammalian lymphatic system. In Prox1(-)(/-) embryos, this budding becomes arrested at around embryonic day (E)11.5, resulting in embryos without lymphatic vasculature. Unlike the endothelial cells that bud off in E11.5 wild-type embryos, those of Prox1-null embryos did not co-express any lymphatic markers such as VEGFR-3, LYVE-1 or SLC. Instead, the mutant cells appeared to have a blood vascular phenotype, as determined by their expression of laminin and CD34. These results suggest that Prox1 activity is required for both maintenance of the budding of the venous endothelial cells and differentiation toward the lymphatic phenotype. On the basis of our findings, we propose that a blood vascular phenotype is the default fate of budding embryonic venous endothelial cells; upon expression of Prox1, these budding cells adopt a lymphatic vasculature phenotype.

Animals↗