Biomedical subjects

Julie Gordon

Publications and source records attributed to Julie Gordon.

7 recordsLinked to original sources

PubMed2006

Bmp4 and Noggin expression during early thymus and parathyroid organogenesis.

The thymus and parathyroids originate from the third pharyngeal pouches, which form as endodermal outpocketings in the pharyngeal region beginning on embryonic day 9 (E9.0) of mouse development. Using organ-specific markers, we have previously shown that thymus and parathyroid-specific organ domains are established within the primordium prior to formation of the organs proper: Gcm2 expression defines the prospective parathyroid cells in the dorsal pouch from E9.5, while Foxn1 is expressed in the thymus domain from E11.25. Bmp (bone morphogenetic protein) signaling has been implicated in thymic epithelial cell differentiation and thymus organogenesis. In the present study, we report expression patterns of Bmp4 and Noggin, a Bmp4 antagonist, in the third pharyngeal pouch using two lacZ transgenic mouse strains. Results from this gene expression study revealed localization of Bmp4 expression to the ventral region of the third pharyngeal pouch endoderm at E10.5 and E11.5, in those cells that will express Foxn1 and form the thymus. Conversely, the expression of Noggin was confined to the dorsal region of the pouch and primordium at these stages, and thus appeared to be co-expressed with Gcm2 in the parathyroid domain. This represents the first detailed study of Bmp4 and Noggin expression during the early stages of thymus and parathyroid organogenesis.

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PubMed2006

Identification of a tandem duplicated array in the Rhox alpha locus on mouse chromosome X.

The Rhox family of homeobox-containing genes maps to three gene dense clusters, alpha, beta, and gamma, on the mouse X chromosome. Rhox genes are expressed primarily in reproductive and extra-embryonic tissues and may be regulated by colinear mechanisms. Uniquely among family members, Rhox4 is also expressed in the developing and adult thymus, where its striking restriction to the third pharyngeal pouch has suggested a role in lineage specification. In this article we describe a previously unreported duplication within the Rhox alpha locus that contains seven copies of Rhox4 and eight copies of Rhox2 and Rhox3 in a tandem array. We further show that all seven Rhox4 copies are expressed, although preferential expression occurs and differs between tissues. In contrast to reproductive tissues, we found no evidence of colinear expression of the Rhox alpha cluster during thymus development. All subspecies of mice examined contained multiple copies of Rhox4. However, the only predicted ortholog of Rhox4, rat Rhox4, is present in a single copy, suggesting that the duplications arose at the time of rat and mouse lineage divergence. Finally, no changes in Rhox4 expression were detected in mice with defects in thymus organogenesis, placing it upstream or outside of established transcriptional pathways.

Amino Acid Sequence↗

PubMed2005

In vivo and in vitro assays of thymic organogenesis.

We describe two complementary methods for the study of early thymus organogenesis in the mouse. The first is an in vitro technique for lineage analysis, where a chosen population of cells within the mouse embryo is labeled with a fluorescent cell tracker dye. The embryos are then transferred to whole embryo culture for a defined period, after which time the location of the labeled cells is determined with respect to the developing thymus. In the second method, an in vivo assay is used to determine the ability of a specific tissue type to form a structurally and functionally normal thymus. This method uses an ectopic grafting technique where the embryonic pharyngeal endoderm containing the prospective thymus tissue is carefully isolated and transplanted under the kidney capsule of an adult mouse. Together, these techniques have allowed the cell types that make a physical contribution to the formation of the thymic epithelium to be identified.

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PubMed2004

Abnormalities of caudal pharyngeal pouch development in Pbx1 knockout mice mimic loss of Hox3 paralogs.

Pbx1 is a TALE-class homeodomain protein that functions in part as a cofactor for Hox class homeodomain proteins. Previous analysis of the in vivo functions of Pbx1 by targeted mutagenesis in mice has revealed roles for this gene in skeletal patterning and development and in the organogenesis of multiple systems. Both RNA expression and protein localization studies have suggested a possible role for Pbx1 in pharyngeal region development. As several Hox mutants have distinct phenotypes in this region, we investigated the potential requirement for Pbx1 in the development of the pharyngeal arches and pouches and their organ derivatives. Pbx1 homozygous mutants exhibited delayed or absent formation of the caudal pharyngeal pouches, and disorganized patterning of the third pharyngeal pouch. Formation of the third pouch-derived thymus/parathyroid primordia was also affected, with absent or hypoplastic primordia, delayed expression of organ-specific differentiation markers, and reduced proliferation of thymic epithelium. The fourth pouch and the fourth pouch-derived ultimobranchial bodies were usually absent. These phenotypes are similar to those previously reported in Hoxa3(-/-) single mutants and Hoxa1(-/-);Hoxb1(-/-) or Hoxa3(+/-);Hoxb3(-/-);Hoxd3(-/-) compound mutants, suggesting that Pbx1 acts together with multiple Hox proteins in the development of the caudal pharyngeal region. However, some aspects of the Pbx1 mutant phenotype included specific defects that were less severe than those found in known Hox mutant mice, suggesting that some functions of Hox proteins in this region are Pbx1-independent.

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PubMed2004

Functional evidence for a single endodermal origin for the thymic epithelium.

T cell development depends critically on several distinct thymic epithelial cell types that are organized into two main compartments: cortex and medulla. The prevailing hypothesis suggests that these derive from ectoderm and endoderm, respectively. Here we show that lineage analysis provides no evidence for an ectodermal contribution to the thymic rudiment. We further demonstrate, via ectopic transplantation, that isolated pharyngeal endoderm can generate a functional thymus containing organized cortical and medullary regions and that this capacity is not potentiated by the presence of pharyngeal ectoderm. These data establish that the cortical and medullary thymic epithelial compartments derive from a single germ layer, the endoderm, thus refuting the 'dual-origin' model of thymic epithelial ontogeny.

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PubMed2003

New serum-free in vitro culture technique for midgestation mouse embryos.

Current in vitro culture methods for mouse embryos are critically dependent on specially prepared rodent serum. Rodent serum requires careful preparation and stringent assessment of serum quality, while commercially available whole embryo culture serum is expensive and shows considerable lot variability. Thus, preparation and testing of suitable serum represents a considerable investment of time and resources, particularly for laboratories with only short-term embryo culture requirements. In addition, serum supplementation of culture medium may introduce unknown serum components that could interfere with interpretation of experimental results, especially where the study is geared towards analysis of a specific growth factor. Here we describe the composition of a standardized serum free culture medium comprised of commercially available stem cell media supplements. With this method, we have successfully cultured midgestation stage mouse embryos and demonstrated, using both morphological and gene expression criteria, that these embryos exhibited proper developmental progression. We believe this method to be a significant advance in whole embryo culture technology that will be of particular use to laboratories needing to utilize whole embryo culture to study midgestation organogenesis.

Animals↗

PubMed2002

Identification and characterization of thymic epithelial progenitor cells.

T cell differentiation and repertoire selection depend critically on several distinct thymic epithelial cell types, whose lineage relationships are unclear. We have investigated these relationships via functional analysis of the epithelial populations within the thymic primordium. Here, we show that mAbs MTS20 and MTS24 identify a population of cells that, when purified and grafted ectopically, can differentiate into all known thymic epithelial cell types, attract lymphoid progenitors, and support CD4(+) and CD8(+) T cell development in nude mice. In contrast, other epithelial populations in the thymic primordium can fulfill none of these functions. These data establish that the MTS20(+)24(+) population is sufficient to generate a functional thymus in vivo and thus argue strongly that all thymic epithelial cell types derive from a common progenitor cell.

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