Putative “Stemness” Gene Jam-B Is Not Required for Maintenance of Stem Cell State in Embryonic, Neural, or Hematopoietic Stem Cells

Abstract

Many genes have been identified that are specifically expressed in multiple types of stem cells in their undifferentiated state. It is generally assumed that at least some of these putative "stemness" genes are involved in maintaining properties that are common to all stem cells. We compared gene expression profiles between undifferentiated and differentiated embryonic stem cells (ESCs) using DNA microarrays. We identified several genes with much greater signal in undifferentiated ESCs than in their differentiated derivatives, among them the putative stemness gene encoding junctional adhesion molecule B (Jam-B gene). However, in spite of the specific expression in undifferentiated ESCs, Jam-B mutant ESCs had normal morphology and pluripotency. Furthermore, Jam-B homozygous mutant mice are fertile and have no overt developmental defects. Moreover, we found that neural and hematopoietic stem cells recovered from Jam-B mutant mice are not impaired in their ability to self-renew and differentiate. These results demonstrate that Jam-B is dispensable for normal mouse development and stem cell identity in embryonic, neural, and hematopoietic stem cells.Embryonic stem cells (ESCs) are derived from mammalian preimplantation embryos and possess the remarkable ability to differentiate into all embryonic cell types. Moreover, they can grow indefinitely without losing this pluripotency if cultured under appropriate conditions. A number of key transcription factors, such as OCT-4, Nanog, and FOXD3 (5,7,12,22,25), have been shown to be essential for sustaining ESC properties. However, it is not known how these molecules contribute to maintenance of the pluripotent state.Somatic stem cells, including neural stem cells (NSCs) and hematopoietic stem cells (HSCs), share some of the properties of ESCs, including multipotency and self-renewal. In the event of severe injury, numerous types of tissue-specific stem cells can give rise to cells of heterologous lineages (39,42,43), although in some cases, fusion of stem cells with other cells appears to be involved in transdifferentiation (21, 29, 46). Thus, it is possible that ESCs and somatic stem cells share a common genetic program that maintains stem cell identity (20,37,40,42). Recently, Ivanova et al. (13) identified 283 genes or expressed sequence tags, including a gene encoding junctional adhesion molecule B (JAM-B) (nomenclature of the protein in NCBI Database is JAM2), that are expressed in three different stem cell lines, by means of DNA microarray analysis. Although it is assumed that at least some of these genes are involved in the maintenance of stem cell properties, no data confirming this have yet been reported.Here we investigate this possibility. We have focused on Jam-B, a putative "stemness" gene identified by Ivanova et al. (13), because of the extreme difference in expression levels between undifferentiated and differentiated ESCs. Jam-B encodes an immunoglobulin superfamily protein that is specific to tight junctions and mediates cell-cell contacts between T cel...

Differential Requirement for Nucleostemin in Embryonic Stem Cell and Neural Stem Cell Viability

“…Southern blot analysis was done as described previously [10] using 5 0 and 3 0 flanking regions of nucleostemin gene. For genotyping by PCR, three different primers were used to amplify a portion of wild-type nucleostemin gene and a boundary region of the b-geo reporter gene.…”

“…Gene expression profiling data from many tissues have led to the identification of genes that are expressed in many types of stem cells, some of which are required for self-renewal [2][3][4][5]. Sox2 [6][7][8], Zfx [9], Jam-B [10], and nucleostemin [11] are examples of genes expressed in a variety of stem cells. Nucleostemin is a nucleolar GTPbinding protein that regulates cell cycle progression and is required for early embryogenesis, with deletion of the gene resulting in embryonic lethality at around 3.5 days postcoitum (d.p.c.)…”

JAM-A is both essential and inhibitory to development of hepatic polarity in WIF-B cells

“…The insights gained by using an in vitro cell system that expresses only one JAM isoform can guide studies of liver development in vivo, where the lack of liver phenotypes in any of the three JAM knockout mice points to overlapping functions for the protein (8,21,56). Future studies using the KD cells to express different JAM isoforms and mutant constructs should also provide further understanding of this protein's role in the complex polarity of hepatic cells.…”

“…Although epithelial functions have been disrupted by JAM-A knockdown (KD) in cell culture models of simple epithelia and recently in cultured hepatic cells (35,54), gene knockout studies of individual JAMs in mice have shown no major defects in development or function of epithelia, most likely a consequence of gene redundancy (8,21,56). Nonetheless, results from the in vitro studies suggest that JAM plays an essential and early role in TJ formation (17,26,38), since it was found at primordial cell-cell contact sites in a bronchial epithelial cell line (31).…”

Junctional Adhesion Molecules (JAMs) - New Players in Breast Cancer?

“…in the bone marrow, with their expression decreasing during the acquisition of a more differentiated state (Nagamatsu et al, 2006;Sakaguchi et al, 2006;Sugano et al, 2008;Praetor et al, 2009). Furthermore JAM-A expression has been reported to be high on undifferentiated HC11 mammary epithelial cells relative to differentiated cells (Perotti et al, 2009).…”