The germ cell lineage in the mouse is not predetermined but is established during gastrulation, in response to signalling molecules acting on a subset of epiblast cells that move through the primitive streak together with extra-embryonic mesoderm precursors. After migration to the site of the future gonads, germ cell sex determination is achieved, with germ cell phenotype in male and female embryos diverging. Evidence suggests that all germ cells spontaneously take the female pathway, entering prophase of the first meiotic division five or six days after the birth of the germ cell lineage, with the exception of those located in the embryonic testis, which exit the cell cycle in response to some inhibitory signal and remain in G_o until after birth, when spermatogenesis begins. In culture, germ cells respond to certain growth factors by proliferating indefinitely. These immortalized embryonic germ (EG) cell lines are chromosomally stable and pluripotent, closely resembling the embryonic stem (ES) cell lines derived from blastocyst-stage embryos. Human EG and ES cell lines have recently been made, raising the hope that their differentiation could be directed to specific cell types, of value in the clinical treatment of degenerative diseases.

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During the peri-implantation development of the mouse embryo from the blastocyst through gastrulation, Pou5f1 (OCT-4) down-regulation is closely linked to the initial step of lineage allocation to extraembryonic and embryonic somatic tissues. Subsequently, differentiation of the lineage precursors is subject to inductive tissue interactions and intercellular signalling that regulate cell proliferation and the acquisition of lineage-specific morphological and molecular characteristics. A notable variation of this process of lineage specification is the persistence of Pou5f1 activity throughout the differentiation of the primordial germ cells, which may underpin their ability to produce pluripotent progeny either as stem cells (embryonic germ cells) in vitro or as gametes in vivo. Nevertheless, intercellular signalling still plays a critical role in the specification of the primordial germ cells. The findings that primordial germ cells can be induced from any epiblast cells and that they share common progenitors with other somatic cells provide compelling evidence for the absence of a pre-determined germ line in the mouse embryo.

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Many vasa homologue genes to Drosophila vasa have been isolated in various animal species. They provide specific molecular probes to analyze the establishment and the differentiation of germ cell lineage. In mammals, the expression of VASA protein becomes detectable in PGCs at the late migrating stage. Interestingly, during spermatogenesis the intracellular localization of VASA protein is closely associated with the chromatoid body.

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Embryonic stem (ES) cells are pluripotent cells directly derived from early stage embryos that retain the ability to differentiate into all cell types. This unique feature is the basis of various applications of ES cell technology such as in vitro models of mammalian development, germline transgenesis to make knockout mice, and a generic source for cell therapy in regenerative medicine. To achieve success in these applications, the pluripotency of ES cells has to be kept stable during long-term culture in vitro, leading to the necessity of determining the molecular basis for maintaining ES self-renewal. This paper summarizes the recent progress in this area, focusing mainly on the LIF signaling pathway and the transcription factor Oct-3/4. Although it is still unclear how these components works together, a model is presented here that provides a plan to solve this problem.

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The recent fascinating breakthrough in the area of stem cell research is the successful production of cloned animals via nuclear transplantation of somatic nucleus by intrinsic trans-acting factors of oocytes and trans-differentiation of somatic stem cells from adult organs induced by extrinsic growth factors. During the process of nuclear reprogramming, epigenetic modification of the somatic nuclei must be achieved to acquire toti-/pluripotential competence. However, the molecular mechanism involved is largely unknown. It has been shown that DNA methylation, histone acetylation and chromatin structure are involved in the establishment of epigenetic modification. Now it is evident that they function cooperatively to establish and maintain active or inactive chromatin state. Here we discuss the mechanisms of epigenetic modification potentially involved in the event of nuclear reprogramming.

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Expression of mouse A2M (MAM), murinoglobulin (MUG), the A2M receptor or LDL-Receptor related protein (A2MR/LRP) and the Receptor Associated Protein (RAP) were measured by northern blotting of mRNA isolated from liver, heart and peritoneal macrophages from C3H/HeJ and C57BL/6J (B6) mice. Marked differences between males of the two mouse strains were observed for MAM and MUG mRNA levels in liver, which were reflected in plasma levels of both proteinase inhibitors, as confirmed by immune-electrophoresis. C3H/HeJ mice had higher levels of the MAM and MUG mRNA and their corresponding plasma proteins than B6 mice. B6 mice expressed higher levels of LRP mRNA relative to C3H/HeJ mice but had lower levels of RAP mRNA. LRP receptor activity, assayed by fluoresceinated-A2M binding, was higher in B6 cells. The present data contribute to the knowledge of genetic background characteristics among male mouse of these two strains, which can take part in many biological events such as lipid metabolism, inflammation and immune response to different infectious agents.

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Melanogenesis cascade may be directly or indirectly linked to the dynamics of endosome-lysosome biogenesis. This study aims to identify how and to what extent the endosome-lysosome system is involved in melanosome biogenesis, by utilizing a novel melanogenesis marker, J1, which we identified in the process of developing monoclonal antibodies (MoAbs) against human melanosomes. The antigenic epitope of MoAb J1 was expressed by all of the melanotic and nonmelanotic cells examined. It was expressed primarily by granular structures located in regions proximal to the Golgi complex. Most of MoAb J1 positive granules were co-stained with melanogenic markers, tyrosinase or tyrosinase-related protein (TRP-1). The epitope of MoAb J1 was also co-expressed by most, but not all, of LGP85 (a lysosomal marker) positive granules in both melanoma and non-melanoma cells, indicating that MoAb J1 recognizes a subset of lysosomal vesicles. MoAb J1 did not, however, react with vesicles with late/early (syntaxin 8/ EEA1) endosomal markers. Further examination using fluorophore-labeled pepstatin, a marker of lysosomal luminal content, confirmed that MoAb J1 specifically recognizes the luminal surface of lysosomes. These results indicate that MoAb J1 possesses an antigen epitope that is expressed in the luminal component of prelysosomal granules which are involved in the biogenesis cascade common to both melanosomes and lysosomes. We suggest that tyrosinase family protein, tyrosinase and TRP-1 are transported to melanosomes from TGN via these prelysosomal granules after being transiently transported to late endosomes.

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Tenascin-C is an oligomeric glycoprotein of the extracellular matrix that has been found to have both adhesive and anti-adhesive properties for cells. Recent elucidation of the two major TNC splice variants (320 kDa and 220 kDa) has shed light on the possibility of varying functions of the molecule based on its splicing pattern. Tenascin-C is prominently expressed in embryogenesis and in pathologic conditions such as tumorogenesis and wound healing. Fibronectin is a prominent adhesive molecule of the extracellular matrix that is often co-localized with tenascin-C in these processes.
We studied the chondrosarcoma cell line JJ012 with enzyme-linked immunoabsorbance assays, cell attachment assays and antibody-blocking assays to determine the adhesive/anti-adhesive properties of the two major tenascin-C splice variants with respect to fibronectin and their effect on chondrosarcoma cell attachment. We found that the small tenascin-C splice variant (220 kDa) binds to fibronectin, whereas the large tenascin-C splice variant (320 kDa) does not. In addition, the small tenascin-C splice variant was found to decrease adhesion for cells when bound to fibronectin, but contributed to adhesion when bound to plastic in fibronectin-coated wells. Antibody blocking experiments confirmed that both the small tenascin-C splice variant and fibronectin contribute to cell adhesion when bound to plastic. The large tenascin-C splice variant did not promote specific cell attachment. We hypothesize that the biologic activity of tenascin-C is dependent on the tissue-specific splicing pattern. The smaller tenascin-C isoform likely plays a structural and adhesive role, whereas the larger isoform, preferentially expressed in malignant tissue, likely plays a role in cell egress and metastasis.

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