Avian TVB (DR5-like) death receptor expression in hen ovarian follicles

Tumor necrosis factor-related apoptosis inducing ligand expression and activity in hen granulosa cells

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) represents one of several cytokine members of the tumor necrosis factor superfamily reported to initiate apoptosis in a wide range of transformed, but not most normal, cell types. The present studies were conducted to evaluate the potential for TRAIL to promote apoptotic cell death in differentiated granulosa cells collected from hen preovulatory follicles. While mRNA encoding critical components (including TRAIL) required for a functional extrinsic cell death pathway are expressed in granulosa cells, TRAIL treatment by itself fails to induce either caspase-3 activity or a decrease in cell viability. On the other hand, preculture of cells with the conventional chemotherapeutic, cisplatin, or the 20S proteosome inhibitor, Z-LLF-CHO, sensitizes granulosa cells to TRAIL as evidenced by enhanced caspase-3 activity after 4 h of culture and loss of cell viability after 24 h when compared with either cisplatin or Z-LLF-CHO treatment alone. Moreover, the sensitizing effect of Z-LLF-CHO on TRAIL-induced loss of cell viability is prevented by the selective caspase-8 inhibitor, Z-IETD-FMK. Interestingly, TRAIL mRNA expression is elevated both in prehierarchal follicles undergoing spontaneous atresia and in prehierarchal follicles induced to undergo atresia for 6 h in vitro. In summary, the data demonstrate the presence of a functional TRAIL signaling pathway in hen granulosa cells, and are consistent with the possibility that TRAIL signaling may directly or indirectly participate in the process of follicle atresia in vivo.

Apoptosis in the ovary: molecular mechanisms

Cell death was first described in rabbit ovaries (Graaffian follicles), the phenomenon being called 'chromatolysis' rather than apoptosis. In humans, the ovarian endowment of primordial follicles is established during fetal life. Apoptotic cell death depletes this endowment by at least two-thirds before birth, executed with the help of several players and pathways conserved from worms to humans. To date, apoptosis has been reported to be involved in oogenesis, folliculogenesis, oocyte loss/selection and atresia. Several pro-survival and pro-apoptotic molecules are involved in ovarian apoptosis with the delicate balance between them being the determinant for the final destiny of the follicular cells. This review critically analyses the current knowledge about the biological roles of these molecules and their relevance to the dynamics of follicle development. It also presents the existing literature and assesses the gaps in our knowledge.

TRAIL and KILLER Are Expressed and Induce Apoptosis in the Murine Preimplantation Embryo1

TRAIL (tumor necrosis factor [TNF]-related apoptosis-inducing ligand) and KILLER are a death-inducing ligand and receptor pair that belong to the TNF and TNF-receptor superfamilies, respectively. To date, only one apoptosis-inducing TRAIL receptor (murine KILLER [MK]) has been identified in mice, and it is a homologue of human Death Receptor 5. Whereas the expression of other death receptors, such as Fas and TNF receptor 1 have been documented in mammalian preimplantation embryos, no evidence currently demonstrates either the presence or the function of TRAIL and its corresponding death receptor, MK. Using reverse transcription-polymerase chain reaction and confocal immunofluorescent microscopy, we found that both TRAIL and MK are expressed from the 1-cell through the blastocyst stage of murine preimplantation embryo development. These proteins are localized mainly at the cell surface from the 1-cell through the morula stage. At the blastocyst stage, both TRAIL and MK exhibit an apical staining pattern in the trophectoderm cells. Finally, using the TUNEL assay, we demonstrated that MK induces apoptosis in blastocysts sensitized to TRAIL via actinomycin D. Taken together, these data are the first to demonstrate the presence and function of TRAIL and MK, a death-inducing ligand and its receptor, in mammalian preimplantation embryos.

Alternatively Spliced Variants of Gallus gallus TNFRSF23 Are Expressed in the Ovary and Differentially Regulated by Cell Signaling Pathways1

As a result of searching recently available chicken (ch) expressed sequence tag databases, a new Tumor Necrosis Factor Receptor Super Family (TNFRSF) member with similarity to the murine (m) TNFRSF23 decoy receptor (DcR) has been identified. However, by comparison with the mTNFRSF23, there exist at least two splice variants of chTNFRSF23, one of which includes an intracellular death domain (TNFRSF23.v1) characteristic of death receptors, and the other with a truncated cytoplasmic domain of a DcR (named TNFRSF23.v2). These two splice variants of chTNFRSF23 display differential patterns of mRNA expression across various hen tissues, with the highest levels observed within reproductive tissues. More specifically, TNFRSF23.v1 is most highly expressed in preovulatory follicle granulosa cells in the ovary, whereas TNFRSF23.v2 mRNA is found at highest levels in ovarian stromal tissue. Primary culture experiments with granulosa cells determined that expression of TNFRSF23.v1 mRNA was decreased by protein kinase A signaling and enhanced by transforming growth factor (TGF) alpha treatment. Interestingly, TGFbeta1 and signaling via protein kinase C also enhanced levels of TNFRSF23.v1 expression but only in undifferentiated granulosa cells from prehierarchal follicles. Based on patterns of mRNA expression and its endocrine/paracrine regulation, we predict that ovarian chTNFRSF23 represents a modulator of granulosa cell survival and/or differentiation. Finally, the characterization of these receptor variants is of considerable interest from an evolutionary perspective in that they provide additional evidence to support a continuing divergence of TNFRSF members throughout vertebrate evolution.

Multiple roles of TNF super family members in corpus luteum function

The main function of the corpus luteum (CL) is the production of progesterone. Adequate luteal progesterone is crucial for determining the physiological duration of the estrous cycle and for achieving a successful pregnancy. The CL is regulated not only by hypophyseal gonadotropin, but also by a number of cytokines that are locally produced. Tumor necrosis factor-alpha (TNF) and its specific receptors (TNFR) are present in the CL of many species. TNF plays multiple and likely important roles in CL function throughout the estrous cycle. TNF appears to have luteotropic and luteolytic roles in the CLs. In contrast, Fas ligand (Fas L), another member of TNF super family (TNF-SF), is primarily recognized for its apoptotic actions. Presumably, Fas L binds its cognate receptor (Fas) to induce structural luteolysis. This review is designed to focus on recent studies documenting the expression of TNF and Fas L, their receptors, and intracellular signaling mechanisms in the CL.

Characterization of chicken TNFR superfamily decoy receptors, DcR3 and osteoprotegerin

Tumor necrosis factor (TNF) family ligands bind to death domain-containing TNF receptors (death receptors), which can subsequently activate intracellular signaling pathways to initiate caspase activity and apoptotic cell death. Decoy receptors, without intracellular death domains, have been reported to prevent cytotoxic effects by binding to and sequestering such ligands, or by interfering with death receptor trimerization. The chicken death receptors, Fas, TNFR1, DR6, and TVB, are constitutively expressed in a relatively wide variety of hen tissues. In this study, two chicken receptors with sequence homology to the mammalian decoys, DcR3 and osteoprotegerin, were identified and their pattern of expression was characterized. Unlike the previously identified chicken death receptors, the newly characterized decoy receptors show comparatively limited expression among tissues, suggesting a tissue-specific function. Finally, characterization of these chicken receptors further contributes to understanding the evolutionary divergence of TNFR superfamily members among vertebrate species.

All in the family: evolutionary and functional relationships among death receptors

Over the last decade, significant progress has been made towards identifying the signaling pathways within mammalian cells that lead to apoptosis mediated by death receptors. The simultaneous expression of more than one death receptor in many, if not all, cell types suggests that functional innovation has driven the divergence of these receptors and their cognate ligands. To better understand the physiological divergence of the death receptors, a phylogenetic analysis of vertebrate death receptors was conducted based upon amino-acid sequences encoding the death domain regions of currently known and newly identified members of the family. Evidence is presented to indicate an ancient radiation of death receptors that predates the emergence of vertebrates, as well as ongoing divergence of additional receptors both within several receptor lineages as well as modern taxonomic lineages. We speculate that divergence among death receptors has led to their functional specialization. For instance, some receptors appear to be primarily involved in mediating the immune response, while others play critical roles during development and tissue differentiation. The following represents an evolutionary approach towards an understanding of the complex relationship among death receptors and their proposed physiological functions in vertebrate species.