Sculpturing digit shape by cell death

Keeping Cell Death Alive: An Introduction into the French Cell Death Research Network

Since the Nobel Prize award more than twenty years ago for discovering the core apoptotic pathway in C. elegans, apoptosis and various other forms of regulated cell death have been thoroughly characterized by researchers around the world. Although many aspects of regulated cell death still remain to be elucidated in specific cell subtypes and disease conditions, many predicted that research into cell death was inexorably reaching a plateau. However, this was not the case since the last decade saw a multitude of cell death modalities being described, while harnessing their therapeutic potential reached clinical use in certain cases. In line with keeping research into cell death alive, francophone researchers from several institutions in France and Belgium established the French Cell Death Research Network (FCDRN). The research conducted by FCDRN is at the leading edge of emerging topics such as non-apoptotic functions of apoptotic effectors, paracrine effects of cell death, novel canonical and non-canonical mechanisms to induce apoptosis in cell death-resistant cancer cells or regulated forms of necrosis and the associated immunogenic response. Collectively, these various lines of research all emerged from the study of apoptosis and in the next few years will increase the mechanistic knowledge into regulated cell death and how to harness it for therapy.

Genetic determinants of syndactyly: perspectives on pathogenesis and diagnosis

The formation of the digits is a tightly regulated process. During embryogenesis, disturbance of genetic pathways in limb development could result in syndactyly; a common congenital malformation consisting of webbing in adjacent digits. Currently, there is a paucity of knowledge regarding the exact developmental mechanism leading to this condition. The best studied canonical interactions of Wingless‐type–Bone Morphogenic Protein–Fibroblast Growth Factor (WNT–BMP–FGF8), plays a role in the interdigital cell death (ICD) which is thought to be repressed in human syndactyly. Animal studies have displayed other pathways such as the Notch signaling, metalloprotease and non-canonical WNT-Planar cell polarity (PCP), to also contribute to failure of ICD, although less prominence has been given. The current diagnosis is based on a clinical evaluation followed by radiography when indicated, and surgical release of digits at 6 months of age is recommended. This review discusses the interactions repressing ICD in syndactyly, and characterizes genes associated with non-syndromic and selected syndromes involving syndactyly, according to the best studied canonical WNT-BMP-FGF interactions in humans. Additionally, the controversies regarding the current syndactyly classification and the effect of non-coding elements are evaluated, which to our knowledge has not been previously highlighted. The aim of the review is to better understand the developmental process leading to this condition.

Short stature leads to a diagnosis of Jansen-de Vries syndrome in two unrelated Taiwanese girls: A case report and literature review

Short stature and intellectual disability are two of the major components of many dysmorphic syndromes. Jansen-de Vries syndrome (JDVS) is a rare syndromic disorder that was discovered recently using next-generation sequencing. It is characterized by hypotonia, developmental delay, a dysmorphic face, short stature, and high pain threshold and is caused by the variants of the protein phosphatase magnesium-dependent 1D (PPM1D) gene. Here, we report the first two cases of PPM1D mutations in Taiwan; both had de novo variants in exon 6. Both presented with short stature, developmental delay, and dysmorphic faces. In addition to the characteristics listed above, syndactyly was noted in one. Genetic studies should be considered when approaching a patient with growth retardation, intellectual disability, and other major or minor dysmorphisms.

Early cellular development induced by ecdysteroid in sex-specific wing degeneration of the wingless female winter moth

The winter moth, Nyssiodes lefuarius, exhibits striking sexual dimorphism in wing form; males have functional wings of normal size, whereas females lack wings. We previously found that the steroid hormone 20-hydroxyecdysone (20E) triggered massive programmed cell death (PCD) only in the female pupal wing epithelium; however, when and how early sexual trait development of the pupal wings is initiated during pupal-adult metamorphosis remains obscure. To clarify the detailed morphological changes and mechanisms underlying early sexual trait development and cell death, we examined the effects of 20E on early ultrastructural and histological changes in the pupal wing epithelium of both sexes. Before the onset of adult differentiation, no morphological differences were observed in the epithelial cells of both sexes at an ultrastructural level. When 5.4 µg of 20E was injected into pupae of both sexes at 15 days after the onset of pupation, retraction of the wing epithelium from the pupal cuticle was initiated at day 2 after 20E injection in both sexes. Although overt degeneration of wing tissue was not still obvious, apoptotic body-like structures and auto-phagosomes were visible at day 3 after 20E injection in females, whereas development of scale precursor cells started on day 4 after injection in males. Our results suggest that (1) the injection of 20E induced sexually dimorphic changes in the pattern of organelle distribution in wing epithelial cells, and (2) abnormally shaped mitochondria in the cytoplasm of the female wing epithelium might be involved in the PCD that occurs during wing tissue degeneration.

Is Senescence-Associated β-Galactosidase a Reliable in vivo Marker of Cellular Senescence During Embryonic Development?

During vertebrate embryonic development, cellular senescence occurs at multiple locations. To date, it has been accepted that when there has been induction of senescence in an embryonic tissue, β-galactosidase activity is detectable at a pH as high as 6.0, and this has been extensively used as a marker of cellular senescence in vivo in both whole-mount and cryosections. Such senescence-associated β-galactosidase (SA-β-GAL) labeling appears enhanced in degenerating regions of the vertebrate embryo that are also affected by programmed cell death. In this sense, there is a strong SA-β-GAL signal which overlaps with the pattern of cell death in the interdigital tissue of the developing limbs, and indeed, many of the labeled cells detected go on to subsequently undergo apoptosis. However, it has been reported that β-GAL activity at pH 6.0 is also enhanced in healthy neurons, and some retinal neurons are strongly labeled with this histochemical technique when they begin to differentiate during early embryonic development. These labeled early post-mitotic neurons also express other senescence markers such as p21. Therefore, the reliability of this histochemical technique in studying senescence in cells such as neurons that undergo prolonged and irreversible cell-cycle arrest is questionable because it is also expressed in healthy post-mitotic cells. The identification of new biomarkers of cellular senescence would, in combination with established markers, increase the specificity and efficiency of detecting cellular senescence in embryonic and healthy mature tissues.

Cell death in the developing vertebrate limb: A locally regulated mechanism contributing to musculoskeletal tissue morphogenesis and differentiation

Our aim is to critically review current knowledge of the function and regulation of cell death in the developing limb. We provide a detailed, but short, overview of the areas of cell death observed in the developing limb, establishing their function in morphogenesis and structural development of limb tissues. We will examine the functions of this process in the formation and growth of the limb primordia, formation of cartilaginous skeleton, formation of synovial joints, and establishment of muscle bellies, tendons, and entheses. We will analyze the plasticity of the cell death program by focusing on the developmental potential of progenitors prior to death. Considering the prolonged plasticity of progenitors to escape from the death process, we will discuss a new biological perspective that explains cell death: this process, rather than secondary to a specific genetic program, is a consequence of the tissue building strategy employed by the embryo based on the formation of scaffolds that disintegrate once their associated neighboring structures differentiate.

We examine the functions of cell death in the formation and growth of the limb primordia.

We analyze the plasticity of the cell death program by focusing on the developmental potential of progenitors prior to death.

Considering the prolonged plasticity of progenitors to escape from the death process and the absence of defined genetic program in their regulation we propose that cell death is a consequence of the tissue building strategy employed by the embryo regulated by epigenetic factors .

Epithelial Migration and Non-adhesive Periderm Are Required for Digit Separation during Mammalian Development

The fusion of digits or toes, syndactyly, can be part of complex syndromes, including van der Woude syndrome. A subset of van der Woude cases is caused by dominant-negative mutations in the epithelial transcription factor Grainyhead like-3 (GRHL3), and Grhl3^-/-mice have soft-tissue syndactyly. Although impaired interdigital cell death of mesenchymal cells causes syndactyly in multiple genetic mutants, Grhl3^-/- embryos had normal interdigital cell death, suggesting alternative mechanisms for syndactyly. We found that in digit separation, the overlying epidermis forms a migrating interdigital epithelial tongue (IET) when the epithelium invaginates to separate the digits. Normally, the non-adhesive surface periderm allows the IET to bifurcate as the digits separate. In contrast, in Grhl3^-/- embryos, the IET moves normally between the digits but fails to bifurcate because of abnormal adhesion of the periderm. Our study identifies epidermal developmental processes required for digit separation.

Up-regulated LINC00261 predicts a poor prognosis and promotes a metastasis by EMT process in cholangiocarcinoma

OBJECTIVE

LINC00261 plays a vital role in tumorigenesis and metastasis of digestive system cancer. However, an influence of LINC00261 on cholangiocarcinoma has a little research. There, we investigated clinical role and molecular mechanisms of LINC00261 in cholangiocarcinoma.

METHODS

The qRT-PCR was performed for the detection of LINC00261 level in 50 paired specimens from CCA patients and six cell lines. Cell proliferation were explored by CCK-8 and colony formation assays in QBC939 and RBE cells after transfected with si-LINC00261 or si-NC. Then, AO/EB double fluorescence staining and flow cytometric assays were performed to assess cell apoptosis. Transwell and wound healing assays were selected to evaluate migratory and invasive property of cells. Protein levels, such as PCNA, Bax, Bcl-2, and several epithelial-to-mesenchymal transition markers, including E-cadherin, N-cadherin and Vimentin, were detected by western blot assays. Furthermore, we use a R2 platform to evaluate the correlation between LINC00261 and EMT makers and predict the overall survival and relapse-free survival for CCA patients by the expression of LINC00261/ EMT makers.

RESULTS

LINC00261 was overexpressed in cancerous tissues and CCA cell lines compared with adjacent tissues and HIBEC, respectively. Up-regulation of LINC00261 was related to larger tumor size (p = 0.009), positive lymph node metastasis (p = 0.021), advanced TNM stages (p = 0.017) and higher postoperative recurrence (p = 0.009) for CCA patients. Additionally, univariate and multivariate analysis displayed that LINC00261 an independent prognostic factor in CCA patients. Knockdown of LINC00261 expression in RBE and QBC939 cell lines inhibited cell proliferation, migration and invasion property and increased cell apoptosis and the EMT progression. Moreover, there was a strong correlation between LINC00261 and E-cadherin (CDH1) (p < 0.05), and low expression of E-cadherin (CDH1) has a poor overall survival and relapse-free survival in CCA patients (p < 0.05).

CONCLUSION

Overall, high level of LINC00261 in CCA predicts a poor prognosis, and promotes a metastasis via EMT process. Thus, LINC00261 could be a promising biomarker and therapeutic target for CCA, and in the high level of LINC00261 in CCA, E-cadherin or CDH1 might be an effective factor for tumor metastasis or poor prognosis.

Agent-based modeling of morphogenetic systems: Advantages and challenges

The complexity of morphogenesis poses a fundamental challenge to understanding the mechanisms governing the formation of biological patterns and structures. Over the past century, numerous processes have been identified as critically contributing to morphogenetic events, but the interplay between the various components and aspects of pattern formation have been much harder to grasp. The combination of traditional biology with mathematical and computational methods has had a profound effect on our current understanding of morphogenesis and led to significant insights and advancements in the field. In particular, the theoretical concepts of reaction–diffusion systems and positional information, proposed by Alan Turing and Lewis Wolpert, respectively, dramatically influenced our general view of morphogenesis, although typically in isolation from one another. In recent years, agent-based modeling has been emerging as a consolidation and implementation of the two theories within a single framework. Agent-based models (ABMs) are unique in their ability to integrate combinations of heterogeneous processes and investigate their respective dynamics, especially in the context of spatial phenomena. In this review, we highlight the benefits and technical challenges associated with ABMs as tools for examining morphogenetic events. These models display unparalleled flexibility for studying various morphogenetic phenomena at multiple levels and have the important advantage of informing future experimental work, including the targeted engineering of tissues and organs.

Cell senescence, apoptosis and DNA damage cooperate in the remodeling processes accounting for heart morphogenesis

During embryonic development, organ morphogenesis requires major tissue rearrangements that are tightly regulated at the genetic level. A large number of studies performed in recent decades assigned a central role to programmed cell death for such morphogenetic tissue rearrangements that often sculpt the shape of embryonic organs. However, accumulating evidence indicates that far from being the only factor responsible for sculpting organ morphology, programmed cell death is accompanied by other tissue remodeling events that ensure the outcome of morphogenesis. In this regard, cell senescence has been recently associated with morphogenetic degenerative embryonic processes as an early tissue remodeling event in development of the limbs, kidney and inner ear. Here, we have explored cell senescence by monitoring β‐galactosidase activity during embryonic heart development where programmed cell death is believed to exert an important morphogenetic function. We report the occurrence of extensive cell senescence foci during heart morphogenesis. These foci overlap spatially and temporally with the areas of programmed cell death that are associated with remodeling of the outflow tract to build the roots of the great arteries and with the septation of cardiac cavities. qPCR analysis allowed us to identify a gene expression profile characteristic of the so‐called senescence secretory associated phenotype in the remodeling outflow tract of the embryonic heart. In addition, we confirmed local upregulation of numerous tumor suppressor genes including p21, p53, p63, p73 and Btg2. Interestingly, the areas of cell senescence were also accompanied by intense lysosomal activation and non‐apoptotic DNA damage revealed by γH2AX immunolabeling. Considering the importance of sustained DNA damage as a triggering factor for cell senescence and apoptosis, we propose the coordinated contribution of DNA damage, senescence and apoptotic cell death to assure tissue remodeling in the developing vertebrate heart.

Dying under pressure: cellular characterisation and in vivo functions of cell death induced by compaction

Cells and tissues are exposed to multiple mechanical stresses during development, tissue homoeostasis and diseases. While we start to have an extensive understanding of the influence of mechanics on cell differentiation and proliferation, how excessive mechanical stresses can also lead to cell death and may be associated with pathologies has been much less explored so far. Recently, the development of new perturbative approaches allowing modulation of pressure and deformation of tissues has demonstrated that compaction (the reduction of tissue size or volume) can lead to cell elimination. Here, we discuss the relevant type of stress and the parameters that could be causal to cell death from single cell to multicellular systems. We then compare the pathways and mechanisms that have been proposed to influence cell survival upon compaction. We eventually describe the relevance of compaction-induced death in vivo, and its functions in morphogenesis, tissue size regulation, tissue homoeostasis and cancer progression.

Long non-coding RNA HOTAIR promotes tumorigenesis and forecasts a poor prognosis in cholangiocarcinoma

Cholangiocarcinoma (CCA) arising from the neoplastic transformation of cholangiocytes with increasing incidence in the worldwide. Unfortunately, a large amount of CCA patients lost their chance for surgery because it is hard to diagnose in the early stages. Long non-coding RNAs (lncRNAs) is closely associated with development and progression of various malignant tumors. Hox transcript antisense intergenic (HOTAIR), a negative prognostic factor for patients with gastric, liver and pancreatic carcinoma. Its transcription levels and functional roles in CCA is still unknown. Therefore, we aimed to explore the effect of HOTAIR in CCA including cell proliferation, apoptosis, migration, invasion and epithelial-to-mesenchymal transition (EMT). The results showed that HOTAIR was highly expressed both in CCA tissue samples and cell lines compared with corresponding normal bile duct tissues and Human intrahepatic biliary epithelial cells (HIBEC). Its overexpression was closely correlated with Tumor size, TNM stage and postoperative recurrence in CCA patients. Moreover, up-regulation of HOTAIR has correlation with prognosis in CCA patients. Knockdown of HOTAIR by siRNAs significantly decreased the migration and invasion but increased apoptosis of CCA cells in vitro. Overall, our study revealed that HOTAIR may play as a new potential therapeutic target and forecast poor prognosis for this fatal disease.

Developmental biology of the upper limb

This article aims to provide hand surgeons with current knowledge on the developmental biology of the upper limb. It will review positioning, limb bud emergence and formation of the apical ectodermal ridge. The development of the limb bud is analyzed in its three axes: proximal-distal, anteroposterior and dorsoventral. The signaling center and primary morphogens that initiate and stimulate the development of each axis will be described. For the proximal-distal axis, the apical ectodermal ridge stimulates the production of FGFs in the underlying distal mesoderm. The anteroposterior (or radio-ulnar) differentiation is a function of the zone of polarizing activity via the small Sonic hedgehog protein, which diffuses in a decreasing concentration gradient from the ulnar to the radial side of the bud. This gradient is essential to digit identity and numbers. For the dorsoventral differentiation, the signaling center is the dorsal ectoderm, which secretes WNT7A. Limb segmentation is described in three parts (arm, forearm and hand) along with the formation of the digital rays until finger separation. An example of congenital anomalies is provided for each step. To keep the length of this lecture within reason, the embryogenesis of nerves, blood vessels, muscles and tendons will not be discussed. On the other hand, the singularity of the thumb relative to the other fingers will be described. With a better understanding of developmental biology, surgeons should have better insight into congenital anomalies of the upper limb. This approach is the basis for the new OMT classification used by the IFFSH.

Downregulation of circular RNA hsa_circ_0001649 indicates poor prognosis for retinoblastoma and regulates cell proliferation and apoptosis via AKT/mTOR signaling pathway

Retinoblastoma (RB) is the most common intraocular malignancy in infants and children with high mortality rate in developing countries. Emerging evidence demonstrated that abnormally expressed circular RNAs (circRNAs) are involved in tumorigenesis and progression in several malignancies. However, their clinical values, biological functions and mechanisms in RB has not been reported before. Recently, hsa_circ_0001649 was found to play imperative roles in cholangiocarcinoma, gastric cancer, and hepatocellular carcinoma. In the current study, qRT-PCR was performed to detect the expression of hsa_circ_0001649 in RB samples and cells. The correlations between hsa_circ_0001649 expression and clinicopathologic characteristics were further analyzed. In addition, we up-regulated hsa_circ_0001649 in Y79 cells and knocked down hsa_circ_0001649 in WERI-Rb1 cells to explore its effect on cell proliferation and apoptosis. The animal study was performed to confirm the in vitro results. Furthermore, AKT/mTOR signaling pathway was detected to clarify the molecular mechanisms of hsa_circ_0001649 exerts in RB cell growth. The results indicated that hsa_circ_0001649 was decreased in RB tissues and cells, and this downregulation was associated with larger tumor size and advanced intraocular international retinoblastoma classify (IIRC) stage in RB patients. Additionally, hsa_circ_0001649 could act as an independent prognostic predictor for overall survival in patients with RB. Moreover, hsa_circ_0001649 inhibits cell growth and promotes cell apoptosis in RB cells. AKT/mTOR signaling pathway is involved in the cell growth alteration affected by hsa_circ_0001649. Overall, hsa_circ_0001649 might be a potentially useful prognostic biomarker and therapeutic target for RB.

Upregulated long non-coding RNA SPRY4-IT1 predicts dismal prognosis for pancreatic ductal adenocarcinoma and regulates cell proliferation and apoptosis

Recently, long noncoding RNAs (lncRNAs) have been emerged as pivotal regulators in various human cancers, including pancreatic ductal adenocarcinoma (PDAC). SPRY4-intronic transcript 1 (SPRY4-IT1) was reported to be upregulated in some kind of human cancers. Here, we elucidated the biological functions and possible clinical values of SPRY4-IT1 on PDAC. In present study, expression of SPRY4-IT1 in PDAC tissues and corresponding normal tissues were explored by qRT-PCR experiments. The link between SPRY4-IT1 expression levels and clinicopathological significance was further analyzed. In addition, the oncogenic role of SPRY4-IT1 was detected both in vitro and in vivo. The results demonstrated that SPRY4-IT1 was abnormally upregulated in PDAC tissues and cell lines. Tumor stage and differentiation grade was closely correlated with SPRY4-IT1 expression. Additionally, decreased SPRY4-IT1 contributed to tumor suppressive effect through attenuating cell growth, clonogenic ability and facilitating apoptosis via Bcl-2/caspase-3 pathway in PANC1 and Capan-2 cells. Furthermore, the xenograft study confirmed the tumor proliferation-promoting role of SPRY4-IT1 in PANC1 cells. Taken together, these findings indicated that SPRY4-IT1 is a potential therapeutic target and prognosis biomarker for the patients with PDAC.

A Tissue-Mapped Axolotl De Novo Transcriptome Enables Identification of Limb Regeneration Factors

Mammals have extremely limited regenerative capabilities; however, axolotls are profoundly regenerative and can replace entire limbs. The mechanisms underlying limb regeneration remain poorly understood, partly because the enormous and incompletely sequenced genomes of axolotls have hindered the study of genes facilitating regeneration. We assembled and annotated a de novo transcriptome using RNA-sequencing profiles for a broad spectrum of tissues that is estimated to have near-complete sequence information for 88% of axolotl genes. We devised expression analyses that identified the axolotl orthologs of cirbp and kazald1 as highly expressed and enriched in blastemas. Using morpholino anti-sense oligonucleotides, we find evidence that cirbp plays a cytoprotective role during limb regeneration whereas manipulation of kazald1 expression disrupts regeneration. Our transcriptome and annotation resources greatly complement previous transcriptomic studies and will be a valuable resource for future research in regenerative biology.

An increased expression of long non-coding RNA PANDAR promotes cell proliferation and inhibits cell apoptosis in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive malignancies worldwide. Emerging evidence indicates that aberrantly expressed long non-coding RNAs (lncRNAs) act as imperative roles in tumorigenesis and progression. PANDAR (promoter of CDKN1A antisense DNA damage activated RNA) is a novel lncRNA that contributes to the development of various cancers. However, its clinical significance and potential effects on PDAC remains unknown. In the present study, qRT-PCR was performed to explore the expression levels of PANDAR in PDAC tissues and corresponding non-tumor tissues, the correlation between PANDAR expression and clinicopathological characteristics was also analyzed. The functional roles of lncRNA PANDAR in PDAC cells were evaluated both in vitro and in vivo. The results indicated that PANDAR was aberrantly overexpressed in PDAC tissues and cell lines, and this overexpression was closely associated with tumor stage and vascular invasion in PDAC patients. Besides, silencing of PANDAR exerted tumor suppressive effect via reducing cell proliferation, colony-forming ability, inducing cell cycle G0/G1 arrest and apoptosis in PANC1 and Capan-2 cells. Further in vivo study confirmed the oncogenesis role of PANDAR in PDAC cells. Overall, our findings may help to develop a potential therapeutic target for the patients with PDAC.

Long non-coding RNA UCA1 indicates an unfavorable prognosis and promotes tumorigenesis via regulating AKT/GSK-3β signaling pathway in cholangiocarcinoma

Long non-coding RNAs (lncRNAs) have been documented to play key roles in a wide range of pathophysiological processes, including cancer initiation and progression. Recently, the aberrant expression of urothelial carcinoma associated 1 (UCA1) was observed in many types of cancers. However, its clinical relevance and exact effects in cholangiocarcinoma (CCA) remains unknown. In the present study, we aimed to investigate the clinical significance of UCA1 and evaluate its prognostic value in patients with CCA. Besides, the functional roles of UCA1 were detected both in vitro and in vivo. Moreover, potential signaling pathways were explored to clarify the molecular mechanisms underlying CCA cell proliferation. The results indicated that UCA1 transcription is enhanced in both CCA tissue samples and cell lines, and this overexpression is associated with tumor stage (P = 0.007), lymph node invasion (P = 0.027), TNM stage (P = 0.004) and postoperative recurrence (P = 0.033) of CCA patients. Besides, UCA1 could function as an independent prognostic predictor for overall survival in patients with CCA (P = 0.014). For the part of functional assays, knockdown of UCA1 could attenuate CCA cell growth both in vitro and in vivo. Besides, UCA1 facilitates apoptosis via Bcl-2/caspase-3 pathway. In addition, UCA1 regulates migration and invasion potential of CCA cells by affecting EMT. Furthermore, AKT/GSK-3β axis was activated to upregulate CCND1 expression due to overexpression of UCA1 in CCA. To summary, UCA1 might be a potentially useful prognostic biomarker and therapeutic target for CCA.

The anti-myeloma activity of bone morphogenetic protein 2 predominantly relies on the induction of growth arrest and is apoptosis-independent

Multiple myeloma (MM), a malignancy of the bone marrow, is characterized by a pathological increase in antibody-producing plasma cells and an increase in immunoglobulins (plasmacytosis). In recent years, bone morphogenetic proteins (BMPs) have been reported to be activators of apoptotic cell death in neoplastic B cells in MM. Here, we use bone morphogenetic protein 2 (BMP2) to show that the "apoptotic" effect of BMPs on human neoplastic B cells is dominated by anti-proliferative activities and cell cycle arrest and is apoptosis-independent. The anti-proliferative effect of BMP2 was analysed in the human cell lines KMS12-BM and L363 using WST-1 and a Coulter counter and was confirmed using CytoTox assays with established inhibitors of programmed cell death (zVAD-fmk and necrostatin-1). Furthermore, apoptotic activity was compared in both cell lines employing western blot analysis for caspase 3 and 8 in cells treated with BMP2 and FasL. Additionally, expression profiles of marker genes of different cell death pathways were analysed in both cell lines after stimulation with BMP2 for 48h using an RT-PCR-based array. In our experiments we observed that there was rather no reduction in absolute cell number, but cells stopped proliferating following treatment with BMP2 instead. The time frame (48–72 h) after BMP2 treatment at which a reduction in cell number is detectable is too long to indicate a directly BMP2-triggered apoptosis. Moreover, in comparison to robust apoptosis induced by the approved apoptotic factor FasL, BMP2 only marginally induced cell death. Consistently, neither the known inhibitor of apoptotic cell death zVAD-fmk nor the necroptosis inhibitor necrostatin-1 was able to rescue myeloma cell growth in the presence of BMP2.

The prognostic potential and carcinogenesis of long non-coding RNA TUG1 in human cholangiocarcinoma

Cholangiocarcinoma (CCA) is a fatal disease with increasing worldwide incidence and is characterized by poor prognosis due to its poor response to conventional chemotherapy or radiotherapy. Long non-coding RNAs (lncRNAs) play key roles in multiple human cancers, including CCA. Cancer progression related lncRNA taurine-up-regulated gene 1 (TUG1) was reported to be involved in human carcinomas. However, the impact of TUG1 in CCA is unclear. The aim of this study was to explore the expression pattern of TUG1 and evaluate its clinical significance as well as prognostic potential in CCA. In addition, the functional roles of TUG1 including cell proliferation, apoptosis, migration, invasion and epithelial-mesenchymal transition (EMT), were evaluated after TUG1 silencing. Our data demonstrated up-regulation of TUG1 in both CCA tissues and cell lines. Moreover, overexpression of TUG1 is linked to tumor size (p=0.005), TNM stage (p=0.013), postoperative recurrence (p=0.036) and overall survival (p=0.010) of CCA patients. Furthermore, down-regulation of TUG1 following RNA silencing reduced cell growth and increased apoptosis in CCA cells. Additionally, TUG1 suppression inhibited metastasis potential in vitro by reversing EMT. Overall, our results suggest that TUG1 may be a rational CCA-related prognostic factor and therapeutic target.

Apoptosis during embryonic tissue remodeling is accompanied by cell senescence

This study re-examined the dying process in the interdigital tissue during the formation of free digits in the developing limbs. We demonstrated that the interdigital dying process was associated with cell senescence, as deduced by induction of β-gal activity, mitotic arrest, and transcriptional up-regulation of p21 together with many components of the senescence-associated secretory phenotype. We also found overlapping domains of expression of members of the Btg/Tob gene family of antiproliferative factors in the regressing interdigits. Notably, Btg2 was up-regulated during interdigit remodeling in species with free digits but not in the webbed foot of the duck. We also demonstrate that oxidative stress promoted the expression of Btg2, and that FGF2 and IGF1 which are survival signals for embryonic limb mesenchyme inhibited Btg2 expression. Btg2 overexpression in vivo and in vitro induced all the observed changes during interdigit regression, including oxidative stress, arrest of cell cycle progression, transcriptional regulation of senescence markers, and caspase-mediated apoptosis. Consistent with the central role of p21 on cell senescence, the transcriptional effects induced by overexpression of Btg2 are attenuated by silencing p21. Our findings indicate that cell senescence and apoptosis are complementary processes in the regression of embryonic tissues and share common regulatory signals.

Genetic variations in apoptosis pathway and the risk of ovarian cancer

BACKGROUND

Apoptosis is a highly conserved form of cell death and aberrant regulation of apoptotic cell death mechanisms leads to variety of major human diseases, especially tumor formation. Genetic variations in apoptosis genes may increase susceptibility to ovarian cancer.

RESULTS

In individual SNP analysis, 12 SNPs in 5 apoptosis pathway genes were significantly associated with ovarian cancer risk after adjustment for multiple comparisons at q-value <0.05. The most significant SNP was rs11152377 in the Bcl-2 gene. The homozygous variant TT genotype was associated with a significantly decreased risk of ovarian cancer (odds ratio [OR] =0.53; 95% confidence interval [CI], 0.37-0.77, P<0.001). Cumulative effect analysis showed joint effects of increased risk of ovarian cancer with increasing number of unfavorable genotypes in patients. Classification and regression tree (CART) analysis further revealed high-order gene-gene interactions and categorized the study subjects into low-, medium-, and high-risk groups. Compared with the low-risk group, medium-risk group and high-risk group conferred 1.76-fold (95% CI: 1.06-2.90) and 3.64-fold (95% CI: 2.37-5.59) increased risk of ovarian cancer (P for trend <0.001)Materials and Methods: In a case-control study of 417 ovarian cancer patients and 417 matched controls, we evaluated the associations of 587 single nucleotide polymorphisms (SNPs) from 65 genes of the apoptosis pathway with the risk of ovarian cancer.

CONCLUSIONS

Our results suggest that genetic variations in apoptosis pathway genes modulate the risk of ovarian cancer individually and jointly.

Spatiotemporal distribution of proliferation, proapoptotic and antiapoptotic factors in the early human limb development

Involvement of proliferation and apoptosis in the human limb development was analyzed electronmicroscopically and immunohistochemically in histological sections of 8 human embryos, 4(th) -10(th) week old, using apoptotic (caspase-3, AIF, BAX), anti-apoptotic (Bcl-2) and proliferation (Ki-67) markers, and TUNEL method. The data were analyzed by Mann-Whitney test, Kruskal-Wallis and Dunn's post hoc test. Initially, developing human limbs consisted of mesenchymal core and surface ectoderm with apical ectodermal ridge (AER). During progression of development, strong proliferation activity gradually decreased in the mesenchyme (from 78% to 68%) and in the epithelium (from 62% to 42%), while in the differentiating finger cartilages proliferation was constantly low (26-7%). Apoptotic caspase-3 and AIF-positive cells characterized mesenchyme and AER at earliest stages, while during digit separation they appeared in interdigital mesenchyme as well. Strong Bcl-2 expression was observed in AER, subridge mesenchyme and phalanges, while BAX expression charaterized limb areas undergoing apoptosis. Ultrastructurally, proliferating cells showed mitotic figures, while apoptotic cells were characterized by nuclear fragmentation. Macrophages were observed around the apoptotic cells. We suggest that intense proliferation enables growth and elongation of human limb primordia, and differential growth of digits. Both caspase-3 and AIF-dependant pathways of cell death control the extent of AER and numer of cells in the subridge mesenchyme at earliest developmental stages, as well as process of digit separation at later stages of limb development. Spatio-temporal co-expresson of Bcl-2 and BAX indicates their role in suppression of apoptosis and selective stimulation of growth during human limb morphogenesis.

BMPs are direct triggers of interdigital programmed cell death

During vertebrate embryogenesis the interdigital mesenchyme is removed by programmed cell death (PCD), except in species with webbed limbs. Although bone morphogenetic proteins (BMPs) have long been known to be players in this process, it is unclear if they play a direct role in the interdigital mesenchyme or if they only act indirectly, by affecting fibroblast growth factor (FGF) signaling. A series of genetic studies have shown that BMPs act indirectly by regulating the withdrawal of FGF activity from the apical ectodermal ridge (AER); this FGF activity acts as a cell survival factor for the underlying mesenchyme. Other studies using exogenous factors to inhibit BMP activity in explanted mouse limbs suggest that BMPs do not act directly in the mesenchyme. To address the question of whether BMPs act directly, we used an interdigit-specific Cre line to inactivate several genes that encode components of the BMP signaling pathway, without perturbing the normal downregulation of AER-FGF activity. Of three Bmps expressed in the interdigital mesenchyme, Bmp7 is necessary for PCD, but Bmp2 and Bmp4 both have redundant roles, with Bmp2 being the more prominent player. Removing BMP signals to the interdigit by deleting the receptor gene, Bmpr1a, causes a loss of PCD and syndactyly, thereby unequivocally proving that BMPs are direct triggers of PCD in this tissue. We present a model in which two events must occur for normal interdigital PCD: the presence of a BMP death trigger and the absence of an FGF survival activity. We demonstrate that neither event is required for formation of the interdigital vasculature, which is necessary for PCD. However, both events converge on the production of reactive oxygen species that activate PCD.

Xenopus Limb bud morphogenesis

Xenopus laevis, the South African clawed frog, is a well-established model organism for the study of developmental biology and regeneration due to its many advantages for both classical and molecular studies of patterning and morphogenesis. While contemporary studies of limb development tend to focus on models developed from the study of chicken and mouse embryos, there are also many classical studies of limb development in frogs. These include both fate and specification maps, that, due to their age, are perhaps not as widely known or cited as they should be. This has led to some inevitable misinterpretations- for example, it is often said that Xenopus limb buds have no apical ectodermal ridge, a morphological signalling centre located at the distal dorsal/ventral epithelial boundary and known to regulate limb bud outgrowth. These studies are valuable both from an evolutionary perspective, because amphibians diverged early from the amniote lineage, and from a developmental perspective, as amphibian limbs are capable of regeneration. Here, we describe Xenopus limb morphogenesis with reference to both classical and molecular studies, to create a clearer picture of what we know, and what is still mysterious, about this process.

The HOX-Apoptosis Regulatory Interplay in Development and Disease

Apoptosis is a cellular suicide program, which is on the one hand used to remove superfluous cells thereby promoting tissue or organ morphogenesis. On the other hand, the programmed killing of cells is also critical when potentially harmful cells emerge in a developing or adult organism thereby endangering survival. Due to its critical role apoptosis is tightly controlled, however so far, its regulation on the transcriptional level is less studied and understood. Hox genes, a highly conserved gene family encoding homeodomain transcription factors, have crucial roles in development. One of their prominent functions is to shape animal body plans by eliciting different developmental programs along the anterior-posterior axis. To this end, Hox proteins transcriptionally regulate numerous processes in a coordinated manner, including cell-type specification, differentiation, motility, proliferation as well as apoptosis. In this review, we will focus on how Hox proteins control organismal morphology and function by regulating the apoptotic machinery. We will first focus on well-established paradigms of Hox-apoptosis interactions and summarize how Hox transcription factors control morphological outputs and differentially shape tissues along the anterior-posterior axis by fine-tuning apoptosis in a healthy organism. We will then discuss the consequences when this interaction is disturbed and will conclude with some ideas and concepts emerging from these studies.

Making quantitative morphological variation from basic developmental processes: Where are we? The case of the Drosophila wing

One of the aims of evolutionary developmental biology is to discover the developmental origins of morphological variation. The discipline has mainly focused on qualitative morphological differences (e.g., presence or absence of a structure) between species. Studies addressing subtle, quantitative variation are less common. The Drosophila wing is a model for the study of development and evolution, making it suitable to investigate the developmental mechanisms underlying the subtle quantitative morphological variation observed in nature. Previous reviews have focused on the processes involved in wing differentiation, patterning and growth. Here, we investigate what is known about how the wing achieves its final shape, and what variation in development is capable of generating the variation in wing shape observed in nature. Three major developmental stages need to be considered: larval development, pupariation, and pupal development. The major cellular processes involved in the determination of tissue size and shape are cell proliferation, cell death, oriented cell division and oriented cell intercalation. We review how variation in temporal and spatial distribution of growth and transcription factors affects these cellular mechanisms, which in turn affects wing shape. We then discuss which aspects of the wing morphological variation are predictable on the basis of these mechanisms. Developmental Dynamics 244:1058-1073, 2015. © 2015 Wiley Periodicals, Inc.

Vascular patterning regulates interdigital cell death by a ROS-mediated mechanism

Blood vessels serve as key regulators of organogenesis by providing oxygen, nutrients and molecular signals. During limb development, programmed cell death (PCD) contributes to separation of the digits. Interestingly, prior to the onset of PCD, the autopod vasculature undergoes extensive patterning that results in high interdigital vascularity. Here, we show that in mice, the limb vasculature positively regulates interdigital PCD. In vivo, reduction in interdigital vessel number inhibited PCD, resulting in syndactyly, whereas an increment in vessel number and distribution resulted in elevation and expansion of PCD. Production of reactive oxygen species (ROS), toxic compounds that have been implicated in PCD, also depended on interdigital vascular patterning. Finally, ex vivo incubation of limbs in gradually decreasing oxygen levels led to a correlated reduction in both ROS production and interdigital PCD. The results support a role for oxygen in these processes and provide a mechanistic explanation for the counterintuitive positive role of the vasculature in PCD. In conclusion, we suggest a new role for vascular patterning during limb development in regulating interdigital PCD by ROS production. More broadly, we propose a double safety mechanism that restricts PCD to interdigital areas, as the genetic program of PCD provides the first layer and vascular patterning serves as the second.

Apico-basal forces exerted by apoptotic cells drive epithelium folding

Epithelium folding is a basic morphogenetic event that is essential in transforming simple two-dimensional epithelial sheets into three-dimensional structures in both vertebrates and invertebrates. Folding has been shown to rely on apical constriction. The resulting cell-shape changes depend either on adherens junction basal shift or on a redistribution of myosin II, which could be driven by mechanical signals. Yet the initial cellular mechanisms that trigger and coordinate cell remodelling remain largely unknown. Here we unravel the active role of apoptotic cells in initiating morphogenesis, thus revealing a novel mechanism of epithelium folding. We show that, in a live developing tissue, apoptotic cells exert a transient pulling force upon the apical surface of the epithelium through a highly dynamic apico-basal myosin II cable. The apoptotic cells then induce a non-autonomous increase in tissue tension together with cortical myosin II apical stabilization in the surrounding tissue, eventually resulting in epithelium folding. Together our results, supported by a theoretical biophysical three-dimensional model, identify an apoptotic myosin-II-dependent signal as the initial signal leading to cell reorganization and tissue folding. This work further reveals that, far from being passively eliminated as generally assumed (for example, during digit individualization), apoptotic cells actively influence their surroundings and trigger tissue remodelling through regulation of tissue tension.

Differential expression of Meis2, Mab21l2 and Tbx3 during limb development associated with diversification of limb morphology in mammals

Bats are the only mammals capable of self-powered flight using wings. Differing from mouse or human limbs, four elongated digits within a broad wing membrane support the bat wing, and the foot of the bat has evolved a long calcar that spread the interfemoral membrane. Our recent mRNA sequencing (mRNA-Seq) study found unique expression patterns for genes at the 5' end of the Hoxd gene cluster and for Tbx3 that are associated with digit elongation and wing membrane growth in bats. In this study, we focused on two additional genes, Meis2 and Mab21l2, identified from the mRNA-Seq data. Using whole-mount in situ hybridization (WISH) we validated the mRNA-Seq results for differences in the expression patterns of Meis2 and Mab21l2 between bat and mouse limbs, and further characterize the timing and location of the expression of these two genes. These analyses suggest that Meis2 may function in wing membrane growth and Mab21l2 may have a role in AP and DV axial patterning. In addition, we found that Tbx3 is uniquely expressed in the unique calcar structure found in the bat hindlimb, suggesting a role for this gene in calcar growth and elongation. Moreover, analysis of the coding sequences for Meis2, Mab21l2 and Tbx3 showed that Meis2 and Mab21l2 have high sequence identity, consistent with the functions of genes being conserved, but that Tbx3 showed accelerated evolution in bats. However, evidence for positive selection in Tbx3 was not found, which would suggest that the function of this gene has not been changed. Together, our findings support the hypothesis that the modulation of the spatiotemporal expression patterns of multiple functional conserved genes control limb morphology and drive morphological change in the diversification of mammalian limbs.

Ecdysteroid-induced programmed cell death is essential for sex-specific wing degeneration of the wingless-female winter moth

The winter moth, Nyssiodes lefuarius, has a unique life history in that adults appear during early spring after a long pupal diapause from summer to winter. The moth exhibits striking sexual dimorphism in wing form; males have functional wings of normal size, whereas females lack wings. We previously found that cell death of the pupal epithelium of females appears to display condensed chromatin within phagocytes. To provide additional detailed data for interpreting the role of cell death, we performed light microscopy, transmission electron microscopy, and TUNEL assay. We consequently detected two modes of cell death, i.e., dying cells showed both DNA fragmentation derived from epithelial nuclei and autophagic vacuole formation. To elucidate the switching mechanism of sex-specific wing degeneration in females of N. lefuarius, we tested the effects of the steroid hormone 20-hydroxyecdysone (20E) on pupal diapause termination and wing morphogenesis in both sexes. When 20E (5.4 µg) was injected into both sexes within 2 days of pupation, wing degeneration started 4 days after 20E injection in females, whereas wing morphogenesis and scale formation started 6 days after 20E injection in males. We discuss two important findings: (1) degeneration of the pupal wing epithelium of females was not only due to apoptosis and phagocytotic activation but also to autophagy and epithelial cell shrinkage; and (2) 20E terminated the summer diapause of pupae, and triggered selective programmed cell death only of the female-pupal wing epithelium in the wingless female winter moth.

Hox targets and cellular functions

Hox genes are a group of genes that specify structures along the anteroposterior axis in bilaterians. Although in many cases they do so by modifying a homologous structure with a different (or no) Hox input, there are also examples of Hox genes constructing new organs with no homology in other regions of the body. Hox genes determine structures though the regulation of targets implementing cellular functions and by coordinating cell behavior. The genetic organization to construct or modify a certain organ involves both a genetic cascade through intermediate transcription factors and a direct regulation of targets carrying out cellular functions. In this review I discuss new data from genome-wide techniques, as well as previous genetic and developmental information, to describe some examples of Hox regulation of different cell functions. I also discuss the organization of genetic cascades leading to the development of new organs, mainly using Drosophila melanogaster as the model to analyze Hox function.

Expression of cyclin D1, cyclin D2, and N-myc in embryos of the direct developing frog Eleutherodactylus coqui, with a focus on limbs

Species of frogs that develop directly have removed the tadpole from their ontogeny and form adult structures precociously. To see whether cell cycle regulators could be involved in this altered embryogenesis, we examined the expression of ccnd1, ccnd2, and mycn in embryos of the direct developing frog, Eleutherodactylus coqui. Notable differences compared to embryos of Xenopus laevis, a species with a tadpole, included prominent expression of ccnd2 in the midbrain and ccnd1 in the mandibular neural crest. The former may contribute to the precocious appearance of the adult-type visual system and the latter to the adult-type jaw. Large domains of ccnd2 and mycn presage the early appearance of limb buds, and ccnd1 and mycn are implicated in digit development.

Early development of the vertebrate inner ear

This is a review of the biological processes and the main signaling pathways required to generate the different otic cell types, with particular emphasis on the actions of insulin-like growth factor I. The sensory organs responsible of hearing and balance have a common embryonic origin in the otic placode. Lineages of neural, sensory, and support cells are generated from common otic neuroepithelial progenitors. The sequential generation of the cell types that will form the adult inner ear requires the coordination of cell proliferation with cell differentiation programs, the strict regulation of cell survival, and the metabolic homeostasis of otic precursors. A network of intracellular signals operates to coordinate the transcriptional response to the extracellular input. Understanding the molecular clues that direct otic development is fundamental for the design of novel treatments for the protection and repair of hearing loss and balance disorders.

Early otic development depends on autophagy for apoptotic cell clearance and neural differentiation

Autophagy is a highly regulated program of self-degradation of the cytosolic constituents that has key roles during early development and in adult cell growth and homeostasis. To investigate the role of autophagy in otic neurogenesis, we studied the expression of autophagy genes in early stages of chicken (Gallus gallus) inner ear development and the consequences of inhibiting the autophagic pathway in organotypic cultures of explanted chicken otic vesicles (OVs). Here we show the expression of autophagy-related genes (Atg) Beclin-1 (Atg6), Atg5 and LC3B (Atg8) in the otocyst and the presence of autophagic vesicles by using transmission electron microscopy in the otic neurogenic zone. The inhibition of the transcription of LC3B by using antisense morpholinos and of class III phosphatidylinositol 3-kinase with 3-methyladenine causes an aberrant morphology of the OV with accumulation of apoptotic cells. Moreover, inhibition of autophagy provokes the misregulation of the cell cycle in the otic epithelium, impaired neurogenesis and poor axonal outgrowth. Finally, our results indicate that autophagy provides the energy required for the clearing of neuroepithelial dying cells and suggest that it is required for the migration of otic neuronal precursors. Taken together, our results show for the first time that autophagy is an active and essential process during early inner ear development.

Microduplication of Xq24 and Hartsfield syndrome with holoprosencephaly, ectrodactyly, and clefting

The combination of holoprosencephaly and ectrodactyly, also known as Hartsfield syndrome, represents a unique genetic entity. An X-linked recessive mode of transmission has been suggested for this condition based on the observation that male patients have preferentially been affected. Thus far, no candidate genes have been suggested on the X chromosome. We report a male patient with a full-blown Hartsfield syndrome phenotype who had microduplication at Xq24 involving four genes. He presented with bilateral ectrodactyly of the hands (both hands had four fingers with a deep gap between the 2nd and 3rd digits), cleft lip and palate, and a depressed nasal bridge. Magnetic resonance imaging of the brain revealed lobar holoprosencephaly. His G-banded karyotype was normal. Array comparative genomic hybridization (CGH) using the Agilent 244K Whole Human Genome CGH array revealed a microduplication at Xq24 of 210 kb. Parental testing revealed that the deletion was derived from the asymptomatic mother. Of the genes on the duplicated interval, the duplications of SLC25A43 and SLC25A5 appeared to be the most likely to explain the patient's phenotype. From a clinical standpoint, it is important to point out that the propositus, who performs relatively well with holoprosencephaly and has a developmental quotient around 70, has survived multiple life-threatening episodes of hypernatremia. Awareness of the risk of hypernatremia is of great importance for the anticipatory management of patients with ectrodactyly and an oral cleft, even in the absence of overt hypotelorism.

Instructive reconstruction: a new role for apoptosis in pattern formation. Instructive apoptotic patterning establishes de novo tissue generation via the apoptosis linked production of morphogenic signals

Apoptosis is not only involved in patterning by removal of tissue (destructive apoptotic patterning), but it can also function in signalling the site of de novo tissue generation via morphogenic signals (instructive apoptotic patterning).

Apoptotic signaling in mouse odontogenesis

Apoptosis is an important morphogenetic event in embryogenesis as well as during postnatal life. In the last 2 decades, apoptosis in tooth development (odontogenesis) has been investigated with gradually increasing focus on the mechanisms and signaling pathways involved. The molecular machinery responsible for apoptosis exhibits a high degree of conservation but also organ and tissue specific patterns. This review aims to discuss recent knowledge about apoptotic signaling networks during odontogenesis, concentrating on the mouse, which is often used as a model organism for human dentistry. Apoptosis accompanies the entire development of the tooth and corresponding remodeling of the surrounding bony tissue. It is most evident in its role in the elimination of signaling centers within developing teeth, removal of vestigal tooth germs, and in odontoblast and ameloblast organization during tooth mineralization. Dental apoptosis is caspase dependent and proceeds via mitochondrial mediated cell death with possible amplification by Fas-FasL signaling modulated by Bcl-2 family members.

Molecular control of cell differentiation and programmed cell death during digit development

During the hand plate development, the processes of cell differentiation and control of cell death are relevant to ensure a correct shape of the limb. The progenitor cell pool that later will differentiate into cartilage to form the digits arises from undifferentiated mesenchymal cells beneath the apical ectodermal ridge (AER). Once these cells abandon the area of influence of signals from AER and ectoderm, some cells are committed to chondrocyte lineage forming the digital rays. However, if the cells are not committed to chondrocyte lineage, they will form the prospective interdigits that in species with free digits will subsequently die. In this work, we provide the overview of the molecular interactions between different signaling pathways responsible for the formation of digit and interdigit regions. In addition, we briefly describe some experiments concerning the most important signals responsible for promoting cell death. Finally, on the basis that the interdigital tissue has chondrogenic potential, we discuss the hypothesis that apoptotic-promoting signals might also act as antichondrogenic factors and chondrogenic factors might operate as anti-apoptotic factors.

Smad8 is expressed in the anterior necrotic zone: evidence for a role of bone morphogenetic proteins/SMAD signaling in the activation of a molecular cascade that culminates in cell death

Bone morphogenetic proteins (BMPs) play a crucial role in programmed cell death (PCD), a biological process required for the sculpturing of the embryonic limbs. However, it is unknown if BMP signaling directly promotes cell death, or if it induces a molecular cascade that culminates in cell death. Given that Smad8, which encodes one component of BMP signaling, is expressed during the regression of interdigital tissue and responds to BMPs, we presumed that it may be expressed in other cell death areas during chick limb development such as the anterior and posterior necrotic zones (ANZ and PNZ). The present study found that the Smad8 expression pattern in the anterior mesoderm of the hindlimb is very similar to that observed in limbs stained to detect cell death. Also, BMPs and retinoic acid, which act as apoptosis-promoting factors, induced expression of Smad8 before the onset of cell death, while sonic hedgehog protein, acting as a survival factor, inhibited Smad8 expression in the ANZ. However, although there was correlation between Smad8 expression patterns and PCD in the ANZ, phosphorylated forms of SMAD1/5/8 and TUNEL staining did not co-localize in dying cells. Interestingly, a short pulse of BMP was sufficient to trigger cell death. On the other hand, most dying cells were located in the avascular region, while many cells expressing Smad8 were located in the vascular region of the ANZ. These results suggest that BMPs mediated by SMAD signaling activate a molecular cascade that culminates in PCD.