Perineal muscles and motoneurons are sexually monomorphic in the naked mole‐rat (Heterocephalus glaber)

Naked mole‐rats are eusocial mammals that live in colonies with a single breeding female and one to three breeding males. All other members of the colony, known as subordinates, are nonreproductive and exhibit few sex differences in behavior or genital anatomy. This raises questions about the degree of sexual differentiation in subordinate naked mole‐rats. The striated perineal muscles associated with the phallus [the bulbocavernosus (BC), ischiocavernosus (IC), and levator ani (LA) muscles], and their innervating motoneurons, are sexually dimorphic in all rodents examined to date. We therefore asked whether perineal muscles and motoneurons were also sexually dimorphic in subordinate naked mole‐rats. Muscles similar to the LA and IC of other rodents were found in naked mole‐rats of both sexes. No clear BC muscle was identified, although a large striated muscle associated with the urethra in male and female naked mole‐rats may be homologous to the BC of other rodents. There were no sex differences in the volumes of the LA, IC, or the urethral muscles. Motoneurons innervating the perineal muscles were identified by retrograde labeling with cholera‐toxin‐conjugated horseradish peroxidase. All perineal motoneurons were found in a single cluster in the ventrolateral lateral horn, in a position similar to that of Onuf's nucleus of carnivores and primates. There was no sex difference in the size or number of motoneurons in Onuf's nucleus of naked mole‐rats. Thus, unlike findings in any other mammal, neither the perineal muscles nor the perineal motoneurons appear to be sexually differentiated in subordinate naked mole‐rats. © 2002 Wiley Periodicals, Inc. J Neurobiol 51: 33–42, 2002     

Haploid loss of bax leads to accelerated mammary tumor development in C3(1)/SV40-TAg transgenic mice: reduction in protective apoptotic response at the preneoplastic stage.

The dramatic increase in apoptosis observed during the development of preneoplastic mammary lesions is associated with a significant elevation in Bax expression in C3(1)/SV40 large T antigen (TAg) transgenic mice. The significance of Bax expression during tumor progression in vivo was studied by generating double-transgenic mice carrying the C3(1)/TAg transgene and mutant alleles for bax. C3(1)/TAg transgenic mice carrying mutant bax alleles exhibited accelerated rates of tumor growth, increased tumor numbers, larger tumor mass and decreased survival rates compared with mice carrying wild-type bax. Accelerated tumorigenesis associated with the bax+/- genotype did not require the loss of function of the second bax allele. Thus, haploid insufficiency of bax is enough to accelerate tumor progression, suggesting that the protective effect of Bax is dose-dependent. While levels of apoptosis in the preneoplastic lesions, but not carcinomas, were reduced in bax+/- or bax-/- mice compared with bax+/+ mice, rates of cellular proliferation in mammary lesions were similar among all bax genotypes. These data demonstrate that bax is a critical suppressor of mammary tumor progression at the stage of preneoplastic mammary lesion development through the upregulation of apoptosis, but that this protective effect is lost during the transition from preneoplasia to invasive carcinoma.     

The role of vacuole in plant cell death

Almost all plant cells have large vacuoles that contain both hydrolytic enzymes and a variety of defense proteins. Plants use vacuoles and vacuolar contents for programmed cell death (PCD) in two different ways: for a destructive way and for a non-destructive way. Destruction is caused by vacuolar membrane collapse, followed by the release of vacuolar hydrolytic enzymes into the cytosol, resulting in rapid and direct cell death. The destructive way is effective in the digestion of viruses proliferating in the cytosol, in susceptible cell death induced by fungal toxins, and in developmental cell death to generate integuments (seed coats) and tracheary elements. On the other hand, the non-destructive way involves fusion of the vacuolar and the plasma membrane, which allows vacuolar defense proteins to be discharged into the extracellular space where the bacteria proliferate. Membrane fusion, which is normally suppressed, was triggered in a proteasome-dependent manner. Intriguingly, both ways use enzymes with caspase-like activity; the membrane-fusion system uses proteasome subunit PBA1 with caspase-3-like activity, and the vacuolar-collapse system uses vacuolar processing enzyme (VPE) with caspase-1-like activity. This review summarizes two different ways of vacuole-mediated PCD and discusses how plants use them to attack pathogens that invade unexpectedly.     

Effects of testosterone on the development of a sexually dimorphic neuromuscular system in ciliary neurotrophic factor receptor knockout mice

Motoneurons in the spinal nucleus of the bulbocavernosus (SNB) innervate the perineal muscles, bulbocavernosus (BC), and levator ani (LA). Testosterone regulates the survival of SNB motoneurons and BC/LA muscles during perinatal life. Previous findings suggest that effects of testosterone on this system may be mediated by trophic factors—in particular, by a factor acting through the ciliary neurotrophic factor α‐receptor (CNTFRα). To test the role of CNTFRα in the response of the developing SNB system to testosterone, CNTFRα +/+ and −/− mice were treated with testosterone propionate (TP) or oil during late embryonic development. BC/LA muscle size and SNB motoneuron number were evaluated on the day of birth. Large sex differences in BC and LA muscle size were present in newborn mice of both genotypes, but muscle volumes were reduced in CNTFRα −/− animals relative to same‐sex, wild‐type controls. Prenatal testosterone treatment completely eliminated the sex difference in BC/LA muscle size in wild‐type animals, and eliminated the effect of the CNTFRα gene deletion on muscle size in males. However, the effect of TP treatment on BC and LA muscle sizes was blunted in CNTFRα −/− females. SNB motoneuron number was sexually dimorphic in oil‐treated, wild‐type mice. In contrast, there was no sex difference in SNB motoneuron number in oil‐treated, CNTFRα knockout mice. Prenatal treatment with testosterone did not increase SNB motoneuron number in CNTFRα −/− mice, but also did not significantly increase SNB motoneuron number in newborn wild‐type animals. These findings confirm the absence of a sex difference in SNB motoneuron number in CNTFRα −/− mice. Moreover, the CNTFRα gene deletion influences perineal muscle development and the response of the perineal muscles to testosterone. Prenatal TP treatment of CNTFRα −/− males overcomes the effects of the gene deletion on the BC and LA muscles without a concomitant effect on SNB motoneuron number. © 1999 John Wiley & Sons, Inc. J Neurobiol 41: 317–325, 1999     

自噬在细胞存活和死亡中的作用

自噬是亚细胞膜结构发生动态变化并经溶酶体介导对细胞内蛋白质和细胞器降解的过程.通过平衡细胞合成和分解代谢,自噬稳定细胞内环境,维持细胞的存活.然而,过度自噬可导致细胞发生Ⅱ型程序性细胞死亡.自噬与凋亡在细胞死亡过程中的关系十分密切.本文对自噬的过程及其在细胞存活和死亡中的作用作一综述.     

Increased Hsp70 expression attenuates cytokine-induced cell death in islets of Langerhans from Shb knockout mice

Type 1 diabetes may depend on cytokine-induced β-cell death and therefore the current investigation was performed in order to elucidate this response in Shb-deficient islets.A combination of interleukin-1β and interferon-γ caused a diminished β-cell death response in Shb null islets. Furthermore, the induction of an unfolded protein response (UPR) by adding cyclopiazonic acid did not increase cell death in Shb-deficient islets, despite simultaneous expression of UPR markers. The heat-shock protein Hsp70 was more efficiently induced in Shb knockout islets, providing an explanation for the decreased susceptibility of Shb-deficient islets to cytokines.It is concluded that islets deficient in the Shb protein are less susceptible to cytotoxic conditions, and that this partly depends on their increased ability to induce Hsp70 under such circumstances. Interference with Shb signaling may provide means to improve β-cell viability under conditions of β-cell stress.     

Ectopic dermal ridge configurations on the interdigital webbings of Hammertoe mutant mice (Hm): another possible role of programmed cell death in limb development

BACKGROUND: The mechanism underlying the development of aberrant phalangeal pads and dermal ridge configurations in malformed limbs is not well understood. The forelimbs of Hammertoe (Hm) mutant mouse fetuses were examined sequentially to clarify the relationship between the occurrence of abnormal programmed cell death (PCD) and the formation of phalangeal pads and dermal ridge patterns. METHODS: Relevant morphological features, with special emphasis on pads and dermal ridge configurations, were inspected on the exposed dermal surface of the forelimbs of adult Hm mutant mice. The forelimbs of Hm mutant mouse fetuses (GD13-18) and newborns were examined histologically. The forelimbs of GD13 fetuses were subjected to Nile blue (NB) vital staining for in situ labeling of PCD. RESULTS: In the forelimbs of +/+ mice, the formation of dermal ridges was confined to pads, while in Hm/+ and Hm/Hm animals, which have interdigital webbing involving digits II-V, dermal ridges were formed also on the ventral side of the webbing, specifically on its lateral margins between the neighboring digits and on the medial margin of the webbing extending toward the palmar pad. PCD was decreased in the interdigital zones II-IV in GD13 Hm/+ and Hm/Hm fetuses. CONCLUSIONS: Reduced PCD interdigital tissue of Hm/+ and Hm/Hm fetuses may result in the failure of physiological elimination of interdigital cells and in the persistence of soft tissue webbing between digits. The failure of PCD to occur may also interrupt the interdigital surviving cells to reach the neighboring digits and the distal area of the palm, thereby producing ectopic dermal ridges. It seems that interdigital PCD contributes not only to digit separation but also to the development of digital and palmar pads.     

Cell death in the sexually dimorphic dorsal preoptic area/anterior hypothalamus of perinatal male and female ferrets

A sexually dimorphic male nucleus (MN) is present in Nissl-stained sections through the dorsal (d) preoptic area/anterior hypothalamus (POA/AH) of male ferrets. The MN-POA/AH is composed of a cluster of large cells which is organized in males by the action of estradiol, formed via the neural aromatization of circulating testosterone (T), during the last quarter of a 41-day gestation. Several recent studies using rodent species have raised the possibility that the hormone-induced masculinization of POA/AH morphology is mediated at least in part by a perinatal modulation of cell death. We asked whether a perinatal reduction in cell death contributes to the differentiation of the MN-POA/AH in the male ferret, which is a carnivore species. The appearance of internucleosomal DNA fragmentation, detected by in situ end labeling (ISEL) using the ApopTag™ kit (Oncor Corp.) and of pyknotic cell nuclei in Nissl-stained sections were used to estimate the occurrence of cell death. Male and female ferret kits were killed at four different ages spanning the perinatal period during which the MN-POA/AH is organized and assumes an adult phenotype. A peak density of dying cells was present in both sexes at postnatal day (P) 2, which is nearly 1 week after the age, embryonic day (E) 37, when the MN-POA/AH is first visible in male ferrets using Nissl stains. The density of cells in the sexually dimorphic dPOA/AH which were either ISEL-positive or pyknotic was similar in males and females on E34, as well as on P2, 10, and 20. In the nondimorphic ventral POA/AH, the highest density of dying cells was present in both sexes at E34, and there were significantly more ISEL-positive cells present in males than females at this particular age. In contrast to previous studies using rodents, our results suggest that in fetal male ferrets a modulation of the incidence of cell death contributes little to estradiol's organizational action in the dPOA/AH. © 1998 John Wiley & Sons, Inc. J Neurobiol 34: 242–252, 1998     

Autophagy plays a protective role in free cholesterol overload-induced death of smooth muscle cells

Smooth muscle cells (SMC) make up most of the vascular system. In advanced atherosclerotic plaques, dying SMCs undergo a complex death mode. In the present study, we examined the activation of autophagy in SMCs overloaded with excess free cholesterol (FC) and investigated the possible role which autophagy plays during the FC-induced cell death. After incubation with excess FC, a robust expression of autophagic vacuoles (AV) was detected using both fluorescence microscopy and transmission electron microscopy (TEM). The results revealed that FC induced a time-dependent upregulation of microtubule-associated protein-1 light chain 3-II (LC3-II). Inhibition of autophagy by 3-methyladenine (3-MA) enhanced both cell apoptosis and necrosis, while on the contrary, rapamycin inhibited cell death following cholesterol application. Furthermore, the impact of the colocalization of fragmented mitochondria with AVs was observed after cholesterol treatment. Our results also revealed that the modulation of autophagy directly influenced the cellular organellar stress. In conclusion, our findings demonstrated that excess FC induced the activation of autophagy in SMCs as a cellular defense mechanism, possibly through the degradation of dysfunctional organelles such as mitochondria and endoplasmic reticulum.     

Active participation of cell death in development and organismal homeostasis

The precise, regional execution of programmed cell death is required for the proper patterning and sculpting of the embryonic primordium during animal development. In addition, cell death that is not directly involved in sculpting is also widely observed. The most abundant morphological form of programmed cell death in developing animals is apoptosis, and identification of the apoptotic genetic pathways has enabled the study of apoptosis' regulation and roles during development. Genetic and bio-imaging studies have permitted the study of the active roles of cell death in development and organismal homeostasis.     

The role of programmed cell death in Plasmodium–mosquito interactions

Many host–parasite interactions are regulated in part by the programmed cell death of host cells or the parasite. Here we review evidence suggesting that programmed cell death occurs during the early stages of the development of the malaria parasite in its vector. Zygotes and ookinetes of Plasmodium berghei have been shown to die by programmed cell death (apoptosis) in the midgut lumen of the vector Anopheles stephensi, or whilst developing in vitro. Several morphological markers, indicative of apoptosis, are described and evidence for the involvement of a biochemical pathway involving cysteine proteases discussed in relationship to other protozoan parasites. Malaria infection induces apoptosis in the cells of two mosquito tissues, the midgut and the follicular epithelium. Observations on cell death in both these tissues are reviewed including the role of caspases as effector molecules and the rescue of resorbing follicles resulting from inhibition of caspases. Putative signal molecules that might induce parasite and vector apoptosis are suggested including nitric oxide, reactive nitrogen intermediates, oxygen radicals and endocrine balances. Finally, we suggest that programmed cell death may play a critical role in regulation of infection by the parasite and the host, and contribute to the success or not of parasite establishment and host survival.     

Trophic effects of androgen: Development and hormonal regulation of neuron number in a sexually dimorphic vocal motor nucleus

In Xenopus laevis, the laryngeal motor nucleus (n. of cranial nerves IX‐X) is part of a sexually differentiated, androgen sensitive neuromuscular system devoted to vocalization. Adult males have more n. IX‐X neurons than females; however, during development of n. IX‐X, the rate of neurogenesis does not appear to differ between the sexes. In this study, we explored the role of naturally occurring cell death in the development of this nucleus and asked whether cell death might be involved in establishing the sex difference in neuron number. Counts of n. IX‐X neurons reveal that at tadpole stage 56, males and females have similar numbers of n. IX‐X neurons, but by stage 64 male neuron numbers are greater. This sex difference arises owing to a greater net loss of neurons in females—males lose ∼25% of their n. IX‐X neurons between stages 56 and 64, while females lose ∼47%. Sexual differentiation of n. IX‐X neuron number coincides with a period of developmental cell death, as evidenced by terminal transferase‐mediated dUTP nick‐end labeling and the presence of pyknotic nuclei in n. IX‐X. A role for gonadal hormones in controlling cell number was examined by treating tadpoles with exogenous androgen and determining the number of n. IX‐X neurons at stage 64. Dihydrotestosterone (DHT) treatment from the beginning of the cell death period (stage 54) until stage 64 had no effect on the number of n. IX‐X neurons in males but did significantly increase n. IX‐X neuron number in females. This increase was sufficient to abolish the sex difference normally observed at stage 64. Although DHT induced increases in female neuron number, it did not induce increases in cell proliferation or addition of newly born neurons to n. IX‐X. DHT may therefore have increased neuron number by protecting cells from death. We conclude that androgens can influence the survival of n. IX‐X neurons during a period of naturally occurring cell death, and that this action of androgen is critical to the development of sex differences in n. IX‐X neuron number. © 1999 John Wiley & Sons, Inc. J Neurobiol 40: 375–385, 1999     

Deletion of the Bax gene disrupts sexual behavior and modestly impairs motor function in mice

Cell death is a nearly ubiquitous feature of the developing nervous system, and differential death in males and females contributes to several well studied sex differences in neuron number. Nonetheless, the functional importance of neuronal cell death has been subjected to few direct tests. Bax, a pro-apoptotic protein, is required for cell death in many neural regions. Deletion of the Bax gene in mice increases neuron number in several areas and eliminates sex differences in cell number in the brain and spinal cord. Here, sexual and motor behaviors were examined in Bax-/- mice and their wild-type siblings to test the functional consequences of preventing Bax-dependent cell death. Animals were gonadectomized in adulthood and provided with ovarian hormones or with testosterone for tests of feminine and masculine sexual behaviors, respectively. Wild-type mice exhibited a sex difference in feminine sexual behavior, with high lordosis scores in females and low scores in males. This sex difference was eliminated by Bax deletion, with very low receptivity exhibited by both male and female Bax-/- mice. Masculine sexual behavior was not sexually dimorphic among wild-type mice, but mounts and pelvic thrusts were nearly eliminated in Bax-/- mice of both sexes. Motor strength and performance at low speeds on a RotaRod apparatus did not differ by sex or Bax gene status. However, Bax-/- animals exhibited impairments on the RotaRod at higher speeds. Thus, developmental cell death may be required for masculine and feminine sexual behaviors and the fine tuning of motor coordination.     

Alzheimer's amyloid beta-peptide (1-42) induces cell death in human neuroblastoma via bax/bcl-2 ratio increase: an intriguing role for methionine 35

Nucleolin associates with various DNA repair, recombination, and replication proteins, and possesses DNA helicase, strand annealing, and strand pairing activities. Examination of nuclear protein extracts from human somatic cells revealed that nucleolin and Rad51 co-immunoprecipitate. Furthermore, purified recombinant Rad51 associates with in vitro transcribed and translated nucleolin. Electroporation-mediated introduction of anti-nucleolin antibody resulted in a 10- to 20-fold reduction in intra-plasmid homologous recombination activity in human fibrosarcoma cells. Additionally, introduction of anti-nucleolin antibody sensitized cells to death induced by the topoisomerase II inhibitor, amsacrine. Introduction of anti-Rad51 antibody also reduced intra-plasmid homologous recombination activity and induced hypersensitivity to amsacrine-induced cell death. Co-introduction of anti-nucleolin and anti-Rad51 antibodies did not produce additive effects on homologous recombination or on cellular sensitivity to amsacrine. The association of the two proteins raises the intriguing possibility that nucleolin binding to Rad51 may function to regulate homologous recombinational repair of chromosomal DNA.     

Essential mesenchymal role of small GTPase Rac1 in interdigital programmed cell death during limb development

Developing vertebrate limbs are often utilized as a model for studying pattern formation and morphogenetic cell death. Herein, we report that conditional deletion of Rac1, a member of the Rho family of proteins, in mouse limb bud mesenchyme led to skeletal deformities in the autopod and soft tissue syndactyly, with the latter caused by a complete absence of interdigital programmed cell death. Furthermore, the lack of interdigital programmed cell death and associated syndactyly was related to down-regulated gene expression of Bmp2, Bmp7, Msx1, and Msx2, which are known to promote apoptosis in the interdigital mesenchyme. Our findings from Rac1 conditional mutants indicate crucial roles for Rac1 in limb bud morphogenesis, especially interdigital programmed cell death.     

Programmed cell death in flight muscle histolysis of the house cricket

We have characterized the process of flight muscle histolysis in the female house cricket, Acheta domesticus, through analysis of alterations of tissue wet weight, total protein content, and percent shortening of the dorsal longitudinal flight muscles (DLMs). Our objectives were to (1) define the normal course of histolysis in the cricket, (2) analyze the effects of juvenile hormone (JH) removal and replacement, (3) determine the effects of cycloheximide treatment, and (4) examine patterns of protein expression during histolysis. Our results suggest that flight muscle histolysis in the house cricket is an example of an active, developmentally regulated cell death program induced by an endocrine signal. Initial declines of total protein in DLMs indicated the JH signal that induced histolysis occurred by Day 2 and that histolysis was essentially complete by Day 3. Significant reductions in tissue weight and percent muscle shortening were observed in DLMs from Day 3 crickets. Cervical ligation of Day 1 crickets prevented histolysis but this inhibition could be reversed by continual topical treatments with methoprene (an active JH analog) although ligation of Day 2 crickets did not prevent histolysis. A requirement for active protein expression was demonstrated by analysis of synthesis block by cycloheximide and short-term incorporation of (35)S-methionine. Treatment with cycloheximide prevented histolysis. Autofluorographic imaging of DLM proteins separated by electrophoresis revealed apparent coordinated regulation of protein expression.     

Maternal care effects on the development of a sexually dimorphic motor system: The role of spinal oxytocin

Maternal licking in rats affects the development of the spinal nucleus of the bulbocavernosus (SNB), a sexually dimorphic motor nucleus that controls penile reflexes involved with copulation. Reduced maternal licking results in decreased motoneuron number, size, and dendritic length in the adult SNB, as well as deficits in adult male copulatory behavior. Our previous findings that licking-like tactile stimulation influences SNB dendritic development and upregulates Fos expression in the lumbosacral spinal cord suggest that afferent signaling is changed by differences in maternal stimulation. Oxytocin afferents from the hypothalamus are a possible candidate, given previous research that has shown oxytocin is released following sensory stimulation, oxytocin modulates excitability in the spinal cord, and is a pro-erectile modulator of male sex behavior. In this experiment, we used immunofluorescence and immediate early gene analysis to assess whether licking-like tactile stimulation of the perineum activated parvocellular oxytocinergic neurons in the hypothalamus in neonates. We also used enzyme immunoassay to determine whether this same stroking stimulation produced an increase in spinal oxytocin levels. We found that stroking increased Fos immunolabeling in small oxytocin-positive cells in the paraventricular nucleus of the hypothalamus, in comparison to unstroked or handled control pups. In addition, 60 s of licking-like perineal stimulation produced a transient 89% increase in oxytocin levels in the lumbosacral spinal cord. Together, these results suggest that oxytocin afferent activity may contribute to the effects of early maternal care on the masculinization of the SNB and resultant male copulatory behavior.     

The JAK2/STAT3 and mitochondrial pathways are essential for quercetin nanoliposome-induced C6 glioma cell death

The formulation of quercetin nanoliposomes (QUE-NLs) has been shown to enhance QUE antitumor activity in C6 glioma cells. At high concentrations, QUE-NLs induce necrotic cell death. In this study, we probed the molecular mechanisms of QUE-NL-induced C6 glioma cell death and examined whether QUE-NL-induced programmed cell death involved Bcl-2 family and mitochondrial pathway through STAT3 signal transduction pathway. Downregulation of Bcl-2 and the overexpression of Bax by QUE-NL supported the involvement of Bcl-2 family proteins upstream of C6 glioma cell death. In addition, the activation of JAK2 and STAT3 were altered following exposure to QUE-NLs in C6 glioma cells, suggesting that QUE-NLs downregulated Bcl-2 mRNAs expression and enhanced the expression of mitochondrial mRNAs through STAT3-mediated signaling pathways either via direct or indirect mechanisms. There are several components such as ROS, mitochondrial, and Bcl-2 family shared by the necrotic and apoptotic pathways. Our studies indicate that the signaling cross point of the mitochondrial pathway and the JAK2/STAT3 signaling pathway in C6 glioma cell death is modulated by QUE-NLs. In conclusion, regulation of JAK2/STAT3 and ROS-mediated mitochondrial pathway agonists alone or in combination with treatment by QUE-NLs could be a more effective method of treating chemical-resistant glioma.     

The role of cell death in the induction of pattern abnormalities in a cell-lethal mutation of drosophila

The effects of 48-hr 29°C temperature treatments on the imaginal leg discs of Drosophila hemizygous for a temperature-sensitive cell-lethal mutation were examined to determine whether the induction of patches of cell death in the imaginal discs is a prerequisite for the induction of pattern triplications. In a statistical analysis, the frequency of induction of cell death was found to be highly correlated with the frequency of induction of triplications. In addition, individual discs in which cell death had been induced were cultured and found to triplicate at frequencies significantly greater than discs with no visible cell death, or unselected discs from the same larvae.