电磁脉冲对孕鼠及其胚胎的影响

目的：探讨电磁脉冲（electromagneticpulses,E脚）对孕期小鼠及其胚胎发育的影响。方法：采用不同场强的EMP（分别为0、50、100、200、400kV·m-1）辐照器官形成期的BALB／c孕鼠,于孕18天解剖小鼠,测量孕鼠体重增长值、脏器／体重,胎盘重、胎鼠体重、身长、尾长,并记录吸收胎、死胎、生长发育迟缓及畸胎的数量。结果：各辐照剂量组孕鼠体重增长值、脏器／体重与对照组相比均无显著性差异（P〉0．05）;胎盘重、胎鼠体重、身长、尾长数值明显低于对照组（P〈O．01）。50、400kV·m-1和100、200、400kV·m-1辐照组可分别导致死胎率和生长发育迟缓率增加（P〈0．05）,在400kV·m-1的EMP辐照组中,畸胎数也有升高的趋势,其中,畸胎主要表现为肢体和骨发育异常。结论：本实验条件下,不同场强的EMP辐照可对器官形成期小鼠胚胎的生长发育产生一定的影响,胚胎肢芽及骨发育可能是EMP作用的特殊靶点。     

Embryotoxicity of sex steroidal hormone combinations in nonhuman primates: I. Norethisterone acetate + ethinylestradiol and progesterone + estradiol benzoate (Macaca mulatta, Macaca fascicularis, and Papio cynocephalus)

Two sex steroid hormone combinations which have been used clinically as tests for detection of early pregnancy were examined for embryotoxic effects in macaques and baboons. Norethisterone acetate and ethinyl estradiol (NEA + EE) were orally administered to rhesus and cynomolgus monkeys and baboons at dosages ranging from one to 1,000 times the human dose equivalent (HDE) during days 20-50 of pregnancy. Progesterone and estradiol benzoate (P + EB) were delivered by two to six intramuscular injections to rhesus and cynomolgus monkeys between gestational days 20 and 35 at 0.1-25 X HDE. Fetuses were examined following cesarean section at 100 +/- 2 days (NEA + EE) or at term (P + EB). The results showed increased embryolethality over controls at 100-1,000 X HDE (NEA + EE) and at 10 and 25 X HDE (P + EB). Besides growth retardation, isolated cases of minor nongenital malformations were observed only in cynomolgus monkeys following treatment with both hormone combinations mainly at embryolethal dose levels and were considered spontaneous in nature. Virilization of female cynomolgus fetuses following NEA + EE treatment was manifested as two cases of clitoral enlargement in the 300 X HDE group and two cases of increased anogenital distance with reduced vaginal opening in the 1,000 X HDE group. The highest dose of NEA + EE was also maternally toxic, as two maternal deaths occurred at the end of the treatment period. One dead female cynomolgus fetus exposed to P + EB (10 X HDE) also exhibited masculinized external genitalia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Teratogen update: clinical aspects of thalidomide embryopathy--a continuing preoccupation

There is much misinformation in the medical community regarding the thalidomide syndrome. Some physicians and scientists are unaware of the fact that organs other than the limbs were frequently affected. Some believe that thalidomide could produce any type of limb reduction defect. Most were aware of the very narrow period of early organogenesis during which the thalidomide-type malformations could be produced. Important features include the fact that limb reduction defects were primarily preaxial, included concomitant girdle hypoplasia when limb reductions were severe, were almost universally bilateral and did not include distal transverse-type defects often called "hemimelia". While it can be said that some spontaneous (non-thalidomide) malformations can mimic the thalidomide syndrome, it can also be said that many limb reduction defects can be determined not to have been produced by thalidomide. The risks of the various defects can be estimated following exposure, with most certainty for limb defects, with less certainty for other defects. Many defects were not associated with exposure to thalidomide such as cleft lip and severe mental retardation.     

The development of resistance to caffeine in Drosophila prosaltans: productivity and longevity after ten generations of treatment.

The productivity of Drosophila prosaltans treated with six concentrations of caffeine (from 50 micrograms/ml to 2,500 micrograms/ml of culture medium) during ten generations (approximately 8 months) decreased in a dosage dependent manner in every generation, but at the end of the treatment the flies in all experiments recovered normal productivity, except for those treated with 2,500 micrograms/ml. Longevity in the tenth generation was significantly reduced in males and females only in the 2,500 micrograms/ml dosage, with males being much more affected than females. In a previous study in which the treatment was done in a single generation, productivity exhibited only a partial recovery when the treatment ceased and longevity was significantly reduced in 1,500 micrograms/ml dosages. The hypothesis of selection occurring in ten generations leading to recovery in productivity and to a reduction in the processes which cause a decrease in longevity is being considered.     

骨与关节系统发生过程中相关调控机制的研究进展

脊椎动物胚胎期骨与关节系统的发生是一种复杂生命现象,起始于中胚层间充质细胞的定向聚集,形成肢芽,然后在一系列作用因子的调控下,肢芽内细胞进一步分化,形成具有骨骼雏形的软骨原基,后者经软骨内骨化发育成骨。四肢骨大多是以这种方式发生的,四肢的滑膜关节系统也随骨骼的发生而形成。详细阐述了近年来对肢体骨与关节系统发生各步骤相关调控机制方面的研究进展。Abstract: The embryonic development of bone and joint involves in complicated events for vertebrate limb. It originates from determined condensation of mesenchymal cells from lateral mesoderm. These cells and the overlying ectodermal jacket form limb buds at presumptive limb levels. Then, under the control of systemic factors, mesenchymal cells aggregate and differentiate to form catilage blastemal elements that prefigure skeletal limb components. The latter develops into skeleton through endochondral ossification. The majority of the bones of the limb form by the endochondral mechanism. The formation of synovial joint system and bone development occur simultaneously. This article reviewed the progress on the related control mechanism in the development of bone and joint recently.     

Valproic acid developmental toxicity and pharmacokinetics in the rhesus monkey: an interspecies comparison

This study was undertaken to assess the developmental toxicity and drug distributional and metabolic characteristics of prenatal valproic acid (VPA) exposure in rhesus monkeys. Oral administration of 20-600 mg/kg/day VPA (approximately 1-15 X human therapeutic dose) to 33 animals on variable gestational days (GD) during organogenesis resulted in dose-dependent developmental toxicity manifested as increased embryo/fetal mortality, intrauterine growth retardation, and craniofacial and skeletal defects. Biphasic plasma elimination curves were observed for total and free VPA on the first (GD 21) and last (GD 50) days of treatment in the 100- and 200-mg/kg/day dose groups. VPA exhibited dose-independent elimination kinetics at the plasma concentrations observed in this study. There was no significant change in pharmacokinetic parameters (maternal plasma elimination rate, area under the curve, peak plasma concentration) between the first and last days of treatment at either dose level. Placental transfer studies indicated that embryos were exposed to half the free VPA concentrations present in maternal plasma on GD 37. Comparisons of interspecies sensitivity to VPA-induced developmental toxicity in the mouse, rat, monkey, and man are made.     

Expression profile of Xenopus banded hedgehog, a homolog of mouse Indian hedgehog, is related to the late development of endochondral ossification in Xenopus laevis

Late development of endochondral ossification occurs at the boundary between the growth cartilage and bone marrow during the formation of long bones in Xenopus laevis. Since the Indian hedgehog (Ihh) is involved in endochondral ossification in mouse, we investigated the expression of Xenopus banded hedgehog (X-bhh), which is a homolog of mouse Ihh. RT-PCR analysis demonstrated that the X-bhh mRNA was detected from an early stage of limb formation to formation of femurs in mature frogs, and it was associated with the expression of Xenopus-ptc1 (X-ptc1), Xenopus-gli1 (X-gli1), Xenopus-type II collagen (X-col II), Xenopus-runx2 (X-runx2), and Xenopus-osteocalcin (X-ocn) mRNAs. In situ hybridization revealed that chondrogenic cells observed at early limb development expressed X-bhh and X-gli1. At later stages of limb development, chondrocytes, located slightly away from the boundary between the cartilage and bone marrow, expressed the X-bhh, X-ptc1, and X-gli1 mRNAs; however, the mesenchymal cells at the boundary failed to express these mRNAs. The X-bhh, X-ptc1, and X-gli1 mRNAs as well as those of X-runx2 and X-ocn were expressed by the mesenchymal cells in the periosteal region at the tip of the cortical bone, indicating an intimate relationship between X-bhh expression and bone formation in this region. Considered collectively, the present study suggests that X-bhh evolutionally acquired the function to induce osteogenesis; however, the expression profile of X-bhh in epiphysis is closely related to the late development of endochondral ossification in X. laevis.     

Methanol exposure during gastrulation causes holoprosencephaly, facial dysgenesis, and cervical vertebral malformations in C57BL/6J mice

BACKGROUND: Exposure of pregnant outbred CD-1 mice to methanol during the period of gastrulation results in exencephaly, cleft palate, and cervical vertebra malformations [Rogers and Mole, Teratology 55: 364, 1997], while inbred C57BL/6J mice are sensitive to the teratogenicity of ethanol. C57BL/6J fetuses exhibit the holoprosencephaly spectrum of malformations after maternal exposure to ethanol during gastrulation, but the sensitivity of C57BL/6J mice to methanol-induced teratogenesis has not been previously described. METHODS: Pregnant C57BL/6J mice were administered two i.p. injections totaling 3.4 or 4.9 g/kg methanol or distilled water four hrs apart on gestation day 'GD' 7. On GD 17, litters were examined for numbers of live, dead and resorbed conceptuses, fetuses were weighed as a litter and examined externally, and all fetuses were double stained for skeletal analysis. RESULTS: No maternal intoxication was apparent, but the high dosage level caused a transient deficit in maternal weight gain. The number of live fetuses per litter was reduced at both dosages of methanol, and fetal weight was lower in the high dosage group. Craniofacial defects were observed in 55.8% of fetuses in the low dosage group and 91.0% of fetuses in the high dosage group, including micro/anophthalmia, holoprosencephaly, facial clefts and gross facial angenesis. Skeletal malformations, particularly of the cervical vertebrae, were observed at both dosages of methanol, and were similar to those previously reported in the CD-1 mouse following methanol exposure. CONCLUSIONS: The types of craniofacial malformations induced in the C57BL/6J mouse by methanol indicate that methanol and ethanol have common targets and may have common modes of action.     

Genesis of alcohol-induced craniofacial dysmorphism

The initial diagnosis of fetal alcohol syndrome (FAS) in the United States was made because of the facial features common to the first cohort of patients. This article reviews the development of an FAS mouse model whose craniofacial features are remarkably similar to those of affected humans. The model is based on short-term maternal treatment with a high dosage of ethanol at stages of pregnancy that are equivalent to Weeks 3 and 4 of human gestation. At these early stages of development, alcohol's insult to the developing face is concurrent with that to the brain, eyes, and inner ear. That facial and central nervous system defects consistent with FAS can be induced by more "realistic" alcohol dosages as illustrated with data from an oral alcohol intake mouse model in which maternal blood alcohol levels do not exceed 200 mg/dl. The ethanol-induced pathogenesis involves apoptosis that occurs within 12 hrs of alcohol exposure in selected cell populations of Day 7, 8, and 9 mouse embryos. Experimental evidence from other species also shows that apoptosis underlies ethanol-induced malformations. With knowledge of sensitive and resistant cell populations at specific developmental stages, studies designed to identify the basis for these differing cellular responses and, therefore, to determine the primary mechanisms of ethanol's teratogenesis are possible. For example, microarray comparisons of sensitive and resistant embryonic cell populations have been made, as have in situ studies of gene expression patterns in the populations of interest. Studies that illustrate agents that are effective in diminishing or exacerbating ethanol's teratogenesis have also been helpful in determining mechanisms. Among these agents are antioxidants, sonic hedgehog protein, retinoids, and the peptides SAL and NAP.     

Nongenital malformations following exposure to progestational drugs: the last chapter of an erroneous allegation

In the late 1960s and 1970s, a number of epidemiological studies were published indicating that pregnant women who were exposed to an array of sex steroids delivered infants with an increased incidence of nongenital congenital malformations. Because of these publications, the Food and Drug Administration (FDA), in conjunction with various pharmaceutical companies, labeled the therapeutic exposure of progestational drugs and contraceptives in pregnant women as a risk factor for limb‐reduction defects (LRDs) and congenital heart defects (CHDs). Subsequently there was a rapid decrease in the exposure of pregnant women to these drugs and the initiation of numerous lawsuits alleging that a particular progestational drug was responsible for a child's nongenital congenital malformation. Wilson and Brent ( 1981 ) published an article indicating that epidemiological and animal studies of these drugs, and basic science did not support the package insert's warnings. Many new and previous animal and epidemiological studies did not support the FDA box warning. In 1987 the FDA held a hearing in which the FDA, the Teratology Society, the Centers for Disease Control and Prevention, the American College of Obstetrics and Gynecology, and other organizations supported the position that progestational agents did not result in nongenital malformations. An editorial appeared in Teratology congratulating the FDA for removing the warning label on oral contraceptives regarding nongenital malformations. In 1999 the FDA published new wording for package inserts that removed warnings for nongenital malformations for all progestational agents. In spite of the recent changes in the package inserts, lawsuits have alleged that progestational drugs cause nongenital malformations. It took 22 years from the time a box warning was required by the FDA until the warnings were removed in 1999. The 1999 FDA publication, which is a scholarly and objective document, should put an end to 2 decades of concern and anxiety for pregnant women or women of reproductive age. Could scientists, the pharmaceutical companies, or the FDA have prevented the mislabeling of progestational drugs with regard to their teratogenic risks? Was the epidemiological or teratology community at fault because they did not critique and respond to the early publications? Did the FDA act too slowly? The epidemiologic analyses, animal studies, and basic science principles have been reviewed, and it is obvious that clinically utilized progestational drugs do not cause nongenital malformations (i.e., LRDs and CHDs). Birth Defects Research (Part A) 2005. © 2005 Wiley‐Liss, Inc.     

A histochemical localization on Maclura pomifera lectin during osteogenesis

Mandibular condyles of 4-week-old Wistar strain rats and mandibles of ICR strain mice from 14 days gestation stage to 2 days postnatal stage were used to investigate the localization of Maclura pomifera lectin (MPA) during two modes of osteogenesis. During endochondral ossification of the mandibular condyle, MPA was only localized at the peripheral regions of calcified cartilage after the destruction of chondrocyte lacunae. Bone extracellular matrix (ECM) was not reacted with MPA. In intramembranous ossification of mice mandibles, MPA was stained intensively in the early bone ECM. The intensity of the MPA reaction decreased during bone development. In both cases of osteogenesis, chondroclasts and osteoclasts showed the strong affinity to MPA. These results indicated that the time- and position-specific changes within ECM proceeded during osteogenesis and that MPA was the useful probe to detect chondroclasts and osteoclasts.     

A histochemical localization on Maclura pomifera lectin during osteogenesis

Summary Mandibular condyles of 4-week-old Wistar strain rats and mandibles of ICR strain mice from 14 days gestation stage to 2 days postnatal stage were used to investigate the localization of Maclura pomifera lectin (MPA) during two modes of osteogenesis. During endochondral ossification of the mandibular condyle, MPA was only localized at the peripheral regions of calcified cartilage after the destruction of chondrocyte lacunae. Bone extracellular matrix (ECM) was not reacted with MPA. In intramembranous ossification of mice mandibles, MPA was stained intensively in the early bone ECM. The intensity of the MPA reaction decreased during bone development. In both cases of osteogenesis, chondroclasts and osteoclasts showed the strong affinity to MPA. These results indicated that the time- and position-specific changes within ECM proceeded during osteogenesis and that MPA was the useful probe to detect chondroclasts and osteoclasts.     

Indian hedgehog signals independently of PTHrP to promote chondrocyte hypertrophy

Chondrocyte hypertrophy is an essential process required for endochondral bone formation. Proper regulation of chondrocyte hypertrophy is also required in postnatal cartilage homeostasis. Indian hedgehog (Ihh) and PTHrP signaling play crucial roles in regulating the onset of chondrocyte hypertrophy by forming a negative feedback loop, in which Ihh signaling regulates chondrocyte hypertrophy by controlling PTHrP expression. To understand whether there is a PTHrP-independent role of Ihh signaling in regulating chondrocyte hypertrophy, we have both activated and inactivated Ihh signaling in the absence of PTHrP during endochondral skeletal development. We found that upregulating Ihh signaling in the developing cartilage by treating PTHrP(-/-) limb explants with sonic hedgehog (Shh) protein in vitro, or overexpressing Ihh in the cartilage of PTHrP(-/-) embryos or inactivating patched 1 (Ptch1), a negative regulator of hedgehog (Hh) signaling, accelerated chondrocyte hypertrophy in the PTHrP(-/-) embryos. Conversely, when Hh signaling was blocked by cyclopamine or by removing Smoothened (Smo), a positive regulator of Hh signaling, chondrocyte hypertrophy was delayed in the PTHrP(-/-) embryo. Furthermore, we show that upregulated Hh signaling in the postnatal cartilage led to accelerated chondrocyte hypertrophy during secondary ossification, which in turn caused reduction of joint cartilage. Our results revealed a novel role of Ihh signaling in promoting chondrocyte hypertrophy independently of PTHrP, which is particularly important in postnatal cartilage development and homeostasis. In addition, we found that bone morphogenetic protein (Bmp) and Wnt/beta-catenin signaling in the cartilage may both mediate the effect of upregulated Ihh signaling in promoting chondrocyte hypertrophy.     

Experimental yolk sac dysfunction as a model for studying nutritional disturbances in the embryo during early organogenesis

Our investigations concerning the importance of cell surface macromolecules during embryonic development led us to the discovery in 1961 that heterologous anti-rat kidney serum produced teratogenesis, growth retardation and embryonic death when injected into the pregnant rat during early organogenesis. It was established that IgG was the teratogenic agent, primarily directed against the visceral yolk sac (VYS) but not the embryo. Heterologous anti-rat VYS serum was prepared which was teratogenic localized in the VYS and served as a model for producing VYS dysfunction and embryonic malnutrition. The role of the yolk sac placenta in histiotrophic nutrition is now recognized to be critical for normal embryonic development during early organogenesis in the rodent. VYS antiserum affects embryonic development primarily by inhibiting endocytosis of proteins by the VYS endoderm, resulting in a reduction in the amino acids supplied to the embryo. Our laboratory has recently developed teratogenic monoclonal yolk sac antibodies (MCA) which can be utilized; to study VYS plasma membrane synthesis and recycling, to compare yolk sac function among different species, and to identify components of the plasma membrane involved in pinocytosis. MCA prepared against certain VYS antigens provide an opportunity to study embryonic nutrition with minimal interference with the nutritional state of the mother. Recent developments in the study of the human yolk sac along with our laboratory's ability to isolate a spectrum of yolk sac antigens, prepare monoclonal antibodies, and perform functional studies, should provide information that will increase our understanding of yolk sac function and dysfunction in the human and determine the relative importance of various amino acids to normal development during mammalian organogenesis.     

Impaired endochondral bone development and osteopenia in Gli2-deficient mice

Mice homozygous for targeted disruption of the zinc finger domain of Gli2 (Gli2(zfd/zfd)) die at birth with developmental defects in several organ systems including the skeleton. The current studies were undertaken to define the role of Gli2 in endochondral bone development by characterizing the molecular defects in the limbs and vertebrae of Gli2(zfd/zfd) mice. The bones of mutant mice removed by cesarian section at E16.5 and E18.5 demonstrated delayed endochondral ossification. This was accompanied by an increase in the length of cartilaginous growth plates, reduced bone tissue in the femur and tibia and by failure to develop the primary ossification centre in vertebral bodies. The growth plates of tibiae and vertebrae exhibited increased numbers of proliferating and hypertrophic chondrocytes with no apparent alteration in matrix mineralisation. The changes in growth plate morphology were accompanied by an increase in expression of FGF2 in proliferating chondrocytes and decreased expression of Indian hedgehog (Ihh), patched (Ptc) and parathyroid-hormone-related protein (PTHrP) in prehypertrophic cells. Furthermore, there was a reduction in expression of angiogenic molecules in hypertrophic chondrocytes, which was accompanied by a decrease in chondroclasts at the cartilage bone interface, fewer osteoblasts lining trabecular surfaces and a reduced volume of metaphyseal bone. These results indicate that functional Gli2 is necessary for normal endochondral bone development and that its absence results in increased proliferation of immature chondrocytes and decreased resorption of mineralised cartilage and bone formation.     

Signaling Cascades Governing Cdc42-Mediated Chondrogenic Differentiation and Mensenchymal Condensation

Endochondral ossification consists of successive steps of chondrocyte differentiation, including mesenchymal condensation, differentiation of chondrocytes, and hypertrophy followed by mineralization and ossification. Loss-of-function studies have revealed that abnormal growth plate cartilage of the Cdc42 mutant contributes to the defects in endochondral bone formation. Here, we have investigated the roles of Cdc42 in osteogenesis and signaling cascades governing Cdc42-mediated chondrogenic differentiation. Though deletion of Cdc42 in limb mesenchymal progenitors led to severe defects in endochondral ossification, either ablation of Cdc42 in limb preosteoblasts or knockdown of Cdc42 in vitro had no obvious effects on bone formation and osteoblast differentiation. However, in Cdc42 mutant limb buds, loss of Cdc42 in mesenchymal progenitors led to marked inactivation of p38 and Smad1/5, and in micromass cultures, Cdc42 lay on the upstream of p38 to activate Smad1/5 in bone morphogenetic protein-2-induced mesenchymal condensation. Finally, Cdc42 also lay on the upstream of protein kinase B to transactivate Sox9 and subsequently induced the expression of chondrocyte differential marker in transforming growth factor-β1-induced chondrogenesis. Taken together, by using biochemical and genetic approaches, we have demonstrated that Cdc42 is involved not in osteogenesis but in chondrogenesis in which the BMP2/Cdc42/Pak/p38/Smad signaling module promotes mesenchymal condensation and the TGF-β/Cdc42/Pak/Akt/Sox9 signaling module facilitates chondrogenic differentiation.     

Gestational ethanol exposure disrupts the expression of FGF8 and Sonic hedgehog during limb patterning

BACKGROUND: Ethanol is known to induce a wide variety of gestational anomalies, including skeletal malformations. Gestational ethanol exposure in mice has been shown to induce postaxial digit loss (ectrodactyly). How ethanol induces limb malformations is not understood. To better understand how ethanol effects limb development, we have utilized a transgenic line of mice that expresses beta-galactosidase in the apical ectodermal ridge (AER) of the limbs throughout gestation. METHODS: Pregnant female mice were injected with 2.9, 3.4, or 3.9 gm/kg ethanol at E9.3 and E9.5; embryos were isolated at E11.25, stained for beta-galactosidase activity, and evaluated for AER defects. Based upon the pattern of defects seen, expression of FGF8 in the AER and Sonic hedgehog in the postaxial mesoderm was evaluated by in situ hybridization. RESULTS: Two distinct phenotypes were seen in response to ethanol that were dose dependent. At 2.9 gm/kg ethanol, the most prevalent phenotype was a mislocalization of the AER to regions both dorsal and ventral to the midline. A higher dosage of 3.4 gm/kg ethanol did not increase the mislocalization phenotype, but resulted in a higher frequency of postaxial loss of the AER and associated mesenchymal tissue. The highest dosage utilized (3.9 gm/kg) resulted in a high frequency of both preaxial and postaxial loss of the AER. Through in situ hybridization, we found that ethanol exposure resulted in a concomitant reduction in FGF8 expression in the AER and Sonic hedgehog expression from the zone of polarizing activity (ZPA). CONCLUSIONS: We propose a model where ethanol disrupts the AER/ZPA positive feedback loop to induce postaxial malformations. Preaxial malformations seen at higher ethanol dosage suggest FGF8 as a critical target of ethanol in producing limb defects.     

The effect of hypoxia in development

There is increasing evidence that the oxygen supply to the human embryo in the first trimester is tightly controlled, suggesting that too much oxygen may interfere with development. The use of hypoxia probes in mammalian embryos during the organogenic period indicates that the embryo is normally in a state of partial hypoxia, and this may be essential to control cardiovascular development, perhaps under the control of hypoxia-inducible factor (HIF). A consequence of this state of partial hypoxia is that disturbances in the oxygen supply can more easily lead to a damaging degree of hypoxia. Experimental mammalian embryos show a surprising degree of resilience to hypoxia, with many organogenic stage embryos able to survive 30-60 min of anoxia. However, in some embryos this degree of hypoxia causes abnormal development, particularly transverse limb reduction defects. These abnormalities are preceded by hemorrhage/edema and tissue necrosis. Other parts of the embryo are also susceptible to this hypoxia-induced damage and include the genital tubercle, the developing nose, the tail, and the central nervous system. Other frequently observed defects in animal models of prenatal hypoxia include cleft lip, maxillary hypoplasia, and heart defects. Animal studies indicate that hypoxic episodes in the first trimester of human pregnancy could occur by temporary constriction of the uterine arteries. This could be a consequence of exposure to cocaine, misoprostol, or severe shock, and there is evidence that these exposures have resulted in hypoxia-related malformations in the human. Exposure to drugs that block the potassium current (IKr) can cause severe slowing and arrhythmia of the mammalian embryonic heart and consequently hypoxia in the embryo. These drugs are highly teratogenic in experimental animals. There is evidence that drugs with IKr blockade as a side effect, for example phenytoin, may cause birth defects in the human by causing periods of embryonic hypoxia. The strongest evidence of hypoxia causing birth defects in the human comes from studies of fetuses lacking hemoglobin (Hb) F. These fetuses are thought to be hypoxic from about the middle of the first trimester and show a range of birth defects, particularly transverse limb reduction defects.     

Developmental basis of limb length in rodents: evidence for multiple divisions of labor in mechanisms of endochondral bone growth

SUMMARY Mammals are remarkably diverse in limb lengths and proportions, but the number and kind of developmental mechanisms that contribute to length differences between limb bones remain largely unknown. Intra- and interspecific differences in bone length could result from variations in the cellular processes of endochondral bone growth, creating differences in rates of chondrocyte proliferation or hypertrophy, variation in the shape and size of chondrocytes, differences in the number of chondrocytes in precursor populations and throughout growth, or a combination of these mechanisms. To address these questions, this study compared cellular mechanisms of endochondral bone growth in cross-sectional ontogenetic series of the appendicular skeleton of two rodent species: the mouse ( Mus musculus ) and Mongolian gerbil ( Meriones unguiculatus ). Results indicate that multiple cellular processes of endochondral bone growth contribute to phenotypic differences in limb bone length. The data also suggest that separate developmental processes contribute to intraspecific length differences in proximal versus distal limb bones, and that these proximo-distal mechanisms are distinct from mechanisms that contribute to interspecific differences in limb bone length related to body size. These developmental "divisions of labor" are hypothesized to be important features of vertebrate limb development that allow (1) morphology in the autopods to evolve independently of the proximal limb skeleton, and (2) adaptive changes in limb proportions related to locomotion to evolve independently of evolutionary changes in body size.     

Morphological and biochemical aspects of monofunctional phosphoramide mustard teratogenicity in rat embryos cultured in vitro

Day 10 rat embryos were exposed in vitro to a monofunctional analog of phosphoramide mustard (MPM) at concentrations of 25 to 200 micrograms/ml (144 to 1,156 X 10(-6) M). After a 24-hour exposure, embryos exhibited a dose-dependent decrease in growth parameters (crown-rump length, number of somites, and protein content) as well as incidence of malformations. Abnormal embryos were characterized by hypoplasia of the prosencephalon as well as hypoplasia of the mandibular arches, tail, and limb buds. Histological analysis revealed abnormal levels of necrotic cells, particularly in the neuroepithelium and surrounding mesenchyme. In all respects embryos exposed to MPM could not be distinguished from embryos exposed to phosphoramide mustard. We also determined using mouse L1210 cells that at the maximum nonlethal concentration used in our embryo exposure experiments, MPM did not cause DNA cross-linking but did cause single-strand DNA breaks. Phosphoramide mustard, at concentrations teratogenic to embryos in vitro, did produce DNA cross-linking. Taken together, our results indicate that although cyclophosphamide (CP)-induced DNA cross-linking may play a role in CP teratogenesis, DNA cross-linking is not an absolute requirement.