ABNORMAL DEVELOPMENT OF THE SUSPENSOR IN AN EMBRYO-LETHAL MUTANT OF ARABIDOPSIS THALIANA

Developmental arrest of the embryo proper in aborted seeds from mutant 50B, a recessive embryo-lethal mutant of Arabidopsis thaliana, was shown to be followed by abnormal growth of the suspensor. Each of the 12 aborted seeds examined in sectioned material contained an abnormally large suspensor and an embryo proper arrested at a preglobular stage of development. Analysis of serial sections revealed that mutant suspensors contained 15–150 cells whereas wild-type suspensors were composed of only six to eight cells. Development of the mutant endosperm continued to a late nuclear or early cellular stage even in the absence of further development of the embryo proper. These results suggest that the missing gene product in mutant 50B is required for development of the embryo proper but not for continued growth of the suspensor or endosperm tissue. The pattern of abnormal development observed in this mutant provides further evidence that continued growth of the suspensor during normal development is inhibited by the developing embryo proper and that the full developmental potential of cells in the suspensor is expressed only when this inhibitory effect is removed through a mutation or experimental treatment that is lethal only to cells of the embryo proper.     

THE EQUIVALENCE OF AGE IN ANIMALS

1. A method of plotting growth curves is presented which is considered more useful than the usual method in bringing out a number of important phenomena such as the equivalence of age in different animals, difference in the shape and duration of corresponding growth cycles in different animals, and also in determinating the age of maxima without resorting to complicated mathematical computations. 2. It is suggested that after the third cycle is past the conceptional age of the maximum of the third cycle may be taken as the age of reference for estimating the equivalent physiological ages in different animals. Before the age of the third cycle, the maxima of the second and first cycles are most conveniently used as points of reference. 3. It is shown that the product of the conceptional age of the maximum of the third cycle by 13, gives a value which is, with the possible exception of man, very near to the normal duration of life of animals under the most favorable conditions of life. In other words, the equivalent physiological ages in different animals bear an approximately constant linear relation to the duration of their growth periods. 4. Attention is called to certain differences in the shape and duration of the corresponding growth cycles in different animals and of the effect of sex on these cycles.     

Correlation between the age of the conceptus and various ultrasonographic measurements during the first 30 days of pregnancy in domestic cats (Felis catus)

We ultrasonographically evaluated the prenatal development in cats, from the early phases to Day 30 of pregnancy, subjecting a group of pregnant cats (n = 12) to a daily ultrasonographic exam. The ultrasonographic images allowed us to measure the minor diameter of the gestational sac and the crown-rump length of the embryo/fetus. Ten subjects underwent ovariohysterectomy at specific intervals during the pregnancy, with the aim of comparing the ultrasonographic data with real data; only two subjects brought their pregnancy to term. The earliest ultrasonographic observation of the gestational sac was on Day 10 after mating, while the embryo could be measured only beginning with Day 18. This study allowed to gather useful new data in order to clinically monitor the normal course of pregnancy in cats and to date the gestational age.     

Born to be young? Prenatal thyroid hormones increase early-life telomere length in wild collared flycatchers

The underlying mechanisms of the lifelong consequences of prenatal environmental condition on health and ageing remain little understood. Thyroid hormones (THs) are important regulators of embryogenesis, transferred from the mother to the embryo. Since prenatal THs can accelerate early-life development, we hypothesized that this might occur at the expense of resource allocation in somatic maintenance processes, leading to premature ageing. Therefore, we investigated the consequences of prenatal TH supplementation on potential hallmarks of ageing in a free-living avian model in which we previously demonstrated that experimentally elevated prenatal TH exposure accelerates early-life growth. Using cross-sectional sampling, we first report that mitochondrial DNA (mtDNA) copy number and telomere length significantly decrease from early-life to late adulthood, thus suggesting that these two molecular markers could be hallmarks of ageing in our wild bird model. Elevated prenatal THs had no effect on mtDNA copy number but counterintuitively increased telomere length both soon after birth and at the end of the growth period (equivalent to offsetting ca 4 years of post-growth telomere shortening). These findings suggest that prenatal THs might have a role in setting the ‘biological'' age at birth, but raise questions about the nature of the evolutionary costs of prenatal exposure to high TH levels.     

Sensitivity of germ cells and embryos to ionizing radiation

Experiments performed in laboratory animals suggest that ionizing radiation can induce DNA damage in the germ cells of exposed individuals and lead to various deleterious effects in their progeny, including miscarriage, low birth weight, congenital abnormalities and perhaps cancer. However, no clear evidence for such effects has been found in epidemiological studies of people exposed to radiation. The predicted risks of hereditary effects of any kinds resulting from parental exposure to relatively low doses of ionizing radiation remain very low, compared to the spontaneous risks in the absence of irradiation. Irradiation of the mouse embryo can lead to various effects (lethality, growth retardation, congenital abnormalities), depending on the period of gestation at which irradiation occurs. In humans, prenatal irradiation has only been exceptionally associated with congenital abnormalities, but irradiation between weeks 8-25 has been shown to be able to induce severe mental retardation. Although being not proven, the risk of developing a childhood cancer following prenatal irradiation may also not be excluded. Like for genetic effects, the risk of adverse effects following exposure of the embryo to relatively low doses remains quite low compared to the natural risks.     

Ultrasonographic fetometry and prenatal fetal sex assessment in camels (Camelus dromedarius)

The aims of this study were to determine the developmental patterns of some fetal parts to achieve a high accuracy level in the assessment of gestational age and to assess the feasibility and accuracy of ultrasonic prenatal fetal sex assessment in camels. Serial ultrasonographic examinations were carried out on seven pregnant dromedary camels. A total of 329 ultrasonographic examinations were conducted between the second and the 54th weeks of pregnancy. Intrauterine fluid accumulation was detected between the second and third weeks of pregnancy. The embryo proper was noticed between the third and fourth weeks. Organization of the embryo was first observed between the sixth and seventh weeks. Ossification was first detected between the seventh and ninth weeks. The accessibility during the total gestational period was 35/329 (10.6%) for crown-rump length, 35/329 (10.6%) for biparietal diameter, 42/329 (12.8%) for abdominal diameter, 42/329 (12.8%) for ruminal length, and 126/329 (38.3%) for eyeball diameter. A high correlation was found between gestational age and each of the studied parameters (P < 0.0001). The highest correlation was found with the crown-rump length and the biparietal diameter during the first trimester and with the eyeball diameter during the third trimester of pregnancy. The overall accuracy of the ultrasonic prenatal fetal sex assessment was 91.7%. The best window was found during the 11th week of pregnancy. It was concluded that sonographic fetometry can be useful for the evaluation of fetal development, the estimation of gestational age, and the prediction of prenatal fetal sex in camels.     

Scanning electron microscopic observations on the 9-day opossum (Didelphis virginiana) embryo

All three germ layers are present in the opossum embryo by the 9th prenatal day. The embryo proper is part of, and continuous with, the remainder of the chorionic wall. The wall of the yolk sac-chorion away from the embryo consists only of an outer covering of ectoderm and an inner layer of endoderm. Ectodermal cells covering the neural folds have dome-shaped apices and often show large, bleb-like expansions. Microvilli are short and few in number. The apical surfaces of ectodermal cells that overlie the parietal mesoderm are relatively smooth and show scattered, short microvilli that tend to be concentrated at cell junctions. The apices of ectodermal cells that cover the extraembryonic region are more rounded, and the cells balloon from the surface. Each cell shows abundant elongate microvilli and occasional cytoplasmic blebs. Endodermal cells that line the chorion and form the third (innermost) layer of the embryo are similar in their surface morphology.     

Comparative embryology and mammalian cloning

A hypothesis has been advanced that logically combines “contradictory” facts concerning the early mammalian development and shows a natural relationship between the embryos developing from a fertilized ovum and from cells of the inner cell mass of blastocyst. When studying the theoretical questions of cloning, it is necessary to take into consideration the peculiarities of prenatal mammalian ontogeny, which make themselves evident upon comparison with other animals. The absence of yolk in the mammalian ovum defines sharp differences in the early development between mammals and other Amniota. The complete asynchronous cleavage results in the formation of morula followed by blastocyst, which hatches from zona pellucida and is implanted into the uterus tissue. This fact allows us to consider the blastocyst as a mammalian larva, which is fed owing to the maternal organism. It is known that, in the body of a larva (blastocyst), a new embryo develops from some somatic cells. This process is known as polyembryony, which is typical of the development of some parasitic insects. Polyembryony in turn is a variant of somatic embryogenesis, which is a form of asexual reproduction. Thus, the two different embryos, “conceptus” and “embryo proper,” have different origins: the first forms by the sexual way and the second, by the asexual way. Investigation of the mechanisms of somatic embryogenesis in mammals will help us to find conditions necessary for full reprogramming of donor somatic nuclei and provide for successful development of reconstructed embryos.     

Growth allometry of the myocardium in human embryos (from stages 15 to 23).

The relative growth of the myocardium was studied in 27 staged human embryos (Carnegie stages). The volume of the myocardium was determined for each embryo according to Cavalieri's principle (by using point-counting planimetry to determine the area of the profiles of the myocardium). The volume of the myocardium (variable Y) was correlated to embryonic crown-rump length (variable X in millimeters) and age (in days). The bivariate allometric equation was used as Y = aXb. The scatterplot was discontinuous, presenting two trends during the postsomitic period. The first part was composed of embryos staged from stages 15 to 20, and the second part by embryos staged from stages 21 to 23. The breakpoint between these different trends was found at the level of stage 20 (embryo of 22 mm in crown-rump length and age nearly of 52 days). From stages 15 to 20, the growth rate of the myocardium was allometrically negative. On the other hand, from stages 21 to 23 this growth rate was moderately allometrically positive. These differences in growth of the myocardium were analyzed and, at least partially, might be due to the functional circulatory increase in the peripheral vascular bed in correlation to the cardiac hemodynamic demand required at the end of the embryonic period proper.     

大麻哈鱼胚胎耳石微结构及其群体环境标记

采用人工调控环境方法对黑龙江、绥芬河大麻哈鱼发眼期胚胎群体耳石日轮进行周期性持续标记。实验分４组: 1组为对照组, 2－3组为变温标记组, 4组为“暴气”-变温标记组, 实验用发眼卵1.2万粒。待胚胎发育至耳石日轮结构形成后实施标记。实验胚胎耳石随着标记期间环境周期性变化及其持续的时间, 形成相应变化节律的日轮标记区。获得各实验组设定环境的日轮标记图谱。人工环境标记的耳石日轮图谱, 暗带色度加深, 明带亮度增大, 并可形成生长轮距不同的标记轮, 与对照组耳石微结构有明显区别, 标记率达到100%。初步建立鱼类耳石标记及其识别技术, 适用于大麻哈鱼等鲑鳟鱼类群体标记。作为安全有效、成本低廉的群体标记技术方法, 鱼类耳石日轮标记在鱼类资源评估和增殖放流效果评价中将会得到广泛应用。       

SECRETION OF α-AMYLASE BY THE EMBRYONIC CHICK PANCREAS IN VITRO

Pancreases taken from chick embryos secrete amylase in vitro when stimulated by cholinergic drugs. Rates of secretion increase with developmental age. The pancreas isolated together with the duodenal loop from the 8 day embryo is already capable of secretion in vitro. It is therefore concluded that the pancreas acquires the ability to secrete digestive enzymes more than 10 days before the beginning of the prominent biochemical and morphological changes associated with the maturation of the gland.     

Effects of prenatal exposure to methylazoxymethanol (MAM) on brain weight, hypothalamic cell number, pituitary structure, and postnatal growth in the rat.

Congenital brain damage syndromes typically are described in terms of behavioral symptoms. Many brain functions are not reflected in behavior, however, and prenatal injury to the developing nervous system could alter these functions, as well. To test the hypothesis that prenatal brain injury can result in postnatal endocrine malfunction, rats were exposed in utero to 20 mg/kg of methylazoxymethanol acetate, a potent neuroteratogen, at two stages of gestation when different sets of growth-controlling neurons of the hypothalamus are forming. The growth hormone releasing factor (GRF) neurons stimulate release of growth hormone from the somatotropes of the anterior pituitary, contributing to rapid growth in the period between weaning and puberty. The somatotropin release inhibiting factor (SRIF) neurons have the opposite effect on the pituitary and can inhibit the GRF cells directly. Growth of treated animals was monitored daily from birth to 40 days and compared to that of controls. Treatment on the 14th day of gestation produced a small number of dwarf animals characterized by normal weight at birth and a sudden decrease in growth rate at the beginning of the fourth postnatal week that led to a body weight about 50% of normal. Treatment on day 16 yielded an acceleration of postnatal growth (significant in males). In each group, most treated animals were like controls in adult size and pattern of growth. As adults, both treatment groups demonstrated massive reductions in brain weight which characterized all the subjects, whether or not they exhibited growth anomalies. The animals treated on day 14 were confirmed to have a significant, selective reduction in growth hormone releasing factor neurons. Reductions were greatest in the middle and posterior levels of the GRF cell distribution, the regions forming most actively at the time of exposure. Unexpectedly, the same group also had increased numbers of periventricular SRIF neurons. Neither type of neurons was significantly altered in the later treatment group. Examination of pituitary structure indicated that dwarfs had very small pituitaries, with an immature pattern of somatotrope distribution, and giants had very large pituitaries, with some hypertrophy of somatotropes. The results suggest that endocrine anomalies which manifest themselves long after birth may originate as birth defects of the nervous system.     

The effect of prenatal stress on the carboxypeptidase H activity in the hypothalamo-pituitary-adrenal-gonadal system of the rat

Effects of dams stress on the carboxypeptidase H: the neuropeptide exchange enzyme in the hypothalamo-pituitary-adrenall-gonadal system, was studied in the litter of different age (0, 14, 28, 45, and 120 day after birth) was studied. The sex differences in dynamic of enzyme activity in intact animals are substantiated. The effect of prenatal stress on carboxypeptidase H activity dependes on age and sex of animals. Prenatal stress is altering during the age dynamics of enzyme activity. This in the pituitary gland and hypothalamus of prenatal stressed female rats was a control for the male rats. In the adrenal and gonadal gland of prenatal stressed males, this was a control for the female rats female. The role of carboxypeptidase H in pubescence and mechanisms of effect of prenatal stress on sex system functional are discussed.     

Early postnatal development of rat brain is accompanied by generation of lipofuscin-like pigments

The increased generation of free radicals results in the formation of fluorescent end-products of lipid peroxidation, lipofuscin-like pigments (LFPs). The authors observed that LFPs are generated in rat brain after a normal birth during 5 postnatal days. The experimental design of the study comprised 10 groups of animals. The authors measured prenatal values 1 day and 7 days before birth, and then the animals were sampled on postnatal day 1, 2, 5, 10, 15, 25, 35, and 90. Maximum LFP concentration is achieved on the postnatal day 2. Starting from postnatal day 10, LFP concentration returns to prenatal values. A new rise in LFP concentration is observed at 3 months of age. This is associated with the beginning of the aging process. LFPs were characterized by fluorescence spectroscopy using tridimensional excitation spectra, synchronous spectra and their derivatives, and HPLC with fluorescence detection. It was possible to discern several tens of fluorescent compounds of unknown structure that are generated and metabolized during early development. The authors suggest that LFPs are formed after respiratory burst of microglia phagocytosing apoptotic cells.     

Genetic prenatal maternal effects on organ size in mice and their potential contribution to evolution

Two embryo transfer experiments were carried out in order to estimate the magnitude of prenatal maternal effects, independent of postnatal maternal factors, on the growth of internal organs and fat pads in mice. Reciprocal embryo transfers between the inbred mouse strains C3HeB/FeJ and SWR/J yielded three significant findings. First, all traits were not equally influenced by prenatal maternal factors. Genetic prenatal maternal factors, stemming from the genotype of the uterine mother, had a significant effect on testis weight, subcutaneous fat pad weight and epididymal fat pad weight in 21 day old progeny, but they had no effect on cranial capacity, an index of brain size, kidney weight, or liver weight. Prenatal litter size, defined as the sum of live and dead pups at birth, had a significant negative relationship with 21 day testis weight and kidney weight, and a significant positive association with subcutaneous and epididymal fat pad weights. Cranial capacity and liver weight at 21 days postnatally were not influenced by prenatal litter size. Second, the experiments demonstrated that there was ontogenetic variability in the strength of prenatal maternal effects. At 70 days of age, only subcutaneous fat pad weight was significantly influenced by genetic prenatal effects, and prenatal litter size had a significant negative relationship only with subcutaneous fat pad weight and body weight. Third, genetic prenatal effects had a significant influence on the among-trait covariances at 21 days postnatally, but not at 70 days. Because multivariate evolution involves covariances among characters, the latter results suggest that prenatal effects due to the mother's genotype can affect phenotypic evolution of mammals, especially for selection imposed early in life.     

被子植物胚柄研究进展

胚柄在胚胎发育过程中是一个暂时性的结构, 但却起着为胚体提供营养和生长调节因子的作用。相对胚体而言, 胚柄具有细胞类型单一、结构相对独立及发育时间短等特点, 其在胚胎发育的基因调控和细胞命运决定研究中具有独特的优势。该文从胚柄的形成及特点、胚柄在胚胎发育中的作用、信号传递系统对胚柄的影响以及与胚柄相关基因的功能等方面进行综述, 以期为研究胚柄在胚胎发育过程中所起的作用以及胚柄的命运决定提供参考信息。     

Development of epiphyseal union in Japanese macaques of known chronological age

Forty epiphyseal unions were studied in the two subspecies of the Japanese macaque at known chronological ages. The age standards of the beginning and completion of epiphyseal union were estimated. The total score of the ratings of the unions revealed significant correlations with chronological age before 9 years of age. The linear regressions were calculated in each group of different sex and different subspecies in order to enable predictions to be made of the chronological age from the total score. Although males and females generally showed the same pattern of sequences, the unions of the females united earlier than those of the males in both subspecies before 9 years of age. The Yaku subspecies demonstrated an earlier union than the common Japanese macaque in both sexes before the age of 9 years old. The epiphyseal union of the Japanese macaque usually developed earlier than the reported union in the rhesus macaque. A large number of epiphyseal unions united at least partially and the total score deviated widely during the range from around 4 to 6 years of age. This period was in accordance with the adolescent growth period, especially in males, with rapid growth of body size as observed based on by somatometrical measurements. The skeletal growth of the trunk was generally late compared with that of the limbs. During the range after 8 years of age, some unions of the trunk united earlier in males than in females. The epiphyseal union could allow a more precise age estimation than the body mass or dental eruption during a certain range of ages. However, developmental estimations obtained from animals fed artificially, as the present samples were, must be applied with caution to wild animals.     

An analysis of the age and size of 483 human embryos

The crown-rump length of 483 fixed human embryos of Carnegie stages 6-23 was analyzed and median and predicted mean lengths were calculated. The results were compared with those of other series and confirmed that early human growth rates are different from those of macaques with which human embryo growth has previously been compared. The study indicated that it is possible to predict: 1. the median size of an embryo of given Streeter horizon or Carnegie stage; 2. the age of a fresh embryo, or one of undisputed Streeter staging, by comparison with mean figures of other authorities; and 3. the corrected age of an embryo of known length or known Streeter staging or both in terms of postovulation age. Since teratogens may reduce the embryonic growth rate this information is relevant in the analysis of teratogenic factors in human development.     

Heterogenous Macromolecular Contributions to Early Mouse Embryo Development

Mouse embryos have been cultured for more than one half of its gestation period by providing sera from definite species of animals as the inducer at the proper stage of development. The processes of normal development at four different but discrete phases have been described.
(1) Fertilized ovum (stage 1) is able to grow up to denuded blastocyst stage and attaches to the culture dish (stage 7) in balanced salt solution with bovine serum albumin as the sole macromolecule. (2) Embryoblast or inner cell mass (ICM) of denuded blastocyst (stage 7) is able to develop in fetal calf serum (FCS), human placenta cord serum (FCS), or sera from mouse (MS), rat (RS) or rabbit (RbS) to the early cylinder stage (stage 11). (3) The early egg cylinder stage (stage 11) of mouse embryo is able to grow in HCS and RS, but not in FCS nor RbS, to the stage of early somite stage (stage 15). (4) Beyond early somite stage (stage 15), mouse embryo is able to develop neural tissues in rat serum. The macromolecular nature of these growth factors in serum has been described (Hsu, 1980).
It indicates that the differential biological activity which induces the early mouse embryogenesis among the sera from different animal species is due to the various degree of sequence homology between the growth factor family among the different species of animals.