Ontogenesis and Morphological Diversification

SYNOPSIS. The role of development in constraining the directionalityand patterns of morphological evolution is examined. The natureof morphological variation and appearance of morphological noveltiesis determined by the epigenetic properties of the organism.Consideration of these properties has profound implicationsfor current theories of morphological evolution. Developmentalconstraints impose severe limitations on the gradualistic actionof directional selection. Evolutionis viewed as the result ofdifferential survival of morphological novelties. However, theproduction of morphological novelties by developmental programsis not random. This non-randomness in morphologically expressedgenetic mutations—an epigenetic property—can resultin phyletic trends, parallelisms and convergences.     

Ontogenesis of primordial germ cells

In sexually reproducing animals all gametes of either sex arise from primordial germ cells (PGC). PGC represent a small cell population, appearing early during embryo development. They represent a key cell population responsible for the survival and the evolution of a species. Indeed, the production of gametes will assure fertilisation and therefore the establishment of the next generation. Until recently only few laboratories were working on PGC biology. A new interest emerged since these cells have the ability to function as pluripotent stem cells when established as cell lines. Indeed, like embryonic stem cells (ESC), embryonic germ cells (EGC) are able to differentiate in a wide variety of tissues. In vivo, EGC are able, after injection into a host blastocyst cavity to colonise the inner cell mass and to participate in embryonic development. In vitro studies in human and mouse have also shown their capacity to differentiate into a large variety of cell types allowing the study of processes involved in cardiomyocyte, haematopoietic, neuronal and myogenic differentiation pathways. We present here the last updates of PGC ontogeny focusing mainly on the murine model.     

Ontogenesis of the scapula in marsupial mammals, with special emphasis on perinatal stages of didelphids and remarks on the origin of the therian scapula

The development of the scapula was studied in embryonic and postnatal specimens of Monodelphis domestica and perinatal specimens of Philander opossum, Caluromys philander, and Sminthopsis virginiae using histological sections and 3D reconstructions. Additionally, macerated skeletons of postnatal M. domestica were examined. This study focused on the detachment of the scapulocoracoid from the sternum and on the acquisition of a supraspinous fossa, a supraspinatus muscle, and a scapular spine, all these events associated with the origin of the therian shoulder girdle. In none of the specimens is there a continuity of the cartilaginous scapulocoracoid with the sternum, even though the structures are in close proximity, especially in S. virginiae. At birth, the first rib laterally presents a pronounced boss that probably contacts the humerus during certain movements. Only the acromial portion of the scapular spine, which originates from the anterior margin of the scapular blade, is preformed in cartilage. The other portion is formed by appositional bone ("Zuwachsknochen"), which expands from the perichondral ossification of the scapula into an intermuscular aponeurosis between the supra- and infraspinous muscles. This intermuscular aponeurosis inserts more or less in the middle of the lateral surface of the developing scapula. Thus, the floor of the supraspinous fossa is present from the beginning of scapular development, simultaneously with the infraspinous fossa. The homology of the therian spine with the anterior border of the sauropsid and monotreme scapula is questioned. We consider the dorsal portion (as opposed to the ventral or acromial portion) of the scapular spine a neomorphic structure of therian mammals.     

Glycosidases and Cerebellar Ontogenesis in the Rat

Abstract: Five glysosidases (α- and β-D-mannosidase, β-D-galactosidase, β- N -acetyl-glucosaminidase, and α-L-fucosidase) were studied during the postnatal development of the rat cerebellum. Each glycosidase has a particular developmental pattern. Transient decreases in the specific activities of β-mannosidase, β-D-galactosidase, and β-D- N -acetyl-glucosaminidase could be correlated with the phase of massive cell multiplication. A possible more specific role for α-D-mannosidase is discussed.     

Patterns of Biochemical Differentiation in Ontogenesis

Here we review original data on biochemical differentiation mechanisms. The patterns of the preprogrammed metabolism of the embryo are studied by comparing biochemical mechanisms in undifferentiated embryonic tissues in the course of differentiation and during the terminal establishment of a specialized tissue. This review is composed of three main sections corresponding to the specifity of biochemical differentiation. The first section covers the material on time-related isozyme pattern during skeletal muscle differentiation in a loach (a teleostean fish). The second section presents the data on incorporated activation, i.e., the appearance of a functional relationship between contractile proteins biosynthesis and the systems of glycogenolysis and glycogen synthesis during the development of chick embryo muscle. The third section covers the data on liver differentiation, the formation of the glycogen organelle with embedded enzymes of glycogen synthesis, and the degradation of chick and rat embryos during development.     

Interaction of Tonic and Phasic Pain in Rabbit Ontogenesis

In the experiments on the 20–25-day-old and adult rabbits, effects of tonic pain focus (a subcutaneous injection of formalin into leg dorsal surface) on behavioral and electrophysiological characteristics of acute pain were studied. The effect of the 40–60-min-long tonic pain was seen as a decrease of defensive reaction threshold and an increase of inhibitory effect of brain rewarding zones on evoked potential recorded in thalamus parafascicular complex in response to a nociceptive electrocutaneous stimulation in narcotized rabbits. The changes observed were biphasic and coincided in time with an enhancement of the earlier described [26] specific behavioral responses to formalin injection. It is established that the effect of tonic pain is more expressed by its intensity and duration in the 20–25-day-old than in adult rabbits.     

Evolutionary Reorganizations of Ontogenesis in Sea Urchins

The data published during recent 15–20 years on comparative, experimental and molecular embryology of unusually developing sea urchins have been reviewed. These animals are characterized by large lipid-rich eggs, highly modified embryogenesis, and the absence of a planktotrophic larva. Such a type of development is evolutionary advanced and arose independently in various phylogenetic lineages of the sea urchins.__________Translated from Ontogenez, Vol. 36, No. 3, 2005, pp. 182–189.Original Russian Text Copyright © 2005 by Desnitskiy.     

Evolutionary Transformations of Ontogenesis in Anuran Amphibians

A review of the recent published data on ontogenesis of direct developing and marsupial frogs. The development of these representatives of anuran amphibians seems to be evolutionary advanced and considerably differs from the development of species traditionally used in amphibian embryology.     

Ontogenesis of Spermatozoa Autoantigens in Guinea Pigs

The ontogenetic appearance of three independant spermatozoa autoantigens (S, P and T) has been studied in guinea pig germinal cells by immunofluorescence and comparison with cytology and histological structures during early maturation of seminiferous tubule cells. The maturation of 120 testes from 60 guinea pigs studied from day 1 to day 50 after birth has shown an evolution in 3 periods. During the first, or negative, period (day 1 to day 25), only spermatogonia (from day 1) and spermatocytes I (from day 16) are present. No significant PAS-positive formations are seen and no autoantigen is detected. During the second, or transitional, period (day 26 to 29), spermatocytes II and spermatids appear as well as paranuclear PAS-positive golgian proacrosomal and acrosomal granules. At the same time, the three autoantigens S, P and T are detected on the same PAS-positive formations with a frequency that increases from day to day. During the third, or positive, period (from day 30) all testes present cells with PAS-positive formation, progressive maturation of acrosomes in spermatids and appearance of spermatozoa (present on day 39) leading to the adult structure of seminiferous tubules. The three autoantigens are constantly present during that period. The simultaneous appearance of the 3 antigens in haploid germinal cells (spermatids and possibly spermatocytes II) as an early expression of cytodifferentiation and their total absence from diploid germinal cells (spermatogonia and spermatocytes I) seem to be of biological significance.     

Ontogenesis of lymph proteins in Drosophila melanogaster

• 1.1. The ontogenesis of proteins in Drosophila melanogaster has been studied by starch-gel electrophoresis.
• 2.2. A total of nineteen discrete fractions appear during development from egg to adult in the stock used.
• 3.3. Three protein fractions are present in the egg, one in the first-instar larva, six in the second-instar, eight in the early third-instar, eleven in the late third-instar, seven in the pupa and nine in the adult. The adult pattern is significantly different from the others.
• 4.4. There is a definite trend for small-molecule proteins to appear early in development, and the larger molecular compounds only in the later stages.
     

Comparative Ontogenesis of Brain Tryptamine, Serotonin, and Tryptophan

The pattern of ontogenetic development of tryptophan (TP), tryptamine (T), indole-3-acetic acid (IAA), 5-hydroxytryptamine (5-HT; serotonin), and 5-hydroxyindole-3-acetic acid (5-HIAA) in the brains of rats aged 1-45 days is presented. Analysis of the five components in each brain allows the calculation of the acid/amine and amine/amino acid ratios. These metabolic indexes are a useful tool to study and compare the metabolic origins and fates of both amines. The ontogenetic patterns of TP, T, and IAA are very similar, especially during the first week postpartum. The highest and lowest levels found for T were 2.2 ng/g and 0.1 ng/g at the 1st and 5th day, respectively. The temporal relationship between the T/TP and IAA/T ratios suggests the existence of mechanisms protecting T against monoamine oxidase (MAO) which develop in parallel to synaptogenesis. Significant correlations were found between TP and IAA during the whole period studied and between TP and T during the first week after birth. The 5-HT peak found during the first postpartum week could be due to a non-neuronal pool of 5-HT protected against MAO and possibly contained in mast cells. Preliminary determinations on leptomeningeal membranes suggest the existence of such a pool.     

Ontogenesis of Adenosine Deaminase Activity in Rat Brain

The activity of adenosine deaminase (ADA) was determined in whole brain of rats at the embryonic age of 15 days through to adulthood and in nine brain regions in rats 1 day old through to adulthood. In 1-day-old rats, the highest activity was seen in olfactory bulbs (550 +/- 15 nmol/mg protein/30 min) and this was 4.5-fold higher than that in the pons, which was the lowest. In adult animals, olfactory bulb still contained the greatest activity, which was about eightfold higher than hippocampus, which had the lowest. Except for hypothalamus, where ADA activity increased nearly twofold in rats between the ages of 1 and 50 days, significant decreases of as much as fivefold were found in whole brain, superior colliculus, cortex, hippocampus, cerebellum, olfactory bulbs, and olfactory nucleus. In contrast, ADA activity in pons and subcortex remained relatively constant throughout the developmental period. The Km values for ADA in whole brain at 18 days gestation (48 +/- 5 microM) were not significantly different from that observed in adult rats (38 +/- 7 microM), whereas the Vmax values decreased significantly from 339 +/- 9 to 108 +/- 8 nmol/mg protein/30 min. Taken together, the developmental patterns observed in the various brain regions appear not to correspond to any one particular process such as periods of rapid cell proliferation, cell death, synaptogenesis, or myelination. Nor do they correspond to known developmental profiles of transmitters, their receptors, or their metabolic enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Respiratory Cardiac Arrhythmia in Postnatal Ontogenesis of Rats

Development of the respiratory cardiac arrhythmia and the role of parasympathetic nervous system in its origin have been studied in rats aged from 4–6 days to 6 months of life. In rat pups of the first week of life, small fluctuations of cardiac rhythm were observed with the frequency close to fluctuations of respiratory rhythm. However, at this age they had neither regular character nor clear connection with phases of the respiratory cycle. On the 2–3rd week the amplitude of fluctuations rose and their association with respiration was established; however, unlike the respiratory arrhythmia observed in other animals and human, in rat pups there was deceleration but not acceleration of heart beating. By to the 6-week age the respiratory arrhythmia reached the maximal values, then its amplitude began to decrease. Bilateral transection of the vagus nerves in rat pups did not cause reduction of the respiratory arrhythmia. Thus, in rats the central influences on the heart can be transduced by bypassing the system of vagus nerves.