Style antigens of Prunus avium L.

Antiserum to a protein fraction of an extract of mature styles of P. avium cv. Lambert (S ₃ S ₄) was raised in rabbits. Two major antigenic components of the style extracts were detected by immunoelectrophoresis and immunodiffusion. The presence of one antigen (S-antigen) correlated with a particular S-genotype (S ₃ S ₄). This antigen is restricted to mature styles of P. avium. The second antigen (P-antigen) was detected in styles of all Prunus species examined, but not in styles of other species of the Rosaceae. The S-antigen is positively charged and the P-antigen negatively charged at pH 8.8.     

Natural hybridization in the sea urchin genus Pseudoboletia between species without apparent barriers to gamete recognition

Marine species with high dispersal potential often have huge ranges and minimal population structure. Combined with the paucity of geographic barriers in the oceans, this pattern raises the question as to how speciation occurs in the sea. Over the past 20 years, evidence has accumulated that marine speciation is often linked to the evolution of gamete recognition proteins. Rapid evolution of gamete recognition proteins in gastropods, bivalves, and sea urchins is correlated with gamete incompatibility and contributes to the maintenance of species boundaries between sympatric congeners. Here, we present a counterexample to this general pattern. The sea urchins Pseudoboletia indiana and P. maculata have broad ranges that overlap in the Indian and Pacific oceans. Cytochrome oxidase I sequences indicated that these species are distinct, and their 7.3% divergence suggests that they diverged at least 2 mya. Despite this, we suspected hybridization between them based on the presence of morphologically intermediate individuals in sympatric populations at Sydney, Australia. We assessed the opportunity for hybridization between the two species and found that (1) individuals of the two species occur within a meter of each other in nature, (2) they have overlapping annual reproductive cycles, and (3) their gametes cross-fertilize readily in the laboratory and in the field. We genotyped individuals with intermediate morphology and confirmed that many were hybrids. Hybrids were fertile, and some female hybrids had egg sizes intermediate between the two parental species. Consistent with their high level of gamete compatibility, there is minimal divergence between P. indiana and P. maculata in the gamete recognition protein bindin, with a single fixed amino acid difference between the two species. Pseudoboletia thus provides a well-characterized exception to the idea that broadcast spawning marine species living in sympatry develop and maintain species boundaries through the divergence of gamete recognition proteins and the associated evolution of gamete incompatibility.     

The active evolutionary lives of echinoderm larvae

Echinoderms represent a researchable subset of a dynamic larval evolutionary cosmos. Evolution of echinoderm larvae has taken place over widely varying time scales from the origins of larvae of living classes in the early Palaeozoic, approximately 500 million years ago, to recent, rapid and large-scale changes that have occurred within living genera within a span of less than a million years to a few million years. It is these recent evolutionary events that offer a window into processes of larval evolution operating at a micro-evolutionary level of evolution of discrete developmental mechanisms. We review the evolution of the diverse larval forms of living echinoderms to outline the origins of echinoderm larval forms, their diversity among living echinoderms, molecular clocks and rates of larval evolution, and finally current studies on the roles of developmental regulatory mechanisms in the rapid and radical evolutionary changes observed between closely related congeneric species.     

Axial patterning of the pentaradial adult echinoderm body plan

Adult echinoderms possess a highly diverged, pentaradial body plan. Developmental mechanisms underlying this body plan are completely unknown, but are critical in understanding how echinoderm pentamery evolved from bilateral ancestors. These mechanisms are difficult to study in indirect-developing species; in this study, we use the direct-developing sea urchin Heliocidaris erythrogramma, whose accelerated adult development can be perturbed by NiCl₂. We introduce a new nomenclature for the adult echinoderm axes to facilitate discussion of the radially symmetric body plan and the events required to pattern it. In sea urchins, the adult oral–aboral axis is often conflated with the long axes of the five rays; we identify these as distinct body axes, the proximodistal (PD). In addition, we define a circular axis, the circumoral (CO), along which the division into five sectors occurs. In NiCl₂-treated larvae, aspects of normal PD pattern were retained, but CO pattern was abolished. Milder treatments resulted in relatively normal juveniles ranging from biradial to decaradial. NiCl₂ treatment had no effect either on mesodermal morphology or on the ectodermal gene expression response to an inductive mesodermal signal. This suggests that the mesoderm does not mediate the disruption of CO patterning by NiCl₂. In contrast, mesodermal signaling may explain the presence of PD pattern in treated larvae. However, variations in appendage pattern suggest that ectodermal signals are also required. We conclude that CO patterning in both germ layers is dependent on ectodermal events and PD patterning is controlled by mutual ectoderm–mesoderm signaling.     

Maternal factors and the evolution of developmental mode: Evolution of oogenesis in Heliocidaris erythrogramma

 Evolutionary change in developmental mode in sea urchins is closely tied to an increase in maternal provisioning. We examined the oogenic modifications involved in production of a large egg by comparison of oogenesis in congeneric sea urchins with markedly different sized oocytes and divergent modes of development. Heliocidaris tuberculata has small eggs (95 μm diameter) and the ancestral mode of development through feeding larvae, whereas H. erythrogramma has large eggs (430 μm diameter) and highly modified non-feeding lecithotrophic larvae. Production of a large egg in H. erythrogramma involved both conserved and divergent mechanisms. The pattern and level of vitellogenin gene expression is similar in the two species. Vitellogenin processing is also similar with the gonads of both species incorporating yolk protein from coelomic and hemal stores into nutritive cells with subsequent transfer of this protein into yolk granules in the developing vitellogenic oocyte. Immunocytology of the eggs of both Heliocidaris species indicates they incorporate similar levels of yolk protein. However, H. erythrogramma has evolved a highly divergent second phase of oogenesis characterised by massive deposition of non-vitellogenic material including additional maternal protein and lipid. Maternal provisioning in H. erythrogramma exhibits recapitulation of the ancestral vitellogenic program followed by a novel oogenic phase with hypertrophy of the lipogenic program being a major contributor to the increase in egg size. Received: 12 August 1998 / Accepted: 25 November 1998     

Unbalanced translocation 8;Y (45,X,dic(Y;8)(q11.23;p23.1)): case report and review of terminal 8p deletions

A boy with a rare unbalanced de novo Y/autosome translocation is presented. Main clinical features in the boy comprised a psychomotor delay, talipes planus, a dolichocephalus, low set and retroverted ears, supraorbital fullness of subcutaneous tissue and a bulbous nasal tip. Chromosomal analysis on amniocytes showed a single X chromosome and a derivative 8p (Karyotype: 45,X,der(8)GTG). The following DAPI staining revealed the inactivated centromere of the chromosome Y located on 8p and the absence of heterochromatic material Yq. Microsatellite analysis on fetal blood DNA using markers between SRY on Yp and DYS 240 on Yq proved presence of the spermatogenetic relevant factors. A terminal deletion of 8p was confirmed by FISH postnatally. Molecular genetic reassessment revealed the monosomy 8p to be of maternal origin; the translocation can thus be proven to have occurred in the zygote. The breakpoint in 8p was localised distal to GATA4, a gene which is involved in heart development; the finding that our patient did not suffer from cardiac problems agrees with the disomic presence of GATA4. Only the application of FISH combined with microsatellite analysis allowed a precise correlation between clinical phenotype and a subtle deletion of terminal 8p; furthermore, a recurrence risk for the parents could be excluded.     

Adrenocortical responses to ACTH in neonatal rats: effect of hypoxia from birth on corticosterone,StAR, and PBR

The adrenocortical response to hypoxia may be a critical component of the adaptation to this common neonatal stress. Little is known about adrenal function in vivo in hypoxic neonates. The purpose of this study was to evaluate adrenocortical responses to ACTH in suckling rat pups exposed to hypoxia from birth to 5-7 days of age compared with normoxic controls. We also evaluated potential cellular controllers of steroidogenic function in situ. In 7-day-old pups at 0800, hypoxia from birth resulted in increased basal (12.2 +/- 1.4 ng/ml; n = 12) and ACTH-stimulated (94.0 +/- 9.4 ng/ml; n = 14) corticosterone levels compared with normoxic controls (basal = 8.3 +/- 0.5 ng/ml; n = 11; stimulated = 51.3 +/- 3.8 ng/ml; n = 8). This augmentation occurred despite no significant difference in plasma ACTH levels in normoxic vs. hypoxic pups before (85 +/- 4 vs. 78 +/- 8 pg/ml) or after (481 +/- 73 vs. 498 +/- 52 pg/ml) porcine ACTH injection (20 microg/kg). This effect was similar in the afternoon at 6 days of age and even greater at 5 days of age at 0800. The aldosterone response to ACTH was not augmented by exposure to hypoxia from birth. Adrenocortical hypoxia-inducible factor (HIF)-1alpha mRNA was undetectable by RT-PCR. Steroidogenic acute regulatory (StAR) protein in adrenal subcapsules (zona fasciculata/reticularis) was augmented by exposure to hypoxia; this effect was greatest at 5 days of age. Peripheral-type benzodiazepine receptor (PBR) protein was also increased at 6 and 7 days of age in pups exposed to hypoxia from birth. We conclude that hypoxia from birth results in an augmentation of the corticosterone but not aldosterone response to ACTH. This effect appears to be mediated at least in part by an increase in controllers of mitochondrial cholesterol transport (StAR and PBR) and to occur independently of measurable changes in endogenous plasma ACTH. The augmentation of the corticosterone response to acute increases in ACTH in hypoxic pups is likely to be an important component of the overall physiological adaptation to hypoxia in the neonate.     

The orientation of cell division influences cell-fate choice in the developing mammalian retina

Asymmetric segregation of cell-fate determinants during cell division plays an important part in generating cell diversity in invertebrates. We showed previously that cells in the neonatal rat retina divide at various orientations and that some dividing cells asymmetrically distribute the cell-fate determinant Numb to the two daughter cells. Here, we test the possibility that such asymmetric divisions contribute to retinal cell diversification. We have used long-term videomicroscopy of green-fluorescent-protein (GFP)-labeled retinal explants from neonatal rats to visualize the plane of cell division and follow the differentiation of the daughter cells. We found that cells that divided with a horizontal mitotic spindle, where both daughter cells should inherit Numb, tended to produce daughters that became the same cell type, whereas cells that divided with a vertical mitotic spindle, where only one daughter cell should inherit Numb, tended to produce daughters that became different. Moreover, overexpression of Numb in the dividing cells promoted the development of photoreceptor cells at the expense of interneurons and Müller glial cells. These findings indicate that the plane of cell division influences cell-fate choice in the neonatal rat retina and support the hypothesis that the asymmetric segregation of Numb normally influences some of these choices.