In search of female sterility causes in the tetraploid and pentaploid cytotype of Pilosella brzovecensis (Asteraceae)

Within the agamic Pilosella complex, apomixis (asexual reproduction through seed) involves apospory, parthenogenesis, and autonomous endosperm development. Observations of reproductive biology in P. brzovecensis throughout four growing seasons in the garden have shown that both tetraploid and pentaploid plants of this species do not produce viable seeds and reproduce exclusively vegetatively by underground stolons. The reasons for the seed development failure were unknown, therefore our research focused on the analysis of reproductive events in the ovules of this taxon. We found that apospory was initiated in the ovules of both cytotypes. Multiple aposporous initial (AI) cells differentiated in close proximity to the megaspore mother cell (MMC) and suppressed megasporogenesis at the stage of early prophase I. However, none of the AI cells was able to further develop into a multi-nucleate aposporous embryo sac (AES) due to the inhibition of mitotic divisions. It was unusual that callose was accumulated in the walls of AI cells and its synthesis was most likely associated with a response to the dysfunction of these cells. Callose is regarded as the isolating factor and its surprising deposition in the ovules of P. brzovecensis may signal disruption of reproductive processes that cause premature termination of the aposporous development pathway and ultimately lead to ovule sterility. The results of our embryological analysis may be the basis for undertaking advanced molecular studies aimed at fully understanding of the causes of female sterility in P. brzovecensis.

Clinical Embryology of Human Larynx for Conservative Compartmental Surgery

The volume shows the morphogenesis and differentiation of the human larynx during the fetal period. This knowledge is relevant to understand laryngeal functions as well as the diffusion of cancer and the therapy of low stage cancer. Through embryological analysis, the anatomical basis of laryngeal functions may be best recognized and consequent indications may be given to perform conservative compartmental surgery. Each chapter of the volume describes a developmental step and compares the findings with the adult condition. Introductory remarks and comments to each chapter are completed by captions to individual figures, so that the text and images are offered to the reader as a single unit. He has authored several full papers, including papers on journals with impact factor, and presentations at scientific meetings.

Morphogenesis of propagules in viviparous species Bryophyllum daigremontianum and B. calycinum

The propagule development in two viviparous <em>Bryophyllum</em> species: <em>B. daigremontianum</em> and <em>B. calycinum</em> (<em>Crassulaceae</em>) has been found to proceed via embryoidogenesis (somatic embryo). In both species, all propagule organs arise from the dormant meristem derivatives, but there are morphogenetic differences at the latest developmental stages (in adventitious root initiation). In both species, the propagule genesis proceeds through the "globular", heartshaped and torpedoshaped stages. Comparative morphological and embryological analysis of propagules in the species in question and sexual embryos revealed a strong similarity in their developmental patterns not with standing their morphological variability. It has been suggested that two <em>Bryophyllum</em> species carry the "dormancy" gene. The present study has confirmed that vegetative propagules of the flowering plants can be either embryoids or buds.

Evolutionary developmental biology of the tetrapod limb

New insights into the origin of the tetrapod limb, and its early development and patterning, are emerging from a variety of fields. A wide diversity of approaches was reported at the BSDB Spring Symposium on `The Evolution of Developmental Mechanisms' (Edinburgh, 1994); here I review the contributions these various approaches have made to understanding the evolutionary developmental biology of the tetrapod limb. The fields covered included palaeontology, descriptive embryology, experimental embryological analysis of interactions within developing limbs plus description and manipulation of homeobox gene expression in early limb buds. Concepts are equally varied, sometimes conflicting, sometimes overlapping. Some concern the limb `archetype' (can the palaeontologists and morphologists still define this with precision? how far is there a limb developmental bauplan?); others are based on identification of epigenetic factors (eg secondary inductions), as generating pattern; while yet others assume a direct gene-morphology relationship. But all the contributors ask the same compelling question: can we explain both the similarity (homology) and variety of tetrapod limbs (and the fins of the Crossopterygians) in terms of developmental mechanisms?

The albino-deletion complex in the mouse defines genes necessary for development of embryonic and extraembryonic ectoderm

A detailed embryological analysis has been undertaken on embryos carrying the c4FR60Hd-, c5FR60Hg- or c2YPSj-albino deletions of mouse chromosome 7. Embryos homozygous for the c4FR60Hd deletion are abnormal at day 7.5 of gestation. The extraembryonic ectoderm does not develop, and primitive-streak formation and mesoderm production do not occur. In contrast, extensive development of the extraembryonic ectoderm, as well as mesoderm production, are observed in the c5FR60Hg- and c2YPSj-homozygous embryos. The mesoderm does not, however, organize into somites and the neural axis does not form. The embryos are grossly abnormal by day 8.5 of development. There are two other albino deletions (c6H and c11DSD) that are known to affect the embryo around the time of gastrulation (Niswander et al. 1988), and the lethal phenotype observed for the c4FR60Hd-homozygous embryos is similar to that described for c6H-homozygous embryos, whereas the c5FR60Hg- and c2YPSj-homozygous embryos display a phenotype that is similar to c11DSD-homozygous embryos. A detailed complementation analysis using these five deletions revealed that the c5FR60Hg, c2YPSj and c11DSD deletions could partially complement the phenotype produced by the c4FR60Hd and c6H deletions in any combination. Extensive development of the extraembryonic structures and production of mesoderm occurs in the compound heterozygotes. These results suggest that the distal breakpoints of the c5FR60Hg, c2YPSj and c11DSD deletions lie more proximal than the distal breakpoints of the c4FR60Hd and c6H deletions.(ABSTRACT TRUNCATED AT 250 WORDS)

The albino deletion complex and early postimplantation survival in the mouse

The albino deletion complex in the mouse represents 37 overlapping chromosomal deficiencies that have been arranged into at least twelve complementation groups. Many of the deletions cover regions of chromosome 7 that contain genes necessary for early embryonic development. The work reported here concentrates on two of these deletions (c6H, c11DSD), both of which were known to be lethal around the time of gastrulation when homozygous. A detailed embryological analysis has revealed distinct differences in the lethal phenotype associated with the c6H and c11DSD deletions. c6H homozygous embryos are grossly abnormal at day 7.5 of gestation, whereas c11DSD homozygous embryos appear abnormal at day 8.5 of gestation. There is no development of the extraembryonic ectoderm in c6H homozygotes, whereas extensive development of this tissue type occurs in c11DSD homozygotes. The visceral endoderm is abnormally shaped and the parietal endoderm appears to be overproduced in c6H homozygotes; these structures are not affected in c11DSD homozygotes. The embryonic ectoderm is runted in both types of embryo and it is not possible to obtain homozygous embryo-derived stem-cell lines for either deletion. Mesoderm formation occurs in the c11DSD but not in the c6H homozygotes. The c11DSD deletion chromosome complements the c6H chromosome in that the lethal phenotype of the compound heterozygote is similar to that of the c11DSD homozygote. These results suggest that a gene(s) necessary for normal development of the extraembryonic ectoderm is present in the c11DSD but deficient in the c6H deletion chromosome.