From a Single Cell to Segmental Structures

Beginning with Aristotle 2400 years ago, research on crustacean embryology has a long tradition. Rathke’s 1829 landmark study on the noble crayfish initiated modern approaches. Crustaceans in general—and most of their large taxa—show a great diversity in all stages of their developmental pathways from the zygote up to the adult animal. This chapter describes the various modes of cleavage, gastrulation, germ band formation, and segmentation found in crustacean taxa. Cleavage is either total, partial, or mixed. Total cleavage can be indeterminate, without predictable cell lineage; or determinate, with a stereotyped cell division pattern. Gastrulation modes can also vary to a high degree. One finds invagination, epiboly, immigration, delamination, and a mix of some of these. Likewise, the stages of germ layer separation and the number of cells that initiate gastrulation differ. In yolk-rich eggs, a germ disk forms at the future ventral side of the embryo, and the axes and orientation of the germ are recognizable. Through elongation in the anteroposterior direction by a posterior growth zone and intercalary cell divisions, the germ disk is transformed into the germ band. As a result of a unique, stereotyped cell division pattern in the germ band of malacostracans, germ band growth and the segmentation process up to the differentiation of neuronal precursors and early limb anlagen can be analyzed at the level of individual cells. Recent morphological and molecular techniques allow a very detailed spatiotemporal resolution of developmental processes and they offer new perspectives on long-standing morphological questions.

Cell-division pattern and phylogenetic analyses of a new ciliate genus Parasincirra n. g. (Protista, Ciliophora, Hypotrichia), with report of a new soil species, P. sinica n. sp. found from northwest China

Background: Ciliated protists, a huge assemblage of unicellular eukaryotes, are extremely diverse and play important roles in ecosystem in almost all kinds of habitats. Even though there is a growing recognition that those organisms associate with many ecological or environmental processes, their biodiversity, due to many reasons, is poorly understood and many biotopes (e.g. the soil in desert area in Asia) remain largely unknown or unconsidered. Here we document an undescribed form found in sludge soil in a halt-desert inland in China and the taxonomic/ morphogenetic surveys indicate that it represents a new genus and new species, Parasincirra sinica n. g., n. sp. which is supported also by molecular data.Results: This new, monotypic genus Parasincirra n. g. is defined by having three frontal cirri, an amphisiellid median cirral row about as long as the adoral zone, one short frontoventral cirral row, cirrus III/2 and transverse cirri present, buccal and caudal cirri absent, one right and one left marginal row and three dorsal kineties. The main morphogenetic features of the new taxon are: (1) frontoventral-transverse cirral anlagen II to VI are formed in primary mode; (2) the amphisiellid median cirral row is formed by anlagen V and VI, while the frontoventral row is generated from anlage IV; (3) cirral streaks IV to VI generate one transverse cirrus each; (4) frontoventral-transverse cirral anlage II generates one or two cirri, while the posterior one will be absorbed in late stages, that is, no buccal cirrus is formed; (5) the posterior part of the parental adoral zone of membranelles is renewed; (6) dorsal morphogenesis follows a typical Gonostomum-pattern; and (7) the macronuclear nodules fuse to form a single mass. Based on the SSU rDNA information, analyses of the phylogenetic relationship inferred from Bayesian inference and maximum likelihood analyses were unable to outline the exact position of this new form among some other species of related genera which are generally assigned in the family Amphisiellidae Jankowski, 1979. The morphological/ morphogenetical differences between the new genus/species and Uroleptoides Wenzel, 1953/ Parabistichella Jiang et al., 2013, as well as other amphisiellids, clearly support the validity of the establishment of this new genus Parasincirra.

Cell-division pattern and phylogenetic position of a new ciliate genus Parasincirra n. g. (Protista, Ciliophora, Hypotrichia), with report of a new soil species, P. sinica n. sp. found from northwest China

Ciliated species, unicellular eukaryotes, are extremely diverse and occupy a very broad spectrum of ecological niches. Even though there is a growing recognition that enormous ciliates associates with key ecosystem processes in different niches, their diversity is not well understood. One reason is that ciliates are very tiny and may often be overlooked in routine biodiversity survey. Furthermore, the morphological and genetic diversity of ciliates per se is vast and dwarfs that among other multicellular eukaryotes. Here, we present the study of a new stichotrichid ciliate, Parasincirra sinica n. g., n. sp. based on classical living morphology, infraciliature, ontogenesis analyses and a comprehensive phylogenetic study, and enhance understanding of ciliates diversity in sludge soil. This new, monotypic genus is defined by having a bipartite adoral zone of membranelles, three frontal cirri, an amphisiellid median cirral row about as long as, or slightly longer than, the adoral zone, one short frontoventral cirral row, cirrus III/2 and transverse cirri present, buccal cirrus and caudal cirri absent, three dorsal kineties. The main morphogenetic features are: (1) five frontoventral-transverse cirral anlagen (excluding undulating membranes anlage) are formed in primary mode; (2) the amphisiellid median cirral row is formed by anlagen V and VI, while the frontoventral row is generated from anlage IV; (3) cirral streaks IV to VI generate one transverse cirrus each; (4) frontoventral-transverse cirral anlage II generates one or two cirri, while the posterior one will be absorbed in late stages, that is, no buccal cirrus is formed; (5) the posterior part of the parental adoral zone of membranelles is renewed; (6) dorsal morphogenesis follows a typical Gonostomum -pattern. Based on the SSU rDNA information, analyses of the phylogenetic relationship inferred from Bayesian inference and maximum likelihood analyses were unable to outline the exact position of this new form among some other species of related genera which are generally assigned in the family Amphisiellida . The morphological/ morphogenetical differences between the new genus/species and Uroleptoides / Parabistichella , as well as other amphisiellids, clearly support the validity of the establishment of this new genus Parasincirra .

Cell-division pattern and phylogenetic position of a new ciliate genus Parasincirra n. g. (Protista, Ciliophora, Hypotrichia), with report of a new soil species, P. sinica n. sp. found from northwest China

Background Ciliated species, unicellular eukaryotes, are extremely diverse and occupy a very broad spectrum of ecological niches. Even though there is a growing recognition that enormous ciliates associates with key ecosystem processes in different niches, their diversity is not well understood. One reason is that ciliates are very tiny and may often be overlooked in routine biodiversity survey. Furthermore, the morphological and genetic diversity of ciliates per se is vast and dwarfs that among other multicellular eukaryotes. A new stichotrichid ciliate, Parasincirra sinica n. g., n. sp. is based on classical living morphology, infraciliature, ontogenesis analyses and a comprehensive phylogenetic studies, and enhance understanding of ciliates diversity in sludge soil.Results This new, monotypic genus is defined by having a bipartite adoral zone of membranelles, three frontal cirri, an amphisiellid median cirral row about as long as, or slightly longer than, the adoral zone, one short frontoventral cirral row, cirrus III/2 and transverse cirri present, buccal cirrus and caudal cirri absent, one right and one left marginal row and three dorsal kineties. The morphogenetic features are: (1) five frontoventral-transverse cirral anlagen (excluding undulating membranes anlage) are formed in primary mode; (2) the amphisiellid median cirral row is formed by anlagen V and VI, while the frontoventral row is generated from anlage IV; (3) cirral streaks IV to VI generate one transverse cirrus each; (4) frontoventral-transverse cirral anlage II generates one or two cirri, while the posterior one will be absorbed in late stages, that is, no buccal cirrus is formed; (5) the posterior part of the parental adoral zone of membranelles is renewed; (6) dorsal morphogenesis follows a typical Gonostomum -pattern; and (7) the macronuclear nodules fuse to form a single mass. Based on the SSU rDNA information, analyses of the phylogenetic relationship inferred from Bayesian inference and maximum likelihood analyses were unable to outline the exact position of this new form among some other species of related genera which are generally assigned in the family Amphisiellida. The morphological/ morphogenetical differences between the new genus/species and other amphisiellids, clearly support the validity of the establishment of this new genus Parasincirra .

Noncanonical auxin signaling regulates cell division pattern during lateral root development

In both plants and animals, multiple cellular processes must be orchestrated to ensure proper organogenesis. The cell division patterns control the shape of growing organs, yet how they are precisely determined and coordinated is poorly understood. In plants, the distribution of the phytohormone auxin is tightly linked to organogenesis, including lateral root (LR) development. Nevertheless, how auxin regulates cell division pattern during lateral root development remains elusive. Here, we report that auxin activates Mitogen-Activated Protein Kinase (MAPK) signaling via transmembrane kinases (TMKs) to control cell division pattern during lateral root development. Both TMK1/4 and MKK4/5-MPK3/6 pathways are required to properly orient cell divisions, which ultimately determine lateral root development in response to auxin. We show that TMKs directly and specifically interact with and phosphorylate MKK4/5, which is required for auxin to activate MKK4/5-MPK3/6 signaling. Our data suggest that TMK-mediated noncanonical auxin signaling is required to regulate cell division pattern and connect auxin signaling to MAPK signaling, which are both essential for plant development.

Variations in the anatomical and branching pattern of the left coronary artery: a cadaveric study

Background: Coronary arteries are the branch of ascending aorta and it is the main arterial supply of the myocardium of the heart. Left coronary artery (LCA) usually arises from left posterior aortic sinus. The site of manifestation of myocardial infarction depends on the occlusion of an artery or its branches involved in atherosclerosis. To know the site of lesion and occlusion of the particular artery, detailed anatomy of its course, branches and variations to be studied in detail.Methods: Study was conducted on 55 heart specimens in Department of Anatomy at Sri Siddhartha Medical College (SSMC), Sri Siddhartha Academy of Higher Education (SSAHE). The left coronary artery was dissected carefully, and it was traced from its origin. Any variation in the course and branching pattern was recorded and photographed.Results: No variation was found in the origin of LCA. In the present study, the most frequent division pattern of the left coronary artery was observed as the bifurcation in 30 specimens (54.54%) followed by trifurcation in 23 specimens (41.82%). Tetrafurcation and pentafurcation of LCA were observed in one specimen each (1.82%).Conclusions: Our study tries to focus on branching pattern of LCA for the better knowledge of accurate diagnosis and therapeutic intervention in the management of coronary artery diseases.

Towards an understanding of spiral patterning in the Sargassum muticum shoot apex

In plants and parenchymatous brown algae the body arises through the activity of an apical meristem (a niche of cells or a single cell). The meristem produces lateral organs in specific patterns, referred to as phyllotaxis. In plants, two different control mechanisms have been proposed – one is position-dependent and relies on morphogen accumulation at future organ sites whereas the other is a lineage-based system which links phyllotaxis to the apical cell division pattern. Here we examine the apical patterning of the brown alga, Sargassum muticum, which exhibits spiral phyllotaxis (137.5° angle) and an unlinked apical cell division pattern. The Sargassum apex presents characteristics of a self-organising system, similar to plant meristems. We were unable to correlate the plant morphogen auxin with bud positioning in Sargassum, nor could we predict cell wall softening at new bud sites. Our data suggests that in Sargassum muticum there is no connection between phyllotaxis and the apical cell division pattern indicating a position-dependent patterning mechanism may be in place. The underlying mechanisms behind the phyllotactic patterning appear to be distinct from those seen in plants.SummaryThe brown alga Sargassum muticum displays spiral phyllotaxis developed from a position-dependent self-organising mechanism, different from that understood in plants.

Lineage tracing of the bivalve shell field with special interest in the descendants of the 2d blastomere

By evolving bilaterally separated shell plates, bivalves acquired a unique body plan in which their soft tissues are completely protected by hard shell plates. In this unique body plan, mobility between the separated shell plates is provided by novel structures such as a ligament and adductor muscles. As a first step towards understanding how the bivalve body plan was established, we investigated the development of the separated shell plates and ligament. Over 100 years ago, it was hypothesized that the development of separated shell plates is tightly linked with the unique cell cleavage (division) pattern of bivalves during development, wherein each bilateral daughter cell of the 2d descendant 2d 1121 develops into one of the bilateral shell fields. In this study, we tested this hypothesis by tracing the cell lineages of the Japanese purple mussel Septifer virgatus . Although the shell fields were found to be exclusively derived from the bilateral descendant cells of 2d: 2d 11211 and 2d 11212 , the descendants of these cells were not restricted to shell fields alone, nor were they confined to the left or right side of the shell field based on their lineage. Our study demonstrated that ligament cells are also derived from 2d 11211 and 2d 11212 , indicating that the ligament cells emerged as a subpopulation of shell field cells. This also suggests that the establishment of the novel developmental system for the ligament cells was critical for the evolution of the unique body plan of bivalves.