Characterization and developmental regulation of a gene expressed specifically in the skeletogenic lineage of the sea urchin embryo

The sea urchin embryonic skeleton, or spicule, is deposited by mesenchymal progeny of four precursor cells, the micromeres, which are determined to the skeletogenic pathway by a process known as cytoplasmic localization. A gene encoding one of the major products of the skeletogenic mesenchyme, a prominent 50 kD protein of the spicule matrix, has been characterized in detail. cDNA clones were first isolated by antibody screening of a phage expression library, followed by isolation of homologous genomic clones. The gene, known as SM50, is single copy in the sea urchin genome, is divided into two exons of 213 and 1682 bp, and is expressed only in skeletogenic cells. Transcripts are first detectable at the 120 cell stage, shortly after the segregation of the skeletogenic precursors from the rest of the embryo. The SM50 open reading frame begins within the first exon, is 450 amino acids in length, and contains a loosely repeated 13 amino acid motif rich in acidic residues which accounts for 45% of the protein and which is possibly involved in interaction with the mineral phase of the spicule.

The important cis-acting regions of the SM50 gene necessary for proper regulation of expression were identified by gene transfer experiments. A 562 bp promoter fragment, containing 438 bp of 5' promoter sequence and 124 bp of the SM50 first exon (including the SM50 initiation codon), was both necessary and sufficient to direct high levels of expression of the bacterial chloramphenicol acetyltransferase (CAT) reporter gene specifically in the skeletogenic cells. Removal of promoter sequences between positions -2200 and -438, and of transcribed regions downstream of +124 (including the SM50 intron), had no effect on the spatial or transcriptional activity of the transgenes.

Regulatory proteins that interact with the SM50 promoter were identified by the gel retardation assay, using bulk embryo mesenchyme blastula stage nuclear proteins. Five protein binding sites were identified and mapped to various degrees of resolution. Two sites are homologous, may be enhancer elements, and at least one is required for expression. Two additional sites are also present in the promoter of the aboral ectoderm specific cytoskeletal actin gene CyIIIa; one of these is a CCAA T element, the other a putative repressor element. The fifth site overlaps the binding site of the putative repressor and may function as a positive regulator by interfering with binding of the repressor. All of the proteins are detectable in nuclear extracts prepared from 64 cell stage embryos, a stage just before expression of SM50 is initiated, as well as from blastula and gastrula stage; the putative enhancer binding protein may be maternal as well.

Signal transduction, regulation, and developmental logic of EGFR signalling in C. elegans

RTKs-mediated signaling systems and the pathways with which they interact (e.g., those initiated by G protein-mediated signaling) involve a highly cooperative network that sense a large number of cellular inputs and then integrate, amplify, and process this information to orchestrate an appropriate set of cellular responses. The responses include virtually all aspects of cell function, from the most fundamental (proliferation, differentiation) to the most specialized (movement, metabolism, chemosensation). The basic tenets of RTK signaling system seem rather well established. Yet, new pathways and even new molecular players continue to be discovered. Although we believe that many of the essential modules of RTK signaling system are rather well understood, we have relatively little knowledge of the extent of interaction among these modules and their overall quantitative importance.

My research has encompassed the study of both positive and negative signaling by RTKs in C. elegans. I identified the C. elegans S0S-1 gene and showed that it is necessary for multiple RAS-mediated developmental signals. In addition, I demonstrated that there is a SOS-1-independent signaling during RAS-mediated vulval differentiation. By assessing signal outputs from various triple mutants, I have concluded that this SOS-1-independent signaling is not mediated by PTP-2/SHP-2 or the removal of inhibition by GAP-1/ RasGAP and it is not under regulation by SLI-1/Cb1. I speculate that there is either another exchange factor for RASor an as yet unidentified signaling pathway operating during RAS-mediated vulval induction in C. elegans.

In an attempt to uncover the molecular mechanisms of negative regulation of EGFR signaling by SLI-1/Cb1, I and two other colleagues codiscovered that RING finger domain of SLI-1 is partially dispensable for activity. This structure-function analysis shows that there is an ubiquitin protein ligase-independent activity for SLI-1 in regulating EGFR signaling. Further, we identified an inhibitory tyrosine of LET-23/ EGFR requiring sli-1(+)for its effects: removal of this tyrosine closely mimics loss of sli-1 but not loss of other negative regulator function.

By comparative analysis of two RTK pathways with similar signaling mechanisms, I have found that clr-1, a previously identified negative regulator of egl-15 mediated FGFR signaling, is also involved in let-23 EGFR signaling. The success of this approach promises a similar reciprocal test and could potentially extend to the study of other signaling pathways with similar signaling logic.

Finally, by correlating the developmental expression of lin-3 EGF to let-23 EGFR signaling activity, I demonstrated the existence of reciprocal EGF signaling in coordinating the morphogenesis of epithelia. This developmental logic of EGF signaling could provide a basis to understand a universal mechanism for organogenesis.

Effects of maternal age and size on embryonic energy reserves, developmental timing, and fecundity in quillback rockfish (Sebastes maliger)

Maternal effects on the quality of progeny can have direct impacts on population productivity. Rockfish are viviparous and the oil globule size of larvae at parturition has been shown to have direct effects on time until starvation and growth rate. We sampled embryos and preparturition larvae opportunistically from 89 gravid quillback rockfish (Sebastes maliger) in Southeast Alaska. Because the developmental stage and sampling period were correlated with oil globule size, they were treated as covariates in an analysis of maternal age, length, and weight effects on oil globule size. Maternal factors were related to developmental timing for almost all sampling periods, indicating that older, longer, and heavier females develop embryos earlier than younger, shorter, or lighter ones. Oil globule diameter and maternal length and weight were statistically linked, but the relationships may not be biologically significant. Weight-specific fecundity did not increase with maternal size or age, suggesting that reproductive output does not increase more quickly as fish age and grow. Age or size truncation of a rockfish population, in which timing of parturition is related to age and size, could result in a shorter parturition season. This shortening of the parturition season could make the population vulnerable to fluctuating environmental conditions.

The conventional facade solution during the developmental period in Gipuzkoa: decline (and end) of a construction system

The article analyses the construction process, the evolution and the disturbing future of the facade enclosure of the collective housing constructions built during the developmental period in the province of Gipuzkoa. 128 residential complexes were checked, and 17 people who directly took part in the construction of many of these buildings were interviewed. After examining the material and elements that make up the conventional facade solution used in Gipuzkoa and in much of Spain not only during those years but also up to the present time, the effects and causes of its main damages and flaws were studied. Its complex and costly adaptation to current demands is going to require a strong effort from society at large, and this raises the question of whether the life cycle of this construction system should be terminated once and for all.

Developmental characters of Psettina Iijimae (Jordan and Starks), bothid flat fishes - Pisces

Post larval stages of Psettina Iijimae ranging from 1.8 mm NL to 44.6 mm SL collected during Naga Expedition and International Indian Ocean Expedition (IIOE) are described. The characteristics which help to identify larval stages of Psettina are: the presence of pigmented urohyal appendage in early stages which is progressively reduced during flexion stages and which disappears in later postflexion stages, the meristics, the spines on urohyal and posterior basipterygial processes and the absence of spines on cleithra. The P. iijimae can be distinguished by the presence of spines on the median fin rays which differentiate near the baseosts along the dorsal and ventral body wall much before the fin rays. The larvae of P.iijimae were more abundant in the Gulf of Thailand compared to South China Sea and Indian Ocean.

On the identification of the early developmental stages of clupeiform fishes from Indian waters

Among about 65 species of clupeiform fishes present in the seas around India, most are distributed along both the east and west coasts and have similar spawning seasons and spawning grounds. The most difficult problem experienced with regard to the identification of their early developmental stages is the overlapping sets of diagnostic features among many species within the same genus as well as among species belonging to two or more genera. From studies carried out recently, the present paper sites a few instances wherein certain subtle characters have been used for distinguishing the early developmental stages of a few allied species.

Early developmental stages of two Secutor species (Family: Leiognathidae) collected from the Bak-khali river estuary of the Bay of Bengal, Bangladesh

Early developmental stages of two Secutor species, Secutor insidiator (Bloch) (11.9-36.0 mm standard length, SL) and Secutor ruconius (Hamilton-Buchanan) (14.0-33.0 mm SL) collected by ichthyoplankton net from the Bak-khali river estuary of the Bay of Bengal, Cox's Bazar, Bangladesh are described and illustrated. All of the fins with supporting spines and rays were present in the smallest collected sizes of both species. With growth of the specimens, significant changes in melanophore patterns were found. S. insidiator is similar to S. ruconius in having upward protracting mouth parts and body colouration, but can be distinguished easily by its more elongate body shape (body depth 38-47% of SL compared with 46-52% of SL in Secutor ruconius). Both the species occurred round the year from August 1998 to July 1999. The surface water temperature and salinity during the study period varied from 22.0-32) C and 10-37 ppt respectively.