Litter thickness, but not root biomass, explains the average and spatial structure of soil hydraulic conductivity in secondary forests and coffee agroecosystems in Veracruz, Mexico.

Secondary forests and coffee agroecosystems are considered good alternatives for conservation of a high capacity for water filtration in the soil where tropical montane cloud forests (TMCF) once grew; however, it is not clear which characteristics of the vegetation modulate the field saturated hydraulic conductivity of the soil (Kfs) and whether these characteristics persist in such derived systems. Here, we explore how changes in vegetation between secondary forests and coffee agroecosystems have consequences for the average value and spatial variation of litter thickness and root biomass, and whether these differences can explain the Kfs and its spatial distribution. We found that the thickest litter, greatest total biomass and thickest roots are in the secondary forest of the north of the study area. The litter is spatially structured in patches of ca. 12m at plot scale in the secondary forest and coffee agroecosystem of the southern area. Like the Kfs, the thickness of the litter and biomass of the thick (>2mm), medium (1-2mm) and fine (<1mm) roots are spatially distributed on a north to south gradient at landscape scale. Our linear model indicates that geographic area (north or south), land use and litter thickness explain the Kfs and its spatial distribution along this gradient. Even on inclusion of the antecedent soil moisture and percentage of clays (found to explain Kfs in a previous study), it was not possible to eliminate from the model geographic area and land use, due to their high explanatory power. However, antecedent soil moisture became redundant on inclusion of the litter layer, which had a greater explanatory power. Our modeling suggests that undiscovered differences prevail between the geographic areas and secondary forest and coffee agroecosystems (possibly related to the edaphogenesis and management practices) that determine the Kfs.

Effects of white grubs on soil water infiltration.

Water infiltration rates k were measured in mesocosms with soil and "white grubs" of Ancognatha falsa (Arrow) (Coleoptera: Melolonthidae). Three third instars of A. falsa and three adult earthworms Pontoscolex corethrurus were selected, weighted, and introduced into the mesocosms setting three treatments: soil + A. falsa, soil + P. corethrurus, and control (soil without any macroorganism). The experiment had a completely random design with four replicates per treatment (n = 4). The infiltration rates of soil matrix were assessed in each mesocosms with a minidisk tension infiltrometer. Six measurements were made along the experiment. Results showed that larvae of A. falsa promoted a higher water infiltration in the soil, compared to the control. On day 7, k values were similar among treatments, but k values after 28 days and up to 100 days were much higher in the A. falsa treatment (k = 0.00025 cm s(-1)) if compared to control (k = 0.00011 cm s(-1)) and P. corethrurus (k = 0.00008 cm s(-1)) treatments. The k values were significantly higher in the presence of larvae of A. falsa compared to the control and P. corethrurus treatments. The larvae of A. falsa are potential candidates for new assays on soil water infiltration with different tensions to evaluate the role of pores and holes created by the larvae on soils.

Mouse paraxial protocadherin is expressed in trunk mesoderm and is not essential for mouse development.

Paraxial protocadherin (PAPC) is a cell adhesion molecule that marks cells undergoing convergence-extension cell movements in Xenopus and zebrafish gastrulating embryos. Here a mouse homologue (mpapc) was identified and characterized. During early- to mid-gastrulation, mpapc is expressed in the primitive streak as the trunk mesoderm undergoes morphogenetic cell movements. At head-fold stage mpapc expression becomes localized to paraxial regions in which somites are formed in the segmental plate. At later stages, mpapc displays a complex expression pattern in cerebral cortex, olfactory bulb, inferior colliculus, and in longitudinal stripes in hindbrain. To analyze the effect of the loss of PAPC function during mouse development, a null allele of the mouse papc gene was generated. Homozygous animals show no defects in their skeleton and are viable and fertile.

The evolutionarily conserved BMP-binding protein Twisted gastrulation promotes BMP signalling.

Dorsal-ventral patterning in vertebrate and Drosophila embryos requires a conserved system of extracellular proteins to generate a positional information gradient. The components involved include bone morphogenetic proteins (BMP/Dpp), a BMP antagonist (Chordin/Short gastrulation; Chd/Sog) and a secreted metalloproteinase (Xolloid/Tolloid) that cleaves Chd/Sog. Here we describe Xenopus Twisted gastrulation (xTsg), another member of this signalling pathway. xTsg is expressed ventrally as part of the BMP-4 synexpression group and encodes a secreted BMP-binding protein that is a BMP signalling agonist. The data suggest a molecular mechanism by which xTsg dislodges latent BMPs bound to Chordin BMP-binding fragments generated by Xolloid cleavage, providing a permissive signal that allows high BMP signalling in the embryo. Drosophila Tsg also binds BMPs and is expressed dorsally, supporting the proposal that the dorsal-ventral axis was inverted in the course of animal evolution.

Zebrafish paraxial protocadherin is a downstream target of spadetail involved in morphogenesis of gastrula mesoderm.

Zebrafish paraxial protocadherin (papc) encodes a transmembrane cell adhesion molecule (PAPC) expressed in trunk mesoderm undergoing morphogenesis. Microinjection studies with a dominant-negative secreted construct suggest that papc is required for proper dorsal convergence movements during gastrulation. Genetic studies show that papc is a close downstream target of spadetail, gene encoding a transcription factor required for mesodermal morphogenetic movements. Further, we show that the floating head homeobox gene is required in axial mesoderm to repress the expression of both spadetail and papc, promoting notochord and blocking differentiation of paraxial mesoderm. The PAPC structural cell-surface protein may provide a link between regulatory transcription factors and the actual cell biological behaviors that execute morphogenesis during gastrulation.

Xenopus chordin: a novel dorsalizing factor activated by organizer-specific homeobox genes.

A Xenopus gene whose expression can be activated by the organizer-specific homeobox genes goosecoid and Xnot2 was isolated by differential screening. The chordin gene encodes a novel protein of 941 amino acids that has a signal sequence and four Cys-rich domains. The expression of chordin starts in Spemann's organizer subsequent to that of goosecoid, and its induction by activin requires de novo protein synthesis. Microinjection of chordin mRNA induces twinned axes and can completely rescue axial development in ventralized embryos. This molecule is a potent dorsalizing factor that is expressed at the right time and in the right place to regulate cell-cell interactions in the organizing centers of head, trunk, and tail development.

Molecular cloning of the human homeobox gene goosecoid (GSC) and mapping of the gene to human chromosome 14q32.1.

Goosecoid is a homeobox gene first isolated from a Xenopus dorsal lip cDNA library. Homologous genes have been isolated from mouse, zebrafish, and chick. In all species examined, the gene is expressed and plays an important role during the process of gastrulation in early embryonic development. We report here the cloning of the human goosecoid gene (GSC) from a genomic library and the sequence of its encoded protein. The genomic organization and protein sequence of the human gene are highly conserved with respect to those of its Xenopus and mouse counterparts: all three genes consist of three exons, with conserved exon-intron boundaries; the sequence of the homeodomain is 100% conserved in most vertebrates. Using somatic cell hybrid and chromosomal in situ hybridization, the gene was mapped to chromosome 14q32.1.

Inhibition of purified Escherichia coli leader peptidase by the leader (signal) peptide of bacteriophage M13 procoat.

The leader peptide of bacteriophage M13 procoat inhibited the cleavage of M13 procoat or pre-maltose-binding protein by purified Escherichia coli leader peptidase. This finding confirms inferences that the leader is the primary site of enzyme recognition and suggests a rationale for the rapid hydrolysis of leader peptides in vivo.