A Positive Regulatory Loop between foxi3a and foxi3b Is Essential for Specification and Differentiation of Zebrafish Epidermal Ionocytes

BACKGROUND: Epidermal ionocytes play essential roles in the transepithelial transportation of ions, water, and acid-base balance in fish embryos before their branchial counterparts are fully functional. However, the mechanism controlling epidermal ionocyte specification and differentiation remains unknown. METHODOLOGY/PRINCIPAL FINDINGS: In zebrafish, we demonstrated that Delta-Notch-mediated lateral inhibition plays a vital role in singling out epidermal ionocyte progenitors from epidermal stem cells. The entire epidermal ionocyte domain of genetic mutants and morphants, which failed to transmit the DeltaC-Notch1a/Notch3 signal from sending cells (epidermal ionocytes) to receiving cells (epidermal stem cells), differentiates into epidermal ionocytes. The low Notch activity in epidermal ionocyte progenitors is permissive for activating winged helix/forkhead box transcription factors of foxi3a and foxi3b. Through gain- and loss-of-function assays, we show that the foxi3a-foxi3b regulatory loop functions as a master regulator to mediate a dual role of specifying epidermal ionocyte progenitors as well as of subsequently promoting differentiation of Na(+),K(+)-ATPase-rich cells and H(+)-ATPase-rich cells in a concentration-dependent manner. CONCLUSIONS/SIGNIFICANCE: This study provides a framework to show the molecular mechanism controlling epidermal ionocyte specification and differentiation in a low vertebrate for the first time. We propose that the positive regulatory loop between foxi3a and foxi3b not only drives early ionocyte differentiation but also prevents the complete blockage of ionocyte differentiation when the master regulator of foxi3 function is unilaterally compromised

Dung beetle assemblage structure across the aridity and trophic resource gradient of the Botswana Kalahari: patterns and drivers at regional and local scales

Understanding pattern and process at both regional and local scales is important for conservation planning although such knowledge of insects is frequently lacking. To assess patterns along a regional gradient of increasing aridity and diminishing food resources in the Botswana Kalahari, Scarabaeine dung beetles were sampled quantitatively using four dung types at three local sites in six regional areas. At regional scale, factor analysis of species abundance extracted a maximum of six factors, each dominated by a single area. Therefore, the statistical significance of regional spatial variation far outweighed that of dung type association. At local scale, six factor analyses of species abundance extracted from four to six factors. The importance of local dung type associations was relatively high but diminished with increasing local spatial heterogeneity. At regional scale, hierarchical analysis of oblique factors divided assemblages into unique local and shared regional components. Primary extended factors accounted for 40–50 % of unique local faunal composition in five out of six areas. Two secondary extended factors showed either high shared proportional contribution to regional assemblage structure in the northeast with a steep decline to the southwest, or an opposite trend. Their point of intersection was consistent with a boundary zone between mesic northeast and arid southwest faunal components in the central Kalahari. Despite some inconsistencies in rank position between regression methods, rainfall, temperature, and mammal density/diversity were the strongest influences on regional patterns defined by secondary factors. Patterns are discussed according to conservation and changes in land usage around reserves.The GEF-Small Grant Programme and the University of Pretoriahttp://www.springerlink.com/content/100177/hb2013ab201