Questions: Do large trees improve the nutrient content and the structure of the grass layer in savannas? Does the magnitude of this improvement differ with locality (soil nutrients) and season (water availability)? Are grass structure and species composition beneath tree canopies influenced by soil fertility and season? Location: South Africa. Methods: We compared grass leaf nutrient contents and grass sward structure beneath and outside tree canopy areas in three savannas of different soil fertility during the dry and the wet seasons. Results: Grass nitrogen contents were twice as high during the wet season as compared to the dry season, being more strongly elevated underneath tree canopies during the wet season. Grasses had significantly less stem material and provided less dead material underneath trees on the high soil fertility site. Grass species composition differed significantly beneath and outside tree canopies, with more nutritious grass species found sub-canopy. Grass species richness was significantly lower beneath than outside of trees at the site of high soil fertility. Conclusions: Trees improve overall quality of savanna grasses by enhancing grass growth and nutrient uptake during the wet season, and by delaying grass wilting in the dry season. The positive effect of trees on the grass layer might attract grazing herbivores in otherwise nutrient-poor savannas. Hence, single standing large trees should be maintained to sustain high grass quality and, consequently, grazer populations in savanna habitats.

CD1d-restricted invariant natural killer T cells (NKT cells) have been well characterized in humans and mice, but it is unknown whether they are present in other species. Here we describe the invariant TCR α chain and the full length CD1d transcript of pig and horse. Molecular modeling predicts that porcine (po) invariant TCR α chain/poCD1d/α-GalCer and equine (eq) invariant TCR α chain/eqCD1d/α-GalCer form complexes that are highly homologous to the human complex. Since a prerequisite for the presence of NKT cells is the expression of CD1d protein, we performed searches for CD1D genes and CD1d transcripts in multiple species. Previously, cattle and guinea pig have been suggested to lack CD1D genes. The CD1D genes of European taurine cattle (Bos taurus) are known to be pseudogenes because of disrupting mutations in the start codon and in the donor splice site of the first intron. Here we show that the same mutations are found in six other ruminants: African buffalo, sheep, bushbuck, bongo, N’Dama cattle, and roe deer. In contrast, intact CD1d transcripts were found in guinea pig, African elephant, horse, rabbit, and pig. Despite the discovery of a highly homologous NKT/CD1d system in pig and horse, our data suggest that functional CD1D and CD1d-restricted NKT cells are not universally present in mammals.

Lipid antigens are presented to T cells by the CD1 family of proteins. In this study, we characterize the complete dog (Canis familiaris) CD1 locus, which is located on chromosome 38. The canine locus contains eight CD1A genes (canCD1A), of which five are pseudogenes, one canCD1B, one canCD1C, one canCD1D, and one canCD1E gene. In vivo expression of canine CD1 proteins was shown for canCD1a6, canCD1a8, and canCD1b, using a panel of anti-CD1 monoclonal antibodies (mAbs). CanCD1a6 and canCD1a8 are recognized by two distinct mAbs. Furthermore, we show differential transcription of the three canCD1A genes in canine tissues. In canine skin, the transcription level of canCD1A8 was higher than that of canCD1A6, and no transcription of canCD1A2 was detected. Based on protein modeling and protein sequence alignment, we predict that both canine CD1a proteins can bind different glycolipids in their groove. Besides differences in ectodomain structure, we observed the unique presence of three types of cytoplasmic tails encoded by canCD1A genes. cDNA sequencing and expressed sequence tag sequences confirmed the existence of a short, human CD1a-like cytoplasmic tail of four amino acids, of an intermediate length form of 15 amino acids, and of a long form of 31 amino acids.

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SummaryAmong the CD1 proteins that present lipid antigens to T cells, CD1d is the only one that stimulates a population of T cells with an invariant T-cell receptor known as NKT cells. Sequencing of a 722 nucleotide gap in the dog (Canis lupus familiaris) genome revealed that the canine CD1D gene lacks a sequence homologous to exon 2 of human CD1D, coding for the start codon and signal peptide. Also, the canine CD1D gene contains three different short tandem repeats that disrupt the expected gene structure. Because canine CD1D cDNA lacks sequences homologous to human exon 2 and 3, the functionality of canine CD1d protein may be affected, and this could have consequences for the development and activation of canine NKT cells. Keywords CD1, dog, microsatellite, NKT cells, simple sequence repeatThe CD1 family is a group of non-polymorphic glycoproteins that present lipid antigens to T cells (Porcelli & Modlin 1999;Brigl & Brenner 2004;Barral & Brenner 2007). Like MHC class I proteins, CD1 proteins are heterodimers of b2 microglobulin and a heavy chain consisting of three extracellular a domains, a transmembrane region and a cytoplasmic tail, each encoded by a separate exon, preceded by an exon that encodes the start codon and signal peptide, and sometimes an additional exon that consists of 5′ UTR only.Large variation exists in the number of CD1A, CD1B, and CD1C genes between mammalian species, whereas one or two CD1D genes are present in all mammalian species studied to date (Dascher et al. 1999;Hayes & Knight 2001;Eguchi-Ogawa et al. 2007;Looringh van Beeck et al. 2008. CD1d is crucial for the selection (Bendelac et al. 1995) and activation (Kawano et al. 1997) of a subset of T cells known as natural killer T (NKT) cells. The canine CD1 locus is located on chromosome 38 and contains one CD1D gene, eight CD1A genes, one CD1C, one CD1B and one CD1E gene (Fig. 1a) (Looringh van Beeck et al. 2008). In the canine genome (CanFam 3.1) and in the sequence of BAC clone XX-14K12 AC183576.27, the canine CD1D gene is incomplete due to an internal gap of unknown length. Upstream from this gap we detected a sequence with 62% nt identity to exon 1 of human CD1D and downstream from the gap a sequence with 68% identity to human exon 3 (ENST00000368171; www.ensembl.org) (Fig. 1b). No canine homolog of the human CD1D exon 2 was found. Putative full-length canine exons were found for CD1D exon 4, 5, 6 and 7, with identities of respectively 76%, 84%, 58% and 56% to the corresponding human exons.To be able to fill the gap in the genomic DNA sequence between exon 1 and exon 3 of canine CD1D, we performed a two-step digestion on BAC clone XX-14K12 DNA using restriction endonuclease HpaI followed by HindIII and NotI (Fig. S1). The two restriction fragments containing the gap were subsequently cloned and sequenced. The complete DNA sequence of the gap was obtained and consists of 722 nt (GenBank GU930707) (Fig. 1c). No canine homolog of the human CD1D exon 2 was found in this DNA sequence.Using Tandem Repeat Finder, three different types ...