Aspects of Molecular Genetics in Dromedary Camel

The immunoglobulin A isotype of the Arabian camel (Camelus dromedarius) preserves the dualistic structure of unconventional single-domain and canonical heavy chains

Introduction

The evolution of adaptive immunity in Camelidae resulted in the concurrent expression of classic heterotetrameric and unconventional homodimeric heavy chain-only IgG antibodies. Heavy chain-only IgG bears a single variable domain and lacks the constant heavy (CH) γ1 domain required for pairing with the light chain. It has not been reported whether this distinctive feature of IgG is also observed in the IgA isotype.

Methods

Gene-specific primers were used to generate an IgA heavy chain cDNA library derived from RNA extracted from the dromedary's third eyelid where isolated lymphoid follicles and plasma cells abound at inductive and effector sites, respectively.

Results

Majority of the cDNA clones revealed hallmarks of heavy chain-only antibodies, i.e. camelid-specific amino acid substitutions in framework region 1 and 2, broad length distribution of complementarity determining region 3, and the absence of the CHα1 domain. In a few clones, however, the cDNA of the canonical IgA heavy chain was amplified which included the CHα1 domain, analogous to CHγ1 domain in IgG1 subclass. Moreover, we noticed a short, proline-rich hinge, and, at the N-terminal end of the CHα3 domain, a unique, camelid-specific pentapeptide of undetermined function, designated as the inter-α region. Immunoblots using rabbit anti-camel IgA antibodies raised against CHα2 and CHα3 domains as well as the inter-α region revealed the expression of a ~52 kDa and a ~60 kDa IgA species, corresponding to unconventional and canonical IgA heavy chain, respectively, in the third eyelid, trachea, small and large intestine. In contrast, the leporine anti-CHα1 antibody detected canonical, but not unconventional IgA heavy chain, in all the examined tissues, milk, and serum, in addition to another hitherto unexplored species of ~45 kDa in milk and serum. Immunohistology using anti-CHα domain antibodies confirmed the expression of both variants of IgA heavy chains in plasma cells in the third eyelid's lacrimal gland, conjunctiva, tracheal and intestinal mucosa.

Conclusion

We found that in the dromedary, the IgA isotype has expanded the immunoglobulin repertoire by co-expressing unconventional and canonical IgA heavy chains, comparable to the IgG class, thus underscoring the crucial role of heavy chain-only antibodies not only in circulation but also at the mucosal frontiers.

Analysis of Genetic Diversity and Population Structure of Tarim and Junggar Bactrian Camels Based on Simplified GBS Genome Sequencing

In view of the severe reduction in Bactrian camel germplasm resources, scientific evaluation, protection, and utilization is particularly important. Therefore, it is necessary to investigate the genetic diversity and genetic structure of this species, and identify the genes that have played important roles in its evolution. In this study, 21,971 SNPs were identified in 118 domestic Bactrian camels from the Tarim (n = 60) and Junggar (n = 58) populations using simplified GBS genome sequencing. The results show that Tarim and Junggar Bactrian camels have high nucleotide diversity. A phylogenetic tree constructed using structural analysis, principal component analysis (PCA), and the adjacency method (NJ) showed that Tarim and Junggar Bactrian camels were clustered together. The selection signals revealed that the Tarim and Junggar Bactrian camels shared 108 genes under positive selection, including WNT1, WNT10B, CD14, SEC61A2, DPAGT1, FOXO6, etc. These selected genes were widely involved in the immune system, embryonic development, lipid metabolism, and other processes. From a genomic analysis perspective, the genetic relationship between TLM and ZGE camels is close, with an average Fst of 0.048 and a relatively low average differentiation coefficient between the two populations. In addition, shared selected genes in the long-term depression pathway were significantly enriched in Tarim and Junggar. These findings will offer support and assistance for the exploration of genetic resource preservation, economically significant traits, and the mechanisms underlying biological characteristics, molecular breeding, and disease.

A Study of the Genetic Structure of Hybrid Camels in Kazakhstan

Camel farming is gaining scientific interest due to its unique agricultural characteristics. Camels are versatile for milk and meat production, wool, racing, transport, and tourism. To use their full potential, it is essential to improve our understanding of the genetic structure of these animals. One-humped and two-humped camels have received detailed genetic descriptions, while there is no such information for their hybrids, which outperform their parent species in several agricultural characteristics. Thus, in this study, for the first time, the whole genome sequencing data (WGS) of five hybrid camels bred in the Almaty region of Kazakhstan are presented in comparison with the WGS data of one-humped, two-humped, and wild camels. A total of 43,552,164 single-nucleotide polymorphisms were found across the studied groups. Further comparison of these SNPs showed the following number of private SNPs among the populations: hybrid camels (3,271,083), wild camels (2,515,591), Bactrians (1,244,694), and dromedaries (531,224). The genetic structure of the studied animals was described, and a phylogenetic tree was built to assess their genetic distance. It was found that the studied hybrids are genetically closer to dromedaries since they were on the close branch of the phylogenetic tree.

Exploiting morphobiometric and genomic variability of African indigenous camel populations-A review

Camels (Camelus dromedarius) in Africa are adapted to arid and the semi-arid environmental conditions, and are valuable for meat, milk and fiber production. On account of the growing demand for camels in this continent, there is a need for knowledge on their phenotypic and genetic diversity. This is fundamental to sustainable herd management and utilization including the design of appropriate breeding and conservation strategies. We reviewed studies on the phenotypic and genetic characterization, breeding objectives, systems of production, productive and reproductive performances, and pathways for the sustainable rearing and use of camels in Africa. The morphological and genetic diversity, productive and reproductive abilities of African camels suggest the existence of genetic variations that can be utilized for breeds/ecotypes' genetic improvement and conservation. Possible areas of intervention include the establishment of open nucleus and community-based breeding schemes and utilization of modern reproductive technologies for the genetic improvement of milk and meat yields, sustainable management of rangelands, capacity building of the pastoralists and agro-pastoralists, institutional supports, formation of centralized conservation centres and efficient and effective marketing systems.

Trajectory of livestock genomics in South Asia: A comprehensive review

Livestock plays a central role in sustaining human livelihood in South Asia. There are numerous and distinct livestock species in South Asian countries. Several of them have experienced genetic development in recent years due to the application of genomic technologies and effective breeding programs. This review discusses genomic studies on cattle, buffalo, sheep, goat, pig, horse, camel, yak, mithun, and poultry. The frontiers covered in this review are genetic diversity, admixture studies, selection signature research, QTL discovery, genome-wide association studies (GWAS), and genomic selection. The review concludes with recommendations for South Asian livestock systems to increasingly leverage genomic technologies, based on the lessons learned from the numerous case studies. This paper aims to present a comprehensive analysis of the dichotomy in the South Asian livestock sector and argues that a realistic approach to genomics in livestock can ensure long-term genetic advancements.

Camel Proteins and Enzymes: A Growing Resource for Functional Evolution and Environmental Adaptation

In less agroecological parts of the Asian, Arabian, and African deserts, Camelus dromedarius play an important role in human survival. For many years, camels have been employed as a source of food, a tool of transportation, and a means of defense. They are becoming increasingly important as viable livestock animals in many desert climates. With the help of camel genetics, genomics and proteomics known so far, this review article will summarize camel enzymes and proteins, which allow them to thrive under varied harsh environmental situations. An in-depth study of the dromedary genome revealed the existence of protein-coding and fast-developing genes that govern a variety of metabolic responses including lipid and protein metabolism, glucoamylase, flavin-containing monooxygenase and guanidinoacetate methyltransferase are other metabolic enzymes found in the small intestine, liver, pancreas, and spleen. In addition, we will discuss the handling of common medications by camel liver cytochrome p 450, which are different from human enzymes. Moreover, camels developed several paths to get optimum levels of trace elements like copper, zinc, selenium, etc., which have key importance in their body for normal regulation of metabolic events. Insulin tolerance, carbohydrate and energy metabolism, xenobiotics metabolizing enzymes, vimentin functions, behavior during the rutting season, resistance to starvation and changes in blood composition and resistance to water loss were among the attractive aspects of camel enzymes and proteins peculiarities in the camels. Resolving the enigma of the method of adaptation and the molecular processes linked with camel life is still a developing repository full of mysteries that need additional exploration.