Abstract
BackgroundThe buffalo, despite its superior milk-producing ability, suffers from reproductive limitations that constrain its lifetime productivity. Male sub-fertility, manifested as low conception rates (CRs), is a major concern in buffaloes. The epididymal sperm surface-binding proteins which participate in the sperm surface remodelling (SSR) events affect the survival and performance of the spermatozoa in the female reproductive tract (FRT). A mutation in an epididymal secreted protein, beta-defensin 126 (DEFB-126/BD-126), a class-A beta-defensin (CA-BD), resulted in decreased CRs in human cohorts across the globe. To better understand the role of CA-BDs in buffalo reproduction, this study aimed to identify the BD genes for characterization of the selection pressure(s) acting on them, and to identify the most abundant CA-BD transcript in the buffalo male reproductive tract (MRT) for predicting its reproductive functional significance.ResultsDespite the low protein sequence homology with their orthologs, the CA-BDs have maintained the molecular framework and the structural core vital to their biological functions. Their coding-sequences in ruminants revealed evidence of pervasive purifying and episodic diversifying selection pressures. The buffalo CA-BD genes were expressed in the major reproductive and non-reproductive tissues exhibiting spatial variations. The Buffalo BD-129 (BuBD-129) was the most abundant and the longest CA-BD in the distal-MRT segments and was predicted to be heavily O-glycosylated.ConclusionsThe maintenance of the structural core, despite the sequence divergence, indicated the conservation of the molecular functions of the CA-BDs. The expression of the buffalo CA-BDs in both the distal-MRT segments and non-reproductive tissues indicate the retention the primordial microbicidal activity, which was also predicted by in silico sequence analyses. However, the observed spatial variations in their expression across the MRT hint at their region-specific roles. Their comparison across mammalian species revealed a pattern in which the various CA-BDs appeared to follow dissimilar evolutionary paths. This pattern appears to maintain only the highly efficacious CA-BD alleles and diversify their functional repertoire in the ruminants. Our preliminary results and analyses indicated that BuBD-129 could be the functional ortholog of the primate DEFB-126. Further studies are warranted to assess its molecular functions to elucidate its role in immunity, reproduction and fertility.
Highlights
The buffalo, despite its superior milk-producing ability, suffers from reproductive limitations that constrain its lifetime productivity
Other classical antimicrobial peptides (AMPs) like the Lingual Antimicrobial Peptide (LAP), Tracheal Antimicrobial Peptide (TAP), Bovine neutrophil BDs (BNBDs) and Enteric BD (EBD), were retrieved from the buffalo reference sequence (RefSeq) assembly. Further analysis of these classical AMPs was excluded as they are known to be well-characterized as AMPs [47], The translated gene products of the identified Buffalo beta-defensin (BuBD) cluster on chromosome 14 (i.e. class-A beta-defensin (CA-BD)) were subject to in silico sequence analyses, which revealed the conservation of the key BD molecular framework characterised by the six cysteine motif and the hallmark spacing between the cysteines similar to their identified orthologs in other mammalian species (Additional file 3)
The multiple sequence alignment (MSA) of class-A BuBDs revealed the presence of unique gene-specific motifs (GSMs), which were either present in all the considered species or only ruminant species (Additional file 3)
Summary
The buffalo, despite its superior milk-producing ability, suffers from reproductive limitations that constrain its lifetime productivity. To better understand the role of CA-BDs in buffalo reproduction, this study aimed to identify the BD genes for characterization of the selection pressure(s) acting on them, and to identify the most abundant CA-BD transcript in the buffalo male reproductive tract (MRT) for predicting its reproductive functional significance. Beta-defensins (BDs), first discovered in Bos taurus [1], are highly conserved innate effector molecules present ubiquitously from the prokaryotes to the higher eukaryotes. This class of host defence peptides (HDPs) possesses antimicrobial activities against a variety of microbes ranging from the virus [2] and bacteria [3] to fungi [4]. Many of the BDs are constitutively expressed in accordance with their pleiotropic functions [7] while others show ‘up-regulation’ during infection and in the presence of pathogens [8]
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