Frequent and recent retrotransposition of orthologous genes plays a role in the evolution of sperm glycolytic enzymes

Abstract

BackgroundThe central metabolic pathway of glycolysis converts glucose to pyruvate, with the net production of 2 ATP and 2 NADH per glucose molecule. Each of the ten reactions in this pathway is typically catalyzed by multiple isozymes encoded by a multigene family. Several isozymes in this pathway are expressed only during spermatogenesis, and gene targeting studies indicate that they are essential for sperm function and male fertility in mouse. At least three of the novel glycolytic isozymes are encoded by retrogenes (Pgk2, Aldoart1, and Aldoart2). Their restricted expression profile suggests that retrotransposition may play a significant role in the evolution of sperm glycolytic enzymes.ResultsWe conducted a comprehensive genomic analysis of glycolytic enzymes in the human and mouse genomes and identified several intronless copies for all enzymes in the pathway, except Pfk. Within each gene family, a single orthologous gene was typically retrotransposed frequently and independently in both species. Several retroposed sequences maintained open reading frames (ORFs) and/or provided evidence of alternatively spliced exons. We analyzed expression of sequences with ORFs and <99% sequence identity in the coding region and obtained evidence for the expression of an alternative Gpi1 transcript in mouse spermatogenic cells.ConclusionsOur analysis detected frequent, recent, and lineage-specific retrotransposition of orthologous glycolytic enzymes in the human and mouse genomes. Retrotransposition events are associated with LINE/LTR and genomic integration is random. We found evidence for the alternative splicing of parent genes. Many retroposed sequences have maintained ORFs, suggesting a functional role for these genes.

Glycogen synthase kinase 3 regulates acrosomal exocytosis in mouse spermatozoa via dynamin phosphorylation

“…Consistent with previous evidence that spermatozoa present enzyme profiles that are distinct from those present in somatic tissues (37, 38), we demonstrated that CDK5 is absent in mature mouse spermatozoa and that a broad spectrum CDK inhibitor had no effect on acrosomal exocytosis. Although GSK3 was detected within these cells, the 2 ubiquitously expressed somatic homologs, GSK3α and GSK3β (39), were not equally represented, with substantially more GSKa being detected in mature spermatozoa.…”

Linking Spermatid Ribonucleic Acid (RNA) Binding Protein and Retrogene Diversity to Reproductive Success

“…Again, this is similar to the GESptd1 rat lentiviral transgene, which was identified in the 11th most-enriched protein spot in elongating spermatid fractions (Table II). A recent study by Vemuganti and colleagues used bioinformatics to study this relationship, and found an over-representation of LINE and LTR elements flanking glycolytic retrogenes in rodent and primate genomes (15). Likewise, EGFP is expressed from a LTR-based lentiviral retroelement we experimentally integrated directly into the germline of GESptd1 rats (Fig.…”

“…Based on biochemical activities in other biological processes, the identified factors are predicted to drive posttranscriptional RNA processing during meiotic and post-meiotic steps in spermatozoan development. Genome-wide studies find testes to express an extraordinarily diverse repertoire of tissue-specific mRNAs (25)(26)(27), alternatively spliced mRNAs (16,17), translationally repressed mRNAs (12)(13)(14), and translated retrogene mRNAs (15). Testes not only express an unusually wide array of total exons compared with most tissues, but also express exons encoding tissue-specific, cis-acting splicing elements; a majority of these elements bind hnRNPfamily proteins that mediate exon skipping (68).…”

“…It is quite interesting that a relatively high percentage of retrogenes are abundantly expressed specifically in spermatids, many of which encode glycolytic enzymes (15). Five of the top seven most-enriched 2D gel spots in elongating spermatid fractions contained proteins predicted to be expressed from retrogene-like elements (Table II).…”

“…This includes numerous testis-specific isoforms of metabolic enzymes required for sperm function (28 -30). Spermatogenic cells also express an unusually high percentage of retrogenes, a subset of which encode glycolytic enzymes hypothesized to have been selected by enhancing sperm fitness (15). Additionally, spermatogenic cells express a most diverse array of alternatively processed mRNAs unique to the germline (16,17).…”