Cross‐species conservation of a transposase‐linked element enables genetic sexing of commercial populations of Russian sturgeon (Acipenser gueldenstaedtii)

Abstract

All-female culture of sturgeon is essential for efficient caviar production.However, Russian sturgeon (Acipenser gueldenstaedtii) does not exhibit external sexual dimorphism, and therefore, commercial farms apply gonadal endoscopy or ultrasound at the earliest age of 4-5 years to separate the sexes, with ~90% accuracy. Recently, a dominant genomic marker (AllWSEX2) has been found with association to femaleness in sturgeons. We developed a duplex PCR (dAllWSEX2) with the adjacent bmp7 gene as an internal control, to validate an effective PCR. Robust amplification of control fragments was observed for all samples of our commercial A. gueldenstaedtii stock (n = 337). The dAllWSEX2 assay was significantly associated with sex (n = 43, p < 1.6 × 10 −8 ), yet four (18%) of the endoscopy-determined females were genetic males. To examine whether some females display a male genetic profile, we tested 96 eggproducing females, which were all verified as genetic females, indicating that the observed mismatches may be attributed to wrong sexing by endoscopy. Application of dAllWSEX2 on 100 7-month-old fish showed no sex-dependent differences in body weight, indicating that weighing is not an applicable tool for sorting females at a young age. Sanger sequencing of the bmp7 fragment revealed octaploidy and sex-independent variation, suggesting that the critical sex-determining region harboring AllWSEX2 is small. In keeping with a model of a single-ploidy encoding female determination, AllWSEX2 showed no variation despite being a transposase-linked repetitive element. Cross-species conservation of AllWSEX2, and absence of annotated sex-determination genes in this region suggests that, in sturgeons, the sex-determining mechanism is different from mechanisms identified in other fish.

Whole-Genome Inter-Sex Variation in Russian Sturgeon (Acipenser gueldenstaedtii)

“…Our results in AG agree with the findings of Kuhl et al [ 14 ] and subsequent studies that successfully used the AllWsex2 marker to identify the sex of different sturgeon species [ 14 , 15 , 16 ]. Furthermore, we identified 15 additional genomic regions in AR with clusters of 30 or more inter-sex variants in the AG WGS reads that map to them.…”

“…Recently, a conserved female-specific region was identified in six species of sturgeon, and a PCR-based genotyping method (AllWSex2) was developed [ 14 ]. The utility of this assay was further validated in studies of lake sturgeon ( A. fulvescens ) [ 15 ], and a modified protocol was tested and implemented in commercial aquaculture of Russian sturgeon [ 16 ]. While these findings have led to significant progress in practical applications, no biological function has been reported for this female-specific sequence.…”

Sturgeon (&lt;i&gt;Acipenser gueldenstaedtii&lt;/i&gt;) Acclimatization to Optimal Growth Conditions—A Case Study of Adaptation, Nutrition, Reproduction, and Sex Determination

“…When caviar costs are lower, this benefit is much larger [20]. The study focused on three important ESD technology indicators: 1) differences in male and female gene expression in various organs; 2) differences in gonad transcription (mRNA level) [17] [18] [27] [64]; 3) genome variation between males and females (DNA sequences) to discover molecular markers [16] [18] [19].…”

“…As reported by [19], DNA was extracted from 3 females and 3 males, and the products were separated on a 0.5% agarose gel stained with ethidium bromide. Open Journal of Animal Sciences…”

“…Endoscopic methods of sex determination can only be used after gonadal differentiation, i.e., at 3 years of age or later. The sample required for the proposed early sex determination is not taken from the gonads, but from the dorsal fin (tissue) of 6-month-old fish, using molecular methods that allow sex discrimination in the months before sex differentiation concerning based on DNA variation (this was confirmed in a study on a Dan River sturgeon farm, unpublished data) [19].…”