Mapping of the Sex Determining Region on Linkage Group 12 of Guppy (Poecilia reticulata)

Abstract

Poecilia reticulata is one of the most popular ornamental fish species with a higher demand for males due to their large colorful fins. The objectives of this study were mapping of the sex-determining (SD) region on linkage group 12 of guppy, and identification of a sex specific marker. We generated eight polymorphic microsatellite markers distributed along the distal 5.4 Mbp sequence of the previously identified SD region on linkage group (LG) 12. The markers were tested for association with sex in 156 individuals of the Red Blonde and Flame strains, and 126 progeny of four full-sibs Red Blonde families. A male-specific allele was found for microsatellite gu1066 at position of 25.3 Mbp on LG12 for both strains, and gu832 at position 24.4 Mbp for the Flame strain. Thus, a region of 0.9 Mbp between these markers, harboring 27 annotated genes, was selected for analysis. Based on association of copy number variation and sex determination we mapped a duplicated region between LGs 9 and 12, of 1.26 Mbp, containing 59 genes on LG12. The common interval between the segment bounded by gu1066 and gu832, and the duplicated region of 0.43 Mbp on LG12 harbors 11 genes of which 6 have multiple copies (54%). Growth arrest and DNA damage inducible gamma-like (GADD45G-like) is a plausible positional and functional candidate gene for its role in male fertility. We characterized the genomic structure of the gene in guppy, and found two isoforms; but no sex-biased differences were evident in genomic sequence and gene expression.

Locating the sex determining region of linkage group 12 of guppy (Poecilia reticulata)

“…Our new results do, however, support all previous results, including those of from the captive 433 material studied by Dor et al (2019), suggesting that the guppy male-determining factor is located 434 within a region between about 21 and 25 Mb (in the current assembly). We describe the first 435 genetic data based on localising X-Y crossovers within families, and the two recombinant individuals 436 both indicate that the male-determining factor is located distal to 21 Mb, and our results also 437 define the PAR boundary, which our families indicate is at about 25 Mb (though assembly errors 438 make it difficult to define its boundary or size precisely).…”

“…Here, we show that the gu1066 microsatellite does not have male-specific alleles in natural 117 populations of Trinidadian guppies, and that a polymorphic SNP (single nucleotide 118 polymorphism) in the candidate gene has no male-specific allele. We also describe new 119 mapping results using multiple microsatellite and SNP genetic markers that narrow down 120 the sex-determining locus to a similar region as that identified by all the previous studies 121 cited above, including Dor et al (2019). 122 123…”

“…LG12 (Supplementary Figure S2). These genes could well be located in the terminal part of the 404 guppy LG12, which might correspond to the region identified by Dor et al (2019). The gene order in 405 the centromere-proximal 20 Mb of the 26.4 Mb guppy LG12 is very similar to that in the 406 homologous platyfish chromosome (Xm8, see Supplementary Figure S4).…”

“…where male-specific probe sequences also hybridize (Nanda et al 1990;Lisachov et al 88 2015). It is therefore likely that this region carries the sex-determining locus (Figure 1 However, population genomic studies suggest that variants on chromosome 12 show weak 92 associations with the sex-determining region, although associations are detectable across 93 5 male fertility, although the sequence did not include any male-specific alleles and its 115 expression was not sex-biased (Dor et al 2019). 116…”

“…Genetic mapping was done as described previously, using microsatellites ascertained from 161 the guppy complete genome sequence assembly, as well as these SNPs. The set of SNPs 162 included one within the candidate gene, GADD45G-like, identified by (Dor et al 2019); the 163 gene is also named LOC103474023, and starts at position 24,968,682 in the guppy LG12 164 assembly (Künstner et al 2017). 165…”