Sex differentiation in Atlantic cod (Gadus morhua L.): morphological and gene expression studies

Abstract

BackgroundIn differentiated gonochoristic species, a bipotential gonad develops into an ovary or testis during sex differentiation. Knowledge about this process is necessary to improve methods for masculinizing genetically female Atlantic cod for the subsequent purpose of producing all-female populations.MethodsGonads were examined histologically in juveniles from 14 to 39 mm total body length (TL). Number and size of germ cells were determined in a subset of the samples. Relevant genes were cloned, and mRNA levels determined by qPCR of amh, cyp19a1a; dax1 (nr0b2); shp (nr0b2a) and sox9b in a mixed-sex and an all-female population ranging from 12–49 mm TL.ResultsIndividuals between 14–20 mm TL could be separated in two subgroups based on gonad size and germ cell number. Ovarian cavity formation was observed in some individuals from 18–20 mm TL. The mixed sex population displayed bimodal expression patterns as regards cyp19a1a (starting at 12 mm TL) and amh (starting at 20 mm TL) mRNA levels. After approximately 30 mm TL, cyp19a1a and amh displayed a gradual increase in both sexes. No apparent, sex-dependent expression patterns were found for dax1, shp or sox9b transcripts. However, shp levels were high until the larvae reached around 35 mm TL and then dropped to low levels, while dax1 remained low until 35 mm TL, and then increased sharply.ConclusionsThe morphological sex differentiation in females commenced between 14–20 mm TL, and ovarian cavities were evident by 18–20 mm TL. Testis development occurred later, and was morphologically evident after 30 mm TL. This pattern was corroborated with sexually dimorphic expression patterns of cyp19a1a from 12–13 mm TL, and a male-specific increase in amh from 20 mm TL.

Divergent and sex‐dimorphic expression of the paralogs of the Sox9‐Amh‐Cyp19a1 regulatory cascade in developing and adult atlantic cod (Gadus morhua L.)

“…Both paralogs were mainly expressed in the larval head at the presumptive stage of sex differentiation. Despite individual variation in both the head and trunk, no apparent sex‐dimorphic patterns were found, in agreement with the sox9b levels measured in mixed‐sex and all‐female populations of Atlantic cod (Haugen et al, ). Expression of sox9a was identified in somatic cells surrounding the germ cells of both sexes before gonadal differentiation in zebrafish and tilapia, contrasting with the expression of the sox9b paralog in medaka (Rodriguez‐Mari et al, ; Kobayashi et al, ; Nakamoto et al, ).…”

Combining next‐generation sequencing with microarray for transcriptome analysis in rainbow trout gonads

“…Among the three transcripts used for in situ hybridization, YGL02.2379.C5, showing the homology to tubulin alpha chain, was expressed in some, but not all, A-SG. In contrast, vasa, Ly75, Plzf, ziwi, and zili, and other two transcripts used for in situ hybridization in this study were uniformly expressed in all A-SG (Kobayashi et al, 2000;Yoshizaki et al, 2000;Xu et al, 2005;Houwing et al, 2007Houwing et al, , 2008Yano et al, 2008;Nagasawa et al, 2009Nagasawa et al, , 2010Nagasawa et al, , 2012Haugen et al, 2012). Thus, this is the first study to demonstrate that the fish A-SG cell population has transcriptome heterogeneity.…”

Effects of elevated dissolved carbon dioxide and perfluorooctane sulfonic acid, given singly and in combination, on steroidogenic and biotransformation pathways of Atlantic cod

“…are associated with female gonadal development in several species (Guiguen et al, 2010;Piferrer, 2001) including, Atlantic cod (Haugen et al, 2012). Androgens also might be involved in directing oocyte development in female fish, as shown for ZP transcription and oocyte growth in Atlantic cod (Kortner et al, 2009a;Kortner et al, 2009b;Kortner et al, 2008).…”