Transcriptional sexual dimorphism in elongating bovine embryos: implications for XCI and sex determination genes

Abstract

Sex chromosome transcripts can lead to a broad transcriptional sexual dimorphism in the absence of concomitant or previous exposure to sex hormones, especially when X-chromosome inactivation (XCI) is not complete. XCI timing has been suggested to differ greatly among species, and in bovine, most of the X-linked transcripts are upregulated in female blastocysts. To determine the timing of XCI, we analyzed in day 14 bovine embryos the sexual dimorphic transcription of seven X-linked genes known to be upregulated in female blastocysts (X24112, brain-expressed X-linked 2 (BEX2), ubiquitin-conjugating enzyme E2A (UBE2A), glucose-6-phosphate dehydrogenase (G6PD), brain-expressed X-linked 1 (BEX1), calpain 6 (CAPN6), and spermidine/spermine N-acetyltransferase 1 (SAT1)). The transcription of five genes whose expression differs between sexes at the blastocyst stage (DNMT3A, interferon tau (IFNT2), glutathione S-transferase mu 3 (GSTM3), progesterone receptor membrane component 1 (PGRMC1), and laminin alpha 1 (LAMA1)) and four genes related with sex determination (Wilms tumor 1 (WT1), gata binding protein 4 (GATA4), zinc finger protein multitype 2 (ZFPM2), and DMRT1) was also analyzed to determine the evolution of transcriptional sexual dimorphism. The expression level of five X-linked transcripts was effectively equalized among sexes suggesting that, in cattle, a substantial XCI occurs during the period between blastocyst hatching and initiation of elongation, although UBE2A and SAT1 displayed significant transcriptional differences. Similarly, sexual dimorphism was also reduced for autosomal genes with only DNMT3A and IFNT2 exhibiting sex-related differences. Among the genes potentially involved in sex determination, Wilms tumor 1 (WT1) was significantly upregulated in males and GATA4 in females, whereas no differences were observed for ZFPM2 and DMRT1. In conclusion, a major XCI occurred between the blastocyst and early elongation stages leading to a reduction in the transcriptional sexual dimorphism of autosomal genes, which makes the period the most susceptible to sex-specific embryo loss.

Treatment of pediatric Grade II spinal ependymomas: a population-based study

“…63 Male embryos are larger, contain more cells, and show differential expression of genes important for glucose metabolism (G6PD and HPRT1), cellular growth (XIAP), and gene regulation (DMNT3A and DMNT3B); these differences are evident at the blastocyst stage, before gonadal differentiation at 8 weeks. 9,10,36,60,67 These differences are reported to have physiologically relevant manifestations; male embryos display increased glucose and pyruvate uptake and lactate production, while female embryos display greater G6PD activity and increased activity through the pentose phosphate pathway. 9,10,23,49 The Warburg effect describes the observation that tumor cells prefer anaerobic glycolysis as an energy source, and thus would be expected to have increased uptake of glucose and production of lactate.…”

“…9,10,36,60,67 These differences are reported to have physiologically relevant manifestations; male embryos display increased glucose and pyruvate uptake and lactate production, while female embryos display greater G6PD activity and increased activity through the pentose phosphate pathway. 9,10,23,49 The Warburg effect describes the observation that tumor cells prefer anaerobic glycolysis as an energy source, and thus would be expected to have increased uptake of glucose and production of lactate. These metabolic differences may affect the probability, rate, or severity of oncogenic transformation in the CNS.…”

HDAC inhibition decreases XIST expression on female IVP bovine blastocysts

“…However, recent studies based on gene expression profile of male and female embryos suggest that dosage compensation occurs in bovine at some stage between hatching and implantation, which is inferred based on the presence of approximately a double amount of X-linked genes, including G6PD, at day 7, and the same amount at day 14, comparing male and female counterparts (Bermejo-Alvarez et al 2011).…”

“…Controversial results were found regarding G6PD expression, which was shown to be increased in some studies (Gutiérrez-Adán et al 2000, Peippo et al 2002, Wrenzycki et al 2002, Lopes et al 2007, Morton et al 2007, Bermejo-Alvarez et al 2011 and decreased in others (Merighe et al 2009), when comparing female and male IVP blastocysts. Considering that G6PD varies its expression according to respiration and metabolism (Lopes et al 2007), their different mRNA levels among systems might be related to stressful culture conditions.…”

Memories of an X-chromosome

“…The mouse model was assumed to be representative of other mammals, including humans, but later studies suggested that it is more an exception than a rule (6). Transcriptional studies in bovine, a species with preimplantation development timing similar to human, observed that XCI was far from being accomplished at the blastocysts stage (7), occurring later, during gastrulation (8). Similar findings were found in human blastocysts, where most blastomeres, including those of the TE, show two Xa that, in contrast to the mouse early epiblast, do express XIST from both Xa (9).…”