Sex and the TEs: transposable elements in sexual development and function in animals

Abstract

Transposable elements are endogenous DNA sequences able to integrate into and multiply within genomes. They constitute a major source of genetic innovations, as they can not only rearrange genomes but also spread ready-to-use regulatory sequences able to modify host gene expression, and even can give birth to new host genes. As their evolutionary success depends on their vertical transmission, transposable elements are intrinsically linked to reproduction. In organisms with sexual reproduction, this implies that transposable elements have to manifest their transpositional activity in germ cells or their progenitors. The control of sexual development and function can be very versatile, and several studies have demonstrated the implication of transposable elements in the evolution of sex. In this review, we report the functional and evolutionary relationships between transposable elements and sexual reproduction in animals. In particular, we highlight how transposable elements can influence expression of sexual development genes, and how, reciprocally, they are tightly controlled in gonads. We also review how transposable elements contribute to the organization, expression and evolution of sexual development genes and sex chromosomes. This underscores the intricate co-evolution between host functions and transposable elements, which regularly shift from a parasitic to a domesticated status useful to the host.

Controlling Apomixis: Shared Features and Distinct Characteristics of Gene Regulation

“…While it has been hypothesized that these chromosomes might be relevant for apomixis expression and in particular possible implications for diplospory have been discussed, transmission of a Het chromosome alone is not sufficient for apomixis to arise [23,59]. Interestingly, the Het chromosomes and heterochromatic chromosomal regions linked to apomixis resemble features of Y-chromosomes in animals and dioecious plants for sex determination with respect to typical accumulation of transposable elements and gene loss [29,46,60]. Therefore, it is tempting to speculate that similarly to well known mechanisms in Y-chromosomes, epigenetic regulatory mechanisms might be major driving forces in regulation of apomixis.…”

Braconidae revisited:Bracon brevicornisgenome showcases the potential of linked-read sequencing in identifying a putativecomplementary sex determinergene

“…brevicornis, A. mellifera, and N. vitripennis (Dechaud et al 2019). Also, tra/fem duplications have been shown in CSD systems before, most notably in A. mellifera where a fem gene duplication event resulted in it becoming a csd locus (Hasselmann et al 2008;Gempe et al 2009).…”

Selfish genes and sexual selection: the impact of genomic parasites on host reproduction

“…Selfish endosymbionts can cause feminization of genetic males, and microbe‐induced parthenogenesis regularly occurs in arthropods (Kageyama, Narita & Watanabe, 2012) (Kageyama et al , 2012). It is also suggested that TEs through their influence on the expression of sexual development genes, often with pronounced sex‐specific effect, can influence sex determination including sex chromosome evolution (Dechaud et al , 2019). Hence, a variety of SGEs has a major influence on the evolutionary dynamics of sex chromosomes.…”

“…Moreover, many SGEs whilst not causing sex ratio distortion also have sex‐specific effects. For example, many TEs show pronounced sex‐specific activity (Dechaud et al , 2019). The differential expression of SGEs in males and females has the potential to generate sexual conflict through their potentially sexually antagonistic effect.…”

“…In mammals, it appears that oocytes are more resilient to TE activity than the male germline, and it is suggested that this difference could be due to the ongoing division of sperm cells, in contrast to oocytes, which undergo a long meiotic arrest. Cell division is required for TE transposition, and many more cell divisions occur in the male germline (Dechaud et al , 2019). But there are also sex differences in expression patterns of TEs that affect reproductive fitness.…”