Functional Equivalence of the SOX2 and SOX3 Transcription Factors in the Developing Mouse Brain and Testes

Abstract

Gene duplication provides spare genetic material that evolution can craft into new functions. and are evolutionarily related genes with overlapping and unique sites of expression during embryogenesis. It is currently unclear whether SOX2 and SOX3 have identical or different functions. Here, we use CRISPR/Cas9-assisted mutagenesis to perform a gene-swap, replacing the ORF with the ORF to investigate their functional equivalence in the brain and testes. We show that increased expression of SOX2 can functionally replace SOX3 in the development of the infundibular recess/ventral diencephalon, and largely rescues pituitary gland defects that occur in null mice. We also show that ectopic expression of SOX2 in the testes functionally rescues the spermatogenic defect of null mice, and restores gene expression to near normal levels. Together, these data provide strong evidence that SOX2 and SOX3 proteins are functionally equivalent.

The transcription factor SOX30 is a key regulator of mouse spermiogenesis

“…For example, SOX3 is expressed in undifferentiated spermatogonia (SG), and is required for their entry into a more differentiated state (Raverot et al, 2005). Interestingly, the infertile phenotype of Sox3 knockout (KO) mice can be rescued by the ectopic expression of SOX2, another member of the SOX A subfamily (Adikusuma et al, 2017). SOX17, the primary role of which is in endoderm induction but not in the specification of primordial germ cells (PGCs) in mouse, has been shown to be crucial in the in vitro induction of human PGCs from pluripotent stem cells (Irie et al, 2015;Viotti et al, 2014).…”

Distinct SoxB1 networks are required for naïve and primed pluripotency

“…SOXB1 redundancy is likely to be evolutionarily conserved since in the chick, Sox2 and Sox3 both promote development of ectoderm and neurectoderm at gastrulation, although interestingly, in this case Sox3 expression occurs before Sox2 (Acloque et al, 2011). Moreover, while genetic knock-ins have shown that placement of Sox2 ORF at the Sox3 locus can rescue pituitary and testes phenotypes caused by Sox3 deletion (Adikusuma et al, 2017), the effects on pluripotent cells were not assessed. It is therefore interesting that while Sox3 null mice can be viable, on a 129 genetic background they exhibit gastrulation-stage lethality (Rizzoti & Lovell-Badge, 2007; Adikusuma et al , 2017).…”

“…Moreover, while genetic knock-ins have shown that placement of Sox2 ORF at the Sox3 locus can rescue pituitary and testes phenotypes caused by Sox3 deletion (Adikusuma et al, 2017), the effects on pluripotent cells were not assessed. It is therefore interesting that while Sox3 null mice can be viable, on a 129 genetic background they exhibit gastrulation-stage lethality (Rizzoti & Lovell-Badge, 2007; Adikusuma et al , 2017). This suggests that aspects of the regulation of SoxB1 expression that we show here to be important in vitro could also contribute to strain-specific differences in the timing or regulation of SOXB1 activity in vivo.…”

“…SOXB1 proteins bind the same DNA sequence in vitro (Kamachi et al, 1999; Kamachi, 2016). Previous studies demonstrated that SOXB1 factors are co-expressed during embryonic development and can substitute for each other in different biological systems, both in vitro and in vivo (Wood & Episkopou, 1999; Niwa et al, 2016; Adikusuma et al, 2017). Here we investigate the requirements of naïve and primed pluripotent states for SOXB1 expression.…”

The 9aaTAD activation domains in the four Yamanaka Oct4, Sox2, Myc, and Klf4 transcription factors essential during the stem cell development

“…Sox2-mediated cell reprogramming could be further enhanced by Sox2 fusion with a strong viral activator VP16 (52). Sox1, Sox3, and Sox15 can replace the function of Sox2 in mouse ES (53,54).…”