Cre recombinase activity specific to postnatal, premeiotic male germ cells in transgenic mice

TLDR

The authors aimed to pinpoint the onset of Cre activity in male germ cells by crossing Stra8‑cre males with Z/EG reporter females and comparing EGFP expression to the PLZF marker of undifferentiated spermatogonia. They generated a Stra8‑cre transgenic mouse expressing Cre under a 1.4 kb Stra8 promoter and assessed recombination by mating Stra8‑cre;Z/EG males with wild‑type partners and examining EGFP in the progeny. Cre activity is confined to male germ cells from postnatal day 3, co‑expressing EGFP with PLZF+ spermatogonia, yielding >95 % recombination in offspring of Stra8‑cre fathers but none from mothers, demonstrating postnatal, pre‑meiotic male‑specific activity.

Abstract

We have generated a transgenic mouse line,Tg(Stra8-cre)1Reb (Stra8-cre), which expresses improved Cre recombinase under the control of a 1.4 Kb promoter region of the germ cell-specific stimulated by retinoic acid gene 8 (Stra8). cre is expressed only in males beginning at postnatal day (P)3 in early-stage spermatogonia and is detected through preleptotene-stage spermatocytes. To further define when cre becomes active, we crossed Stra8-cre males with Tg(ACTB-Bgeo/GFP)21Lbe (Z/EG) reporter females and compared the expression of enhanced green fluorescent protein (EGFP) with the protein encoded by the zinc finger and BTB domain containing 16 (Zbtb16) gene, PLZF-a marker for undifferentiated spermatogonia. Co-expression of EGFP is observed in the majority of PLZF+ cells. We also tested recombination efficiency by mating Stra8-cre;Z/EG males and females with wild-type mice and examining EGFP expression in the offspring. Recombination is detected in >95% of Z/EG+ pups born to Stra8-cre;Z/EG fathers but in none of the offspring born to transgenic mothers, a verification that cre is not functional in females. The postnatal, premeiotic, male germ cell-specific activity of Stra8-cre makes this mouse line a unique resource to study testicular germ cell development.