<i>Wisp3</i>^GFP-Cre activity occurs in spermatocytes early during meiosis I.

<p>Fluorescence microscope images of seminiferous tubules from <i>Wisp3</i>^+/GFP-Cre;<i>ROSA26</i>^+/mTmG male mice at 5, 10, 14, 15, 17, 19 and 27 days-of-age (P5 – P27). Cell nuclei are imaged with DAPI dye. Spermatocytes expressing membrane bound Green Fluorescent Protein (GFP) instead of Tomato Fluorescent Protein (TFP), which indicates that Cre-mediated recombination has occurred, become visible by P15 and increase in abundance with age. Germ cells and spermatogonial cells, which reside near the periphery of seminiferous tubules, do not express GFP. The location of the GFP expressing cells in the seminiferous tubules, coupled with PCR evidence of recombination by P10 (data not shown), suggests that the <i>Wisp3</i>^GFP-Cre allele is expressed in spermatocytes between the leptotene and pachytene stages of male meiosis I.</p

Endogenous <i>Wisp3</i> expression and <i>Wisp3</i>^{<i>GFP-Cre</i>} expression are not identical.

<p>(Upper panel) RT-PCR amplimers indicating the presence of <i>Wisp3</i> transcript in total RNA from a several different mouse tissues. A schematic of <i>Wisp3</i> mRNA is indicated (not drawn to scale) along with the locations of the intron-spanning PCR primers and the expected amplimer size for correctly splice mRNA (Lower panel). A schematic of the <i>ROSA26</i>^mTmG allele before and after Cre-recombination (not drawn to scale) along with the locations of the PCR primers and the expected amplimer sizes for the non-recombined and recombined alleles. PCR amplimers indicating non-recombined <i>ROSA26</i>^mTmG DNA (upper gel) in all tissues and Cre-mediated recombination (lower gel arrowheads) in testis, heart, and brain recovered from <i>Wisp3</i>^{+/GFP- Cre};<i>ROSA26</i>^+/mTmG mice (floxed and recombined template DNA serves as controls for the two primer pairs). Note that there is poor correlation between endogenous <i>Wisp3</i> expression (upper panel) and <i>Wisp3</i>^GFP-Cre activity (lower panel).</p