Stra8 expression is elevated in the absence of CYP26B1.

<p>Reverse transcription- PCR was performed with RNA collected from E15.5 and E16.5 <i>Cyp26b1^SC+/SC−</i> and <i>Cyp26b1^SC−/SC−</i> testes. <i>Stra8</i> is only detected in RNA from E16.5 <i>Cyp26b1^SC−/SC−</i> testes. <i>Mvh</i> expression was analyzed as a positive control for RNA integrity.</p

Generation of Sertoli cell-specific <i>Cyp26b1</i> knockout mice (<i>Cyp26b1^SC−/SC−</i>).

<p>(A) Floxed <i>Cyp26b1</i> locus showing position of primers (P1, P2, P3) used for genotyping. LoxP sites are indicated by triangles, and the exons of <i>Cyp26b1</i> are numbered. In Sertoli cells, exons 3–6 will be excised <i>(Cyp26b1^SC−/SC−)</i>, thus allowing for PCR amplification of a 364 bp product using P1 and P3. (B) PCR genotyping using P1, P2 and P3 showing detection of an excised allele (364 bp) only in the testes of a <i>Cyp26b1^fl/fl</i> mouse also expressing Cre (mouse #1).</p

Re-entry into mitotic cell cycle in embryonic <i>Cyp26b1^SC−/SC−</i> male germ cells.

<p>Sections of testes from <i>Cyp26b1^SC+/SC+</i> (A, B, C, G, H, I) and <i>Cyp26b1^SC−/SC−</i> (D, E, F, J, K, L) littermates at E15.5 (A–F) and E16.5 (G–L) stained for the mitotic marker Ki67 (B, E, H, K, red) and the germ cell marker MVH (A, D, G, J, green). Overlays of images show Ki67 expressing germ cells are observed only in <i>Cyp26b1^SC−/SC−</i> fetuses (F, arrowheads). Bar, 20 µm.</p

Proposed model for the role of CYP26B1 in maintaining male germ cells in an undifferentiated state during embryogenesis.

<p>In wild-type gonads, germ cells exhibit sex-specific divergence during embryogenesis as male germ cells enter mitotic arrest, while female germ cells enter mitosis followed by meiosis. However, in <i>Cyp26b1^SC−/SC−</i> fetuses, Cyp26b1 activity is inactivated after E15.5, thus elevating levels of retinoic acid within the testes. As a result, male germ cells exit from G0 to re-enter the cell cycle and initiate meiotic prophase, which subsequently culminates in loss of male germ cells.</p

<i>Cyp26b1^SC−/SC−</i> male germ cells enter meiosis prematurely.

<p>Sections of testes from <i>Cyp26b1^SC+/SC+</i> (A) and <i>Cyp26b1^SC−/SC−</i> (B) littermates at E16.5 stained for the meiotic marker SCP3 (green). Sections were counterstained with DAPI. Bar, 20 µm.</p

Neonatal loss of germ cells in the absence of CYP26B1.

<p>Postnatal day 0 (P0) testes stained for TRA98 show a loss of germ cells in <i>Cyp26b1^SC−/SC−</i> mice. Bar, 20 µm.</p

Implications of Using On-Farm Flood Flow Capture To Recharge Groundwater and Mitigate Flood Risks Along the Kings River, CA

The agriculturally productive San Joaquin Valley faces two severe hydrologic issues: persistent groundwater overdraft and flooding risks. Capturing flood flows for groundwater recharge could help address both of these issues, yet flood flow frequency, duration, and magnitude vary greatly as upstream reservoir releases are affected by snowpack, precipitation type, reservoir volume, and flood risks. This variability makes dedicated, engineered recharge approaches expensive. Our work evaluates leveraging private farmlands in the Kings River Basin to capture flood flows for direct and <i>in lieu</i> recharge, calculates on-farm infiltration rates, assesses logistics, and considers potential water quality issues. The Natural Resources Conservation Service (NRCS) soil series suggested that a cementing layer would hinder recharge. The standard practice of deep ripping fractured the layer, resulting in infiltration rates averaging 2.5 in d^–1 (6 cm d^–1) throughout the farm. Based on these rates 10 acres are needed to infiltrate 1 cfs (100 m³ h^–1) of flood flows. Our conceptual model predicts that salinity and nitrate pulses flush initially to the groundwater but that groundwater quality improves in the long term due to pristine flood flows low in salts or nitrate. Flood flow capture, when integrated with irrigation, is more cost-effective than groundwater pumping