Diving into broad-scale and high-resolution population genomics to decipher drivers of structure and climatic vulnerability in a marine invertebrate.

Species with widespread distributions play a crucial role in our understanding of climate change impacts on population structure. In marine species, population structure is often governed by both high connectivity potential and selection across strong environmental gradients. Despite the complexity of factors influencing marine populations, studying species with broad distribution can provide valuable insights into the relative importance of these factors and the consequences of climate-induced alterations across environmental gradients. We used the northern shrimp Pandalus borealis and its wide latitudinal distribution to identify current drivers of population structure and predict the species' vulnerability to climate change. A total of 1514 individuals sampled across 24° latitude were genotyped at high geographic (54 stations) and genetic (14,331 SNPs) resolutions to assess genetic variation and environmental correlations. Four populations were identified in addition to finer substructure associated with local adaptation. Geographic patterns of neutral population structure reflected predominant oceanographic currents, while a significant proportion of the genetic variation was associated with gradients in salinity and temperature. Adaptive landscapes generated using climate projections suggest a larger genomic offset in the southern extent of the P. borealis range, where shrimp had the largest adaptive standing genetic variation. Our genomic results combined with recent observations point to further deterioration in southern regions and an impending vulnerable status in the regions at higher latitudes for P. borealis. They also provide rare insights into the drivers of population structure and climatic vulnerability of a widespread meroplanktonic species, which is crucial to understanding future challenges associated with invertebrates essential to ecosystem functioning.

The catalytic function of hormone-sensitive lipase is essential for fertility in male mice.

In male mice, deficiency of hormone sensitive lipase (HSL, Lipe gene, E.C.3.1.1.3) causes deficient spermatogenesis, azoospermia, and infertility. Postmeiotic germ cells express a specific HSL isoform that includes a 313 amino acid N-terminus encoded by a testis-specific exon (exon T1). The remainder of testicular HSL is identical to adipocyte HSL. The amino acid sequence of the testis-specific exon is poorly conserved, showing only a 46% amino acid identity with orthologous human and rat sequences, compared with 87% over the remainder of the HSL coding sequence, providing no evidence in favor of a vital functional role for the testis-specific N-terminus of HSL. However, exon T1 is important for Lipe transcription; in mouse testicular mRNA, we identified 3 major Lipe transcription start sites, finding numerous testicular transcription factor binding motifs upstream of the transcription start site. We directly explored two possible mechanisms for the infertility of HSL-deficient mice, using mice that expressed mutant HSL transgenes only in postmeiotic germ cells on a HSL-deficient background. One transgene expressed human HSL lacking enzyme activity but containing the testis-specific N-terminus (HSL-/-muttg mice). The other transgene expressed catalytically inactive HSL with the testis-specific N-terminal peptide (HSL-/-atg mice). HSL-/-muttg mice were infertile, with abnormal histology of the seminiferous epithelium and absence of spermatozoa in the epididymal lumen. In contrast, HSL-/-atg mice had normal fertility and normal testicular morphology. In conclusion, whereas the catalytic function of HSL is necessary for spermatogenesis in mice, the presence of the N-terminal testis-specific fragment is not essential.

Expression of human hormone-sensitive lipase (HSL) in postmeiotic germ cells confers normal fertility to HSL-deficient mice.

Hormone-sensitive lipase (HSL, Lipe, E.C.3.1.1.3) is a multifunctional fatty acyl esterase that is essential for male fertility and spermatogenesis and that also plays important roles in the function of adipocytes, pancreatic beta-cells, and adrenal cortical cells. Gene-targeted HSL-deficient (HSL-/-) male mice are infertile, have a 2-fold reduction in testicular mass, a 2-fold elevation of the ratio of esterified to free cholesterol in testis, and unique morphological abnormalities in round and elongating spermatids. Postmeiotic germ cells in the testis express a specific HSL isoform. We created transgenic mice expressing a normal human testicular HSL cDNA from the mouse protamine-1 promoter, which mediates expression specifically in postmeiotic germ cells. Testicular cholesteryl esterase activity was undetectable in HSL-/- mice, but in HSL-/- males expressing the testicular transgene, activity was 2-fold greater than normal. HSL transgene mRNA became detectable in testes between 19 and 25 days of age, coinciding with the first wave of postmeiotic transcription in round spermatids. In contrast to nontransgenic HSL-/- mice, HSL-/- males expressing the testicular transgene were normal with respect to fertility, testicular mass, testicular esterified/free cholesterol ratio, and testicular histology. Their cauda epididymides contained abundant, normal-appearing spermatozoa. We conclude that human testicular HSL is functional in mouse testis and that the mechanism of infertility in HSL-deficient males is cell autonomous and resides in postmeiotic germ cells, because HSL expression in these cells is in itself sufficient to restore normal fertility.