Formation of kidney tissue requires the generation of kidney precursor cells and their subsequent differentiation into nephrons, the functional filtration unit of the kidney. Here we report that the gene odd-skipped related 1 (Odd1) plays an important role in both these processes. Odd1 is the earliest known marker of the intermediate mesoderm, the precursor to all kidney tissue. It is localized to mesenchymal precursors within the mesonephric and metanephric kidney and is subsequently downregulated upon tubule differentiation. Mice lacking Odd1 do not form metanephric mesenchyme, and do not express several other factors required for metanephric kidney formation, including Eya1, Six2, Pax2, Sall1 and Gdnf. In transient ectopic expression experiments in the chick embryo, Odd1 can promote expression of the mesonephric precursor markers Pax2 and Lim1. Finally, persistent expression of Odd1 in chick mesonephric precursor cells inhibits differentiation of these precursors into kidney tubules. These data indicate that Odd1 plays an important role in establishing kidney precursor cells, and in regulating their differentiation into kidney tubular tissue.

Ventricular septal defects are common in human infants, but the genetic programs that control ventricular septation are poorly understood. Here we report that mice with a targeted disruption of the cardiovascular basic helix-loop-helix factor (CHF)1͞Hey2 gene show isolated ventricular septal defects. These defects result primarily in failure to thrive. Mice often succumbed within the first 3 wk after birth and showed pulmonary and liver congestion. The penetrance of this phenotype varied, depending on genetic background, suggesting the presence of modifier genes. Expression patterns of other cardiac-specific genes were not affected. Of the few animals on a mixed genetic background that survived to adulthood, most developed a cardiomyopathy but did not have ventricular septal defects. Our results indicate that CHF1 plays an important role in regulation of ventricular septation in mammalian heart development and is important for normal myocardial contractility. These mice provide a useful model for the study of the ontogeny and natural history of ventricular septal defects and cardiomyopathy. V entricular septal defects (VSD) are the most common congenital cardiac defects in human infants, if bicuspid aortic valve is excluded (1). The ontogeny of atrioventricular septation is complex (2). Multiple primordia contribute to the formation of the interatrial and interventricular septa, including endocardial cushion tissue and myocardium. The muscular portion of the interventricular septum arises from ingrowth and folding of the myocardial wall of the developing ventricle, whereas the membranous portion of the interventricular septum is derived primarily from endocardial cushion tissue. The genetics of ventricular septation are poorly understood, and in human populations, no single gene disorder primarily causing isolated VSD exists. Isolated VSD can occur in patients heterozygous for mutations in Nkx2.5 (3) or Tbx5 (4); however, this phenotype is less common. In mice, a number of gene disruptions have been shown to cause VSDs, but all of these occur in the context of anomalies involving other cardiac structures such as the semilunar valves, ventricular outflow, compaction of myocardium, etc. (5-11). To our knowledge, no genes in mice or humans have been linked primarily to isolated ventricular septal defects without other associated anatomic findings.Members of the cardiovascular basic helix-loop-helix factor (CHF) family of hairy-related transcription factors (also called gridlock, Hey, Hesr, Hrt, and HERP) have been suggested to play important roles in cardiovascular development (12)(13)(14)(15)(16)(17). In zebrafish, the gridlock mutation is associated with coarctation of the aorta (13). Loss-of-function and gain-of-function studies using morpholino-antisense oligonucleotides or microinjected RNA showed that gridlock expression favors the development of arteries instead of veins from undifferentiated vascular precursors (18). CHF1 (also called Hesr2, Hey2, Hrt2, and HERP1, henceforth to be referred to as CHF1) is ex...

Zebrafish are an established research organism that has made many contributions to our understanding of vertebrate tissue and organ development, yet there are still significant gaps in our understanding of the genes that regulate gonad development, sex, and reproduction. Unlike the development of many organs, such as the brain and heart that form during the first few days of development, zebrafish gonads do not begin to form until the larval stage (≥5 dpf). Thus, forward genetic screens have identified very few genes required for gonad development. In addition, bulk RNA sequencing studies which identify genes expressed in the gonads do not have the resolution necessary to define minor cell populations that may play significant roles in development and function of these organs. To overcome these limitations, we have used single-cell RNA sequencing to determine the transcriptomes of cells isolated from juvenile zebrafish ovaries. This resulted in the profiles of 10,658 germ cells and 14,431 somatic cells. Our germ cell data represents all developmental stages from germline stem cells to early meiotic oocytes. Our somatic cell data represents all known somatic cell types, including follicle cells, theca cells and ovarian stromal cells. Further analysis revealed an unexpected number of cell subpopulations within these broadly defined cell types. To further define their functional significance, we determined the location of these cell subpopulations within the ovary. Finally, we used gene knockout experiments to determine the roles of foxl2l and wnt9b for oocyte development and sex determination and/or differentiation, respectively. Our results reveal novel insights into zebrafish ovarian development and function and the transcriptome profiles will provide a valuable resource for future studies.