Fig 1.
‘Pre-hatching’ in cloudy catshark.
Schematic drawing and pictures of developing catshark embryo around pre-hatching period. The external yolk sac is attached to an embryo via the yolk stalk. Yolk contents inside the external yolk sac start to be transferred into the internal yolk sac and embryonic intestine through the stalk at stage 31L (arrowheads), but not in the embryo at stage 31E (before pre-hatching). Asterisk indicates the site where egg case opens during pre-hatching period. EYS, external yolk sac; IYS, internal yolk sac.
Table 1.
Amino acid transporter genes expressed in yolk sac membrane and intestine identified in transcriptome analysis.
Table 2.
Lipid absorption genes, cathepsin, and LIPA genes expressed in yolk sac membrane and intestine identified in transcriptome analysis.
Fig 2.
Developmental changes in gene expression of amino acid transporters of putative apical locality.
(A) slc3a1; (B) slc6a18; (C) slc6a19; (D) slc6a20; (E) slc7a9; (F) slc36a1; (G) slc15a1 (Pept1). Data are presented using box and whisker diagrams of N = 5. Uppercase and lowercase letters indicate significant developmental differences in embryonic intestine and yolk sac membrane, respectively after one way ANOVA, Tukey’s test (P<0.05).
Fig 3.
Developmental changes in gene expression of amino acid transporters of putative basolateral locality.
(A) slc3a2; (B) slc7a6; (C) slc7a7; (D) slc7a8; (E) slc38a2; (F) slc43a2. Data are presented using box and whisker diagrams of N = 5. Uppercase and lowercase letters indicate significant developmental differences in embryonic intestine and yolk sac membrane, respectively after one way ANOVA, Tukey’s test (P<0.05).
Fig 4.
Developmental changes in gene expression involved in lipid absorption.
(A) apob; (B) mtp; (C) apoa1; (D) abca1. Data are presented using box and whisker diagrams of N = 5. Uppercase and lowercase letters indicate significant developmental differences in embryonic intestine and yolk sac membrane, respectively after one way ANOVA, Tukey’s test (P<0.05).
Fig 5.
Developmental changes in gene expression of lysosomal digestive enzymes.
(A) ctsa; (B) ctsb; (C) ctsf1; (D) ctsf2; (E) ctsl1; (F) ctsl2; (G) lipa. Data are presented using box and whisker diagrams of N = 5. Uppercase and lowercase letters indicate significant developmental differences in embryonic intestine and yolk sac membrane, respectively after one way ANOVA, Tukey’s test (P<0.05).
Fig 6.
Localization of the mRNAs involved in lipid absorption and lysosomal digestive enzyme in the yolk sac membrane.
Morphological observations of the YSM shown by hematoxylin and eosin staining (A-C). In situ hybridization staining of slc43a2 (D-F), apob (G-I), ctsl1 (J, K), and ctsl2 (L, M). Arrows indicate the positive signals. END, endoderm; EP, epithelial cells; FCL, fibrous connective layer; HC, hematopoietic cell; SM, submucosa; BC, blood cells. Bars, 100μm.
Fig 7.
Electron microscopic ultrastructural observations on the developing yolk sac membrane.
(A-C) Ultrastructure of the boundary between yolk contents and epithelial cells of the YSM in different developmental stages. (A’-C’) Small boxes in panels A-C are magnified to show the fine structures. Arrows indicate membrane packets containing yolk granules. BV, blood vessels; END, endodermal cells; GC, granular cells; YSL, yolk syncytial layer. Bars, 10μm (A-C), 1μm (A’-C’).