RESUMEN
The sea urchin larval skeleton offers a simple model for formation of developmental patterns. The calcium carbonate skeleton is secreted by primary mesenchyme cells (PMCs) in response to largely unknown patterning cues expressed by the ectoderm. To discover novel ectodermal cues, we performed an unbiased RNA-Seq-based screen and functionally tested candidates; we thereby identified several novel skeletal patterning cues. Among these, we show that SLC26a2/7 is a ventrally expressed sulfate transporter that promotes a ventral accumulation of sulfated proteoglycans, which is required for ventral PMC positioning and skeletal patterning. We show that the effects of SLC perturbation are mimicked by manipulation of either external sulfate levels or proteoglycan sulfation. These results identify novel skeletal patterning genes and demonstrate that ventral proteoglycan sulfation serves as a positional cue for sea urchin skeletal patterning.
Asunto(s)
Tipificación del Cuerpo/genética , Proteoglicanos/metabolismo , Erizos de Mar/embriología , Erizos de Mar/genética , Análisis de Secuencia de ARN/métodos , Sulfatos/metabolismo , Animales , Tipificación del Cuerpo/efectos de los fármacos , Proteínas de Transporte de Catión/metabolismo , Diferenciación Celular/efectos de los fármacos , Ectodermo/efectos de los fármacos , Ectodermo/enzimología , Embrión no Mamífero/efectos de los fármacos , Embrión no Mamífero/metabolismo , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Mesodermo/citología , Modelos Biológicos , Níquel/toxicidad , Erizos de Mar/efectos de los fármacos , Transducción de Señal/efectos de los fármacos , Factor A de Crecimiento Endotelial Vascular/metabolismo , Proteínas Quinasas p38 Activadas por Mitógenos/antagonistas & inhibidores , Proteínas Quinasas p38 Activadas por Mitógenos/metabolismoRESUMEN
Characterizing australopith pelvic morphology has been difficult in part because of limited fossilized pelvic material. Here, we reassess the morphology of an under-studied adult right ilium and pubis (Sts 65) from Member 4 of Sterkfontein, South Africa, and provide a hypothetical digital reconstruction of its overall pelvic morphology. The small size of the pelvis, presence of a preauricular sulcus, and shape of the sciatic notch allow us to agree with past interpretations that Sts 65 likely belonged to a female. The morphology of the iliac pillar, while not as substantial as in Homo, is more robust than in A.L. 288-1 and Sts 14. We created a reconstruction of the pelvis by digitally articulating the Sts 65 right ilium and a mirrored copy of the left ilium with the Sts 14 sacrum in Autodesk Maya. Points along the arcuate line were used to orient the ilia to the sacrum. This reconstruction of the Sts 65 pelvis looks much like a "classic" australopith pelvis, with laterally flared ilia and an inferiorly deflected pubis. An analysis of the obstetric dimensions from our reconstruction shows similarity to other australopiths, a likely transverse or oblique entrance of the neonatal cranium into the pelvic inlet, and a cephalopelvic ratio similar to that found in humans today.